Space Mechanisms Lessons Learned Study

FOREWORD

Data were obtained through various sources, such as: (1) An extensive literature review that included government contractor reports and technical journals.  (2) Communication and visits (when necessary) to the various NASA and DOD centers and their designated contractors.  This included contact with project managers of current and prior NASA satellite programs as well as their industry counterparts.  (3) Requests for unpublished information were made to NASA and industry.  (4) A mail survey which was designed to establish specific mechanism experience and also to solicit opinions of what should be included in a future Space Mechanisms Design Guidelines Handbook.

The majority of the work was done at MTI under contract NAS3-27086.  The following acknowledgement section also lists some organizations and individuals who contributed to the work.

ACKNOWLEDGEMENTS

LIST OF FIGURES

1. Space Mechanisms Survey Form
2. ESTL Vacuum Chamber
3. Boundary Lubrication Accelerated Screening Tester
4. Honeywell Environmental Test Facility
5. Honeywell Environmental Thermal Chamber
6. Honeywell Shaker Table Facility and Control Room
7. Pyrotechnic Test Facility at NASA - Langley
8. Pyrotechnic Test Cells at NASA - Langley
9. Pyrotechnic Test Cells Outside at NASA - Langley

LIST OF TABLES

1. Anomalies of Pyrotechnic Devices
2. Tribomaterials for Deployment Mechanisms
3. Lockheed Solutions to Limitations of Conventional Designs
4. General Guidelines for Worm Gear Systems
5. Actuators Using Brush Motors
6. Partial Listing of Momentum/Reaction Wheel, Control Moment Gyroscope, and Gyroscope Experience
7. Factors Tending to Increase Blocking

INTRODUCTION

Three major categories of mechanisms were selected: deployable appendages, rotating systems, and oscillating systems.  Subsystems of these major categories are as follows.

Deployable Appendages

• Solar Arrays
• Retention and Release Mechanisms
• Bearings, Lubrication, and Tribology Considerations
• Antennas and Masts
• Actuators, Transport Mechanisms, Switches
• General and Miscellaneous

Rotating Systems

• Momentum Wheels
• Reaction Wheels
• Control Moment Gyroscopes
• Gears
• Motors
• Bearings and Lubrication
• Slip Rings and Roll Rings
• Miscellaneous

Oscillating Systems

Information for the Lessons Learned study was retrieved from a number of sources including:

Available Literature.  The literature review proved to be the most significant source of information.  In particular, the 28 Annual Proceedings of the Aerospace Mechanism Symposium was an extremely valuable resource.  Also, a NASA-Goddard publication on deployable appendages was very informative.  In compiling the literature review, a specific format was adhered to.  The ingredients of the format are described in Volume II, Literature Review.

The constraints of the literature search limited publications to those that described anomalies and/or lessons learned.  Mechanism descriptions contained in these publications were also summarized and documented for subsequent use in generation of the handbook.

Industrial Survey.  A survey form was created, which is presented in the Survey Results section of this report.  Over 600 surveys were mailed with approximately 30 responses.  Some significant information was provided, especially by the Satellite Systems Operation and the Electro Components Division of the Honeywell Corporation, who spent considerable time in preparing information.  Other responses provided additional reference material.

Subcontracts. The European Space Tribology Laboratory (ESTL) contributed a review of the European Literature and provided a listing of European experts.  Also Bobby McConnell, of Tribotech Consultants, who has considerable experience with military applications of space mechanisms contributed information.

This report is organized into two volumes.  Volume I provides a summary of the lessons learned, the results of a needs analysis, the survey responses, a listing of experts, a description of some available facilities, and a compilation of references.  The completed literature reviews comprise Volume II.

SUMMARY OF LESSONS LEARNED

Deployable Appendages

Solar Arrays

• Cosmic background explorer [Farley]
  • One damper required replacement because of an air bubble (reason not stated).  However, it could be attributed to the selection of the viscous damper fluid.  McGhan-Nusil CY7300 silicone fluid is preferred because of stable viscosity and low outgas characteristics.
  • A pin puller shaft fractured and rebounded into an unfired position.  Excessive hole drilling in this puller caused the failure.  Pin pullers should be x-ray inspected.
  • The array experienced inconsistent behavior of a microswitch; quality assurance needed improvement.
• Earth Radiation Budget Satellite (ERBS) [Mollerick]
  • Excessive bearing friction was experienced due to poor characteristics of molybdenum disulfide (MoS2) lubricant at cold conditions.  Under conditions of cold temperature (-44 F) and the balling up phenomenon of MoS2, moisture molecules could create frozen balls in the path of the rolling elements impeding available driving torque.  In fact, this is the major contributor believed to have prevented the solar array from initially deploying while the spacecraft was attached to the orbiter remote manipulator system.  Application of sputter-coated MoS2 with proper run-in may have avoided some of these problems.  [Fleischauer, Hilton]
  • Spring drives must use a minimum torque ratio of four.  The deployment drive systems each had a torque ratio of less than three.  However, each drive had redundant torsion springs and analysis indicated ample capacity for successful deployment.  In looking at the ERBS solar array deployment, it is conceivable that a combination of cold temperatures, thermal gradients, MoS2 lubricant, and insufficient torque margins are likely to result in deployment problems.
• Torque increases and fluctuations can be caused by wire harnesses due to cold temperatures and complex wiring paths.  Testing is required at simulated environments to resolve torque problems.  [ESTL, Hostenkamp]
• MILSTAR employed a flexible substrate solar array.  A summary of lessons learned during its development are as follows: [Gibb]
  • Minimize deployed mass at the deployed end of the array or mast (leave the cover at the base).
  • Conduct analyses and test to ensure adequate blanket container preload.  Testing should include acoustic and shock testing.
  • Maximize spreader bar stiffness in the deployment plane, and perform analysis to ensure acceptably low deflection to avoid panel warping or wrinkling.
  • Be aware that MoS2 coatings have a coefficient of friction dependent upon humidity.  Variations are on an order of magnitude between ambient and vacuum conditions.  Do not apply MoS2 coatings to both surfaces of a mating pair or else a higher coefficient of friction will result than if only one surface is coated.
  • To avoid panel sticking, insist on high-cleanliness standards during cell bonding, especially when the process involves cutting film adhesives.
  • Do not rely on preload and friction to hold a blanket stack in place during ascent; use a positive mechanical device, such as pins, skewers, or interlocking sections.

Retention and Release Mechanisms

• Pip pins are used on many space mechanisms.  Pip pins are most often used when an astronaut will have direct interface with the mechanism.  The main reason for incorporating pip pins is convenience and their ability to provide quick release of interfacing parts.  [Skyles]
  • To prevent locking balls from vibrating out of their sockets, four balls instead of two should be installed to provide redundancy if one ball falls out of its socket.
  • Swaged tethers could create a tear hazard to an astronauts pressure suit.  Tether rings should be solid or have welded ends.  Split rings can allow disconnect and are also a tear hazard.
  • Dowel pins for handle attachments could loosen from vibration and thermal effects.  The handles should be welded to the pins to avoid loosening.
  • Liquid lubricants or grease could freeze and cause seizure of the pins.  Dry film lubricants should be used to lubricate all internal parts of the pip pin.
  • Double-acting pins should be provided that allow release capability when the handle is either pushed or pulled to facilitate operation.
  • A Teflon sleeve should cover the tether swage fitting and cable termination, providing a smooth surface and preventing the possibility of astronauts contacting frayed or broken cable strands.
  • Hitch pins are recommended where the pip pin only has to be removed and not reinstalled.
  • Further development of ball retention is required.  The present method is by staking which is subject to error.  Inspections have shown incomplete staking that would allow the balls to fall out.  Also, the staked material is relatively thin and stress concentrations can be created at the tip of the staked material.  Vibrations can cause fracture and subsequent failure by ball loss.
• Problems experienced with pyrotechnic pin pullers include:
  • Blow-by across O-ring seals caused by wearing of the MoS2 coating on the pin that deposited on the O-ring preventing the seal.  For pistons, an electro-deposited, nickel/Teflon coating is recommended.  Hard-anodized aluminum uncoated housings were recommended, although in an earlier paper it was indicated that steel housings would not distort as much as aluminum and combined with a durable dry coating on the pin improved functional performance.  [Bement]
    For pyrotechnic devices, tests must be carried out to ensure that a device has an acceptable functional margin where the functional margin is a comparison of the energy that can be delivered to the device and the energy required to operate the device.  [Bement]
  • For pyrotechnic devices, material impact strength is usually a more critical variable than inertia load capability especially when the temperature drops.  When the inertia load of a deployable system is low, a ductile material should be selected, as opposed to a brittle material, for the actuator housing and piston.  [Phan]
  • For a pin puller lot acceptance test, at least one puller should be exposed to 125% explosive power in a cold environment.  [Phan]
  • If the spacecraft requires a high level of cleanliness, then multiple pyrotechnic seals must be used to prevent gas leakage.  A hybrid sealing system consists of Viton O-rings and silicon O-rings in tandem.  [Phan]
• A resettable binary latch mechanism was developed utilizing a paraffin actuator as a motor.  The polyamide rail failed due to unexpected high inertia loads.  Substitution of titanium resulted in galling.  CDA 630 aluminum nickel-bronze was finally selected because of its resistance to corrosion and superior wear characteristics.  After initial wear-in (approximately 50 cycles), the toggle was burnished from contact with the rail and neither part demonstrated significant wear during subsequent testing to 20,000 cycles.  [Maus]
  • For the same binary latch mechanism discussed above, thermal testing revealed interference between the output shaft and its bushing at low temperatures.  The bushing, fabricated from polyamide, shrank into the output shaft at -60o C and created friction.  Enlarging the bushing bore corrected the problem.  Thermal binding must be considered not only for high-temperature operation, but for low temperature as well.
  • Iteratively designing a complex mechanism in computer-aided design (CAD) and using pasteboard mock-ups can be a more efficient process than detailed mathematical analysis of component geometries (components can be visualized throughout their range of motion, interferences can be identified and eliminated, and kinematics and component shapes can be easily optimized by simultaneously seeing the effect of changes in all positions).
• The patented Lockheed Super*Zip spacecraft separation joint was planned for use on the space shuttle to release the Centaur vehicle (120 in. diameter), the inertial upper stage (91 in.) at the same separation plane as the Centaur, and the Galileo spacecraft.  Following functional failures of two out of a group of five Lockheed Super*Zip spacecraft separation joints in a shuttle/Centaur thermal development test series to quantify thermal effects, an evaluation program was initiated on this and the related inertial upper stage and Galileo systems to assist in preventing a recurrence of failure.  The results of the investigation revealed that thin ligaments are better than thick ones because they are more difficult to sever under explosive conditions.  Also, a single-cord configuration indicated no trend toward tube rupture with increased explosive load as did a double-cord configuration.  [Bement]
• A survey has been compiled on pyrotechnic devices for a 23-yr period that included 84 serious component or system failures, 12 of which occurred in flight with fully developed and qualified hardware.  Table 1 lists anomalies.
• The 1987 failure of two Magellan pin pullers has far greater potential impact than is initially apparent.  This pin puller was the same unit fully qualified for the Viking Lander spacecraft for the 1976 landing on the surface of Mars.  After this experience and with its pedigree, two units from a duplicate lot of pin pullers failed to function in a failure mode not recognized in the original design, development, and qualification.  First, the extremely dynamic pressure impulse output of the NSI (as designed) when fired into a small eccentrically vented cavity was severely attenuated, reducing the energy available to stroke the piston.  Furthermore, the bottom of the cavity was deformed by the pressure into a groove in the piston, which had to stroke to pull the pin.  This device may have always been marginal when operated by a single-cartridge input.

• For the source of failures, the shocking statistic is that 35 out of 84 (42%) of the failures were caused by lack of understanding; that is, the personnel working the problem at the time, did not have the technology needed to understand and correct the failure.  Unfortunately, 24 were mistakes caused by poor designs and misapplication of hardware, which means that personnel did not apply the known technology.  The next 23 failures have to be categorized as carelessness through manufacturer's poor procedures and quality control.
• Since pyrotechnics are single-shot devices, past approaches for demonstrating reliability have relied heavily on developing statistical verification without a clear understanding of functional mechanisms and the relative importance of system parameters.  That is, once a successful performance was achieved, emphasis was placed on accomplishing large numbers of consecutive successes.  (More than 2000 units are needed to establish a 99.99% reliability at a 95% confidence level.) However, the current approach often is to run full-scale systems tests on as few as six assemblies or less with no statistical guarantee of reliability, and without an adequate understanding of how the mechanisms function, which can be a prescription for disaster.  [Bement]
• The high-output paraffin actuator provides an alternative device to the mechanism designer requiring significant mechanical work from a small, compact, reliable component.  The work can be generated from heat provided by internal electrical resistance elements or from environmental temperature changes.  [Tibbits]
• In internally heated configurations, the advantages over conventional electrically powered actuators can be significant (low weight, resetability, full verification before flight, high force, long stroke, gentle stroke, and flexibility in materials of construction).  [Tibbits]
• Structural latches for modular assembly of spacecraft and space mechanisms are exposed to a number of problems.  Problems and suggestions are as follows.  [McCown]
  • Load control is a particular problem with hook systems where the load is usually preset by rigging.  Load changes due to thermal or dynamic fluctuations cannot be compensated.
  • The selection methodology described by McCown, is an excellent guideline for designers.
  • For roller screw latches, thread engagement is improved by providing lead-ins.
  • Rolling element latch interfaces reduce particle generation.  The addition of Teflon wiper seals control loose particles in the roller screw structural latch and receptacle nut.
  • A run-in and clean-up procedure reduces particle generation from initial actuations.  The only reliable method to control the roller screw structural latch preload was to limit motor power.
• At launch, the near-infrared mapping spectrometer of the Galileo spacecraft had two covers in place to protect the instrument from contamination.  Two and a half months after launch, initial attempts to eject the covers were unsuccessful.  It was subsequently determined that this was due to differential expansion caused by the shield heater being energized.  The shield heater was turned off, the covers allowed to cool, and they were successfully ejected.  Untested flight sequences frequently result in unexpected events.  Because of concern for contamination caused by spacecraft outgassing, a flight rule was modified prior to launch requiring the shield heater to be energized before cover deployment.  The flight rule was in error by not requiring heater shutoff before deployment.  The lessons learned are that the cover should have been tested in the flight environment and the consequences of flight rule changes should be carefully evaluated.  [JPL SSEF, Schaper]
• During one of the solar array deployment tests in 1989, a pin puller in a release mechanism was actuated, the pin was retracted inside its housing to release the solar array, but then rebounded back out of its housing.  The normal function of a pin puller is to retract and stay flush inside the pin puller housing.  The malfunction of this pin puller did not stop the deployment of the solar array because of the mechanical redundancy of the release mechanism.  The rebound of the pin outside the housing forced us to investigate our pin puller design.  The result of this investigation showed that an extra shear pin hole was accidentally drilled at 120o away from the original shear pin hole on the pin puller.  From past pyroactuator design experience, it was determined that material impact strength is usually a more critical variable than the ability of the pin puller to withstand the high inertia load of a deployable system, especially if the device is required to operate in a cold environment.  Material impact strength drastically drops when the temperature drops.  It is recommended that when the inertia load of the deployable system is low, a more ductile material be selected over a brittle material for the actuator housing and piston.  It is also recommended that for the pin puller lot acceptance test, that at least one test include subjecting the pin puller to zero inertia load in the shear direction, and in a cold operating temperature, actuate the pin puller with 125% explosive power.  [Hinkle]
• Some gas molecules will leak out of a pyrotechnic actuator assembly during the actuation and some over a period of time after actuation, because most pyrotechnic actuators have only a single Viton O-ring.  If the spacecraft requires an extremely high level of cleanliness, then a hybrid sealing system must be designed for the actuator assembly.  Hybrid sealing systems design consists of a Viton O-ring and a silicon O-ring that are located side by side in the leakage path.  [Hinkle]
• Microwelding of high-load contact areas can occur from induced random vibrations that will prevent smooth transition of linear devices.  [ESTL, Coquelet]
• Thermal problems are prevalent with actuators and retention and release mechanisms.  Differences in coefficients of thermal expansion must be thoroughly explored to avoid jamming and excessive torque.  [ESTL, del Campo]
• Vibrations can cause unwanted deployment of components.  Additional restraint is sometimes required.  [ESTL, Henton-Jones]
• Microswitches on the Magellan were mounted such that they would detect the position of the solar panels (as opposed to the status of the latching mechanism).  As a result, they were just a position indicator and not a "panels locked" indicator.  Care should be taken in deciding where to mount telemetry transducers to assure that the desired function is actually being measured and not just a related function.  [JPL SSEF, Wagoner]
• The mechanical joint between the biaxial drive assembly and its mounting to the spacecraft allowed the ACTS transmit antenna to shift locations during launch.  The four bolts did not maintain the proper preload and the joint slipped during launch loading.  This has reduced the available design adjustment for the ACTS transmit antenna.
  All mechanical joints that require precise alignments should not use friction to maintain alignments during any type of loading.  All types of alignment joints should be matched drilled with body-bound bolts or be drilled and pinned after assembly.  [Survey, Collins]
• A paraffin actuator used to open and close the main sensor cover on the Clementine spacecraft experienced a heater failure during acceptance testing.  There were two causes of the problem: excessive temperature and stress from driving the heater at high voltage (36 V), and mechanical stress on the heater element from flowing wax within the actuator during heating.  The problem was resolved by remounting the heater and dropping voltage by incorporating a resistor in series with the heater.  In the future, a circuit with a zener diode will be installed to keep the operating voltage from varying excessively.
  A similar approach will be considered for other mechanisms sensitive to variations in supply voltage and especially for other heat-actuated mechanisms.  [Survey, Purdy]
• Mechanisms that depend on frictional characteristics to restrain a load during launch vibration may slip and relieve the applied load.  Components such as worm gears and lead screws are normally considered to be nonbackdrivable.  Certain conditions of vibration can cause backdriving to occur.  [Survey, Fink]
• Because of concerns about the nonconductive Tufram coating allowing a charge buildup that might affect instruments for the Polar satellite, a change to a conductive coating (NEDOX) was directed.  Although, the coefficient of friction of NEDOX was better than that of Tufram, the NEDOX-coated V-band failed to release during acceptance testing.  Previously, an engineering unit with a Tufram-coated V-band was successfully released more than a dozen times.  Extreme care should be used when changing even the simplest process or procedure from what had worked previously.  Testing of the new coating prior to acceptance test was bypassed due to budget and schedule constraints and the similarity of the two coatings.  In the end, neither schedule nor budget was saved and testing had to be repeated with the final V-band design, which consisted of Tufram coating only on the contacting surfaces of the band to minimize surface area for charge buildup.  [Survey, Osterberg]
• The x-ray telescope covers for the Alexis spacecraft failed to operate consistently during thermal vacuum testing.  On orbit, three of the six covers failed to open on the initial command.  The lifting mechanism was not sufficient to completely break the O-ring seal.  Avoid covered O-rings if at all possible.  Spring-energized Teflon seals are a better solution.  If O-ring seals are used, ensure that the complete seal area is actively broken through by high-force actuation.  If it is not possible to actively break the seal, kick-off springs opposite the hinge line should be used to supply the initial torque rather than additional hinge line spring force.  [Survey, Tibbits]

Bearings, Lubrication, and Tribology Considerations

• Thin-section, four-point contact ball bearings are increasingly employed in spacecraft mechanisms because of the potential advantages they offer.  Internal preload, housing design and external axial clamping force on the bearing rings all have a strong influence upon torque, conductance, and stiffness.  The thermal conductance of a dry or marginally lubricated bearing depends upon the thermal strain and varies linearly with radial temperature difference between the rings.  Additionally, conductance is a function of type and quantity of lubricant.  The Coulomb torque exhibits almost a square relation with thermal strain.  [Rowntree]
• MoS2 solid lubricant films were prepared by radio frequency magnetron sputtering on 440C steel, 52100 steel, and silicon substrates.  [Hilton]
  • Multilayered films exhibited excellent endurance in sliding wear and thrust bearing tests.  Friction coefficients in ultra-high vacuum ranged between 0.05 and 0.08.
  • With metal multilayer films, the optimum structural spacing is in the order of 10 Nm.
  • Minimum metal layer thickness is best.
  • A thin surface overlay of pure MoS2 seems to facilitate transfer to an uncoated surface.
• Solid lubricant films are used in a variety of mechanisms on various spacecraft and launch vehicles.  Relative to liquid lubricants, solid lubricants generally have lower vapor pressures, better boundary lubrication properties and relative insensitivity to radiation effects, and operate in wider temperature ranges.  [Hilton]
  • Lead coating has had good success as a solid lubricant in vacuum applications.
  • Optimum performance of lead and other metals is achieved at approximately 1 um (micron) thickness.
  • Deposition of soft metals (Pb, Au, Ag, In) by ion plating provides excellent adhesion.  These films have been particularly effective in spacecraft bearings found in solar array drive mechanisms in European satellites and on the Hubble space telescope.
  • A particular disadvantage of lead is that it oxidizes rapidly and must be stored in vacuum dry environments.
  • Gold and silver are used in situations requiring electrical conductivity.
  • Sputter-deposited MoS2 has a lower coefficient of friction than ion-plated Pb (0.01 versus 0.1), which means that MoS2 components should develop less torque.
• General lubrication problems and lessons learned with spacecraft deployable appendages include: [Devine]
  • Seizures of relative motion surfaces caused by excessive friction.
  • Vibration-induced fretting and adhesion due to excessive clearance in caging devices.
  • Unlubricated surfaces exceeding bearing yield strength of substrate on hard-coated materials.
  • Seizures caused by dissimilar materials with high mutual solubility.
  • Maximum utilization of rolling surfaces as opposed to sliding motion should be employed.
  • Lubrication or separation of all moving surfaces either by suitable aerospace grease or dry lubricant coating should be used.  No exceptions are allowed, even for lightly loaded friction-compatible surfaces.
  • On hard mating surfaces where hard coatings are used (such as Type III anodizing on aluminum), loads must be kept below the bearing yield strength of the substrate material (e.g., 60 ksi for 6061-T6 aluminum).
  • Smooth and polished surfaces are preferred.
  • Dissimilar material mating surfaces should have no mutual solid solubility or at least one of the two should have a heavy dissimilar coating (e.g., nitride, carbide, or oxide).
  • Caging devices should be designed to positively preclude relative motion between clamped surfaces when subjected to shipment or launch vibration.
  • Wet lubrication is generally preferred because friction is low and predictable.  The grease with the most heritage is the Braycote 600 series, a synthetic-fluorinated oil-thickened grease with micron-size Teflon powder.  The grease has extremely low outgassing (TML <0.1% and CVCM <0.05% for the standard 125 C 24-hr test) and concerns relative to contamination are negligible for virtually all spacecraft applications.  The wet lubricant usable temperature range is -80 to 200 C.
  • For extreme low temperatures and cryogenic applications, solid lubricants are preferred.  Epoxy and polyamide-bonded films can be successfully employed with proper application and burnishing to remove excess material.
• Table 2 summarizes the technology shortfalls currently affecting Air Force and Strategic Defense Initiative Organization (SDIO) mission requirements for deployable components, together with suggested tribomaterials (or design) solutions to overcome shortfalls.  [Fehrenbacher]

• Based upon a detailed study of the performance records of almost 400 satellites between 1958 and 1983, it was established that about 10% of the successfully launched satellites had some type of deployment anomaly, the majority of which were mechanical.  [Feherenbacher]
• Many of the problems experienced by satellites were due to thermal or thermal gradient problems that reduced clearances or caused lubricants to fail.  [Feherenbacher]
• It was demonstrated, on a test of a spacecraft oscillating scanner that the polyalpholefin (PAO) oil provided excellent lubrication, consistent torque with negligible torque noise, and good wear to 22,000 hr with the test still running.  The other oils (chloroaryalkylsiloxane (CAS), originally used in the application, and a perfluoropolyalkylether (PFPE)) exhibited a reduction in torque (loss of preload) and an increase in torque noise, as well as extensive wear after a few thousand hours.  [Feherenbacher]
• The best options for solid lubricant films for space applications appear, at present, to be ion-plated lead and ion-sputter deposition of, and/or ion-assisted deposited, MoS2.  These lamellar films have demonstrated very low friction operation in sliding and/or high low-load rolling bearings and latch and release mechanisms.  They are under development for a variety of ball bearing applications.  For solid lubricants for satellite gears, lead films were found to provide good lubrication after a breaking in period that produced a 100 Angstrom elastic film.  Best results were obtained for a film thickness of 1 micron.  Solid films of MoS2 and TiN in the same application resulted in unacceptably short gear lives, demonstrating that tribomaterials must be tailored to the system design.  MoS2 has, in fact, been shown to be an excellent lubricant for many space applications, although its reaction with atomic oxygen requires further study.  Recent sputtered-deposited films have shown a 10 to 100% increase in film life over previous MoS2-coated bearings.  [Feherenbacher]
• Both titanium carbide and titanium nitride have been demonstrated to be effective wear coatings under appropriate conditions.  Titanium carbide has been applied to gyroscope ball bearings and has increased operational lifetime by an order of magnitude in this application when used with an uncoated steel raceway and superrefined mineral oil.  To date, titanium nitride has been used only on tool steels, but the Aerospace Corporation is currently testing both gimbal and spin bearings with titanium-carbide and titanium-nitride-coated balls.  [Feherenbacher]
• The development of new polymeric bearing retainer materials is a critical need to achieve required bearing lifetime.  The phenolic materials that are commonly used have been demonstrated to absorb oil in a time-dependent and nonreproducible manner.  These retainer materials are unacceptable for the missions under consideration unless an active lubricant supply system is used.  [Feherenbacher]
• Avoid the use of wet lubricants where optical devices or sliding electrical contacts are employed.  [Rowntree]
• PFPE fluids have produced high torque noise and excessive ball bearing wear.  The precise mechanism of degradation is still not established.  In Europe, the evidence points to chemical reaction between nascent wear particles and the exposed oxygen in the Z-type molecule.  The product is described as a metal polymer, or "brown sugar", which is autophobic and thus repels the oil from the ball/raceway contact region.  [Rowntree]
• Ion-plated lead films are extensively used in Europe.  In solar array drives alone, more than 2 million operational hours in orbit have been accumulated.  [Rowntree]
• An important property of the lead film is its high load-carrying ability.  Under Hertzian contact, the as-deposited film flows plastically until a thin film (10 Nm thickness or less) remains and then elastically deforms the substrate.  In this condition, the film can survive contact loads approaching the static load capacity of a rolling element bearing.  [Rowntree]
• Thin films of gold have also been investigated as a bearing lubricant, but the higher yield strength and ductile adhesional property results in work-hardened debris and thus high torque noise.  Silver and indium have been investigated too, but actual usage in space is not reported.  [Rowntree]
• Sputtered application of MoS2 is the preferred and, perhaps, necessary method.  Sputtered films of MoS2 are currently applied to numerous space components such as screw threads, ball bearings, sleeves, and bushes.  [Rowntree]
• An investigation at ESTL of MoS2 films deposited by magnetron RF sputtering in which the rate of evaporation of the MoS2 target is greatly increased by magnetic field intensification of the plasma, led to significant gains in triboproperties under vacuum.  Not only is the friction coefficient remarkably low under pure sliding motion (values of 0.005 to 0.04 are typical), but the wear resistance of the film is greatly improved.  [Rowntree]
• Ion-beam application of MoS2 also appears promising, although it has not been used in space mechanisms.  A feature of this method is an increase in the density of the film and it is possible that this compaction may help in extending film lifetime.  [Rowntree]
• MoS2 works well with ceramics, such as titanium carbide and hot-pressed silicon nitride.  [Rowntree]
• An extensive study restricted to air usage in the United Kingdom over 10 years ago, showed that the PTFE/glass fiber/MoS2 combination was preeminent in terms of friction torque and endurance, provided that the maximum Hertzian contact stress was kept below 1200 MPa at room temperature.  [Rowntree]
• Friction torque of ball bearings under thrust load and low temperature is difficult to predict.  Unexpected increases in friction torque have been experienced.  Testing at temperature is recommended to determine torque levels.  [ESTL, Kaese]
• Linear rolling elements and cages can creep, which leads to high torque spikes at the end of travel.  These high forces were generated as the cages were driven into contact with the bearing end stops, at which point any further movement of the nonstationary races resulted in sliding motion between the races and the sliding elements.  In addition to causing higher friction forces, the effect also resulted in more rapid wear of the MoS2 film.  To prevent roller and cage creep, and thus eradicate high end forces, a cage speed control device is required to ensure the correct cage to ball speed ratio.  [ESTL, Roberts]
• Considerable care must be exercised when mounting close-clearance bearing components into aluminum structures that must operate at cold temperatures.  Contraction of the aluminum must be accounted for.  [Survey, Lowenthal]

Antennas and Masts

• Tracking and data relay satellite (TDRS) [Luce]
  • The field of view of one of the single-axis antennas was restricted, probably due to a pinched or snagged electrical cable that runs across one of the single-axis antenna gimbal joints.  The joint cable operation should have been checked on the ground and the design modified accordingly.  Cable circuitry should avoid regions where the cable can get caught or snagged.
  • The single-axis antenna delayed deployment by nearly 3 hr when one of the compartment attachment lugs came into contact with the compartment kick-off spring mechanism.  Interference between actuation devices and attachment lugs should be avoided.
  • One of the single-axis antenna drive motors stalled because the biax service loop harness became pinched between the boom and compartment.  The motor was reversed to relieve the pinch, and deployment proceeded normally.  Reversible motors can help correct deployment problems.
• On the second flight of the INTELSAT V spacecraft, the time required for successful deployment of the north solar array was longer than originally predicted.  The south polar array deployed as predicted.  The difference in deployment time was found to be due to a significant increase in hinge friction at low temperatures and vacuum.  The hinge friction problem was overcome by increasing the bearing clearances to allow for greater temperature variations and giving the hinges special lubrication.
• The Galileo's high-gain antenna, which opens like an umbrella, never reached the fully deployed condition.  [Johnson]
  • The failure was caused by galling and excessive friction in the midpoint restraint pins and V-groove socket of the struts, which required mechanical drive torques in excess of motor capacity to free the pins and permit deployment.
  • Contact stress of any mating surfaces should not be great enough to cause plastic deformation and/or destroy applied coatings.
  • Friction in vacuum can substantially exceed friction in atmosphere, especially when coatings are destroyed and galling occurs.
  • Moments applied to ball screws severely degrade their capacity.
  • The use of a dry lubricant, specifically MoS2, on a mechanism that is going to be operated in an atmosphere should be carefully evaluated.  The wear rate of the MoS2 in air is so much higher than in a vacuum, that any coatings could be worn out by air testing and shipping lubrication, and not provide the desired lubrication when needed.  Replacing dry lubricated surfaces just prior to launch, so that virgin lubricant surfaces are available is recommended, if feasible.
  • Shipping vibrations and ground testing can destroy coatings and dry lubricants.
  • Vacuum deployment tests on the ground, should include simulated vibrations prior to deployment.
• During ground testing of the dynamics explorer, an end-of-travel shutoff switch failed to activate during Astromast deployment.  The microswitch failure in space could have been catastrophic and points to the necessity for switch redundancy for mission critical components.  [Metzger]
• The mechanism was to deploy/restow two large Hubble space telescope deployable appendages in a varying but controlled manner.  The initial predicted aperture door mechanism temperatures could be well below -125 F. This proved to be a problem for the grease plating of Braycote 3L-38RP on the angular contact bearings.  The solidification temperature of this lubricant is approximately -120 F. The resulting stiffness of the lubricant caused unacceptably high bearing torques even though the mechanism would operate to as low as -160 F.  Braycote 3L-38 RP grease works well in angular-contact bearings in a vacuum if the temperature is kept above the grease solidification temperature.  The range of motion of the hinges is approximately 90.  For the aperture door mechanism, this motion takes place over 1 min, and for the high-gain antenna hinge, the time is 7 min.  [Greenfield]
• During subsystem testing of the high-gain antenna configuration, the tests were plagued by a problem that was finally diagnosed as lost motion.  This resulted in variable performance at the stowed position.  In a mechanism, it is important to eliminate all backlash to avoid lost motion.  [Greenfield]
• The Gamma Ray Observatory (GRO) had two solar array wings weighing approximately 500 lb each and one high-gain antenna boom assembly weighing approximately 525 lb.  The high-gain antenna did not deploy when it was initially commanded.  A portion of the antenna release mechanism (close to the antenna dish) was caught by a piece of thermal insulation blanket.  The lessons learned are: [Hinkle]
  • Deployment tests should be accomplished with the final configuration including thermal blankets.  Spacecraft attachments should be simulated accurately.
  • Interference that might be caused by thermal blankets should be evaluated during the design process.
• Mechanisms must be evaluated for vibration problems and appropriate damping applied.  Vibrations can cause unwanted deployment that must be constrained.  [ESTL, Abarrategui]
• Stowage time can inhibit deployment mechanisms, especially at soft-contact interfaces that require relative motion at deployment.  Rubber contact could cause separation problems by sucking or sticking.  MoS2 coatings can alleviate this problem.  [ESTL, Barho]
• Brush contact encoders are prone to a wear problem that renders them unsuitable for use on high-accuracy, high-reliability space mechanisms.  [ESTL, Gallagher]
• After positioning GEOS in its final orbit, its eight booms and five mechanisms were deployed.  Two axial booms showed anomalies during deployment and one of these, a long axial boom, extended to only about 80 to 90%.  To reduce the possibility of friction due to cold flow of guide rings, the tightening torque was reduced and the Teflon guide modified.  The release mechanism modification mainly concerned the ball release piston and ball cage area.  The hard edge of the titanium sleeve was replaced by a soft aluminum chamfer to prevent indentation of the balls.  The ball cage holes that were cylindrical in GEOS-1 are now conical to improve the ball release.  [ESTL, Schmidt]
• During the Hubble space telescope antenna pointing system testing, the internal thermostats failed making the internal heaters inoperable.  External heaters were bonded to the outside surface of the gimbal housing with externally mounted thermostats, completely bypassing the external circuit.  Where possible, the wiring for internal heaters and thermostats should be completely accessible in case the internal components fail, during protoflight tests.  [Ruebsamen]
• During acceptance testing of space telescope antenna pointing system gimbals, the external cover of the heater dislodged during thermal cycling test.  The cause was incompatibility of the coefficient of thermal expansion between the cover materials with the housing materials and the fact that the cover and housing were gold plated, which prevented a proper epoxy bond between two parts.  Three lessons learned were:
  • Heater covers should include a mechanical means of mounting along with the epoxy bond (i.e., screws). 
  • The area where the epoxy bond is to occur should be free of gold plating.
  • If external heaters are to be used, an epoxy designed for use as a thermal conductor should be designated and its coefficient of thermal expansion should match that of the major structure.  [Survey, Ruebsamen]

Actuators, Transport Mechanisms, and Switches

• A deployment actuator mechanism was developed for the Topex satellite.  Post-vibration testing showed that the dry lubricant film in the journal bearing was flaking causing an increase in torque.  The problem was determined to be excessive lubricant film thickness.  Applying the lubricant to one bearing surface rather than both and burnishing the film to reduce thickness resolved the problem.  [Jones]
• Thermal vacuum testing of the Topex deployment actuator viscous fluid rotary damper revealed a region of undamped travel, immediately after deployment had been initiated, followed by normal operation throughout the remainder of the travel.  The result was unacceptably high-impact loads in the damper input shaft as damper operation returned to normal.  Potential explanations included air pockets and ineffective thermal compensation.  The reason for the anomaly was never confirmed and another damper was installed.  Further investigation of rotary dampers is required.  [Jones]
• For a mirror transport mechanism, loads were developed during vibration testing that caused a rocking motion of the dihedral platform resulting in a pivoting motion about the latch cone axis.  This placed excessive loads on the pivot flexures, causing them to fail.  To limit the load, the pivots were enclosed in sleeves that restricted radial movement to acceptable levels.  [Stark]
• On April 11, 1991, a command to unfurl the Galileo spacecraft high-gain antenna resulted in a stalled motor about 50 sec into deployment [Johnson], which was considerably short of full antenna deployment.  The prevalent theory of cause has been that the undeployed ribs' locating pins were still locked or stuck in their receptacles due to a misalignment taper plus a high-friction condition.  Tests revealed that the transportation environment resulted in a classic fretting condition.  Since the fretting condition of small oscillatory translational movement coupled with high-frequency cycling was not duplicated in friction testing, a coefficient of friction greater than 1.4 could have resulted.  The lesson learned was: [Glenn]
  • Packaging for shipment should not allow relative motion between components.
• Redundant push-off springs should be incorporated for initial release of all spacecraft deployable appendages.  [Sharma]
• An anomaly occurred with a plunger-activated, hermetically sealed switch during ground testing of the Upper Atmosphere Research Satellite (UARS).  Gravity effects caused the plunger to deflect away from the switch preventing motor cutoff at the desired position.  The solution was to redesign the switch activation device so it was not gravity sensitive.  The lessons learned are: [Leary]
  • Mechanisms must be designed for both ground test and space operation.
  • Plunger designs of switches could pose problems on ground test due to gravity.  Cam actuation may be preferable.
• For harmonic drive support bearings, two oils were tested: NPT-4 (a neopentylester spacecraft oil) and Pennzane SHF 2000 (a synthetic hydrocarbon oil).  The effects of antiwear additives tricresyl phosphate (TCP) and naphthenate (PbNb) were also investigated.  Pennzane with TCP gave the longest life.  The failure mechanisms with the two oils were different.  Bearings tested with oils plus TCP failed due to wear.  Bearings tested with oils plus PbNb failed due to a hard, lead-containing carbon film, which resulted in high friction.  From this it appeared that TCP would be effective in light-load applications where low friction was important, while PbNb would be more suitable for high-load applications where friction was of secondary importance.  [Kalegoras]
• An optical actuator required accuracy better than conventional systems.  Table 3 summarizes the approaches taken by Lockheed to overcome the limitations of conventional designs.  [Lorell]
  • The use of a motor-driven screw or gear mechanism was rejected because of mechanical inaccuracies.  Piezoelectric devices require high voltages.  The best choice appears to be a voice coil-type actuator that can have high bandwidth capabilities and is both simple and reliable.
  • The force unloading system proposed by Lockheed may be useful in other satellite applications where it is necessary to maintain a continuous power input.  Eliminating the need for bearings and lubricants by the use of flex pivots also has merit.
• Dehydration of brake materials and accumulation of wear debris, trapped between the opposing surfaces, can cause a marked reduction in friction of brake materials.  Problems have been encountered with the asbestos/phenolic friction elements of the shuttle remote manipulator system.  When slip tested under load, the pads showed a greatly diminished friction in vacuum, which is fully recovered on return to atmosphere.  Polymers are also unacceptable because they will not provide sufficient friction as a brake material in vacuum.  Lessons learned are as follows: [Hawthorne]
  • Some ceramics or cermets can provide stable and moderately high friction as brake materials.  This group includes Cr2O3 and Al2O3/SiC.
  • To ensure in-vacuo stable friction, run-in of opposed surfaces is recommended.

• During development of robotic arms, the Europeans have found that phenolic/asbestos brake materials present torque anomalies under thermal vacuum conditions.  [Priesett]
• A movable stop mechanism activated flaps to change telescope aperture on command.  The mechanism consists of a rotary solenoid that drives dual four-bar linkages in synchronism to rotate butterfly flaps into position.  During testing, the mechanism jammed in the open position.  Galling and scuffing of the surfaces of a fixed stop and the mating stop surface on the actuating arm had occurred.  Some lessons learned are as follows: [Tweedt]
  • Ion-plated lead lubrication proved to be satisfactory for a lightly loaded, low-speed, intermittent journal bearing type of application at cryogenic temperature and in a vacuum.
  • Tungsten-carbide coating was effective in preventing galling and cold welding of the contacting surfaces on the fixed stop and the mating surface of the actuator arm when subjected to impact on contact.
  • The importance of exactly replicating the fits, geometry, and assembly parameters of the engineering models in the subsequent production of flight units has been very positively demonstrated.
  • Low temperature can cause reduction in clearance and consequent high torques.  Heaters may have to be applied to gear heads and other devices if excessive friction results.  [ESTL, Cawsey]

General and Miscellaneous

• Anomalies
  • Nonredundancy of the motion-producing elements.
  • Insufficient torque margin.
  • Snagging.
  • Stiction.
  • Binding of panel hinges.
  • Excessive impact loads from deployment.
  • Poor selection of solid lubricants. Molydisulfide solid lubricants absorb water, which can freeze and jam hinges and V-cone guides.
  • Improper cone angle for cone supports.
  • Excessive bending stiffness of wire harness at low temperatures.
• Lessons Learned
  • Torque Ratio: Tr = available torque/resisting torque > 4
    Torque margin: Tm = (available torque -resisting torque)/resisting torque > 3
    Tm = Tr -1.
  • Panel hinges should have spherical bearings with axial clearance to avoid binding.
  • Dampers are necessary to reduce kinetic energy at impact.
  • Tioxode-V provides an acceptable hard slippery coating.  Avoid molydisulfide solid lubricants.
  • Cone support angle <30 to avoid locking.
  • Joint actuators must have sufficient margin to overcome low-temperature wire harness torque.  Capability should be tested at temperature with wire harness.
  • Sensors should be applied to deployment devices to determine initial motion, intermediate position, and latch-lock indication
  • For articulation motors, sensors should be applied for output shaft position, null reference indication, speed, and current.
• United States Air Force Mil Standard, MIL-A-83577B, sets forth general requirements for the design, manufacture, quality control, and testing of moving mechanical assemblies to be used on space launch vehicles.  Many of the requirements listed are based on anomalies in spacecraft.  Deployables shall (where practicable) be designed so that they are self supporting when placed in any orientation relative to gravity while in either the stowed or deployed configuration.  Deployables shall be designed with sufficient motive force to permit full operation during ground testing without depending upon the assistance of gravity to demonstrate deployment.
  • Retention and Release Devices.  Positive retention provisions shall be provided for deployables in the stowed and in the deployed position.  The effects of deflections such as those induced by centrifugal forces or differential thermal growth of any deployable with respect to its space vehicle attachments shall be considered in the design of the attachments.  Devices that may be subject to binding due to misalignment, adverse tolerances, or contamination shall not be used.  Slip joints shall be avoided (where practicable).
  • Pin Pullers.  Where pin pullers are used, such as cartridge-actuated or nonexplosive pin pullers, they shall be designed to be in double shear.  The design, installation, and checkout procedures for pin pullers shall ensure that loads due to misalignment of the pin are within design limits.  A minimum retraction force margin of safety of 100% at worst-case environmental conditions and under worst-case tolerances shall be maintained for all nonexplosive pin pullers.
  • Bearings.  For deployables, hinges, and linkages, self-aligning bearings shall be used (where practicable) to preclude binding due to misalignments.  Bearings shall not be used for ground current return paths or to carry electric current.  All ferrous material bearings shall employ (where practicable) a corrosion-resistant steel that is in accordance with QQ-S-763.  Rolling element bearings shall (where practicable) be of 440C stainless steel; however, 52100 or M50 steels may be employed providing they are suitably protected from corrosion.
  • Dry Film Lubrication.  Application of dry film lubricants to the surfaces of bearings, V-band clamps, coil springs, leaf springs, clock springs, constant force springs, gears, or other items shall be by an appropriate process.  Bonding, peening, sputtering, vacuum deposition, ion plating, or any other process that provides a predictable, uniform, and repeatable lubricant film may be appropriate.  Composite materials containing dry film lubricant in their composition may be used in appropriate applications.  Where appropriate, dry film lubricants should be burnished to provide a uniform film that reduces the coefficient of friction from the as-applied condition and minimizes the generation of lubricant powder.  Corrosion-resistant materials shall be used in bearings employing dry film lubricants.  Consideration shall be given to protection of MoS2 dry film lubricants from adverse affects due to exposure to atmospheric humidity.  Testing in a humid environment shall (where practicable) either be avoided or minimized.
  • Hard Coatings.  Hard coatings such as titanium carbide, titanium nitride, and chromium may be used to extend life, reduce wear, prevent welding, reduce friction, and prevent corrosion either with or without a liquid dry film lubricant.
• Cryogenic cooling is necessary for infrared detectors.  There is a need for a remotely controlled, motorized cryovalve that is simple, reliable, and compact and can operate over extended periods of time in cryovac conditions.  The lessons learned are as follows: [Lorell]
  • In general, the mechanical problems that are encountered with cryomechanisms are the result of: a) mismatches in the coefficients of thermal expansion, and b) the friction and wear properties of moving parts.
  • Motors should be of the brushless or stepper design because brushes are unreliable in vacuum.  They must have adequate power to overcome friction even with unlubricated surfaces.  Motor leads to the outside are also thermal paths along which heat can travel.
  • There are two sources of heat that can be of concern.  One is the thermal energy generated by the equipment inside the shell and the other is thermal energy from the outside traveling along the wires.
  • Since the mechanisms are usually located inside the shell where they are inaccessible, it is critical that they function with a high degree of reliability.
• A 10-yr review of the major test observations at ESTL is given, during which time some totally unexpected failure modes have been detected.  Full confidence now exists in many mechanisms and component designs, and much valuable data have been obtained that are available to mechanism designers for improving reliability.  Lessons learned are as follows: [Parker]
  • Thermal vacuum testing has proved to be essential in providing a detailed assessment of the reliability of complex mechanisms by subjecting them to realistic simulations of the anticipated flight conditions, where lifetimes in excess of 10 yr are now expected.
  • Thermal vacuum tests have been proved to be cost-effective in avoiding delays and disturbances to a number of European projects, as several previously unknown failure modes have been detected.  There is now complete confidence in many designs following independent, fully documented performance assessment.
  • Much valuable data have been obtained on many mechanisms and components about their operational parameters, power dissipation, and wear processes.  There is frequent evidence of how important it is to implement comprehensive inspection and product assurance systems at all stages of mechanism development and construction, to avoid the human factors of accidents, errors, and poor judgment.
• The solar maximum mission satellite was launched into orbit with experiments to monitor solar activity.  To obtain common object observations, experiments must be coaligned within 90 sec of the spacecraft pointing vector.  Lessons learned are as follows: [Federline]
  • Using kinematic principles and good design practices, it is possible to produce a stable support platform that is isolated mechanically and thermally from its supporting structure and from experiments mounted on it.
  • Through the use of reference surfaces, gages, and optical measuring techniques, it is possible to coalign experiments to a high degree of accuracy.
• Several panels on the long-duration exposure facility were coated with Everlube 620C, a common solid lubricant.  It was completely degraded due to ultraviolet exposure.  Phenolic systems are susceptible to ultraviolet degradation, a fact that should be transmitted to design engineers.  [Survey, Gresham]
• Almost every deployment device related to a spacecraft on-orbit configuration change is a mission-catastrophic single-point failure if it does not function properly.  The following are some ground rules from lessons learned for designing such devices: [Hinkle]
  • All deployed appendage programs must have engineering test units.
  • All flight units and engineering test units must be testable to determine deployment margins.
  • Analyses must be verified by judicious hardware testing programs.
  • There must be adequate life testing early in the program.
  • There must be redundant backup systems in all critical areas.
  • Worst-case analyses and failure modes effects and critical analyses must be performed and verified by actual hardware testing.  Conditions that must be considered include worst-case friction, misalignment, and excessive preload.
  • All devices should be designed to be as simple as possible to do an adequate job.
  • Consider the effects of mounting system redundancy and structure-induced input forces not only on the devices but also on the internal components of the devices.
  • Look for all possible hostile environmental effects and design to minimize their impact.  Pay particular attention to vacuum, thermal control, and g effects that are not always intuitive to the designer.
  • Select devices that are directly testable and reusable to be qualified by analysis rather than single-use devices that are statistically qualified to a pass/fail criterion.
  • Use the largest possible margin of operation in all devices consistent with consideration of undesirable effects on the surrounding hardware.  These undesirable effects include large forces developed by end-of-travel latch-up and shock from pyrotechnic device firing.
  • Proper installation should be verifiable.  Knowledge of preloads, position of parts, status of switches or other electrical interfaces should be known or testable.

Rotating Systems

Momentum Wheels

• Bearing lubricant depletion between the ball race retainer causes cage instability and subsequent pointing errors, increased bearing torque, and wheel vibration.  [Feherenbacher]
• The practice of using steel bearings lubricated with mineral-oil-based greases or superrefined mineral oils with porous phenolic cages is unacceptable.  Tests by Aerospace Corporation have shown that the phenolic cages continue to absorb oil from the bearing ball contact regions during operation instead of supplying oil, thereby hastening the onset of cage instability.  [Feherenbacher]
• An active oiling system can be incorporated to periodically lubricate the bearings and avoid erratic torque behavior.  The trade-off is added complexity.  [Feherenbacher]
• The characteristic cage instability frequency is an inherent geometric mass property of the cage/bearing system and is essentially invariant to external vibration, bearing speed, or lubrication condition.  [Lowenthal]
• A biased cage has a different instability pattern and frequency than the commercial unbiased cage.  Both the cage motion pattern and the instability frequencies are reasonably predictable.  [Lowenthal]
• Each cage-bearing design has a critical friction coefficient for instability.  The ball cage interface is much more critical than the cage land.  This was also predicted by computer simulation.  [Lowenthal]
• Increased lubricant viscosity enhances the chances and severity of instability.  Room temperature grease triggered instability, while room temperature oil and warm grease did not.  [Lowenthal]
• Simulation computer codes can predict cage instabilities for steady-speed conditions.  They cannot predict stability onset as speed is ramped up.  Commercial codes are available from P.K. Gupta and Avcon Corporation.  [Lowenthal]
• Bearings shall meet ABEC 7, 7P, or 7T tolerance (or better) in accordance with the AFBMA standards.  [USAF MIL Standard, MIL-A-83577B; 1 February 1988]
• Momentum wheel bearings shall operate in the elastohydrodynamic film regime and confirmed by analysis or test.  [USAF MIL Standard, MIL-A-83577B; 1 February 1988]
• Magnetic bearings have the potential to provide a superior alternative to ball bearings.  [Yabu-uchi]
• For a combined Earth scanner and momentum wheel, the bearing lubricant condensation on the rotating scan mirror cannot interfere with the infrared radiation reflection of the mirror.  Pennzane X2000 was the preferred lubricant over Bray 815Z because it has a much higher transmission in the region of the horizons sensor's infrared bandpass.  With the exception of its lower viscosity index, the Pennzane X2000 was superior to the Bray 815Z.  [Bialke-3]
• Ball bearing lubrication remains the principal life-limiting problem on momentum and reaction wheels.  [Auer]
• Means for lubricant replenishment can improve life characteristics.  A lubrication reservoir actuated by centrifugal force to relubricate the bearings is described.  The base oil is stored as a grease in a ring-type chamber which is centrifuged out through orifices.  The rate is limited by the thickener of the grease that forms a microporous filter in the vicinity of the orifices.  Overlubrication, as measured by torque increase, does not appear to be a problem for this system.  [Auer]
• Oil lubrication is favored over grease because of superior torque characteristics and means of replenishment.  [Auer]
• The minimum amount of initial lubricant required is 2 mg.  [Auer]
• With the replenishment device, extended life appears promising.  The test results and flight operations are promising and not conclusive.  Two ground test wheels (3000 and 3800 rpm) had run for 16 yr after full qualification.  These wheels had been subjected to temperature cycling and showed minimal changes in torque.  The longest operational time in space was the OTS wheel, which had run 11.5 yr at the time this paper was presented.  [Auer]

Reaction Wheels

• Passive oilers, which are programmed to release lubricant at a predetermined rate, do not apply lubricant as needed.  Overlubrication or underlubrication can occur.  Data from the digital signal processor indicate that after about 3 yr of operation, the spacecraft again manifests instabilities associated with lubricant depletion.  A need exists for an active oiler, commandable from the ground.  [McConnell]
• Bray 815Z lubricant, which has the positive qualities of low vapor pressure and high viscosity index, is not a suitable lubricant for a reaction wheel.  Bray 815Z is a synthetic fluorocarbon which is unable to dissolve antiwear additives.  It performs well when the operating speed is sufficient to form an elastohydrodynamic film, but it has poor performance in the boundary lubrication regime.  Thus, the Bray lubricant is not acceptable for a reaction wheel that must go through zero speed.  [Bialke]
• An acceptable lubricant for reaction wheels available from Pennzoil is Pennzane X2000 (a synthetic hydrocarbon) with 5% PbNp as an antiwear additive.  It has a very low vapor pressure, good viscosity index, and good boundary lubrication qualities.  [Bialke]
• An ironless armature motor is ideal for the reaction wheel drive being both power and weight efficient.  [Bialke]
• A Hall generator is the preferred tachometer.  It has good accuracy, low complexity, low power consumption, and zero speed measurement.  [Bialke]
• Stability of highly accurate pointing devices, such as those on the Hubble space telescope, can be destroyed by reaction wheel assembly induced vibrations.  A Sperry damping device alleviated the problem.  The central element is a viscous fluid damped coil spring suspension system.  Each reaction wheel assembly is suspended on three units.  Damping is provided by a low-volatility silicone-based fluid (Dow Corning 200 series) confined by metal bellows to internal cavities.  [Hasna]
• Conical Earth sensors on several satellites experienced lubricant failures because the Bray 815Z lubricant is unstable at boundary lubrication conditions.  Changing to a chemically stable hydrocarbon lubricant (Pennzane 2000) with extreme pressure additives, such as TCP or PbNp, resolved the problems.  [Bialke-2]
• The lifetime of oil-lubricated bearings is very temperature dependent.  Higher temperature results in higher evaporation rates and more surface migration.  Also, higher temperature lowers the viscosity which reduces the elastohydrodynamic film.  [Bialke-2]
• The disturbing torques produced by reaction wheels at near-zero speed are considerably greater than the normal torque noise level, with consequent reduction in attitude control.  For sensitive missions, adequate tests are indispensable for the controller design.  Bearing cage instability can be catastrophic and is difficult to predict.  This occurred on a reaction wheel.  ESTL and SNFA arranged a cure by using cages with loose-fit pockets and applying 10 ml of oil.  Flight bearings will have nonequispaced pockets of the original diameter.  [ESTL, Stapf]
• For reaction wheel support bearings, three oils were tested: SRG-40 (a highly refined mineral oil), Nye 179 (a synthetic PAO oil), and Nye UC-7 (a synthetic polyolester (POE) oil).  All of the oils were formulated with TCP, and tests were carried out in different atmospheres.  The tests showed that the TCP did not function as an antiwear additive in UC-7.  Nye 179 was considered the best choice for this application.  Its performance in vacuum was far better than that of SRG-40, and its performance in helium was the best of all oils tested.  [Kalegoras]
• The use of oxygen as a component of the fill gas of reaction wheels was determined to be unnecessary and generally harmful to the life of the bearing lubricant.  [Kalegoras]

Control Moment Gyroscopes

• The major contributor to torque noise is the dc offset in the drive voltages and the transmission gearing.  [Cook]
• A small amount of cross coupling between the inner and outer gimbal servo loops causes variations in frequency response as a function of the inner gimbal angle.  These variations appear to be acceptable for current applications but future improvements are needed.  [Cook]
• A single gimbal can provide greater torque capability for the same angular momentum than a double gimbal.  However, a double gimbal has less complex control laws and greater flexibility to support a large variation in vehicle inertia.  [Cook]
• The wheel material and dimensions should provide the necessary angular momentum with a safety factor of 4 based on a yield stress at 105% of nominal speed.  [Cook]
• A two-stage parallel-path spur gear transmission with installed windup of one gear with respect to the other will eliminate undesirable backlash.  [Cook]
• A control moment gyroscope bearing did not receive adequate lubrication from a centrifugal lube nut.  The following modifications were made to improve oil supply:
  • Cage oil feed hole was reduced to overlap outer race groove under all conditions.
  • An additional set of feed holes was provided to centrifuge oil into the center of the outer race contact area.
  • The retainer flange was widened and the ID slope changed to accommodate the oil hole angle and increase lube nut overlap.
  • The retainer OD was increased to allow maximum extension into the race groove of oil feed holes.  [Survey, Dolan]

Gears

• Worm gears can experience excessive torque under cold vacuum conditions due to lubricant starvation.  Soft extreme pressure greases that contain MoS2 are effective in alleviating the problem (e.g., Braycote 608).  [Purdy]
• Careful worm gear run-in is essential to good operation for worm gears.  The break-in should be gradual with light loads and abundant lubrication.  Purdy]
• Techniques for replenishing the lubricant as it is wiped off the tooth surfaces are beneficial to worm gear operation.  On the Rexnord mechanism, a wiper system was installed to force grease back onto the gear teeth.  [Purdy]
• In worm gears, unacceptable lubricant starvation can be caused by allowing the gears to reach a stall condition.  [Purdy]
• General design guidelines for worm gears are given in Table 4.

• In a dual-wound dc brush motor gearhead, a shaft failure occurred by a fracture in the cross section from the gear face to the bearing spigot.  The failure was attributed to excessive stress concentration and was ameliorated by increasing the blend radius from 0.125 to 0.250 mm and thus reducing the stress concentration factor from 4 to 1.5.  The lesson is to examine the design for stress concentrations carefully and ensure adequate safety margin.  [Henson]
• In a dual-wound dc brush motor gearhead, bearing failures were experienced.  Bearing loads should be carefully examined and a double bearing applied, if necessary.  A Tuftride process applied to the bearing spigots reduces wear debris and avoids bearing contamination.  The Tuftride process should be applied after the bearing spigot is finished ground.  The growth of the Tuftride process is insignificant, and if applied prior to grinding, it could be removed by wear.  [Henson]
• All gears used in moving mechanical assemblies shall be in accordance with the standards of the American Gear Manufacturers Association (AGMA).  Hunting-tooth gear ratios shall be used, where the application is appropriate, to distribute wear.  For better protection of the gear teeth, the through hardness or surface hardness (or both) may be increased, and the surface finish of the teeth improved through grinding, honing, lapping, and prerun-in.  The through hardness may be increased by material or heat treatment changes.  The surface hardness may be increased by nitridng, carburizing, induction hardening, or anodizing.  Undercutting of spur gear pinions should be avoided.  [MIL Standard, MIL-A-83577B; 1 February 1988]
• An harmonic drive flex spline galled severely at the bearing/flexcup interface.  The anomaly occurred due to poor material selection.  Materials must be carefully selected to avoid galling of sliding surfaces.  Also, lubrication helps to prevent galling.  [Survey, Farley]

Motors

• BRUSH-TYPE MOTORS SHOULD BE AVOIDED.  CARBON BRUSHES WEAR EXCESSIVELY IN VACUUM.  Wear debris contaminates the bearings, increasing drag and reducing life.  Accumulated debris shorts the commutator, increasing current and resulting in motor failure.  Some organizations take necessary precautions in material selection and coatings that permit brush motors to perform satisfactorily (see Table 5).  The use of these motors, however, require substantiation by experience and/or test.  [Sharma]

• Brushless dc, permanent-magnet dc, and brushless stepper motors are the preferred motors.  [Sharma]
• Stepper motors can have positioning errors due to:
  • The encoder
  • The drive electronics
  • The attitude control electronics
  • A power supply interruption
  • A single-event upset in the electronics
  • A mechanical failure of the unit.  [Sharma]
• The torque margin for any motor > 3, where TM = Ta/Tr - 1
  Ta = available torque
  Tr = resistance torque
  TM = torque margin.  [Sharma]
• The design torque margins should be verified during flight testing.  [Sharma]
• In rotary actuators, a hard-stop collision can cause the rotor to continue to turn, which elastically winds up the harmonic drive.  The spring energy of the harmonic drive can catapult the motor backward three steps as it unloads.  The motor then picks up the pulse signals as if it were starting from standstill and drives into the hard stop repeating the same series of events over and over.  A hard stop must be avoided by proper application of end-of-travel limit switches.  [Sharma-2]
• Motor drives for rotary actuators should be a dc torque motor or stepper motor.  The dc motor should be of the brushless permanent-magnet type with position and velocity sensors.  [Sharma-2]
• The output shafts of rotary actuators should be supported by a pair of back-to-back duplex bearings (for high-moment resistance) preloaded for a desired stiffness and life span.  [Sharma-2]
• In a brush motor gearhead, brush debris caused problems and reinforces the view that brushless motors should be applied if possible.  The brush material was Boeing Compound 046-45 because of good wear resistance in vacuum.  It consists primarily of MoS2, which requires purging for operation in normal atmosphere.  Post-test examination revealed brush debris that had blown around the gaseous purge applied during air operation.  During the initial phase of the ambient life test, the winding current trace became noisy and the shaft speed reduced.  It was concluded that the temporary anomalous performance was caused by a brush fragment.  [Henson]
• Motor winding redundancy is recommended in the event of winding or connection failure.  A clever scheme is described by Henson.  [Henson]
• Stepper motor stability is very dependent on friction and damping and it is important to ensure that adequate friction and damping are present over the range of operating conditions.  [Kackley]
• Superimposing rotordynamic behavior and separatrices on the phase plane technique is a valuable tool for analyzing stepper motor stability.  [Kackley]
• Simulation analyses is valuable to determine problems and solutions prior to building and testing expensive hardware.  [Kackley]
• High bearing torque was encountered on the despin drive assembly of two flight models of the HELIOS solar science satellite.  Improving the perpendicularity of the lower bearing inner race seat from 0.8 to 0.3 arc-min dropped bearing drag at -50 C about 40%.  [Phinney]
• Bearing distortions can increase bearing torque.  On the HELIOS despin drive assembly, a favorable indexed rotation of the end plate reduced torque significantly.  The end plate and aluminum housing were distorted.  [Phinney]
• Small, fractional horsepower motors are likely to experience cold-temperature performance problems if Pennzane or Rheolube bearing lubricant is used.  The lubricants become very stiff at cold temperatures and start-up torque becomes appreciable.  A lubricant-channeling phenomenon was observed, which interfered with cold motor start-up and running capability.  Braycote Micronic 601 bearing lubricant did not interfere with motor performance.  Small rotary components may be sensitive to lubricant effects not seen in larger hardware.  Special testing should be planned to evaluate cold-temperature lubricant start-up as well as running torque in small components.  [Survey, Marks]

Bearings and Lubrication

• Retainer instability is a major cause of bearing failure in control moment gyroscopes, momentum wheels, and reaction wheels.  [Boesiger]
• There is a critical friction level associated with each retainer design, beyond which the retainer is unstable.  [Boesiger]
• Ball pocket friction is more critical to stability than retainer land friction for the bearings investigated by Boesiger.  [Boesiger]
• Optimization of the retainer design was accomplished by computer simulations coupled with experimentation.  Computer codes were useful tools and qualitatively compared with experiment.  [Boesiger]
• Operating ball bearings lubricated with Z25 (a perfluoroether) in a vacuum results in an interaction between the lubricant and the races.  This resulted in race wear and oil degradation.  [Baxter]
• When ball bearings lubricated with YVAC 40/11 (a perfluoroether oil recommended for instrument bearings) are operated in a vacuum, there is no oil degradation and no wear.  However, the higher viscosity of the YVAC 40/11 leads to undesirable running torque.  [Baxter]
• Modification of the bearing surfaces with inert coatings, that results in decoupling of the lubricant from the bearing surfaces offers the best course to ensure maximum lubricant life.  [Baxter]
• Most mechanical problems with momentum/reaction wheels, control moment gyroscopes, and gyroscopes are lubrication problems.  Table 6 provides a sample of experience.  [Fleischauer]
• There are two primary types of lubrication problems:
  • Supply or loss of lubricant
  • Chemical reaction (oxidation, polymerization) of lubricant. [Fleischauer]
• Synthetic oils can increase life by a factor of 10.  [Fleischauer]
• Sputter-deposited solid lubricant thin films provide low friction and long life.  [Fleischauer]
• Hard coatings and ceramic parts are used for low torque noise.  [Fleischauer]
• Lubricant additives, such as TCP, provide protection of contacting surfaces to reduce wear and minimize torque.  [Fleischauer]
• The relative wear life of PAO lubricants is significantly greater than PFPE lubricants.  [Fleischauer]
• Lubricant replenishment is a major problem with spacecraft bearings.  A centrifugal bearing cartridge design, invented at the Draper Laboratories, provides a method for a continuous and controlled supply of lubricant without incurring excessive torque.  [Singer]

• Retainerless instrument bearings avoid cage instability and are advantageous if ball impact is not a problem.  [Singer]
• Screening tests provide an accurate and expeditious approach to predict bearing cartridge performance.  [Singer]
• Accuracy, mobility, and lifetime requirements require tribological interaction early in the design phase.  A significant number of spacecraft anomalies are attributable to tribology problems as outlined in Volume II, page 329, Table 1. [Fleischauer]
• Problems in rotating assemblies are often caused by ineffective lubricant supply, caused by inadequate initial amount, loss via transport processes, normal consumption without resupply, and chemical degradation.  [Fleischauer]
• Perfluorinated lubricants cannot dissolve antiwear additives, and thus are not suitable for boundary-lubricated applications (reaction wheels, gimbals).  [Fleischauer]
• PAO lubricants significantly outlast a silicone oil for oscillatory motion.  It is expected that these synthetic oils can be applied to high-speed applications to provide added protection against retainer instability and wear.  [Fleischauer]
• Titanium-carbide-coated balls have been used in gyroscope bearings with uncoated steel raceways and superrefined mineral oil to produce operational lifetimes a factor of ten or more longer than for uncoated balls.  The commercial process for coating bearing parts with TiC is available in the United States but has only been used for instrument bearings of the type used in gyroscopes.  Titanium-nitride coatings are used for tool steels to provide much longer service lives and considerable research and development is underway to use TiN for bearings and gears.  Tests are currently under way to test the performance of both gimbal and spin bearings with TiC- and TiN-coated balls.  [Fleischauer]
• Analysis of lubricants from laboratory tests in control moment gyroscope bearings show depletion of oil from grease samples taken from control moment gyroscope spin bearing cage surfaces and no depletion from samples of bulk grease.  Analysis of metal parts show little evidence of wear although some metal is found in degraded lubricant.  Analytical simulations and measurements of bearing motions suggest cage instability may be involved in retainer wear and ultimate bearing torque increases.  [Fleischauer]
• PAO and multiple-alkylated cyclic compounds (Pennzane) are excellent candidates for use in spin bearings of reaction/momentum wheels, in solar array drives, and in rate gyroscopes.  The PAO lubricant did well in both hard vacuum and in atmosphere of 380-torr helium gas.  [Fleischauer]
• The formulation of Pennzane with TCP in solution outperformed the other systems tested, however, considerable wear was noted.  [Fleischauer]
• Pennzane plus Naphthalene had less torque life than with TCP additive, but there was no evidence of wear.  The increased torque failure was caused by the accumulation of excessive protective additive film containing metallic lead and carbonaceous material.  The conclusion is that varying the amount of Napthenate could lead to superior friction and wear performance.  Future tests are planned.  [Fleischauer]
• A run-in period is recommended for lubricated ball bearings to transfer lubricant from the ball pockets of the sacrificial retainer to the balls and then to the raceways.  Approximately 1.3 106 cycles of run-in were accomplished.  [Fleischauer-3]
• An optical chopper assembly had power beyond specifications.  The bearing power loss is very sensitive to the amount of lubricant present and, from observations during testing, this was the probable cause of the anomaly.  [Allen]
• For low-speed operation (<3000 rpm) a fixed lubricant oil quantity in a shielded bearing is adequate for a 10-yr life.  Bendix applies shielded contact bearings: R4A, R6, R8, and R10.  Lubricants include Winsor lube (MIL-L-6085A) plus 5% TCP.  [Allied Signal Aerospace (Bendix)]
• For high-speed operation (>3000 rpm), a make-up mechanism must be provided to overcome the oil loss due to centrifugal force.  Angular-contact bearings (104H, 106H, 107H, and 305H) are applied.  Bendix uses proprietary design phenolic retainers and an active continuous lubrication system.  KG-80 (MIL-L-83176A) superrefined mineral oil is utilized.  [Allied Signal Aerospace (Bendix)]
• Grease lubrication for momentum/reaction wheels is not recommended because of high running torque, torque variations, uncertain lubricant supply, and retainer instability.  [Allied Signal Aerospace (Bendix)]
• To produce a boundary lubricating film using a liquid lubricant, a run-in must be performed.  [Vest]
• For high-load boundary-lubricated contacts, a bonded solid film lubricant, such as MoS2, is recommended.  [Vest]
• For slow-speed ball bearing rotation, a Teflon or MoS2 filled grease, or a transfer film lubricating polymeric cage is recommended.  [Vest]
• Sliding motion applications are mostly boundary lubricated.  A high load-carrying grease with an extreme pressure gradient additive must be used.  The grease produces a high load-carrying solid film, such as Teflon, MoS2, graphite, or TCP between the rubbing surfaces.  [Vest]
• Despin bearings lubricated with ion-plated lead were capable of meeting the GIOTTO mission life with an insignificant noise spectrum.  [Todd]
• Tests of the complete energized despin mechanism on GIOTTO showed that the stepper motor harmonics excited a strong undamped torsional resonance of the antenna at certain speeds.  [Todd]
• After approximately three months of life testing, the lubricant in the Galileo slip ring bearing (KG80 oil) had a thick, black, gooey appearance and the bearing friction torque was higher than expected.  Even careful cleaning of spacecraft components can leave residues that may eventually react with adjacent materials.  Cleaning processes must be followed by an outgassing vacuum-bake treatment.  This is particularly important for porous materials that may have absorbed various fluids, including the cleaning medium itself.  [JPL SSEF, Langmaier]
• Phenolic retainers must be carefully and thoroughly dried to remove any absorbed moisture before they are impregnated with oil.  Otherwise, the retainer will not saturate and can absorb and remove oil from the bearing it is intended to lubricate.  Thus, the retainer becomes a liability rather than an asset.  [Bertrand]
• Current telemetry can detect spin motor current, which is proportional to the drag torque, and an increase in bearing temperature, which is also indicative of the increase in drag torque.  These measurements provide an indication of the need to supply fresh oil to the system.  The authors propose to use Coray 100 (an uninhibited napthenic-base machine and engine oil with a viscosity of about 110 cs at 40 C) to resupply the Andock C grease that lubricates the control moment gyroscope bearings.  The system is essentially a pressurized reservoir with a solenoid activated by the loss of lubricant sensor.  [Smith] In the reviewer's opinion, in a weightless environment there are questions about how a drop of oil will behave.  Even at a distance of 0.004 in., the drop may not transfer smoothly.  It may touch and then be slung off the moving surfaces to create a number of finer droplets that will float around the bearing housing.  Any lubrication scheme should be evaluated in a weightless environment.  [Murray]
• X-rays can be used to provide images of balls in a bearing that are not directly visible.  Using the x-ray technique, it is possible to measure the contact angle in assembled bearings.  [Fowler]
• Advanced elastohydrodynamic computer simulation techniques can provide benefit in design of space lubrication systems.  [Benzing]
• Failure modes of despin mechanical assemblies operation include the following:
  • Insufficient bearing lubricant film thickness
  • Lubricant incompatibility with system materials
  • Inadequate lubricant quantity
  • Improper lubricant transfer
  • Lubricant creep
  • Lubricant dewetting
  • Lubricant degradation
  • Bearing and cage instability
  • Torque variations
  • Slip ring and brush wear
  • Lubricant volatility
  • Cage wear.  [Benzing]
• Bearings operating in the boundary lubrication regime (i.e., contact asperities) shall be avoided where practicable.  If bearings must be operated in the boundary lubrication regime, a boundary lubricant with good antiwear characteristics shall be used.  Perflourinated polyether and silicone lubricants should be avoided in this regime except where light loads and limited travel are expected.  Where bearing lubricant reservoirs are used, the reservoir shall be attached, where practicable, to an area of relatively high temperature to enhance molecular and surface flow into the bearing.  Barrier films or shielding or both may be used to separate the bearing from reservoirs to minimize surface migration such as that caused by loss of lubricant due to wicking action of the reservoir.  Incorporation of the above techniques dictates that the lubricant transfer mechanism be primarily by molecular flow.  The preferred approach to lubrication of bearings involves placing the reservoirs in intimate contact with the bearing races and adding a larger amount of lubricant than would be ordinarily required to provide acceptable lubricant films.  The above method of lubrication is preferred providing that any increase in churning torques can be tolerated.  [MIL Standard, MIL-A-83577B; 1 February 1988]
• Bearing lubrication tests and supporting analyses shall be used to show that the chosen lubricant transport mechanisms, such as surface migration, vaporization, and wick action provide effective lubricant films over the expected operating temperatures, thermal gradients, and internal environments.  If providing adequate life of bearings depends on their operating in an elastohydrodynamic lubrication regime and not in the boundary lubrication regime, and it cannot be clearly shown by analysis that the bearing operating range as well is well within the regime, then a test method (such as contact resistant measurements) shall be used to establish that an elastohydrodynamic film is being generated.  In general, the lubrication system variables that should be substantiated by component development tests include (as appropriate) amount of lubricant, retainer design, reservoir design, and the reservoir proximity to the areas requiring lubrication.  When liquid lubrication is used, the design shall ensure that migration of the lubricant through the seals is not excessive or detrimental to the space vehicle.  [MIL Standard MIL-A-83577B; 1 February 1988]

Slip Rings and Roll Rings

• Roll rings are effective rotary joint electrical transfer devices and avoid the deficiencies of slip rings and flex capsules.  Flex capsules are limited with respect to rotation and fatigue life.  Slip rings wear due to sliding electrical contacts, generate debris, and require lubrication.  [Batista]
• Roll rings have had considerable development for both high- and low-power applications.  They are reliable, low-noise, drag-torque devices and should receive primary consideration for rotary joint electrical transfer applications.  [Batista]
• To accomplish noise reduction, plating processes, plating purity, and cleaning processes must be carefully controlled.  [Batista]
• High-purity plating and elimination of metallic oxides from surfaces by stringent reduction of low-nobility metals in the gold-plating process enhances noise reduction.  [Batista]
• Software that models geometric tolerances and maximizes rolling efficiency is very helpful to roll ring design.  [Batista]
• Flexure fatigue of the roll rings must be considered and the rings designed to accommodate the specified life cycling.  Fatigue tests carried out on beryllium-copper roll rings made from bar stock showed that the endurance limit was approximately 20% lower than published data.  The published data were generated from test samples that had grains oriented in the most advantageous direction.  Thus, the design of the roll ring should be based on a lower endurance limit with adequate safety margin.  [Smith]
• Contamination of the flexures and ring surfaces can cause high noise.  A principal source of the noise is copper and lead oxides on the surface.  Contamination can come from plating, migration of substrate materials through the plating, or migration from adjacent components.  Great care must be taken to ensure that contamination is not introduced during plating and is not allowed to take place after plating.  [Smith]
• Corona effects can be prevented by avoiding line of sight between conductors of different potential and by using appropriate insulation.  [Smith]
• A high correlation was found between the presence of silicones in the system and resultant electrical noise.  The primary source was silicone grease used to lubricate other components.  Silicone sources should be eliminated around roll rings.  [Smith]
• Primary sources of outside contamination include: organic films, silicone, and metal oxides.  Migration of metallic oxides can come from solder used to attach the lead wires.  In the Holloman roll ring design, solder was separated from critical surfaces by plastic rings with good results.  [Smith]
• Particularly important in a signal roll ring application is the isolation of adjacent circuits.  [Smith]
• For high power transfer, a multiple-flexure design in which the flexures are separated by rolling idlers is required.  [Smith]
• Slip ring assemblies were constructed of gold- or silver-plated rings and wire wipers lubricated with the same fluid lubricants used in the bearings of the despin mechanical assemblies.  However, extreme care is required to prevent excessive oxidation of the MoS2 lubricant and simultaneous tarnish formation that results in unacceptable electrical noise and even measurable torque increases.  Many such problems with electrical noise can be traced to the fabrication and assembly practices during construction of the slip ring mechanisms, but even after incorporation into satellites it is still necessary to protect the brushes from atmospheric exposure.  [Fleischauer]
• Anomalous values of contact resistance was found in both pyrotechnic and power/signal slip ring assemblies.  Contamination of slip rings can occur if they are exposed to atmosphere for any length of time.  The material chosen was Ag/C/MoS2 (12% MoS2).  Subsequent high resistance was due to surface contamination (possibly Ag2O or Ag2S).  [Atlas]
• For slip ring assemblies, provide adequate and proper lubrication of the rings and brushes when self-lubricating contacts are not employed.  A liquid lubricant is necessary if significant rotation is involved.  Ball Aerospace Systems Division's (BASD) most widely used lubricant consists of a highly refined mineral oil with extreme pressure additive.  Recently, a synthetic oil with improved characteristics has come into use.  With the mineral oil, reservoirs are placed along the brush access slots in the housing.  Vapor pressure of the new oil is so low that surface films are sufficient for multiyear missions and reservoirs are not required.  [Phinney]
• Measure brush forces and correct, if required.  Brush force must be set carefully.  BASD rings have used 3 to 5 gm of force and lubricants that produce a friction coefficient of 0.3 to 0.5.  [Phinney]
• Brush wear particles remain under the brush pad and provide an additional lubricating medium that prevents further wear.  [Phinney]
• The precaution of side-by-side brushes is unnecessary because of the 5-yr demonstrated life with single-groove bearings.  [Phinney]
• For self-lubricating brushes: [Phinney]
  • Coat the brush springs with thin films of polyurethane.
  • To minimize vibration problems on brush assemblies of this type, maintain brush height <0.090 in.
  • The Ag/MoS2 brush on silver is outstanding in vacuum but it is not good in air.  To eliminate electrical noise, slip rings with this brush material should only be operated in dry nitrogen or vacuum.
  • Remove all humidity before starting.
  • For space applications, power brushes are operated at current densities in the 100- to 150-A/in.2 range and contact pressures of 6 psi.  Signal brushes commonly have pad face areas in the 0.007 in.2 range (0.060 0.12 in.) or less and brush force is set about 20 gm.
  • Friction coefficients are in the 0.25 to 0.50 range.
  • Conduct hard vacuum run-in tests, followed by disassembly, run-in wear debris removal, reassembly, and checkout.
  • Evaluate slip ring performance during drive acceptance tests, which should always include thermal vacuum operation.
  • Maintain coordination with suppliers.  They have developed significant experience and knowledge.  Sources include: Electro-Minatures Corp, Moonachie, New Jersey; KDI Electro-Tec, Blacksburg, Virginia; and Poly-Scientific Division, Litton Industries, Inc., Blacksburg, Virginia.
  • Prepare definitive specifications.
  • Conduct detailed review of suppliers design, materials selection, and processes.
  • Inspect critical manufacturing and test operations at the supplier's facility.
• Some experiences have indicated the need to improve the dynamic noise performance of dry film lubricated, silver bearing slip ring/brush combinations.  [Matteo]
• To initiate noise, some form of dielectric contamination must exist at the slip ring/brush interface.  [Matteo]
• A reduction in brush spring force to significantly less than the design minimum force must occur to render the slip ring assembly susceptible to contamination.  [Matteo]
• The fewer the number of brush/ring sets in contact with each signal circuit, the more statistically susceptible the circuit is to contamination-induced resistance variations.  [Matteo]
• Critical sensor signals should be carried by two parallel slip rings, thus, placing four brushes in parallel.  [Matteo]
• Synchronization of sensor sampling times and drive pulses must be maintained at all times.  [Matteo]
• Slip ring assemblies of the dry lubricant type must be purged with clean, dry nitrogen at all times (except when precluded by other tests) up to as close to launch time as possible.  [Matteo]
• Margin above normal brush force (approximately 80%) should be provided to account for in-process or in-service degradation.  [Matteo]
• The individual brushes of a brush pair should be electrically separated to enable in-process measurement of individual brush/ring contact resistances during testing.  [Matteo]
• Whenever possible, critical signals should be amplified before passing across the slip rings.  [Matteo]
• Long storage times can result in slip ring contamination.  They must be examined and cleaned prior to installation.  Also, investigations should be conducted to provide nonpollutant materials.  [ESTL, Atlas]
• During flight assembly, an open shield and a shield shorted to a conductor were discovered on a flight slip ring assembly.  X-rays of the unit revealed that the assembly had been improperly reworked at the vendor.  Inspectors should look for obvious signs of rework, such as a different color of epoxy, and the paperwork should be checked if the rework was recorded.  The data sheet should have a line for each measurement and require that the actual meter reading be recorded.  The specification should have then been listed and a check mark placed in either a pass or fail column.  A quick scan would then tell if any failures were present and still allow the detailed information to be recorded.  The test equipment, calibration, and temperature should also be required on the data sheet.  [Survey, Osterberg]
• After accelerating to 30 rpm, the Teflon toroid ball separators on the GGS slip rings shredded.  The failure was traced to exceeding the pressure-velocity limits of the toroid material.  Toroids should be used with only lightly loaded bearings due to the stress on the nonconforming outer diameter of the toroid to the adjacent ball, which was three times higher than the pocket stress for GGS.  Toroids allow balls to bunch up, making it difficult to predict dynamic performance.  Bearing drag torques are less predictable with toroids.  Accelerated testing of bearings is not recommended because even at subelastohydrodynamic speeds, the wear mechanisms can be very nonlinear.  Pressure-velocity curves should be determined and used to check all new retainer designs.  These curves need to be established for the various materials used and the method of analysis made consistent for all programs.  [Survey, Osterberg]

Miscellaneous

Potentiometers

• A potentiometer for a position sensor experienced excessive electrical noise, unacceptable wear of beryllium copper contacts, and beryllium-copper contact breakage.  When lubricated with Bray 815Z, the lubricant beaded and contained wear debris.  Wiper contacts of Paliney-7 (a precious metal alloy primarily comprised of Palladium), silver, gold, and platinum proved effective.  To assure adequate contact, the contact force was increased to 204 cN.  The material combinations must be compatible for rubbing contact and have low coefficient of friction, and the mating surfaces must have sufficient preload to assure contact.  [Iskenderian]
• Hub connections should not loosen during vibrations.  In this instance, each steel hub was first mechanically fastened to the shaft with two set screw joints (one cone point, one cup point) at 90o to each other, then bonded with a bead of epoxy at the shaft hub interface.  The set screws themselves were blocked from backing out by a drop of epoxy.  [Iskenderian]
• The potentiometers should not be contaminated by shipping packages.  Individual nylon bags were employed.  [Iskenderian]

Cryogenic Grating Drive Mechanism

• To avoid undesirable temperature gradients and barreling of the bearing, flexible copper thermal strapping (shunts) were added to both rotating and stationary components.  [Dubitschek]
• To ensure precise accuracy control of bearing preload over the temperature range, a flexible diaphragm of similar thermal characteristics was incorporated.  [Dubitschek]

Payload Spin Assembly

• The dc drive motor assemblies failed insulation testing because of brush wear debris and insulation cracking.  The problem was resolved by applying a coating of chemglaze to the windings.  Anomaly reinforces use of brushless motors.  [Robinson]
• The spin bearing drag torque, especially at -23 , was too high.  The problem was due to a mismatch in the coefficient of thermal expansions of aluminum housings and steel bearing races.  This was resolved by interference fitting the steel races into the aluminum housings and then final grinding the steel raceways in place.  Thermal mismatch of bearing components and housing can cause serious torque and cage problems.  The potential problem should be recognized and analyzed prior to build.  [Robinson]
• During run-up for a room-temperature operational test on the flight payload spin assembly, the unit shut down after achieving an approximate speed of 30 rpm.  All of the power FETS were blown due to a runaway oscillating condition.  No problems were experienced during testing of the engineering model.  S-level FETS were used in the flight unit, while low-quality FETS were used in the engineering unit.  Investigation revealed that the S-level FETS were too fast for the snubber circuits and created instability, leading to a major failure.  The low-quality engineering FETS were slow enough for the snubber circuits to handle.  The lesson learned is that any changes made to a successful engineering model design should be analyzed before incorporation into qualification/flight hardware.  [Survey, Robinson]

Multichannel Chopper System

• Special floating mounts had to be developed for the slit plate and chopper disk to maintain their dimensional accuracy and alignment.  [Krueger]
• To maintain dimensional tolerances under varying environmental conditions and in the presence of thermal gradients, the slit plate and chopper disk were made from INVAR 36, a low expansion metal.  [Krueger]
• To achieve the desired accuracy and minimize possible distortion from internal machining-induced stresses, electrical discharge machining was used for the final machining of the slit plate and the chopper disk and for machining the apertures for these components.  [Krueger]
• For a close sliding fit of two shafts with limited motion, the dry lubrication approach was unsatisfactory and increased the friction between the two parts to an unacceptable level.  A very small amount of Krytox oil applied to the inner shaft was the solution.  [Krueger]

Vapor Compressor

• Oil lubrication is not feasible for reciprocating machines in space because of zero gravity.  Grease-packed rolling elements are generally used.  Cam interfaces are critical life-limiting elements because of the large radius of curvature of the cam's surface compared with the roller radius.  Cams made of nitrided steel or coated with tungsten carbide or titanium carbide deteriorated rapidly.  Excellent results were obtained with through-hardened steels for cam and roller and also with boronized cam surfaces.  [ESTL, Berner]
• The original design of the ISTP despin platform employed 8-in. thin-section bearings, a one-piece phenolic retainer, a hollow steel shaft, and an aluminum scalloped housing with a band of titanium around the bearings.  The bearings ran at 10 rpm.  The one-piece phenolic cage warped causing high torques.  Teflon toroids were installed and a full titanium scalloped housing was incorporated.  Lobing in the bearing due to mounting caused ball speed variations, high retainer loads, and badly damaged toroids.  Finally, a four-piece segmented phenolic retainer was installed and life tests did not result in torque anomalies.  [Survey, Woods]

Oscillating Systems

• General information on anomalies and lessons learned for gimbal systems from NASA-Goddard is as follows: [Sharma]
  • Oil replenishment for small oscillatory motions as experienced by gimbal bearings is difficult.  Torque magnitudes increase significantly due to oil breakdown or bearing starvation.
  • In a test conducted at Hughes Aircraft Company, Bray 815Z had half the initial torque of Apiezon C (with an extreme pressure additive) in a 4 gimbal bearing test.  However, after 7 104 cycles, the Bray lubricant turned to brown sugar and the bearing torque quickly increased by a factor of 10.  The Apiezon Z continued without torque increase to the end of the test (8 106 cycles).
  • Lessons learned are: 1) to prevent destructive chemistry; surfaces in contact must be passivated in some manner; and 2) ceramic hard coatings, such as TiN or TiC, will eliminate catalytic action; replacing stainless steel 440C balls with ceramic SiN4 balls eliminates lubricant breakdown; and, to prevent oil starvation, it is good practice to use a porous ball retainer, which functions like a reservoir of oil and dilutes breakdown products.
• For typical gimbal mechanisms, ball bearings are forced to oscillate over very small arcs (dither) and then turn to a new position and continue to dither.  The gimbal system combines the severity of boundary lubrication with fretting motion of contacting surfaces.  Gimbals are critical elements of most pointing mechanisms, antennas, sensors (telescopes) and weapons platforms, and of control moment gyroscopes.  Usually, performance levels are met when systems are first tested, but with time, lubricant degradation, bearing wear (or both) degrade performance levels so that mission requirements no longer can be satisfied.  [Fleischauer]
• Gimbals and electrical contacts have consistently been a source of anomalies and failures.  Gimbal bearings that operate in an oscillatory (dithering) mode and rarely make a full revolution are troublesome.  [Fleischauer]
• Ultra-low friction-durable films of MoS2 are deposited by various ion-sputter deposition processes.  They can be used for some sliding applications, very low load bearings, or for latching and release mechanisms.  There is very encouraging evidence that ion-assisted, sputter-deposited MoS2 films can provide ultra-low friction operation even in air applications.  [Fleischauer]
• For oscillating gimbal applications, sputter-coated MoS2 films were recommended.  Benign ball retainers (those that do not transfer films) were tested with good results.  [Fleischauer]
• During the thermal vacuum test phase of the GOES-7 spacecraft, the primary scan mirror system exhibited unacceptably high drive friction.  The observed friction was found to correlate with small misalignments of the mirror structure and unavoidable loads induced by the vehicle spin.  The friction became very high at the end of the oscillation.  During the spacecraft spin tests, the torque was found to be sensitive to spin speed and load.  The solution to these problems was to reduce the moment loads by using larger race curvature to reduce alignment sensitivity.  Also, the frame limit was shifted 5 whenever the torque became too high, so the balls could roll over the torque bumps at the end of travel.  [Bohner]
• CAS and PFPE oils were seriously degraded under oscillating load and vacuum testing and produced excessive bearing wear and torque noise for <2500 hr of operation.  A PAO lubricant with a TCP wear additive did not cause bearing failure and had run 11,000 hr with no indication of a problem.  Its success has been (attributed by the authors) to the TCP additive.  This type oil should be used for oscillating applications.  [Carre]
• When properly made and installed, lightly preloaded duplex bearings having phenolic laminate separators and lubricated with thin films of BASD 36234 liquid lubricant can withstand more than 16 million low-angle oscillating cycles without any signs of degradation and without significant torque variation.  [Phinney]
• Blocking can occur in oscillating duplex bearings even at extremely narrow angles of motion.  Blocking is a condition where some of the bearing balls jam into ends of the separator pockets as a result of creeping away from their centered position.  [Phinney]
• Table 7 shows the effects of various factors on blocking.  [Lowenthal]
• Races should be slip fits, if possible, to assure proper performance and prevent blocking.  [Phinney]
• Soft (spring) preloading is better than hard preloading if bearing torque is critical.  [Phinney]
• Bearings must be scrupulously clean.  [Phinney]

• Torque spikes are the result of buildup of debris at the ends of the ball travel.  The debris was primarily aluminum particles with small amount of titanium debris and dry lubricant from the inner race retaining nut threads.  [Phinney]
• Using aluminum tools during assembly can produce aluminum debris that contaminates the bearings; use titanium tools instead.  [Phinney]
• Race conformity and separator type can have a dramatic effect on bearing torque.  Slightly opening the race conformity and switching to alternating ball toroid separators reduced the excessive torque problem to an acceptable level.  Particular attention must be paid to gimbal bearings to avoid blocking.  Blocking torque phenomena for gimbal bearings is very much dependent on friction levels between the ball and race as well as the retainer ball pocket.  The bearing should be well aligned, the race conformity should be increased as much as possible without incurring a contact stress problem, and the ball retainers should have either generous pocket clearance, slots or alternating ball toroids.  [Survey, Lowenthal]
• Bearing computer codes are useful in determining appropriate race conformity.  [Lowenthal]
• Excessive thermal gradients across the races can have a significant effect on internal preload and contact stress and can cause torque problems in gimbal bearings.  Bulk temperature effects are much less severe.  If tight control over preload is necessary, heaters are recommended to maintain proper temperature.  Bearing computer codes are useful in establishing an acceptable operating temperature envelope.  [Lowenthal]
• Large, thin-sectioned bearings in stiff mounts are particularly vulnerable to torque excursions from rolled over debris and degraded lubricant.  Prolonged dither gimbal cycles should be minimized and periodic, have a longer stroke, and maintenance cycles should be included to maximize bearing life.  [Lowenthal]
• Conformity ratio has a dramatic effect on torque levels.  A buildup of compacted debris in the contact zone, reduces the ball/race conformity ratio and can cause a torque increase of a factor of five above normal torque levels.  [Gill]
• Liquid lubricant torque levels are less than cage lubricants or solid lubricants.  [Gill]
• Of many lubrication systems tested, Pennzane SHF 2000 lubricant was the best for all conditions of operation.  [Gill]
• Torque levels dramatically increase when direction changes.  [Gill]
• Variable angle of oscillations are preferred, particularly for solid lubricants.  [Gill]
• For oscillating scanner bearings, three oils were tested: G.E. Versilube F-50 (a CAS oil); Brayco 815Z (PFPE oil); and Nye 188B (a synthetic hydrocarbon oil, PAO).  The PAO oil outperformed the other oils by a wide margin.  The primary reason for this was the presence of the antiwear additive, TCP, in the PAO oil.  The other two oils suffered rapid degradation.  [Kalegoras]
• For the angular-contact ball bearings in the shutter and filter wheel mechanisms of the Michelson Doppler Imager (MDI), lubrication with Bray 815Z oil met and exceeded the design life goals.  [Akin]
• For the thin-section ball bearings in the tuning motors of the MDI, lubrication with Bray 815Z oil did not meet the design life goals, but lubrication with Braycote 600 grease did meet the goals.  [Akin]
• Using bearings for small rocking motion applications has its problems.  Even with a porous retainer, there is no fresh supply of oil to replenish the contacting surfaces when the motions are small oscillatory.  Torque can skyrocket as either the oil breaks down or the bearing starves.  In a test conducted at Hughes, Bray 815Z had half the initial torque of Apiezon C (with an extreme pressure additive) in a 4 gimbal bearing test.  But after 7 104 cycles, the Bray turned to brown sugar and the bearing torque quickly increased by a factor of 10.  [Hinkle]
  • To prevent destructive chemistry, the surfaces in contact need to be passivated in some manner.  Ceramic hard coatings, such as TiN or TiC, will eliminate catalytic reaction.  Conventional nitride hard coatings are also effective.  In the case of ball bearings, replacing the stainless steel 440C balls with ceramic SiN3 balls eliminates breakdown.  To prevent starvation, it is always good practice to use a porous ball retainer that functions like a reservoir of oil and dilutes any breakdown products.
• Each of the beta gimbals on space station Freedom have four 18-in. diameter ball bearings with a specified 30-yr life.  The original bearings failed after one week.  The cause of failure was incompatible bearing materials and lubricant.  Using the SEM/AES/XPS Tribometer, a substantial number of accelerated tribological tests were run in simulated low Earth orbit environment on a variety of bearing materials and solid lubricated composites.  Based on these tests, improved materials were recommended and subsequent testing for an equivalent 35-yr life was successfully completed.  Simple material tests should be run before selecting materials and building full-scale hardware.  With suitable equipment, it is also possible to accelerate the testing while controlling the critical parameters.  [Survey, Naerheim]
• Many gimbal systems have travel limited by physical features and protection against contact of these features in the form of stops, both mechanical and electrical.  With the very high forces available due to large gear ratios, significant damage can be done if the motor is driven past the normal stopping range.  Equipment should be designed with a foolproof means of stopping the motor drive when approaching the limit of travel to prevent damage to the equipment or operator injury.  Even though the position can be easily monitored, it is likely that during initial checkout the unit will be driven beyond its normal range of travel.  [Survey, Sutter]
• Maximum torque was exceeded during gimbal checkout of the Hubble space telescope.  The problem was harness interference.  Where possible, preflight testing of the gimbal over its whole gimbal travel must be performed to determine if the wire harness or any other obstruction, such as thermal blankets, will prevent gimbal travel.  The wiring harness must be designed to eliminate service loops where they are not necessary to prevent harness obstruction.  [Survey, Ruebsamen]
• A gimbal torque anomaly occurred during space telescope antenna pointing system testing for the Hubble telescope.  The cause was a tight curvature ratio of the balls to the race.  The curvature ratios were changed to 53% on the inner race and 54% on the outer race.  Also the rigid phenolic cage was replaced by a set of Teflon toroids.  [Survey, Ruebsame]
• A gimbal Kapton strip heater burned out during testing of the high-gain antenna pointing system.  The failure was due to excessive input power coupled with epoxy vaporization.  The epoxy was changed from a standard structural epoxy to a thermally conductive material.  Also, bonding voids were eliminated when bonding the heaters to the shaft.  Lessons learned were:
  • Minimize power density below 9 W/in.2.
  • Eliminate voids when bonding heaters to the shaft.
  • The epoxy must be a highly filled, thermally conductive material and must be able to handle high power densities.  [Survey, Ruebsamen]

NEEDS ANALYSIS

Deployable Appendages

• Solid lubricant hard coatings, that will not produce wear debris are desirable to improve actuator reliability.  Relative to liquid or grease lubricants, solid lubricants generally have lower vapor pressures, better boundary lubrication properties and relative insensitivity to radiation effects, and operate in wider temperature ranges.  Investigation of ion-plated lead coatings, which have enjoyed good success in Europe should be undertaken, as well as ion-sputtered MoS2.  In European solar array drives alone, more than 2 million operational hours have been accumulated with ion-plated lead films.  An important property of the lead film is its high load-carrying ability.  Under Hertzian contact, the as-deposited film flows plastically until a thin film (10 Nm or less thickness) remains and then elastically deforms the substrate.  In this condition, the film can survive contact loads approaching the static load capacity of a rolling element bearing.  Burnishing of epoxy and polyamide films to remove excess material may be acceptable and should receive further attention.
• Thermal problems (binding) are prevalent with actuators and retention and release mechanisms.  Differences in coefficients of thermal expansion must be thoroughly explored to avoid jamming and excessive torque.  Most problems occur at low temperatures.  Considerable care must be exercised when mounting close clearance bearing components into aluminum structures that must operate at cold temperatures.  More detailed finite-element analyses to establish clearances and tolerances is needed.
• The functional margin of pyrotechnic devices must be determined by test to assure actuation.  The functional margin is a comparison of the energy that can be delivered to the device and the energy required to operate the device.  Consultation with Bement at NASA-Langley is recommended.
• Increased use of the latest CAD software is needed.  Iteratively designing a complex mechanism in CAD and using pasteboard mockups can be a more efficient process than detailed mathematical analysis of component geometries.
• Improved quality control of microswitches is required.
• Harnesses and cables have caused torque problems because of snagging and stiffness at low temperatures.  These problems should be further addressed through analytical and empirical methods.

Rotating Systems

• The development of new polymeric bearing retainer materials is critical to achieve bearing lifetime.  The phenolic materials that are commonly used have been demonstrated to absorb oil in a time-dependent and nonreproducible manner.  These materials are unacceptable for the missions under consideration unless an active lubricant supply system is used.  Retainerless bearings should be further studied and developed.
• Bearing lubricant depletion between the ball race retainer causes cage instability and subsequent pointing errors, increased bearing torque and wheel vibration.  Phenolic cages continuously absorb oil from the contact regions instead of supplying oil, thereby hastening the onset of cage instability.  A concentrated effort to develop active oil systems that periodically or continuously lubricate the bearings should be undertaken [Singer, Auer]. 
• Lubricant degradation is a common failure mode and is not amenable to accelerated testing.  Continued development of vacuum tribometers such as those at NASA- Glenn is needed (see "Facilities" section), and extensive experimentation conducted to better understand and combat lubricant degradation.
• Both titanium carbide and titanium nitride have demonstrated to be effective wear coatings under appropriate conditions.  Titanium carbide has been applied to gyroscope ball bearings and has increased operational lifetime by an order of magnitude in this application when used with an uncoated steel raceway and superrefined mineral oil.  To date, titanium nitride has been used only on tool steels, but the Aerospace Corporation is currently testing both gimbal and spin bearings with Titanium-carbide and titanium-nitride-coated balls.  These investigations should continue and effectiveness quantified.
• In a weightless environment, there are questions about how a drop of oil will behave.  Even at a distance of 0.004 in., the drop may not transfer smoothly.  It may touch and be slung off the moving surfaces to create a number of finer droplets that will float around the bearing housing.  Lubrication phenomenon should be examined in a weightless environment by, for example, shuttle experiments.
• Bearing simulation computer codes can predict cage instabilities for steady-speed conditions, bearing performance parameters, elastohydrodynamic lubricant thickness, etc.  More extensive use and continued development of computer codes is recommended and should include nonsymmetric cages, lubricant starvation, thermal effects, retainerless bearings, and acceleration and deceleration.
• Roll rings have demonstrated excellent performance; continued development is recommended.
• Small, fractional horsepower motors have experienced cold-temperature performance problems, primarily due to high lubricant viscosity.  Development should be planned to evaluate and improve cold-temperature lubricant start-up as well as running torque in small components.
• Development of screening tests for various components can improve reliability in an expeditious and accurate manner.  Screening tests are presently being used, with good success, for bearing cartridges, and extension to other components is recommended.

Oscillating Systems

• Gimbal bearings, which operate in an oscillatory (dithering) mode and rarely make a full revolution, are the primary problem area.
• For oscillating gimbal applications, solid dry lubricants, such as sputter-coated MoS2, with benign ball retainers (those that do not transfer films) are recommended.  Continued development of solid lubricants for gimbal races, with objectives of low torque and no debris formation is suggested.
• Race conformity and separator type can have a dramatic effect on bearing torque.  Blocking phenomenon should be avoided.  Computer code development for oscillating bearings, that can determine effects of race conformity, predict blocking, and establish consequences of debris formation on driving torque would be a useful design tool and is recommended.

SURVEY RESULTS

Over 600 survey forms were transmitted and approximately 30 replies were received.  The replies varied in quality from scribbles to detailed amounts of lessons learned.  Honeywell Electro Components and the Honeywell Satellite Systems Operation were particularly responsive.  The significant responses follow.

LISTING OF EXPERTS

Deployable Appendages

Retention and Release Mechanisms

Hinkle, K.
NASA-Goddard Space Flight Center
Engineering Directorate
Greenbelt, Maryland 20771

Maus, Daryl
Starsys Research Corp.
5757 Central Avenue, Suite E
Boulder, Colorado 80301
(303) 444-6707

McCown, William
Rexnord Aerospace Mechanisms
2530 Skypark Drive
Torrance, California 90505

Phan, M.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Schaper, P.W.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2140

Schimmel, Morry L.
Schimmel Company
St. Louis, Missouri

Sevilla, D.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3644

Skyles, Lane P.
Lockheed Engineering & Sciences Company
1150 Gemini Avenue
Houston, Texas 77058
(713) 333-6456

Tibbitts, Scott
Maus Technologies
Boulder, Colorado

Wagoner, B.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3644

Bearings, Lubrication, and Tribology Considerations

Didziulis, Stephen V.
The Aerospace Corporation
2350 East El Segundo Boulevard
Los Angeles, California 90009-2957

Divine, E.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Dugger, Michael T.
Sandia National Laboratories
Albuquerque, New Mexico 87185-5800

Fehrenbacher, L.
Technology Assessment and Transfer, Inc.
Annapolis, Maryland

Fleischauer, P.D.
The Aerospace Corporation
2350 East El Segundo Boulevard
Los Angeles, California 90009-2957

Hilton, M.D.
The Aerospace Corporation
2350 East El Segundo Boulevard
Los Angeles, California 90009-2957
(310) 336-0440

Keem, John M.
Ovonic Synthetic Materials Corporation
Troy, Michigan 48084

Rowntree, Robert A.
European Space Tribology Laboratory
UKAEA, Risley, Warrington, England

Rowntree, Robert A.
National Center of Tribology
Northern Research Laboratories
UKAE, Risley, Warrington, United Kingdom

Scholhamer, James
Ovonic Synthetic Materials Corporation
Troy, Michigan 48084

Todd, M.J.
National Center of Tribology
Northern Research Laboratories
UKAE, Risley, Warrington, United Kingdom

Antennas and Masts

Hinkle, K.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Johnson, Michael R.
Jet Propulsion Laboratory/California Institute of Technology
4800 Oak Grove Drive
Pasadena, California 91109-8099

Metzger, J.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Actuators, Transport Mechanisms, and Switches

Farley, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Hawthorne, H.M.
Tribology and Mechanics Laboratory
NRCC
Vancouver, Canada

Jones, Stephen R.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Leary, W.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Lewis, D.F.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099

Lorell, K.R.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

O'Donnel, T.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099

Perez, E.O.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Poulsen, R.N.
Hughes Aircraft Company
P.O. Box 902
El Segundo, California 90245

Priesett, Klaus
Dornier GmbH
Friedrichshafen, Germany

Sharma, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Stark, Kenneth W.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Tweedt, R.E.
Hughes Aircraft Company
P.O. Box 902
El Segundo, California 90245

Tyler, A.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Wilson, Meredith
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Zacharie, D.F.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

General and Miscellaneous

Aubrun, J.N.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Devine, E.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Farley, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Federline, Robert E.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Frank, D.J.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Lorrell, K.R.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Parker, K.
European Space Tribology Laboratory
Risley, Warrington, United Kingdom

Zacharie, D.F.
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Rotating Systems

Momentum Wheels

Anonymous
United States Air Force Space Division, SD/ALM
P.O. Box 92960
Los Angeles, California 90009-2960

Auer, W.
TELDIX GmbH
Heidelberg, Germany

Bialke, B.
ITHACO, Inc.
735 W. Clinton Street
Ithaca, New York 14851-6437
(607) 272-7640

Boesinger, E.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Donley, A.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Fehrenbacher, L.L.
Technology Assessment and Transfer
Annapolis, Maryland

Inoue, M.
Mitsubishi Electric Corporation
Amagasaki, Japan

Lowenthal, S.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Murakami, C.
National Aerospace Laboratory
Tokyo, Japan

Okamoto, O.
National Aerospace Laboratory
Tokyo, Japan

Warner, Mark H.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Yabu-uchi, K.
Mitsubishi Electric Corporation
Amagasaki, Japan

Reaction Wheels

Hasna, Martin D.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Control Moment Gyroscopes

Cook, Lewis
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812

Golley, Paul
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812

Gurrisi, Charles
Allied Signal Aerospace Company
Guidance Systems Division
Teterboro, New Jersey 07608

Kolvek, John
Allied Signal Aerospace Company
Guidance Systems Division
Teterboro, New Jersey 07608

Krome, Henning
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812

Gears

Motors

Farley, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Henson, Barnie W.
European Space Agency
Noordwijk, Holland

Kackley, Russell
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

McCully, Sean
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Sharma, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Tyler, A.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Bearings and Lubrication

Anonymous
Allied Signal Aerospace Company (Bendix)
Guidance Systems Division
Teterboro, New Jersey 07608

Baxter, Bryan H.
British Aerospace plc.
Stevenage, England

Benzing, R.J.
Air Force Materials Laboratory
Wright-Patterson AFB, Ohio 65433

Bertrand, P.A.
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Boesiger, Edward A.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Fleischauer, P.D.
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Fowler, Peter H.
TRW Space and Technology Group
Redondo Beach, California 90278

Gelette, Erik
The Charles Stark Draper Laboratory
Cambridge, Massachusetts

Hall, Barry P.
British Aerospace plc.
Stevenage, England

Hilton, Michael
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Hooper, Fred L.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Kingsbury, Dr. Edward
The Bearing Consultants
1063 Turnpike Street
Stoughton, Massachusetts 02072

Langmaier, J.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2031

Manders, Frank
Ball Aerospace Systems Division
960 6th Street
Boulder, Colorado 80302

Parker, K.
European Space Tribology Laboratory
Risley Nuclear Power Development Laboratory
UKAEA, Risley, Cheshire, England

Phinney, Damon D.
960 6th Street
Boulder, Colorado 80302
(303) 442-7824

Rowntree, R.A.
National Tribology Center (ESTC)
United Kingdom

Singer, Herbert
The Charles Stark Draper Laboratory
Cambridge, Massachusetts

Smith, Dennis W.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Strang, J.R.
Air Force Materials Laboratory
Wright-Patterson AFB, Ohio 65433

Todd, M.J.
National Tribology Center (ESTC)
United Kingdom

Vest, C.E.
Applied Physics Laboratory
Pennsylvania

Warner, Mark H.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Slip Rings and Roll Rings

Batista, J.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Langmaier, J.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2031

Matteo, Donald N.
General Electric Company
Space Systems Operations
Valley Forge, Pennsylvania

Phinney, Damon D.
Ball Aerospace Systems Division
960 6th Street
Boulder, Colorado 80302

Smith, Dennis W.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Thomin, G.
Centre National d'Etudes Spatiales (CNES)
Toulouse, France

Vise, J.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Young, K.
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Miscellaneous

Isekenderian, Theodore C.
Jet Propulsion Laboratory/California Institute of Technology
Guidance and Control Section
4800 Oak Grove Drive
Pasadena, California 91109-8099

Krueger, Arlin J.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771

Pech, Greg
Martin Marietta
Denver, Colorado

Robinson, Wilf
Honeywell Inc.
Satellite Systems Operation
19019 N. 59th Avenue
Glendale, Arizona 85308-9650

Weilbach, August O.
Helvart Associates
Fullerton, California

Oscillating Systems

Oscillating Mechanisms

Bohner, John J.
Hughes Aircraft Company
Space and Communications Group
Los Angeles, California

Carre, David
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Conley, Peter L.
Hughes Aircraft Company
Space and Communications Group
Los Angeles, California

Didziulis, Stephen
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Farley, R.
NASA-Goddard Space Flight Center
Mail Code 731
Greenbelt, Maryland 20771

Fleischauer, Paul
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Gill, Steven
European Space Tribology Laboratory
AEA Technology
Risley, Warrington, United Kingdom

Hilton, Michael
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Hinricks, J.T.
Ball Aerospace Systems Division
960 6th Street
Boulder, Colorado 80302

Horber, Ralph
H. Magnetics Corporation

Kalogeras, Chris
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Loewenthal, Stuart H.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086

Phinney, D.D.
Ball Aerospace Systems Division
960 6th Street
Boulder, Colorado 80302

Pollard, C.L.
Ball Aerospace Systems Division
960 6th Street
Boulder, Colorado 80302

Sharma, R.
NASA-Goddard Space Flight Center
Mail Code 731
Greenbelt, Maryland 20771

Wolfson, Jake
Lockheed Palo Alto Research Laboratory
3251 Hanover Street
Palo Alto, California 94304

Woods, C.
NASA-Goddard Space Flight Center
Mail Code 731
Greenbelt, Maryland 20771

Survey Responses

Rotating Mechanisms

Christiansen, Scott
Starsys Research Corp.
5757 Central Avenue, Suite E
Boulder, Colorado 80301
(303) 494-6707

Christy, R.
(310) 457-2261

Dekramer, C.
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Devine, E.
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Dolan, Fred
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812
(205) 544-2512

Ellis, Robert
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4261

Farley, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771
(301) 286-2252

Fink, Richard
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 4264

Gallaher, Jack
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771
(301) 286-9567

Golley, Paul
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812
(205) 544-3434

Herald, Michelle K.
Space Systems/Loral
3825 Fabian Way, M/S G44
Palo Alto, California 94303-4604
(415) 852-5175

Hodges, Charles
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4290

Jones, William R.
NASA-Glenn Research Center
21000 Brookpark Road, MS 23-2
Cleveland, OH 44135
(216) 433-6051

Lake, Mark
NASA-Langley Research Center
MS 199
Hampton, Virginia 23681-0001

Loewenthal, Stuart
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086(408) 743-2491

Mikulas, Prof. Martin Jr.
University of Colorado
MS 429
Boulder, Colorado 80303

Peterson, Prof. Lee
University of Colorado
MS 429
Boulder, Colorado 80303

Raymond, Bruce
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4206

Sevilla, D.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2136

Wai, Leilani C.
P.O. Box 2755
Sunnyvale, California 94087-0755

Scanning Mechanisms

Bar-Cohen, Dr. Y.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2610

Bearman, Dr. Greg
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3285

Christy, R.
(310) 457-2261

Devine, E.
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Henry, Dr. Paul
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3106

Herald, Michelle K.
Space Systems/Loral
3825 Fabian Way, M/S G44
Palo Alto, California 94303-4604
(415) 852-5175

Jones, William R.
NASA-Glenn Research Center
21000 Brookpark Road, MS 23-2
Cleveland, OH 44135
(216) 433-6051

Lilienthal, G.W.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-9082

Loewenthal, Stuart
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086
(408) 743-2491

Wai, Leilani C.
P.O. Box 2755
Sunnyvale, California 94087-0755

Deployable Mechanisms

Bar-Cohen, Dr. Y.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2610

Bearman, Dr. Greg
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3285

Bement, Laurence J.
NASA-Langley Research Center
Mail Stop 433
Hampton, Virginia 22681-0001
(804) 864-7084

Brown, Lee
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Christiansen, Scott
Starsys Research Corp .
5757 Central Avenue, Suite E
Boulder, Colorado 80301
(303) 494-6707

Christy, R.
(310) 457-2261

Dekramer, C.
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Devine, E.
Swales and Associates
5050 Power Mill Road
Beltsville, Maryland 20705
(301) 595-5500

Dolan, Fred
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812
(205) 544-2512

Ellis, Robert
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4261

Farley, R.
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771
(301) 286-2252

Fink, Richard
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4264

Gallaher, Jack
NASA-Goddard Space Flight Center
Greenbelt, Maryland 20771
(301) 286-9567

Gogely, James
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Golley, Paul
NASA-Marshall Space Flight Center
Huntsville, Alabama 35812
(205) 544-3434

Henry, Dr. Paul
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-3106

Herald, Michelle K.
Space Systems/Loral
3825 Fabian Way, M/S G44
Palo Alto, California 94303-4604
(415) 852-5175

Hodges, Charles
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4290

Hunter, Alex
The Boeing Company
Space and Lunar Deployment Mechanisms
Huntsville, Alabama 35812
(205) 461-2085

Lake, Mark
NASA-Langley Research Center
MS 199
Hampton, Virginia 23681-0001

Lilienthal, G.W.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-9082

Manning, Hugh E.
The Boeing Company
Materials and Processes
Huntsville, Alabama 35812
(205) 461-5858

Menichelli, Vince
TRW, Norton Air Force Base
P.O. Box 1310
San Bernadino, California 92402

Mikulas, Prof. Martin Jr.
University of Colorado
MS 429
Boulder, Colorado

Peterson, Prof. Lee
University of Colorado
MS 429
Boulder, Colorado 80303

Raymond, Bruce
Honeywell Corporation
921 Holloway Street
Durham, North Carolina 27702
(919) 956-4206

Schimmer, Morry L.
8127 Amherst Avenue
St. Louis, Misourri 63130

Sevilla, D.
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, California 91109-8099
(818) 354-2136

Wai, Leilani C.
P.O. Box 2755
Sunnyvale, California 94087-0755

Wittschen, Barry
NASA-Johnson Space Flight Center
Houston, Texas 77058

Miscellaneous

Dursch, H.
Boeing Defense and Space Group
Seattle, Washington
(206) 773-0627

Gresham, Robert M.
E/M Corporation
2801 Kent Avenue
West Lafayette, Indiana 47906-0400
(317) 497-6340

Hopple, George
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086
(408) 746-2502

Hustad, Gary
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086
(408) 743-7455

Loewenthal, Stuart
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086
(408) 743-2491

Putnam, David
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94086
(408) 743-2987

ESTL Space Mechanisms

Andersson
Saab Ericsson Space AB
S-58188 Linkoping
Sweden
Phone: 13-286400

Atlas, G.
SEP
Forest De Vernon - BP 802
27207 Vernon, France
Phone: 32-21-72-00

Bekaert, G.
Sabca
Departement Etudes Aerospatiales
1470 Chaussee de Haecht
B-1130 Brussels, Belgium
Phone: 2-216-80-10

Banerjee, S.K.
Vikram Sarabhai Space Centre
Indian Space Research Organisation
Trivandrum 695 022, India
Phone: 0471-562621

Barho, R.
Dornier GmbH
RST 123, Postfach 1420
D-7990 Friedrichshafen, Germany
Phone: 7545-80

Bentall, Dr. R.H.
ESA/ESTEC
Keplerlaan 1
220 AG Noordwijk ZH, The Netherlands
Phone: 1719-86555

Bialke, W.E.
ITHACO, Inc.
735 West Clinton Street, P.O. Box 6437
Ithaca, New York 14851
(607) 272-7640

Birner, R.
MBB, Unternehmensbereich Raumfahrt
Postfach 801169
8000 Munchen 80 (Munich), Germany
Phone: 089-607-22643

Bohner, J.J.
Hughes Space and Communications Group
P.O. Box 92919, S12/V361
Los Angeles, California 90009
(213) 648-2393

Bollinger, W.
Carl Zeiss
P.O. Box 1369/1380
D-7082 Oberkochen, Germany
Phone: 07364-20-3354

Borrien, A.
CNES
18 Av. Edouard Belen, F-31055 Toulouse
Cedex, France
Phone: 61-27-3131

Briscoe, H.M.
Tykes Barn
Goose Street
Southwick, Wiltshire, United Kingdom
Phone: 0225-753100

Caslini, D.
Fiat Avio
112, Corso Ferrucci
1-10138 Torino (Turin), Italy
Phone: 11-33 02 12

Clemmet, J.F.
British Aerospace (Space Systems) Ltd.
Argyle Way
Stevenage, Herts, United Kingdom SG1 2AS
Phone: 0438-313456

Comparetto, V.
I.A.M. Rinaldo Piaggio SpA
I-17024 Finale Ligure, Italy
Phone: 19-692741

Corcorcuto, I.S.
Fiat Avio
Corso Ferrucci, 112
1-10138 Torino, Italy
Phone: 11-3302-644

Cracknell, D.
GEC Marconi Research Centre
West Hanningfield Road
Great Baddow
Chelmsford, Essex, United Kingdom
Phone: 0245-473331

del Campo, F.
Sener
Avda Zugazarte 56
E-48930 Las Arenas-Vizcaya, Spain
Phone: 4-481-7500

Edeline, E.
SEP
Division Propulsion A Liquides et Espace
Foret de Vernon, BP802
F27207 Vernon, France
Phone: 32 21 54 50

Escobar, J.
CASA
Avenida Aragon, 404
E-28022 Madrid, Spain
Phone: 1-586 3700

Etzler, C-Chr.
Dornier GmbH
RST 123, Postfach 1420
D-7990 Friedrichshafen, Germany
Phone: 7545-80

Eyles, C.J.
School of Physics and Space Research
Chancellor's Court
The University of Birmingham
P.O. Box 363
Birmingham, United Kingdom B15 2TT
Phone: 021-414-4565

Fabbrizzi, F.
Officine Galileo
via Einstein, 35
I-50013 Campi Bisenzio
Firenze (Florence), Italy
Phone: 055 8950380

Felkai, R.
Erno Raumfahrttechnik GMBH
Huenefeldstrasse 1-5
P.O. Box 105909
D 2800 Bremen 1, Germany
Phone: 0421 539 4378

Fleischauer, Dr. P.D.
The Aerospace Corporation
P.O. Box 92957
2350 East El Segundo Boulevard
Los Angeles, California 90009-2957
(213) 336-6098

Flew, A.
Norcroft Dynamics, Ltd.
Fellows House
High Street
Pewsey, Wiltshire, United Kingdom SN9 5AF
Phone: 0672-62169

Gallagher, K.
Marconi Space Systems Ltd.
Anchorage Road
Portsmouth, Hants, United Kingdom PO3 5PU
Phone: 0705-664966

Gomm, M.A.
Devtev, Ltd.
20 Viscount Avenue
Airways Industrial Estate
Cloghran
Dublin 17, Eire
Phone: 1-426668

Graftas, O.
Raufoss A/S
P.O. Box 2
N-2831 Raufoss, Norway
Phone: 4761 52 281

Greener, B.
Met Office 19
Remote Sensing Instrumentation
Room 8, Building Y 70
Royal Aircraft Establishment
Farnborough, Hants, United Kingdom GU14 6TD
Phone: 0252-515523

Hartwig, H.
Max-Planck-Institut fur Aeronomie
Postfach 20, D3411 Katlenburg
Lindau, Germany
Phone: 05556 4011

Hawthorn, Dr. H.M.
National Research Council
Tribology and Mechanics Laboratory
Division of Mechanical Engineering
3650 Westbrook Mall
Vancouver, BC
Canada V6S 2L2
Phone: 604-663-2603

Henton-Jones, W.A.
Sira Research and Development Division
Sooth Hill
Chislehurst, Kent, United Kingdom BR7 5EH
Phone: 081-467-2636

Hostenkamp, R.G.
Dornier GMBH
Postfach 1360
7990 Friedrichshafen, Germany
Phone: 7545-80

Humphries, M.
British Aerospace (Space Systems)Ltd.
Earth Observation and Science Division
FPC 321
P.O. Box 5
Filton, Bristol, United Kingdom BS12 7QW
Phone: 0272-693831

Huomo, H.
Technical Research Centre of Finland
VTT Instrument Laboratory
P.O. Box 107
SF-02151 ESPOO, Finland
Phone: 0-4561

Kemper, Ir. C.A.L.
Stork Product Engineering PV
70 Oostenburgervoorstraat
1010 MR Amsterdam
P.O. Box 379
1000 AJ, The Netherlands
Phone: 20 6262011

Koller, F.
ORS
Operngasse 20b
A-1040 Wien (Vienna), Austria
Phone: 222-58814-240

Kong Chang, Soo
Spar Aerospace, Ltd.
1700 Ormont Drive
Weston, Ontario
Canada M9L 2W7
Phone: 416-745-4680

Kose, Dr. S.
Oerlikon-Contraves AG
580 Schaffehauserstrasse
CH-8052 Zurich, Switzerland
Phone: 01-829-4534

Lavadoux, M.
Sagem
Avenue du Gros Chene
PB 51
F-95612 Cergy-Pontoise
CeDEX, France
Phone: 1-34-30-52-74

Leefe, S.E.
BHR Group
Cranfield, Bedford, United Kingdom MK43 0AJ
Phone: 0234-750422

Leveille, A.R.
The Aerospace Corporation
2350 East El Segundo Boulevard
P.O. Box 92957
Los Angeles, California 90009

Loewenthal, S.
Lockheed Missiles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, California 94089-3504
(408) 743-2491

Long, J.S.
Serc Rutherford Appleton Laboratory
Chilton
Didcot, Oxen, United Kingdom OX11 0QX
Phone: 0235-21900

Magani, P.G.
Tecnopsazio Spa
via Delle Mercantesse, 3
20021 Branzate di Bollate
Milan, Italy
Phone: 023560950

Marchetto, C.
GE Astra Space
P.O. Box 800
Princeton, New Jersey 08543-0800
(609) 490-3392

Maus, D.
Starsys Research Corporation
5757 Central Avenue, Suite E
Boulder, Colorado 80301
Phone: (303) 444-6707

Morris, N.
Rutherford Appleton Laboratories
Space and Astrophysics Department
Chilton
Didcot, Oxfordshire, United Kingdom OX11 0QX
Phone: 0235-445210

Mueller, G.
Matra Marconi Space
31 Rue Des Cosmonautes
Z.I. du Palays
31077 Toulouse
CeDex, France
Phone: 6224 75 86

Nieuwenhuizen, M.
Fokker Space and Systems PV
P.O. Box 12222
1100 AE Amsterdam-Zuidoost, The Netherlands
Phone: 20-605 9111

Patin, J.F.
Aerspatiale Space and Strategic Systems Division
Establishment De Cannes
100 Boulevard Du Midi, BP 99
F-06322 Cannes la Bocca, CeDex, France
Phone: 92-92-74-07

Patrick, T.J.
Mullard Space Science Laboratory
Holmburg St. Mary
Dorking, Surrey, United Kingdom RStrong 6NT
Phone: 0483-274111

Privat, M.
CNES
18 Avenue Edouard Belin
F-31055 Toulouse, CeDex, France
Phone: 61 27 3131

Rockly, G.
TELDIX GmBh
Postfach 10 56 08
D-6900 Heidelberg, Germany
Phone: 06221-5120

Roth, M.
MBB Space Systems Group
P.O. Box 801169
D-8000 Munich 80, Germany
Phone: (089)-60006302

Schwarzinger, D.C.
ORS
The Austrian Aerospace Company
Operngasse 20B
A-1040, Wien, Austria
Phone: 0222-58814

Shmulevitz, M.
Israel Aircraft Industries
Electronics Division/MBT
Yehud, Industrial zone 56 000
Israel
Phone: 3-4024

Smith, B.
British Aerospace (Space Systems) Ltd.
Argyle Way
Stevenage, Herts, United Kingdom SG1 2AS
Phone: 0438-313456

Smith, D.
Honewell Inc.
P.O. Box 52199
Phoenix, Arizona 85072-2199
(602) 561-3237

Sneiderman, G.
NASA-Goddard Space Flight Center
Greenbelt Road
Greenbelt, Maryland 20221
(301) 286-2000

Tasker, J.
Moore Reed Ltd.
Walsworth Ind. Estate
Andover, Hampshire, United Kingdom
Phone: 0264-324155

Turner, R.F.
Rutherford Appleton Laboratory
British National Space Centre
Chilton
Didcot, Oxfordshire, United Kingdom OX11 0QX
Phone: 0235-21900

Whiteman, P.
Marconi Space Systems Ltd.
Anchorage Road
Portsmouth, Hampshire, United Kingdom P03 5PU
Phone: 0705-664966

Zwanenburg, R.
Fokker Space and Systems BV
P.O. Box 12222
100 AE Amsterdam-Zuidoost, The Netherlands
Phone: 20-605 9111

FACILITIES

• Boeing Company
• European Space Tribology Laboratory
• Honeywell Electromagnetic Controls
• Lockheed Missiles & Space Company, Inc.
• Miniature Precision Bearings
• NASA Johnson Space Flight Center
• NASA Langley Research Center
• NASA Glenn Research Center
• NASA Marshall Space Flight Center
• Rockwell Science Center
• Space Systems/Loral
• University of Maryland
• Viking/Metrom Laboratories

Boeing Company

• One sun thermal input capability
• Space vacuum
• Space temperature
• Mechanical pass-throughs
• Large working area.

European Space Tribology Laboratory

There are some 25 vacuum chambers, 4 physical vapor deposition chambers for lubricant application, and 3 tribometers.

ESTL's facilities are designed for versatility and flexibility.  A wide range of mechanisms and components can be accommodated.  Laboratory systems can be adapted and modified to suit customers' requirements.

Clean Room

Vacuum Chambers

Emphasis is laid on vacuum chamber cleanliness and pump reliability.  Turbomolecular pumps are used for initial pumping; the lowest pressures are achieved with ion pumps or cryogenic pumps.  With such systems, there is no risk of chamber contamination.  Long-term performance (more than eight years with ion pumps) can be guaranteed.

Each large chamber is equipped with two or more thermal-radiation shrouds and electric heaters.  With these, a wide range of thermal conditions (including rapid changes of temperature can be achieved.

Dedicated facilities include those for testing the torque disturbance and qualification of solar array drives, measuring directional accuracy of antenna pointing mechanisms, gearbox performance evaluations (from 1- to 500-Nm output torque), scanner simulation, and motor/gearhead evaluation.

Experimental rigs that have been used in the above chambers include those to study separable electrical and fluid connectors, slip rings, motor commutation, oscillatory bearing behavior, gears (four-square arrangement) and thermal conductance measurements of Hertzian contacts.

Specific Test Facilities

Vacuum Cryogenic Test Rig.

Pin-on-Disk Tribometers.

Ball Bearing Test Facilities.

Gearbox Test Facility.

Boundary Lubrication Accelerated Screening Tester (BLAST).

High-Temperature Reciprocating Tribometer.

Instrumentation

• Ion gages or various types for pressure measurement mass spectrometers
• Spectrometers for residual gas analysis
• Vacuum-compatible torque transducers (RVDT and piezo)
• Fast Fourier transform (FFT) frequency analyzers
• Digital frequency analyzers
• Digital storage oscilloscopes
• X-ray fluorescence for thin film thickness determination
• Temperature sensors (thermistors, thermocouples, solid-state devices)
• Theodolite
• Vacuum-compatible tilt sensors
• Linear and rotary encoders.

Data Logging

Related Facilities

• CAD design and finite-element thermal and mechanical stress modeling
• Materials examination chemical analysis: infrared spectrometry, x-ray diffraction
• Metallography: sample preparation
• Surface examination and analysis: scanning electron microscopy (SEM), SIMS, Auger, x-ray photoelectron spectroscopy (XPS)
• Surface coating thickness: x-ray fluorescence
• Workshops and NAMAS accredited calibration and measurement facility
• Nondestructive testing and crack detection
• Surface metrology and examination equipment Talysurf 6 (linear and rotary), Talyrond 3-D surface profilometer, macro/micro/ultra-low hardness testers
• CRAY supercomputer.

Honeywell Electromagnetic Controls

Test Capabilities

• Thermal chambers (temperature range from -73 to +125 C)
• Thermal vacuum chambers (cryogenic and diffusion: vacuum to 1*10^-6 torr)
• Thermal vibration chambers
• Vibration equipment (sine and random vibration capability)
• Thermal humidity chamber
• Computerized automatic test equipment.

Functional Test Capabilities.

Augmenting the functional test laboratory equipment are direct-drive rate tables for testing drag torque and detent torque, various phase angle voltmeters that determine the phase relationship of ac voltage at various frequencies, digital oscilloscopes for troubleshooting and monitoring rotor calibration, and a Digasine AA gage for checking rotational accuracy to within 0.1 min.

Environmental Test Capabilities.

Life Test Capabilities.

Lockheed Missiles and Space Company, Inc. (LMSC)

LMSC Testing Facilities

Bearing Test Laboratory.

• Four computerized bearing life testers capable of testing bearings from 0.25 to 14 in. diameter under any duty cycle at vacuums to 10^-7 torr
• Bearing assembly and diagnostics equipment contained in Class 5000 clean room
• Special bearing equipment for setting bearing preload, measuring bearing angular runout, bearing torque signature with precision rate table, and measuring bearing defect frequencies
• Bearing retainer friction test rig for measuring ball pocket friction of instrument bearings at ball speeds from 5 to 25,000 rpm and loads as low as 1 gm.

Mechanisms Laboratory.

• Specialized mechanisms deployment test setups with computer data acquisition systems
• Mechanisms assembly clean room
• Variety of thermal enclosures and thermal/vacuum chambers
• Variety of large and small general-purpose environmental test equipment including: thermal/vacuum, pyroshock, random vibration, etc. equipment.

Failure Analysis Laboratory.

• Surface analysis capabilities including: SEM, EDS, XPS, XRD, FTIR, GCMS.

Miniature Precision Bearings

• Ball bearing and rotating assembly torque testing per MIL-STD-206 and a wide range of speed and load combinations
• Dry-film lubrication testing of axially loaded bearings from 1 to 50,000 rpm in an Argon atmosphere from room temperature to 1000 F; instrumented with a force transducer
• Special testing for ball quality including thin, layered film coating adhesion on balls
• Milliwatt power consumption testing
• Extensive clean room and laboratory facilities focused on processing and testing of ball bearings.

NASA - Johnson Space Flight Center

Structures Test Lab (STL)

Thermal Facilities

Vibration and Acoustic Test Facility (VATF)

Materials Technology Laboratory (MTL)

• Failure investigations of both metallic and nonmetallic materials
• Chemical analyses of contaminants and material samples.
• Evaluation of mechanical properties of materials
• Nondestructive testing of materials
• Evaluation of the compatibility of materials with the space environment
• Preparation and evaluation of special elastomeric compounds
• Preparation of TPS tiles and test articles.

• Scanning electron microscopes
• Fourier transform infrared spectrometer.
• Ultraviolet-visible spectrometer
• Vacuum microbalances
• Nondestructive test equipment
• Materials evaluation equipment
• Instron mechanical test device
• Gas chromotographs
• X-ray fluorescence and diffraction, metallograph, atomic oxygen testing apparatus
• Tile coating furnace
• Rubber mill used for the preparation of special formulations
• Metallurgical specimen preparation facility.

Lubrication and Wear

NASA - Langley Research Center

Pyrotechnic Test Facility

Hazardous Materials Test Area

Pyrotechnic Storage.

Control Room and Test Cells

NASA - Glenn Research Center

NASA - Marshall Space Flight Center

• Block-on-ring friction and wear testing machine
• Four ball wear testers for measurement of extreme pressure properties of lubricating fluids
• Falex multipurpose friction and wear tester
• Cryogenic traction tester
• Rolling contact fatigue tester
• Pin and Vee-block wear tester
• Vacuum manifold with 12 independent stations with feed-throughs for electrical power and thermocouples.  Some stations have water feed-throughs and there are several blanked off ports available for other feed-throughs.

Rockwell Science Center

SEM/AES/XPS Tribometer

Experiments can be performed either in ultra-high vacuum or up to one atmosphere of oxygen, hydrogen, and a variety of other gases.  The disk and cylinder samples can be internally cooled to liquid nitrogen temperature.  Design provisions have been made to accommodate high-temperature testing using laser heating.  The temperature is monitored at the cylinder/disk contact separation point with an infrared thermometer with a focal point smaller than the Hertz contact ellipse.  The total wear is monitored with a capacitance displacement probe.  A 500-kHz acoustic emission detector monitors sample contact and film breakdown.

The facility is equipped with an 8-channel computer data acquisition system that displays in real time on a color monitor and stores on a hard disk drive the disk/cylinder and pin/cylinder normal forces and the disk/cylinder friction force, the motor speeds, the wear, and the temperature.  The data retrieval, reduction, calculations, and graphing have been automated using a dedicated 486/33 computer.

The test chamber is equipped with an SEM, a scanning Auger electron spectroscope (AES) and a small-area multichannel x-ray photoelectron spectroscope (XPS) operated via an Apollo 3500 computer and PHI surface analysis software to examine the topography and chemically analyze the wear track as the test is running.  The chemical composition of the test environment is monitored by a VG triple-filter quadropole mass spectrometer via a 386/20 computer using VG software.  Chemical composition depth profiling of the wear track can be done using the ion sputter gun.  The facility is also equipped with a high-speed video camera operated as a strobe to obtain real-time freeze-frame images of the wear track using a dedicated 486/66 computer image analysis system.

Space Systems/Loral

• Vibration tables (5)
• Thermal vacuum chamber (30 ft f)
• Compact RF range
• Near-field range
• Small thermal/vacuum chambers (~20)

University of Maryland

The University of Maryland offers one of the four neutral buoyancy facilities in the country.  The Neutral Buoyancy Research Facility houses a 50-ft diameter, 25-ft deep neutral buoyancy tank.  This is used to simulate the weightlessness of space while performing various operations.

Viking/Metrom Laboratories

• Vibration facilities
• Environmental (numerous)

REFERENCES

Some additional references were supplied via the survey responses.  These are included below.  A strong list of Pyrotechnic publications was provided by Bement.  The publications listed below by Fusaro provide an informative prospective of space mechanism technology. Most of the Fusaro reports below are available for download.

1. Fusaro, R.L. "Tribology Needs for Future Space and Aeronautical Systems.", NASA Technical Memorandum 104525, December 1991.
2. Fusaro, R.L. "Government/Industry Response to Questionnaire on Space Mechanisms/ Tribology Technology Needs.", NASA Technical Memorandum 104358, May 1991.
3. Fusaro, R.L. "Lubrication of Space Systems - Challenges and Potential Solutions.", NASA Technical Memorandum 105560, April 1992.
4. Fusaro, R.L. and M.M. Khonsari. "Liquid Lubrication for Space Applications.", NASA Technical Memorandum 105198, July 1992.

Index of Papers Sorted by Topic

Aerospace Mechanism Symposia Proceedings (Volumes 1 through 28)

Center for Aerospace Structures

Department of Aerospace Engineering Sciences

University of Colorado

1. Murphy, T.J., K.E. David, and H.W. Babel. "Solid-Film Lubricants and Thermal Control Coatings Flown Aboard the E01M-3 MDA Sub-Experiment." McDonnell Douglas Aerospace Report MOC 93H1394, Presented at 32nd Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 1994.
2. Freeman, Michael. "On-Orbit Deployment Anomalies: What Can Be Done?" 17th Space Simulation Conference (N93-15603), pp. 113-136.
3. Heard, Walter L., Watson, Judith J. "Results of the Access Construction Shuttle Flight Experiment." AIAA Space Systems Technology Conference, San Diego, California, AIAA #86-1186, June 1992.
4. Masri, S.F., Miller, R.K., Traina, M.I. "Development of Bearing Friction Models from Experimental Measurements." Journal of Sound and Vibration, Vol. 148, pp. 455-475, 1991.
5. Misawa, M., Yasaka, T., Miyake, S. "Analytical and Experimental Investigations for Satellite Antenna Deployment Mechanisms." Journal of Spacecraft and Rockets, Vol. 26, No. 3, AIAA Paper No. 88-2225, pp. 181-187, May-June.
6. Misawa, Masayoshi. "Deployment Reliability Prediction for Large Satellite Antennas Driven by Spring Mechanisms." AIA Paper No. 93-1621.
7. Nuss, H.E. "Space Simulation Facilities and Recent Experience in Satellite Thermal Testing." Vacuum, Vol. 37, No. 3, 4, pp. 297-302, 1987.
8. Parker, K. "Some Experiences of Thermal Vacuum Testing of Spacecraft Mechanisms." Vacuum, Vol. 37, No. 3, 4, pp. 303-307, 1987.
9. Rhodes, Marvin D. "Design Considerations for Joints in Deployable Space Truss Structures." First NASA/DOD CSI Technology Conference, Norfolk, Virginia, November 1986.
10. NASA Contract No. NAS8-31352. "Solar Array Flight Experiment Final Report." April 1986.
11. Tzou, H.S., Rong, Y. "Contact Dynamics of a Spherical Joint and a Jointed Truss-Cell System." AIAA Journal, pp. 81-88, January 1991.
12. Young, Leighton E., Pack, Homer C. "Solar Array Flight Experiment/Dynamic Augmentation Experiment." NASA Technical Paper 2690, 1987.
13. Adams, L.R. "Hing Specification for a Square-Faceted Tetrahedral Truss." NASA Contractor Report 172272, January 1984.
14. Bowden, M. Dugundji, J. "Effects of Joint Damping and Joint Nonlinearity on the Dynamics of Space Structures." AIAA SDM Issues of the International Space Station Conference, Williamsbury, Virginia, AIAA No. 88-2480, April 1988.
15. Freudenstein, F., Maki, E.R. "The Creation of Mechanisms According to Kinematic Structure and Function." Journal of Environment and Planning B, pp. 375-391, 1979.
16. Heimerdinger, H. "An Antenna Pointing Mechanism for Large Reflector Antennas." 15th Aerospace Mechanisms Symposium, NASA Conference Publication 2181, 1981.
17. Kellemaier, H. Vorbrugg, H. Pontoppidan, K. "The MBB Unfurlable Mesh Antenna (UMA) Design and Development." AIAA 11th Communication Satellite Systems Conference, San Diego, California, March 1986.
18. Marks, G., Anders, C., Draisey, S., Elzeki, M. "The Olympus Solar Array Development and Test Program." Proceedings of the 4th European Symposium, "Photovoltaic Generators in Space," Cannes, September 1984, ESA SP-210, November 1984.
19. Rowntree, R.A., Roberts, E.W., Todd, M.J. "Tribological Design - The Spacecraft Industry." 15th Leeds-Lyons Symposium, September 1988.
20. Satter, C.M., Kuo, C. "Thermal/Mechanical Analysis of a Panel Attachment System for the PSR." SPIE Conference, Orlando, Florida, SPIE Proceedings, Vol. 1114, pp. 1114-51, March 1989.
21. Wada, B.K., Kuo, C.P., Glaser, R.J. "Extension of Ground-Based Testing for Large Space Systems." AIAA 26th SDM, AIAA Paper No. 85-0757, pp. 477-483, 1985.

References Provided Through Survey

From Jones

1. Masuko, M., W.R. Jones Jr., and L.S. Hemlick. "Tribological Characteristics of Perfluoropolyether Liquid Lubricants under Sliding Conditions." NASA TM 106257, July 1993.
2. Masuko, W.R. Jones Jr., R. Jansen, B. Ebihara, and S.V. Pepper. "A Vacuum Four-Ball Tribometer to Evaluate Liquid Lubricants for Space Applications." NASA TM 106264, July 1993.
3. Jones, W.R. Jr.The Properties of Perfluoropolyethers Used for Space Applications." NASA TM 106275, July 1993.
4. Jones, W.R. Jr., et. al. "The Preliminary Evaluation of Liquid Lubricants for Space Application by Vacuum Tribology." Preprint from 28th Aerospace Mechanisms Symposium, NASA Lewis Research Center, May 1994.

References Provided Through Survey

Pyrotechnic Test Facility

1. Lake, E.R., Thompson, S.J., and Drexelius, V.W. "A Study of the Role of Pyrotechnics on the Space Shuttle Program." NASA CR-2292, September 1973.
2. Bement, Laurence J., and Schimmel, Morry L. "Integration of Pyrotechnics into Aerospace Systems." Presented at the 27th Aerospace Mechanisms Symposium, NASA Ames Research Center, May 1993.
3. Bement, Laurence J. "Pyrotechnic System Failures: Causes and Prevention." NASA TM 100633, June 1988.
4. Bement, Laurence J., and Schimmel, Morry L. "Determination of Pyrotechnic Functional Margin." Presented at the 1991 SAFE Symposium, Las Vegas, Nevada, November 1991.
5. Elern, Herbert. "Modern Pyrotechnics." Chemical Publishing Company, 1961.
6. MIL-P-46994/B, Amendment 3. "General Specification for Boron/Potassium Nitrate."
7. Drexelius, V.W., and Schimmel, M.L. "A Simplified Approach to Parachute Mortar Design." Presented at the Seventh Symposium on Explosives and Pyrotechnics, Philadelphia, Pennsylvania, September 1971.
8. SKB26100066. "Design and Performance Specification for NASA Standard Initiator-1 (NSI-1)." January 1990.
9. Meyer, Rudolph. "Explosives." Printed by Verlag Chemie, 1977.
10. "Properties of Explosives of Military Interest." AMCP 706-177, AD 764340, U.S. Army Materiel Command, January 1971.
11. Rouch, L.L., and Maycock, J.N. "Explosive and Pyrotechnic Aging Demonstration." NASA CR-2622, February 1976.
12. WS5003J. "Material Specification for HNS Explosive." Naval Surface Weapons Center, February 1981.
13. Kilmer, E.E. "Heat-Resistant Explosives for Space Applications." Journal of Spacecraft and Rockets, Vol. 5, No. 10, October 1968.
14. MIL-STD-1576 (USAF). "Electroexplosive Subsystem Safety Requirements and Test Methods for Space Systems, July 1984.
15. DOD-E-83578A (USAF). "Explosive Ordnance for Space Vehicles (Metric), General Specification for." October 1987.
16. NSTS 08060, Revision G. "Space Shuttle System Pyrotechnic Specification."
17. Lake, E.R. "Percussion Primers, Design Requirements." McDonnell Douglas Corporation Report MDC A0514, Revision B, April 1982.
18. Schimmel, Morry L. "The F-111 Crew Module: Major Challenge for Thermally Stable Explosives." U.S. Naval Ordnance Laboratory, White Oak, Silver Spring, Maryland, June 1970.
19. Schimmel, Morry L., and Kirk, Bruce. "Study of Explosive Propagation Across Air Gaps." McDonnell Aircraft Corporation Report B331, December 1964.
20. Schimmel, Morry L. "Quantitative Understanding of Explosive Stimulus Transfer." NASA CR-2341, December 1973.
21. Bement, Laurence J. "Helicopter (RSRA) In-Flight Escape System Component Qualification." Presented at the Tenth Symposium on Explosives and Pyrotechnics, San Francisco, California, February 1979.
22. Persson, Per-Anders. "Fuse." U.S. Patent 3,590,739, July 1971.
23. Chenault, Clarence F., McCrae, Jack E. Jr., Bryson, Robert R., and Yang, Lien C. "The Small ICBM Laser Ordnance Firing System." AIAA 92-1328.
24. Ankeney, D.P., Marrs, D.M., Mason, B.E., Smith, R.L., and Faith, W.N. "Laser Initiation of Propellants and Explosives." Selected Papers, SP93-09 on Laser Ignition, Published by the Chemical Propulsion Information Agency, September 1993.
25. Drexelius, V.W., and Berger, Harold. "Neutron Radiographic Inspection of Ordnance Components." Presented at the Fifth Symposium on Electroexplosive Devices, Philadelphia, Pennsylvania, June 1967.
26. Bement, Laurence J. "Monitoring of Explosive/Pyrotechnic Performance." Presented at the Seventh Symposium on Explosives and Pyrotechnics, Philadelphia, Pennsylvania, September 1971.
27. Schimmel, Morry L., and Drexelius, Victor W. "Measurement of Explosive Output." Presented at the Fifth Symposium of Electroexplosive Devices, the Franklin Institute, June 1967.
28. Bement, Laurence J., and Schimmel, Morry L. "Cartridge Output Testing: Methods to Overcome Closed-Bomb Shortcomings." Presented at the 1990 SAFE Symposium, San Antonio, Texas, December 1990.
29. Bement, Laurence J., Schimmel, Morry L., Karp, Harold, and Magenot, Michael C. "Development and Demonstration of an NSI-Derived Gas Generating Cartridge (NGGC)." Presented at the 1994 NASA Pyrotechnic Systems Workshop, Albuquerque, New Mexico, February 1994.
30. Bement, Laurence J., and Schimmel, Morry L. "Ignitability Test Method." Presented at the 1988 SAFE Symposium, Las Vegas, Nevada, December 1988.
31. Bement, Laurence J., and Schimmel, Morry L. "Ignitability Test Method, Part 2." Presented at the 1989 SAFE Symposium, New Orleans, Louisiana, December 1989.
32. Bement, Laurence J., Doris, Thomas A., and Schimmel, Morry L. "Output Testing of Small-Arms Primers." Presented at the 1990 SAFE Symposium, San Antonio, Texas, December 1990.
33. Bement, Laurence J., and Schimmel, Morry L. "Approach for Service Life of Explosive Devices for Aircraft Escape Systems." NASA TM 86323, February 1985.
34. Bement, Laurence J., Kayser, Eleonore G., and Schimmel, Morry L. "Service Life Evaluation of Rigid Explosive Transfer Lines." NASA TP2143, August 1983.
35. Bement, Laurence J., and Schimmel, Morry L. "Investigation of Super*Zip Separation Joint." NASA TM 4031, May 1988.

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