[345] BY the end of 1962 it was apparent that, although most of the Ames Center's research continued to fall in the "applied" category, a small but "Towing part of it could be called "pure"-performed mainly to satisfy human curiosity with no immediate practical objective in mind. Some work on meteors fell in this category, for example, as did some in the field of space science.
Work on aircraft and airplane flight problems was not neglected, but certainly the work on spacecraft and space flight predominated. While the space research, for the most part, followed the familiar pattern of experimentation and theoretical analysis conducted in the laboratory, it nevertheless also introduced two new forms of activity. One of these was the planning of specific space experiments (including the design of the required instruments) to be carried out by some other group. The other new activity was the management of space-flight research projects which were intended to carry out experiments designed by others.
Notable features of Ames research during this period were (1) the emphasis on reentry aerothermodynamics, particularly on the phenomena of radiation and ablation; (2) the acceleration of the movement toward the development and use of flight simulators; (3) the work on V/STOL aircraft; and (4) the beginning of work in the fields of human factors, biology, meteors, and space physics.
Boundary-Layer Transition. It had long been recognized that the maintenance of a laminar boundary layer was of "Teat benefit to the performance of both subsonic and supersonic airplanes, and that a laminar-flow condition could be maintained more easily in an accelerating flow than in a decelerating flow. The flow over an airplane wing and fuselage involved both accelerating and decelerating flows but more of the latter, since the net [346] reaction of these components in the line of motion was drag. There was a question, however, as to the degree of flow deceleration a boundary layer could tolerate without going turbulent, and there was also a question of the effects on transition of sweepback. Dr. Werner Pfenninger of the Northrop Aircraft Co. was of the opinion that the installation of carefully designed suction slots at many points over the whole surface of a wing would make possible the maintenance of laminar flow over the whole wing. The same result might also be achieved with the fuselage although in this case 100 percent laminar flow was perhaps too much to expect. The benefit of such an installation, if the system were light and efficient, would clearly be great. The speed of an airplane so equipped would be enhanced and, in the case of a bomber, a tremendous increase in range could be achieved.
The Ames 12-foot tunnel was the ideal instrument in which to check out some of Dr. Pfenninger's theories as well as to investigate boundary-layer transition. Ames worked closely with Dr. Pfenninger on his project and at the same time pursued the matter of boundary-layer transition on a more general level. Gary Chapman of the SSFF tunnel undertook in TN D-1066 and TN D-1075 to demonstrate and analyze the generally deleterious effects of wing sweep on transition at supersonic speed. At about the same time, Fred Boltz, George Kenyon, and Clyde Allen of the 12-foot tunnel were demonstrating (e.g., TN D-338) that the bad effects of sweep on transition also prevailed at high subsonic speeds. It appeared from the tests that the lateral component of flow caused by wing sweep produces boundary-layer vortices which precipitate transition. As a matter of related interest, Don Jillie and Edward Hopkins of the 8- by 7-foot Unitary tunnel investigated the combined effects of Mach number, leading-edge bluntness, and sweep on transition. This work, reported in TN D-1071, confirmed the adverse effects of sweep for Mach numbers from 2.0 to 4.0 and further revealed that, for straight wings with blunt leading edges, an increase of Mach number favors the maintenance of laminar flow.
Basic Configurations. Many of the airplane-configuration studies undertaken during this period were concerned with the design of the North American B-70 Mach 3 bombing airplane and with preliminary designs for a commercial supersonic transport (SST) . The SST had become of interest as a national development project and it was felt to be the responsibility of NASA to take the lead in determining the most promising general configurations from which a successful SST might be developed. Toward this end, the NASA Langley Research Center sponsored what was known as the SCAT (supersonic commercial air transport) program to investigate four basic SST configurations designated SCAT 4, 15, 16, and 17. SCAT designs 4 and 15 were quickly disposed of, leaving SCAT 16, having a wing with controllable sweep, and SCAT 17, having a canard configuration with a [347] fixed delta wing. These two design arrangements were studied intensively both by NASA, in its wind tunnels, and by certain major aircraft companies. Ames, because of its long-standing interest in delta-wing and canard configurations, gave most of its attention to SCAT 17; whereas Langley, for similar reasons, devoted most of its efforts to SCAT 16. The Boeing and the Lockheed aircraft companies were later awarded Government contracts for SST designs based essentially on the SCAT 16 and the SCAT 17 configurations.
Ames studies of both the B-70 and the SST (SCAT 17) represented largely a continuation of earlier work on canard and delta configurations. Numerous reports issued from this effort. There were, for example, TM X-363 by Richard Petersen and TM X-392 by Victor Peterson and Loren Bright, which determined the extent to which the stability of a delta-wing airplane would be benefited by deflecting downward a portion of the wing tips. There were also TM X-651 and TM X-781 by LeRoy Fletcher, which reported on the static and dynamic stability of delta-wing canard configurations at Mach numbers up to 3.50. In addition, TN D-690 by Victor Peterson and Gene Menees, revealed the adverse aerodynamic interference produced by a horizontal canard control surface on the wing and vertical tail surfaces. The slow-speed performance of SST configurations was established in the 40- by 80-foot tunnel by the team of Jim Brady, Dave Koenig, and Virgil Page. Typical reports from this work are TM X-643 and TM X-644. The work by the Ames staff on the SCAT 17 configuration is best indicated, perhaps, by the paper (ref. C-3) entitled "A Critical Study of Delta Wing Configurations for the Supersonic Transport Application," by J. L. Jones, L. W. Hunton, T. J. Gregory, and W. P. Nelms.
Inlets. This period saw a continuation of research directed toward the development of efficient supersonic inlets. Inlet work was conducted in the 8- by 8-inch, the 1- by 3-foot, and the Unitary tunnels and some of it was specifically intended to develop an inlet for the B-70 airplane. Among the contributors to this effort were Norman Sorenson, Tom Gregory, John Gawienowski, Richard Kurkowski, Earl Watson, William Peterson, John Lundell, Richard Scherrer, and Lewis Anderson. In TN D-584, the latter three described work conducted in the 1- by 3-foot tunnel on an idealized form of circular internal-compression inlet. A pressure recovery of nearly 90 percent was obtained with this inlet at a Mach number of 3.8. This was perhaps the highest recovery ever obtained at that Mach number and demonstrated the possibilities of internal-compression inlets. Despite the high performance theoretically possible with internal-compression inlets, an inlet combining external and internal compression was generally regarded as being more practicable.
Vortex Flows. The wings, bodies, and control surfaces of aircraft produce vortices which interact strongly with the general airflow pattern....
[349] ....around the aircraft. Over the years these interactions were the subject of numerous theoretical studies at Ames by such men as William Pitts, Jack Nielsen, George Kaattari, Max Heaslet, John Spreiter, and Al Sacks. Those early studies produced very useful results but did not, by any means, exhaust the field. Thus, during this period, J. Richard Spahr of the Fluid Mechanics Branch was able to make a very real contribution in developing a general method for calculating the paths of vortices generated by wing-body combinations and for determining the effects of such vortices on the load distribution and stability of aircraft. This work, which was performed in 1960, was reported in TR R-101 (ref. C-4).
As earlier noted, NASA Headquarters in late 1959 ruled that flight research involving the flying of airplanes would be conducted exclusively at the NASA Flight Research Center at Edwards, Calif. One exception to this rule was to be flight research on V/STOL aircraft. The Headquarters ruling in this matter accelerated Ames efforts in the application of ground-based flight simulators to flight research. Variable-stability airplanes were also flight simulators but, since they were not ground-based, they too were transferred to Edwards. The transferral of the variable-stability airplanes was a painful blow to Ames since the Center had pioneered in the development and application of these highly useful devices. The original variable-stability airplane developed by Ames was a Grumman F6F-3. Following that development were the North American F-86 variable-stability and the F-86 variable-control airplanes. Finally during 1958 and 1959, a North American F-100 had been converted into one of the most elaborate and fully automated variable-stability airpIanes ever built. Much of the responsibility for the development of the F-100 variable-stability airplane fell on John Foster....
[350] ....of the Instrument Research Division. Some of the basic design principles for the F-100, and earlier, variable-stability airplanes are given in the paper "Servomechanisms as Used on Variable-Stability and Variable-Control-System Research Aircraft," which Foster presented in October 1957 at a meeting in Chicago of the National Electronics Conference. Unhappily, the just completed F-100, along with the other research airplanes, was shipped off to Edwards.
Shortly before the airplanes were moved to Edwards, a rather interesting study was made with the F-86 variable-stability and variable-control airplanes by Norman McFadden, Richard Vomaske, and Don Heinle. At this stage, the design features and operational ranges of airplanes were so extreme that one could scarcely expect an airplane to have adequate inherent static and dynamic stability under all flight conditions. It was clear that certain "black boxes" in the form of stability-augmentation devices would be required. Such devices were fine as long as they worked, but forever lurking in the designer's mind was the question of what would happen if they failed. An airplane would have to be designed so that the failure of a black box would not be catastrophic; the airplane in that event must at least be manageable even though its flying qualities were far from ideal. It was now necessary to determine the worst control and stability characteristics that could be accepted from a safety standpoint. The variable-stability airplane was the best available instrument for such a study and was used for this purpose in the just-mentioned investigation by McFadden, Vomaske, and Heinle; the results are presented in TN D-779, "Flight Investigation Using Variable Stability Airplanes of Minimum Stability Requirements for High-Speed, High-Altitude Vehicles." Pilot opinion was, of course, a vital element of this study.
Ground-Based Simulations. The study by McFadden, et al., of minimum acceptable stability under emergency conditions (black-box failure) could, of course, have been accomplished with a ground-based simulator. However, Ames did not have a ground-based simulator in which all motions of an airplane could be simulated, and thus the perennial question arose as to the importance of incomplete or imperfect motion simulation in such a study. Considerable enlightenment on this question came from a cooperative research program jointly undertaken by NASA and the Navy using the huge centrifuge of the U.S. Naval Air Development Center at Johnsville, Pennsylvania. One of the reports emanating from this program was TN D-348, "A Study of Longitudinal Control Problems at Low and Negative Damping and Stability with Emphasis on Effects of Motion Cues," by Melvin Sadoff, Norman M. McFadden, and Donovan R. Heinle.
The cab of the centrifuge, as used in the study, was equipped with an airplane cockpit with control stick and instruments; the rotor motion was controlled by an analog computer that had been programed with the [351] dynamic characteristics of some selected airplane. The centrifuge was thus the motion-generator portion of a simulator which simulated motions imperfectly but nevertheless did provide normal accelerations in accordance with stick motions. Pilot opinion of tolerable emergency stability limits was determined, for a simulated airplane, in the centrifuge and these data were compared with similar results from simulators (fixed cab, pitch-roll chair, and variable-stability airplane) having different motion-generating characteristics. From such comparisons, it was possible to determine the stability ranges in which motion simulation was necessary and which kinds of motion simulation were of most value.
The study also investigated the interesting possibility, in a simulation, of replacing the pilot with his response equation programed into the computer. It was recognized that if the response of a pilot to the usual flight stimuli could he expressed in mathematical form, flight problems could then be solved with a computer alone. While the development of an accurate human-response equation was too much to hope for, this study of the matter produced some useful results.
SST Studies. The use of ground-based simulators for flight studies not only eliminated the hazard to life and property inherent in flight testing but also made possible the acquisition of important design information applicable to an airplane prior to its construction. Flight simulators were thus extremely useful for studying critical flight problems to be expected in the operation of the projected supersonic commercial transport airplane. Such studies were pursued at Ames by the team of Maurice White, Richard Vomaske, Walter McNeill, and George Cooper. The work was undertaken with the new five-degrees-of-freedom (centrifuge) simulator at Ames as well as with a simulator providing only angular motions, i.e., the cab portion of the five-degree simulator with centrifuge inoperative. Of particular interest to...
[352] ...the investigators was the determination of the need for stability augmentors in the SST. Of equal interest was the effect of the failure of a stability augmentor as a separate emergency, or combined with the failure of an engine. In such emergencies, the airplane is momentarily out of equilibrium if not out of control and, before control can be restored, may achieve speeds and attitudes from which recovery is impossible.
The SST simulator work carried out by White, Vomaske, McNeill, and Cooper during this period is reported in two papers, one TN D-1888 and the other (ref. C-5) a paper entitled "Assessment of Critical Problem Areas of the Supersonic Transport by Means of Piloted Simulators," which was published in the May 1962 issue of Aerospace Engineering.
The authors concluded from their investigation that motion simulation provided by available flight simulators left much to be desired and that, for representing the emergency flight upsets that might be encountered by the SST, a simulator providing substantial translational as well as angular motions would be required.
A rather deep chasm had long existed between aircraft which derived lift and control force from their motion through the air (airplanes) and aircraft which derived these forces largely from the direct application of engine power to special lifting surfaces (helicopters). Efforts to bridge the gap, to build a craft that would fly with the efficiency of an airplane yet be capable of vertical takeoffs and landings (VTOL), were now meeting with some success as a result of the growing sophistication of airplane and powerplant designers. More commonly, the gap was not wholly bridged and the resulting craft was capable only of short takeoff and landing (STOL). The general class of V/STOL aircraft was of growing interest to aircraft users, particularly the military, and both the Army and the Air Force had let contracts with industry for the development of prototype V/STOL configurations. The old NACA laboratories (Ames and Langley) had been drawn into this work and when in 1959, under NASA, all flight research at the laboratories, except V/STOL research, was proscribed, their interest and efforts in V/STOL research greatly increased.
Ames was in a particularly favorable position to pursue research on V/STOL aircraft because of the availability of the 40- by 80-foot tunnel in which V/STOL aircraft could be tested at full scale. The Center's background of handling-qualities research as well as its experience with variable-stability aircraft and other flight simulators was also helpful. Ames' earlier boundary-layer-control work provided a natural entry into V/STOL research; indeed, BLC was the first practical step toward achieving a V/STOL airplane. The downward deflection of the propeller slipstream by means of elaborate multicomponent flaps was perhaps the next step. Another...
....approach might be to have the engines, and perhaps also the wings on which the engines were mounted, capable of being rotated in flight so that the propellers could lift more effectively for takeoff. Still another possibility might be to install separate lifting engines and propellers in the wings or fuselage, to be used only for takeoff and landing; for this system, special types of engines would be needed. All of these schemes and many more were under investigation and the whole field was wide open for inventive genius. At this stage, only the simpler V/STOL arrangements were ready for application. The more radical ones were still very much in the study stage of development.
Ames concerned itself mainly with the slow-speed aspects of V/STOL research and particularly with the control and handling qualities of such craft No one really knew what handling qualities were required for V/STOL aircraft and one of the first tasks undertaken by Ames was, on the basis of its large experience with such matters, to analyze the situation and establish tentative V/STOL handling-qualities criteria. This worthwhile task was undertaken by Seth Anderson, whose work on this subject was published as TN D-331 (ref. C-6), "An Examination of Handling Qualities Criteria for V/STOL Aircraft."
There was much to be done in actually determining the flying qualities of V/STOL airplanes and the ability of the pilot to take full advantage of such slow landing and takeoff potential as the airplane might have. The piloting technique for a V/STOL aircraft was definitely more difficult than for conventional aircraft owing in part to the more complicated controls and [354] the low inherent stability of the airplane at a very slow speed. The flying problems of STOL aircraft were investigated quite extensively at Ames by the team of Hervey Quigley and Robert Innis. Bob Innis was an engineering test pilot who had joined the Ames staff in 1954. The work of Quigley and Innis in this field was first concerned with two large cargo airplanes which were capable of STOL operation by virtue of boundary-layer-control installations. One was the two-engine Stroukoff YC-134A on which the suction type of BLC was applied to the flaps and also to the ailerons, which moreover were drooped, in landing, to give additional lift. The other airplane was a four-engine Lockheed C-130 airplane on which BLC and high lift were obtained by blowing air over the flaps and drooped ailerons. In the C-130, the air for BLC was provided by two jet engines mounted in outboard wing pods.
As reported in TN D-862, Innis and Quigley investigated the lift, drag, and stalling characteristics of the YC-134A as well as its stability and control characteristics-the latter particularly in approach and landing operations. Among other things, the airplane, at slow speed, was observed to have a bad stall characterized by an uncontrollable rolloff and large sideslip angles. In the tests of the C-130, reported in TN D-1647, the lateral-directional handling characteristics were closely observed and were found, under landing conditions, to be so poor as to render the landing of the airplane at a speed of less than 65 knots very difficult. Several special techniques for operating the airplane under STOL conditions were developed.
The flight tests of the BLC cargo-type airplanes were correlated with information obtained in the 40- by 80-foot wind tunnel and from flight simulator tests. Of the wind-tunnel tests, typical results for a four-engine tilt-wing model with blowing BLC are described in TN D-1034 by James Weiberg and Curt Holzhauser. The simulator tests, described in TN D-1773 by Hervey Quigley and Herbert Lawson, constituted a study of the C-130 lateral-directional characteristics which were known to be deficient. This study, which was made on the fixed-cockpit landing-approach simulator incorporating the DALTO visual (TV) simulating device, revealed much about the stability and control characteristics of the airplane and suggested ways in which the lateral-directional stability faults of the airplane might be corrected.
The BLC cargo airplanes represented an important, but conservative, approach to the V/STOL airplane development problem. Much interest had developed in more radical types such as the X-14A VTOL test-bed (prototype) vehicle built for the Air Force by the Bell Aircraft Co. and flown extensively by Fred Drinkwater in Ames flight research programs The X-14A was a rather small, fixed-wing, jet-propelled aircraft in which the jet slipstream could, by means of a cascade of flaps, be diverted downward as required to produce any desired combination of thrust and lift. By [355] controlling the flaps, the pilot could make the airplane rise vertically and then move off horizontally. Air jets were required for control at speeds below that at which conventional lifting-surface controls became effective.
The X-14A represented a type of airplane for which stability, control, and handling characteristics were largely unknown. It was for the purpose of studying these factors that the airplane was turned over to the Ames Research Center. To increase the extent and usefulness of the information obtained. from the X-14A, Ames modified the airplane's control system to provide variable-stability and variable-control characteristics. The first flight study made with the X-14A is reported in TN D-1328 (ref. C-7), "A Flight Determination of the Attitude Control Power and Damping Requirements for a Visual Hovering Task in the Variable Stability and Control X-14A Research Vehicle," by L. Stewart Rolls and Fred J. Drinkwater III. The X-14A was a very versatile aircraft and was used at Ames not only for V/STOL. flight studies but also for simulating the flight of a spacecraft landing on the moon.
Still more radical designs of V/STOL airplanes envisioned the use of lifting propellers built into wings and fuselage. Such applications had become more practical as a result of the development by the General Electric Co. of gas generators and turbine-driven fans especially designed for the purpose. As a joint project, the Army, NASA (Ames), and General Electric made conceptual designs and preliminary evaluations of a number of different....
[356] ....lifting-fan V/STOL configurations. Models of the configurations were evaluated aerodynamically in the 40- by 80-foot tunnel. Several test reports were written, but the results of the whole project were summarized in the paper "Characteristics of Aircraft with Lifting-Fan Propulsion Systems for V/STOL," by Robert H. Goldsmith (GE) and David H. Hickey (Ames). This paper was presented at the annual meeting of the Institute of the Aero space Sciences in New York in January 1963.
Numerous experiments had been made to determine the tolerance of animals and humans to acceleration forces but in general these tests had not been particularly informative with respect to the effect of acceleration on the ability of experienced pilots to perform piloting tasks. The latter question, however, was one of several related matters investigated in a cooperative research program undertaken by the NASA Ames Research Center and the Aviation Medical Acceleration Laboratory of the Naval Air Development Center, Johnsville, Pennsylvania. In this program, the Navy's centrifuge at Johnsville was incorporated as a motion generator within the control loop of a flight simulator.
Several reports resulted from the joint program, one of which (TN D-348) has already been mentioned. Two additional reports (TN D-337 and TN D-345) dealt more specifically with the human-factors aspects of the program. These were authored by Brent Creer and Rodney Wingrove of Ames and Captain Harald A. Smedal of the USN Medical Corps. Captain Smedal, as earlier noted, eventually joined the staff of the Center and favorably influenced the decision to establish the NASA life sciences activity at Ames. A fourth report generated by the joint program (TN D-91) described a special restraint system which greatly helped a pilot maintain control of his craft while subjected to high and varying accelerations. This report was authored by Captain Smedal and two Ames test pilots, Glen Stinnett and Robert Innis.
The two human-factors reports revealed that a well-trained pilot could adequately carry out a control task during moderately high accelerations for prolonged periods of time; however, his ability to precisely control a vehicle of marginal dynamic stability deteriorated rapidly at accelerations over 4 g. The pilots could nevertheless tolerate accelerations of 6 g for as much as 6 minutes. Physiological measurements were made during the tests, and it was found that the respiratory function was one of the more limiting factors with respect to acceleration tolerance. This factor, however, was less critical when the direction of the acceleration was such as to tend to throw the eyeballs out of the head. The "eyeballs out" acceleration, to use the vernacular of the trade, is in contrast to the reverse "eyeballs in" acceleration and the most common "eyeballs down," or normal, acceleration.
The Ames Research Center was now taking an increasing interest in the dynamic loads to which aircraft and spacecraft structures were subjected and thus also to the materials and structures used in such craft. Aerodynamic loads continued to be of primary interest, but loads caused by the sloshing of liquid fuel in a booster rocket or by the impact of landing on the moon were also under consideration. The use of such materials and structures in spacecraft as best to resist the impact of meteoroids had become a problem for research, as had also the erosion of spacecraft surface materials by the steady flux of fragmented atoms (ions) in space. In the materials field, the study of substances for use in ablation heat shields was, of course, of primary interest.
The long-standing problem of wing flutter received some attention during this period, as best indicated by reports TN D-344 by Henry Lessing, John Troutman, and Gene Menees, and TN D-1206 by Reuben Bond, Barbara Packard, Robert Warner, and Audrey Summers. The first report, from the 6- by 6-foot tunnel, demonstrated a rather clever technique for measuring pressure distributions on a wing while it was undergoing forced bending oscillations at supersonic airspeeds. The second provided some useful analytical tools for dealing with flutter and gust-response problems.
Bond and Packard also, in TN D-859, provided an analytical method for calculating the elastic-dynamic behavior of a launch vehicle in flight. This report was useful not only for calculating structural loads but also for determining the effects of missile bending on the design of the control system. The unsteady airloads on ascending missiles were generally greatest at the point in the trajectory where the missile passed through the transonic range, and these loads unfortunately were aggravated by the blunt-nosed "hammerhead" shape of the missile. The bulbous, hammerhead nose shape was often unavoidable because the diameter of the spacecraft (payload) sitting atop the booster was greater than that of the booster. Certain nose shapes caused an unsteady separating flow that excited a longitudinal bending vibration (flutter) of the missile. This vibration could, depending on the damping characteristics of the missile, be quite destructive. A study of the dynamic-load problem of hammerhead missiles was undertaken in the 14-foot tunnel. Charles Coe and Henry Cole were important contributors to the study; one of the more notable reports resulting from it was TN D-1982 (ref. C-8), "Dynamic Response of Hammerhead Launch Vehicles to Transonic Buffeting," by Henry Cole, who was well recognized at the Center for his accomplishments in the field of structural dynamics.
In any study of the structural dynamics (flutter) of a launch vehicle, the structural or internal damping of the missile was a critical factor. An important element of the internal damping, it had been found, was the sloshing of the liquid fuel in the fuel tanks of the missile. The effect of fuel [358] sloshing, and the design of baffles to control the sloshing, thus became a rather important subject for study. Here again the abilities of Henry Cole came into play. As reported in TN D-694, he and Bruno Gambucci made a very useful study of fuel sloshing and baffle design.
The simulation in the laboratory of conditions existing in space was always difficult and in many cases impossible. The zero-g condition, for example, could not be simulated for any very useful period of time on earth, and the interacting radiation and magnetic fields in space could not be simulated at all or at least not until their basic nature had been determined through actual spaceflight tests. On the other hand, the flux of ions that prevailed in space, and their erosive effect on spacecraft materials could on a small scale be simulated in the laboratory. The first task here was to develop a facility for generating ions and for accelerating them in a narrow beam of uniform speed or energy. Ion beams of different energy levels could then be allowed to impinge on specimens of spacecraft materials to determine the erosive effect. The test specimens could thus be exposed at various angles and for different periods of time to ion beams having different energy levels. The resulting erosion, called "sputtering," was a function of angle, exposure time, and energy level. The energy level of the ions, as represented by their mass and speed, was expressed in the electrical units of electron-volts (eV) or more often in units of thousands or millions of electron-volts (keV or MEV). Sputtering effectiveness, or yield, was measured by the number of atoms of the target material that were knocked out by each ion that hit the target. The bombardment had to be carried out in a near vacuum, of course, and delicate measurements were obviously involved.
The development of an ion-beam apparatus was one of the projects undertaken by Michel Bader not long after he arrived at the laboratory from Caltech in 1955. His objective was a device of a type not built before which would produce a beam containing many particles of relatively low speed and energy. The energy level ranged from 0 to 8 keV. A description of how this device was developed and used in sputtering research is given in TR R-105 (ref. C-9), "Sputtering of Metals by Mass-Analyzed N2+ and N+," by Michel Bader, Fred C. Witteborn, and Thomas W. Snouse.
The sputtering that occurred in space flight was known to be a slow process not likely to endanger the structural integrity of a spacecraft. Nevertheless its roughening effect could seriously alter the performance of surfaces intended to absorb, transmit, reflect, or emit radiation. Power-generating solar cells, for example, would be affected, as would the surfaces of optical instruments and radiating elements. In space flight, the temperature control of the spacecraft was often a critical matter and the only method for disposing of unwanted heat was to radiate it to cold outer space. Special radiation surfaces were often provided for this purpose and it was obviously necessary for the radiating efficiency (emissivity) of these surfaces to remain [359] constant, at the design value, during flight. Such surfaces were usually smooth at the beginning of a flight but sputtering soon roughened them and changed their emissivity
The effect of sputtering on the emissivity of surfaces was clearly an important matter, so its investigation was undertaken by the Ames Research Center. The results of this work are contained in TN D-1646, "Effects of Sputtering with Hydrogen Ions on Total Hemispherical Emittance of Several Metallic Surfaces," by Donald L. Anderson and George J. Nothwang. Following a different tack in the emissivity study, Carr Neel prepared an experiment by means of which the thermal radiation characteristics of several surfaces were measured in an actual space flight. The experiment which Carr devised was carried in the S-16 Orbiting Solar Observatory launched in March 1962 and was one of the first Ames experiments to be conducted in space. Some of the results of Carr's work are contained in a paper which he read in May 1963 before the Ninth Aerospace Instrumentation Symposium in San Francisco. It was subsequently published by NASA as TM X-51,196.
Spacecraft configuration and airflow studies at Ames during this period were largely concerned with (1) blunt nonlifting reentry bodies, (2) lifting reentry bodies including boost-glide-vehicle configurations, and (3) dynamic stability of reentry bodies.
Nonlifting Bodies. In the blunt-body area, the analytical and numerical methods for calculating the flow existing between blunt bodies and the bow shock waves they produced were extended by a number of Ames research men. The resulting reports included TN D-791 by Frank Fuller and TN D-1426 by Mamoru Inouye and Harvard Lomax. Also included in this group of reports were TN D-1423, "Predicted Gas Properties in the Shock Layer Ahead of Capsule-Type Vehicles at Angles of Attack," by George E. Kaattari, and TN D-1979, "Experimental and Theoretical Pressures on Blunt Cylinders for Equilibrium and Nonequilibrium Air at Hypersonic Speeds," by Donald M. Kuehn.
Kaattari's paper notably considered the case of the blunt body at an angle of attack; in this situation the shock wave is not symmetrically disposed with regard to the body and this adds to the difficulty of calculating the shape and position of the resulting shock wave and of determining the character of the airflow behind it. The experimental portion of the study reported by Don Kuehn was carried out in a 6-inch arc-jet facility in the 1-by 3-foot wind-tunnel building. The tests were run at a nominal Mach number of 15 and at a stagnation enthalpy of 1000 Btu per pound. The results were correlated with a number of available theories and found to be represented best by a theory (blast wave) that had been developed to explain the aerodynamic effects of explosions.
[360] One of the blunt-body configurations that received attention at Ames during this period consisted of a blunt-nose cylinder the rear end of which flared suddenly into a conical skirt. The flare was intended to stabilize the body in flight; but Ames research men found that within the general blunt nose flow pattern, the flare produced an occlusion of alien flow the effects of which, on drag and stability, had not been anticipated. Within the occlusion, the flare produced oblique shock waves and sometimes boundary-layer separation. Although, as just noted, the blunt-nose flare configuration introduced a flow peculiarity, it was nevertheless considered worthy of study as a promising shape for the Polaris ballistic missile warhead and perhaps for other applications.
The stability characteristics of blunt-nose flare configurations were investigated quite extensively in the Unitary (11-foot )and the 6- by 6-foot tunnels. The principal contributors to this effort were Phillips Tunnell, David Reese, William Wehrend, Victor Peterson, and Willard Smith. At about the same time, Don Kuehn of the Fluid Mechanics Branch reported in TR R-117 and TR R-146 on studies he had made of boundary-layer separation caused by flares mounted on both blunt-nose and sharp-nose reentry bodies. Additionally, a rather extensive series of experimental and theoretical investigations of blunt-nose flare configurations was conducted by Alvin Seiff and Ellis Whiting of the SSFF tunnel. From the latter program, came a series of important reports including TM X-377, TN D-1147, TN D-1148, and TN D-1304. In general, Seiff and Whiting found that the stabilizing effects of flares on cylindrical bodies was less than had been expected and, also unexpectedly, varied with speed. On the other hand, the effectiveness of flaps or flares on conical bodies was greater than had been anticipated.
Aside from the studies just mentioned, many other investigations of nonlifting bodies were made during these years. Among them was the interesting undertaking described in TN D-1300, "Effects of Simulated Retrorockets on the Aerodynamic Characteristics of a Body of Revolution at Mach Numbers From 0.25 to 1.90," by Victor L. Peterson and Robert L. McKenzie. This study provided an insight as to what happens to the flow over a reentry body when it is being decelerated by forward-firing retrorockets.
Still more important were the studies undertaken during this period of the effects of gas mixtures representing the atmospheres of Mars and Venus on the aerodynamic behavior of various spacecraft configurations. This pioneering work was initiated by a 6- by 6-foot-tunnel group which included Jack Boyd, W. Pat Peterson, and Willard Smith.
Lifting Reentry Bodies. Although the relative simplicity of nonlifting reentry bodies gave such configurations an initial priority in spaceflight operations, the numerous advantages of lifting reentry bodies were well recognized and the investigation of lifting bodies at Ames was intensively pur-...
....-sued. As uncertainty existed regarding the optimum shape for such bodies, a variety of configurations was investigated at subsonic, transonic, and supersonic speeds. Among the configurations tested were slender, blunt-edge delta wings and lenticular or disk-shape bodies equipped with fins and control flaps. Perhaps the most promising configuration, which had been suggested by Al Eggers and his associates in the 10- by 14-inch tunnel, was a blunted, flat-top semicone with control flaps and vertical stabilizing fins. Eggers, whose design conceptions were now appreciated more than ever, was given the AIAA Sylvanus Albert Reed Award in 1961.
Numerous investigations of lifting-body configurations were undertaken in the Unitary, the 6- by 6-foot, and the 12-foot tunnels. Semicone configurations were studied in the Unitary tunnel by Jack Tunnell and in the 6- by 6-foot tunnel by Ralph Holtzclaw. At the same time, disk-shape, or lenticular, configurations were investigated at transonic and supersonic speeds by Fred Demele and Frank Lazzeroni. In the 12-foot tunnel, semicones were investigated by George Kenyon and Fred Sutton, lenticular configurations by Fred Demele and Jack Brownson, and blunt deltas by George Edwards. A useful summary of the lifting-body test work, authored by David Dennis and George Edwards, was published in TM X-376 (ref. C-10) .
The lifting bodies so far mentioned were designed to develop only low values of L/D and were thus expected to provide but a small amount of [362] reentry-path control. Also investigated were configurations representing boost-glide vehicles which were to be rocket-boosted to the fringes of space and then glide long distances on airplane-like wings. The Air Force s new research vehicle, Dynasoar, then in the study phase of development, was of the boost-glide type. Dynasoar-type configurations received a considerable amount of research attention at Ames, and resulting reports included TN D-341 by Al Seiff and Max Wilkins, TM X-659 by George McCullough, and TM X-656 by Horace Emerson, John McDevitt, and John Wyss. The investigation by Seiff and Wilkins provided information on drag and boundary-layer transition on a complete glider model at Mach 6.0 and at full-scale Reynolds number. The significance of TM X-656 was that it proposed an original design for a folding-wing vehicle which would be rocket launched but would thereafter use four jet engines to fly and land like an airplane. This project was said to have inspired the formation of a mission analysis group at Ames.
Dynamic Stability. In most of the reentry-body studies just mentioned, the static-stability characteristics of the body were determined and in some cases, through the use of techniques invented by Ben Beam and Henry Lessing, their dynamic-stability characteristics were also evaluated. Still other investigations, to be mentioned, were largely concerned with dynamic stability.
Static stability, the tendency of the body to return to some preferred attitude when displaced, was of course an essential characteristic of a reentry body; but, since the body was thermally protected for flight in but one direction, it was unfortunate when it had two "preferred" attitudes about which it was stable. Unhappily some of the reentry bodies with square-cut rear ends were statically stable rear-end forward as well as front-end forward. Thus an initially tumbling body might well choose the rear-end-forward attitude for reentry and burn up for lack of thermal protection on that end. It had been found, however, that the rear-end-forward flight regime could be rendered unstable, and thus eliminated, by adding a conical projection to the flat base of the reentry body. A useful evaluation of this benefit was reported in TN D-1327, "Static Aerodynamic Characteristics of Short Blunt Cones with Various Nose and Base Cone Angles at Mach Numbers From 0.6 to 5.5 and Angles of Attack to 180°," by Stuart Treon.
Dynamic stability, the tendency of an oscillation once started about the statically stable attitude to damp out, was another important requirement for reentry bodies, since violent, large-amplitude oscillations could not be tolerated in most cases. However, as demonstrated by Allen, Tobak, and others, the dynamic-stability problem was eased considerably by the fact that a reentry vehicle was accorded a degree of pseudodynamic stability throughout that portion of its reentry path in which air density and dynamic pressure were increasing. This period of grace often carried the body past the [363] peak of aerodynamic heating but, for bodies containing people or instruments to be recovered intact, an inherent dynamic stability was desirable.
Dynamic-stability investigations of reentry bodies were conducted in several wind tunnels as well as in the new pressurized ballistic range, which was ideally adapted for such work. Among the wind-tunnel investigations was one on the damping in pitch of blunt-nose flare models reported in TM X-648 by James Monfort and Jack Tunnell. This study was conducted in the Unitary Plan tunnels, as was an investigation of the static and dynamic stability of a flat-top wing-body model reported in TM X-361 by Bedford Lampkin and Kenneth Endicott of the 8- by 7-foot-tunnel staff.
The free-flight facilities at Ames were very useful for stability investigations and during this period were used quite extensively for this purpose. The pressurized ballistic range, owing to its high Reynolds number capabilities, was particularly applicable to stability research and was used for the investigation of the static and dynamic stability of blunt-cone bodies reported by Peter Intrieri in TN D-1299. Similarly, the supersonic free-flight tunnel was used by Simon Sommer and Barbara Short (TM X-373) to examine the stability characteristics of the Mercury capsule and by Ellis Whiting (TM X-G57) to investigate the stabilizing effect of fins mounted on blunt-nose missiles. Important work of the same kind was carried out by Don Kirk and Robert Carros of the SSFF Tunnel Branch.
The static and dynamic stability of a model tested in a free-flight facility had to be deduced from its motions. If the motions of the model could be described by a mathematical formula, the stability coefficients were thus generally defined. In the dynamic-stability formulas devised for this purpose, it was usually assumed that the static stability of the test body-its tendency to return to the preferred attitude-varied linearly with the angle of pitch; but at the higher angles of pitch encountered by a reentry body, the relationship was definitely not linear and the dynamic-stability formulas...
[364] ....were thus not accurate. It remained for Maurice Rasmussen, a Stanford man temporarily employed at Ames, to develop a mathematical method for deal ing with these nonlinearities in stability analyses. Rasmussen's work, a very useful contribution, is contained in TN D-144 (ref. C-11), Determination of Nonlinear Pitching-Moment Characteristics of Axially Symmetric Models From Free-Flight Data."
The theory of satellite orbits was a subject which fitted in well with Bill Mersman's interests and with the electronic computing facilities of which he was in charge. Out of these interests and facilities came two erudite reports of which the titles offer as much information as can readily be absorbed by the layman. The first of these reports was TR R-99, "Theory of the Secular Variation in the Orbit of a Satellite of an Oblate Planet"; the second was TR R-148, "The Critical Inclination Problem in Satellite Orbit Theory." Studies such as these made possible the prediction of satellite orbits.
Dean Chapman followed his classical, 1958, study (TR R-ll) of entry into planetary atmospheres with a second important entry study, reported in TR R-55 (ref. C-12), "An Analysis of the Corridor and Guidance Requirements for Supercircular Entry Into Planetary Atmospheres."
Spaceflight trajectories, it might be mentioned, could generally be described in terms of conic sections-circles, ellipses, parabolas, and hyperbolas-and each trajectory so described was associated with a range of launching and reentry speeds. The lowest speed range was associated with circular satellite orbits. The circular speed had to be increased to produce an elliptical orbit and increased still more for parabolic and hyperbolic trajectories. The ellipse, moreover, was the path requiring minimum-energy expenditure and least fuel consumption for travel between two circular orbits- such as those of the earth and Mars-but unfortunately for long trips the minimum-energy route was too time consuming to be useful. The speed associated with a parabolic trajectory was unique in that it represented escape speed-the lowest launching speed for which the spacecraft would leave the earth never to return unless power was exerted to bring it back. Escape speed for launchings from the earth 1 was about 36,000 feet per second (25,000 miles per hour).
It was clear from the title of TR R-55 that Chapman was concerned with speeds higher than those encountered in ordinary circular orbits. Dean showed in his study that the corridor in space through which a spacecraft must enter the earth's atmosphere, if it is to return safely to earth, is very narrow and rapidly becomes narrower as entry speed increases. On one side [365] of the corridor is the undershoot boundary, beyond which the spacecraft will be destroyed by excessive deceleration or heating. On the other side lies the overshoot boundary, beyond which air drag will be insufficient to keep the spacecraft from shooting completely past the earth. Thus a nonlifting spacecraft returning, say, from Mars must be guided with sufficient precision to hit a layer of the earth's atmosphere that, relative to the earth's diameter, might correspond in thickness to the skin of an apple. If the spacecraft has some lifting capabilities, can generate a lift-drag ratio of as much as 1.0, the entry corridor-though still narrow-is considerably widened. Thus, for spacecraft returning from deep-space missions, the ability to generate a positive lift-drag ratio is very valuable. Chapman pointed out that additional benefit from lift might be available if the values of lift (L), drag (D), or the ratio L/D could be modulated or varied throughout the entry process.
The critical heating, deceleration, and corridor problems of supercircular reentry arose directly, of course, from the use of air drag as the sole braking mechanism. While it was fully appreciated that these problems could be greatly relieved by killing off the supercircular velocity with retrorockets prior to entering the atmosphere, such a procedure involved weight and cost penalties too severe to contemplate except as a last resort.
Following Chapman's work, other entry studies, aimed at showing the benefits of modulating L, D, or L/D, were undertaken at Ames. Among these were the studies reported in TR R-80 by Tom Wong and Robert Slye, in TN D-1145 by Elliott Katzen and Lionel Levy, and in TN D-1427 by Lionel Levy. Another reentry study which gave particular attention to the heating problem was reported in TN D-334 by Tom Wong, Glen Goodwin,...
[366] ....and Robert Slye. All of these studies dealt with supercircular reentry speeds such as those encountered by spacecraft returning from deep space.
One of the more outstanding studies of reentry at supercircular velocities was made by Rodney Wingrove and reported in TR R-151 (ref. C-13), "A Study of Guidance to Reference Trajectories for Lifting Reentry at Supercircular Velocity." His study provided the detailed analytical basis for the design of guidance systems capable of dealing with exceedingly critical guidance problems involved in lift-controlled reentry from supercircular orbits. A steppingstone to Wingrove's analysis was an earlier study which he and Robert Coate had reported in TN D-787, "Piloted Simulator Tests of a Guidance System Which Can Continuously Predict Landing Point of Low L/D Vehicle During Atmospheric Re-Entry."
The report just named represented one of the early uses at Ames of a flight simulator for spaceflight research and also one of the first spaceflight guidance-system studies attempted at the Center. Soon to be undertaken, however, were other space-guidance-system studies, representative of which was the one reported in TR R-135, "Application of Statistical Filter Theory to the Optimal Estimation of Position and Velocity on Board a Circumlunar Vehicle," by Gerald L. Smith, Stanley F. Schmidt, and Leonard A. McGee.
A certain amount of effort was expended during this period on mission, or system, studies. Of these the titles of the resulting reports are sufficiently descriptive. There was, for example, TN D-1207, "An Analytical Study of Orbital Rendezvous for Least Fuel and Least Energy," by Harold Hornby. There was also TN D-1143, "Orbital Payload Reductions Resulting From Booster and Trajectory Modifications for Recovery of a Large Rocket Booster," by Alan D. Levin and Edward J. Hopkins. Levin and Hopkins produced a second report, TN D-1295, which also dealt with the problem of recovering the first-stage rocket booster. Booster recovery was, indeed, a matter of great economic significance inasmuch as the one-shot use of costly first stage rockets appeared to be a tremendously wasteful practice.
General Problem. The speeds of interest to
Ames engineers in the Space Age were much higher than those they had
been concerned with in earlier years. The ballistic-missile warhead,
for which Allen had suggested a blunt-nose configuration, had a
reentry speed of 18,000 feet per second or less. Spacecraft, however,
had reentry speeds of about 25,000 feet per second when returning
from circular orbits or as much or more than 36,000 feet per
second-earth parabolic speed-when returning from deep-space missions.
Inasmuch as aerodynamic heating was known to vary as some multiple
power (
3) of velocity,
it was obviously much higher for returning spacecraft than for
returning missile warheads.
It was in the layer of air between the body and the bow shock wave-a...
[368] ....layer commonly called the gas cap or shock layer-that aerodynamic-heating phenomena were most strikingly evident. At parabolic reentry speeds, this layer reaches temperatures much higher than that of the surface of the sun. As a bell, when struck by a hammer, jangles for a moment before settling into its fundamental tone, so also a mass of air, slugged by a shock wave, jangles in brief but violent discord before relaxing into a more orderly state of activity. Strange things happen to the air molecules during this transient but hectic period of disequilibrium. First, the molecules are set in violent motion, bouncing back and forth, hitting each other and raising the temperature and pressure of the gas to a sharp peak. Then their energy penetrates the molecules, setting up various natural modes of vibration by and between the atoms. In consequence of their relative motion, the atoms of some molecules break the chemical bonds which tie them together and fly apart in the process called dissociation. Then, if the shock is severe enough, the very electrons which circle the nucleus of the atom become so agitated that they break away from their parent nucleus and fly away on their own in the process called ionization.
Following the initial pressure and temperature rise, each of the processes that successively takes place absorbs energy and decreases temperature. Quickly the molecules and fragments settle down to an equilibrium state of activity and temperature but, even in the equilibrium state, their activity and temperature are very high. The time required for the air to relax to the equilibrium state depends on the frequency with which the molecules collide with one another, thus with the air density, and thus with the flight altitude. Whether or not the relaxation process is completed before the air reaches the body which produced the shock wave depends on the distance of the shock wave ahead of the body, which in turn depends on the size and shape of the body. If the relaxation process is not completed by the time the out-of-equilibrium air reaches the body, the body will obviously be exposed to an unusually high air temperature. This condition, it has been found, is likely to occur only at high altitude during the early, usually uncritical, stage of spacecraft reentry heating.
A flow which remains in a constant state of dissociation is said to be "frozen," but ordinarily the forces of recombination, tending to heal the shattered molecules, are dominant. Moreover, recombination is sometimes precipitated by the catalytic action of the body surface. Inasmuch as the recombination process itself generates heat, the air temperature to which a catalytic body surface is exposed is unusually high.
Allen's blunt-body principle was based on the assumption that the heat generated by the shock wave, some distance from the body, could not reach the body through the normal process of convection. The assumption was demonstrably correct, but convection was not the only mode of heat transfer: there was also radiation. Radiation varies with the fourth power of the absolute [369] temperature and, in the case of ballistic missiles, the gas cap does not get hot enough for radiation to be a significant factor. But as reentry speeds increase, the highly heated, dissociated, and ionized gas cap radiates intensely and the body is no longer isolated from the heat of the shock wave.
Radiation affected the aerodynamic heating process as the forward pass affected football-it changed the whole game. The heat of the shock wave no longer had to buck the line to reach the body; it was passed directly to this receiver largely unhindered by the intervening gas. But the effects of radiation were not quite that simple. The intervening gas did not transmit the radiation without some resistance. It absorbed radiation in proportion to its density and thus altered its own convective and radiative heat-transfer properties. Moreover, the incandescent gases of the shock layer radiated forward as well as backward. Thus, though the body was traveling at hypersonic speed, the air along its path could feel its hot presence before either the body or its preceding shock wave arrived. Indeed, the air ahead of the shock wave absorbed some of this radiated heat and carried it back to the body. On the other hand, the energy of the incandescent gas suffered a depletion or decay of its energy as a result of radiation; thus the gas had less heat to transport by convection. Radiation intensity also depended on the chemical composition of the radiating gas. Owing to the high carbon-dioxide content of the atmosphere of Mars and Venus, a spacecraft descending for a landing on either of these planets would suffer more intense radiation than one landing on the earth.
Radiation was recognized as a serious aerodynamic-heating threat in spacecraft design and considerable effort was spent at Ames, and elsewhere, in determining the earth reentry speed at which it became a significant factor. Research engineers were relieved to find that radiation became of serious consequence only at earth parabolic speeds and higher, but they noted with some awe the rapidity with which its effect developed, once started. Following onset, the radiative factor for blunt bodies was found to increase at something like the 15th power of the velocity, quickly becoming the dominating influence in aerodynamic heating. Inasmuch as a body could not be shielded from the radiated heat of the bow shock, it was obviously essential to reduce the intensity of the shock by changing its shape from normal to inclined. This objective, it was realized, could only be accomplished by making the body pointed. The point of the body, in contact with the inclined shock, would be subjected to terrific convective heating and would certainly melt, but this was a problem that would have to be faced if the devastating effects of radiation were to be avoided.
It was clear that the phenomena of dissociation, ionization, and radiation had added tremendously to the problem of comprehending and analyzing reentry aerodynamic heating. It was also clear that very effective thermal protection for spacecraft must be provided. Sweat cooling was known to be [370] very effective, but the problems of providing a porous nose, of carrying fluid in the spacecraft, and of forcing the fluid through the pores at the proper rate were extremely troublesome. How much simpler it would be if the cooling material were a solid, such as a plastic, which could be coated over the front face of the spacecraft and allowed to melt, evaporate, or sublime with attendant cooling! A material passing from a solid to a gaseous state could normally be expected to absorb more heat than one (sweat-cooling fluid) passing only from a liquid to a gas. Moreover, the solid material would insulate the spacecraft structure from the convected and radiated heat. The insulation might, indeed, be so effective as to allow its surface temperature to be elevated to such a level that a substantial portion of the body's heat load would be disposed of by radiation to outer space.
Considerations of this kind led to the belief that the ablation heat shield, as the protective layer was called, was the most promising means for providing thermal protection for spacecraft. Much remained to be learned, however, about the physical-chemical processes of ablation and about the selection of specific ablation materials for applications involving a variety of thermal exposure patterns. It seemed possible that optimum ablation materials might be obtainable only through synthetic development.
Nonequilibrium Flows. The aerodynamic and
heat-transfer properties of nonequilibrium airflows, and the chemical
processes of dissociation and recombination, were subjects for
numerous studies at Ames during this period. Among those who made
contributions to these efforts were Paul Chung, Aemer Anderson,
Ernest Winkler, Roy Griffin, Glen Goodwin, John Howe, and Jack
Stephenson. One of the outstanding reports in this field is TR R-109
(ref. C-14), "Hypersonic Viscous Shock Layer of Nonequilibrium
Dissociating Gas," by Paul Chung. Chung had earlier joined with Aemer
Anderson in a study of "Dissociative Relaxation of Oxygen over an
Adiabatic Flat Plate at Hypersonic Mach Numbers," which was reported
in TN D-140. These two studies were purely analytical in character.
Also analytical was the paper, by Glen Goodwin and Paul Chung, on
"Effects of Nonequilibrium Flows on Aerodynamic Heating During Entry
Into the Earth's Atmosphere From Parabolic Orbits." This paper was
presented in Zurich at the Second international Congress for
Aeronautical Sciences. In still another paper the authors, Goodwin
and Howe, introduced the similarity parameter 
where 
and P0 are respectively,
the rate of heat transfer and the pressure at the nose of a body and
r is the nose radius. This parameter proved very useful in
correlating heat-transfer data obtained experimentally, in
nonequilibrium, gas-cap flows.
Experimental studies of dissociation and recombination phenomena were also undertaken at this time. One was conducted in an arc-jet facility and reported by Ernie Winkler and Roy Griffin in TN D-1146, "Effects of Surface Recombination on Heat Transfer to Bodies in a High Enthalpy [371] Stream of Partially Dissociated Nitrogen." The purpose of this study was to investigate the effect of surface catalysis on recombination and heat transfer. Another study, of experimental character, had to do with the development of a technique for determining relaxation time in free-flight model tests. It was carried out by Jack Stephenson and reported in TN D-327.
Radiation Studies. Radiation and its effects on heat transfer to reentry bodies was the subject of numerous research investigations at Ames. One of the major contributors to this effort was John Howe of the Heat Transfer Branch of the Aero-Thermodynamics Division. One of John's interesting studies was an analytical investigation of the possibility of blocking the radiation from the gas cap to the body by injecting an opaque gas into the boundary layer. As reported in TR R-95, he found that the technique was effective in some cases and that its overall effect on the heat transfer to the body varied somewhat with the reflectivity of the body surface. Howe also produced TN D-1031, "Radiation Emission Effects of the Equilibrium Boundary Layer in the Stagnation Region," but his most noteworthy contribution, perhaps, was the analytical study he carried out with the help of John Viegas, which is reported in TR R-159 (ref. C-15), "Solutions of the Ionized Radiating Shock Layer, Including Reabsorption and Foreign Species Effects, and Stagnation Region Heat Transfer."
A notable experimental study of radiation
effects was carried out in the pilot hypervelocity free-flight
facility during this period. It is described in a paper (ref. C-16)
entitled "Measurements of Radiation From the Flow Fields of Bodies
Flying at Speeds up to 13.4 Kilometers per Second," by Thomas N.
Canning and William A. Page. This paper was presented at an AGARD
2 meeting in Brussels in April 1962. The velocities
(13.4 kps44,000 fps) at
which the tests of this investigation were conducted were perhaps the
highest yet attained at Ames. Photographs of the model, itself
speeding at 10 kilometers per second, were taken with a camera the
exposure time of which was limited by a Kerr cell to 50 billionths of
a second.
Radiation from the gas cap was measured by special instrumentation involving the use of photomultiplier tubes. It was learned, among other things, that the vaporized material from the ablation heat shield was itself a source of radiation, particularly in the model wake. Later the radiation from ablation by-products was more specifically investigated by Roger Craig and William Davey, whose work is reported in TN D-1978.
At the previously mentioned AGARD meeting in Brussels, Bradford Wick presented a paper (ref. C-17) entitled "Radiative Heating of Vehicles Entering the Earth's Atmosphere." Brad's paper was concerned with the prediction of radiation heating effects. The latest research results were utilized in the analysis and special attention was given to two spacecraft, one assumed to be returning from the moon at a speed of 37,000 feet per second....
....and the other from a trip to Mars at a speed of about 50,000 feet per second. The extreme conditions represented by these examples brought out all aspects of the radiative-heating problem.
A fairly basic analytical study of radiative heat transfer was produced by Kenneth Yoshikawa and Dean Chapman and reported in TN D-1424 (ref. C-18), "Radiative Heat Transfer and Absorption Behind a Hypersonic Normal Shock Wave." This study, which considers the emission, absorption, and decay of radiant energy in the shock layer for gas temperatures up to 15,000 ° Kelvin (centigrade absolute), provides useful analytical methods and data. Temperatures of the degree mentioned, it was indicated, could be encountered by spacecraft at earth entry speeds of from 40,000 to 60,000 feet per second.
It was surprising how many of the current heat-transfer studies at Ames made use of Fred Hansen's report (ref. B-55) on the thermodynamic and transport properties of high-temperature air. For its all-around usefulness, Hansen's report deserves special mention in the Ames hall of fame. Originally published as TN 4150 in 1948, it was subsequently republished in more permanent form as T R R-50. John Viegas and John Howe performed the useful service in TN D-1429 of converting Hansen's tabular data into analytical forms that could readily be handled by computing machines.
The efforts of Max Heaslet and Frank Fuller in theoretical aerodynamics ceased with the formation of NASA. Their attention turned to equally abstruse radiation theory, a subject which they proceeded to attack with the support of their colleagues, Barrett Baldwin and W. Prichard Jones. An example of the work of Heaslet and Baldwin is their paper, "Predictions of the .Structure of Radiation-Resisted Shock Waves," which in June 1963 was published in the Journal of the Physics of Fluids. Another example of work [373] in this field is TR R-138, "The Propagation of Plane Acoustic Waves in a Radiating Gas," by Barrett Stone Baldwin, Jr.
Ablation. Although research on ablation heat shields may have had little bearing on the conception of the Ames atmosphere-entry simulator, it became the principal function of the facility soon after the simulator was put to use. One of the early reports issuing from the AES group was TM X-394, The Ames Atmospheric Entry Simulator and Its Application to the Determination of Ablative Properties of Materials for Ballistic Missiles," by Frank M. Hamaker. As time went on, the capability of the AES for ablation studies was continually increased through the incorporation of improved guns. The original one-stage gun was replaced by a two-stage gun, which in turn was replaced by a three-stage gun capable of firing projectiles at speeds up to 25,000 feet per second.
Among the men active in ablation research in the AES were Raymond Savin, Gary Bowman, Hermilo Gloria, and Richard Dahms. Typical of their work is the study reported in TN D-1330 ,"The Determination of Ablative Properties of Materials in Free-Flight Ranges," by Savin, Gloria, and Dahms. In this study, small blunt conical models, made of various thermoplastic (ablation) materials, were launched at speeds of 15,000 feet per second and were caught after decelerating to about 1000 feet per second. The erosion of the front face was observed and the loss of material through ablation was determined from the difference in their weights before and after launching. The weight-loss data and other test information were introduced into analytical formulas to provide a better quantitative definition of ablation as well as to provide a comparison of the several materials tested.
Plastic ablation materials were adopted for the models tested in the AES because such materials had earlier been found to have promising ablation characteristics. Such materials as Teflon, ethyl cellulose, and high-density polyethylene, which in flight appeared to go quickly from the solid to the gaseous state (sublime), were investigated. For each, a quantity known as the "heat of ablation"-the amount of heat necessary to ablate one pound of material-was determined.
Other free-flight facilities were used for ablation and aerodynamic-heating studies and a number of ingenious techniques were developed for such investigations. In one, for which Layton Yee and William Kerwin were largely responsible, the temperature at some critical point on the model was measured by a tiny thermocouple carried in the model. The thermocouple in the speeding model in effect transmitted its readings by radio by generating a magnetic field that was picked up by a coil surrounding the flight path. An example of the use of this device is given in TN D-777, of which Yee was coauthor. Still another clever device developed by the SSFF staff was a technique in which the model was quickly slowed, then caught in a special calorimeter which measured its heat burden. This technique was originally....
[375] ....suggested by Al Seiff, but Gary Chapman exercised much skill in developing it to a practical stage. The technique is described in TN D-1890 (ref. C-19), "Measurement of the Heat Transfer to Bodies of Revolution in Free Flight by Use of a Catcher Calorimeter," by Gary T. Chapman and Charles T. Jackson, Jr.
The arc-jet, which had been under continuous development at Ames, became a more useful tool for ablation studies than the AES. It provided more manageable test conditions, its heat was delivered over a longer period of time, and the test model was held firmly in place. By the end of 1962, the AES was essentially passe, its mission largely taken over by the arc-jet.
Among the ablation studies conducted with the arc-jet was the analytical-experimental investigation reported in TN D-1205, "The Performance of Ablative Materials in a High-Energy, Partially Dissociated, Frozen Nitrogen Stream," by Nick S. Vojvodich. This study, made with teflon, nylon, and polyethylene ablative materials, was aimed at determining the effect of recombination, as promoted by surface catalysis, on ablator performance. Rather incidentally, but quite importantly, the tests revealed that, at low heating rates, the nylon and polyethylene materials remained in the liquid phase so long that the liquefied material was swept off the ablator surface by the airstream before it evaporated. Under these conditions, the effectiveness of these two materials, as ablators, was much reduced.
Another ablation study in which an arc-jet was used was reported in TN D-1332 (ref. C-20), "Measurements of the Effective Heats of Ablation of Teflon and Polyethylene at Convective Heating Rates from 25 to 420 Btu/Ft2 Sec," by Dale L. Compton, Warren Winovich, and Roy M. Wakefield. This study confirmed the liquid-phase problem of polyethylene at low heating rates. Teflon, on the other hand, seemed to go directly from the solid to the gaseous phase and thus maintained its ablation cooling effectiveness even at low heating rates. It appeared that ablation materials having a prolonged liquid phase would not be suitable for applications where the heating occurred at low intensity but for relatively long periods of time. These conditions could occur on the nose of a reentry vehicle which used lift to reduce heating intensity and they could also occur on the afterbody of any reentry vehicle.
For applications in which the heat load was prolonged, the insulating qualities of the ablation material became important as did also the ability of such materials to avoid structural failure as a result of softening or embrittlement. It was also recognized that, to insulate against radiation heating, the ablation material must be opaque. A study of the insulating qualities of several ablation materials was reported in TN D-1889, "The Influence of Heating Rate and Test Stream Oxygen Content on the Insulating Efficiency of Charring Materials," by Nick S. Vojvodich and Ernest L. Winkler. This study took cognizance of the oxidation or combustion of ablation material [376] that might occur during entry into an atmosphere containing oxygen. The combustion problem would presumably not be present for entry into the atmospheres of Venus and Mars, which are believed to be composed largely of nitrogen and carbon dioxide.
Projections. For 10 or 15 years, Harvey Allen had concentrated much of his attention on the problems of aerodynamic heating as affecting missile and spacecraft design. He not only guided the research work of his division or directorate but also made use of all available new knowledge in analytical projections aimed at uncovering and solving future design problems relating to aerodynamic heating. The projection process was continuous and one which exercised his extraordinary abilities for finding hidden pathways through confusing masses of physical evidence. Harvey's projections were of much interest to the scientific community and he was in great demand as a speaker at technical meetings. His numerous papers often overlapped one another in content, but each new one carried his projections a little farther.
One of Allen's papers, on "Problems in Atmospheric Entry from Parabolic Orbits," was presented in 1961 to the Japanese Society for Aeronautical and Space Sciences. Another notable paper (ref. C-21), entitled "Hypersonic Aerodynamic Problems of the Future," was presented at a NATO specialists meeting in Belgium in 1962. Allen also joined with two of his colleagues in producing one of the outstanding Ames reports of this period. This report, TR R-185 (ref. C-22), was entitled "Aerodynamic Heating of Conical Entry Vehicles at Speeds in Excess of Earth Parabolic Speed," by H. Julian Allen, Alvin Seiff, and Warren Winovich. TR R-185 was reminiscent of the original blunt-body report by Allen and Eggers as it dealt with the optimum nose shape for a reentry vehicle and made use of the mathematical stratagems for which Allen was well known. In contending with a problem as tremendously complex as aerodynamic heating, an instinct for tolerable approximations was a wonderful asset.
In their report, Allen and his colleagues deliberately chose to deal with the reentry speed range, above 37,000 feet per second, in which radiation effects were important. Allen had long ago shown that the heating of a reentry body by convection could be minimized by using a blunt nose. However, the normal shock wave produced by a blunt body generated very high temperatures in the gas cap and thus, at high reentry speeds, very intense radiation. At speeds well above parabolic, it would clearly be essential to reduce radiation to the body even at the expense of increasing convection. The question was: How could this objective be best accomplished?
It was known that the heat, and particularly the radiation, produced by a shock wave decreased rapidly with the backward inclination of the shock wave. Indeed, radiation intensity was believed to vary by as much as the 15th power of the sine of the angle of shock inclination-the angle being referred to body axis. The shape of the reentry body required for operating....
.....in a radiation environment was clearly one that produced an inclined shock wave and the cone was a rather obvious choice. With such a shape, the shock inclination and radiation intensity could be controlled by varying the cone angle. The cone shape also offered the advantage of being readily applicable to lifting-body configurations-much more so, in fact, than a blunt shape. The authors of TR R-185 found that the optimum cone angle (included angle) for the entry-speed range from 37,000 feet per second (parabolic) to 74,000 feet per second (twice parabolic) varied from about 110° to about 55°. With these optimum, radiation-reducing configurations it was found, rather surprisingly, that the heat burden imposed on the body still came largely (85 to 90 percent) via the convective route.
One of the more serious problems in the application of conical noses to reentry bodies arose from the fact that the sharp point was quickly melted and flattened by convection heating. Once the nose was rounded to any significant degree, a normal shock wave would form in front of the rounded area and the radiation in this region would become extremely intense. Somehow, Allen and his partners concluded, the shape of the cone must be maintained. This objective might be accomplished, they decided, if the point of the cone could be cooled in some fashion or continuously renewed. The use of ablation materials (Teflon or quartz) was contemplated, of course, but unless a long projecting spike of the material were mounted on the nose of the cone, the flattening would still occur. And the spike seemed impractical. A better way, it was felt, was to renew the point continuously, like the lead of a mechanical pencil, by propelling a rod of ablation material through a hole in the nose of the body.
[378] These then were some of the conclusions arrived at by Allen, Seiff, and Winovich. They are simply stated but were reached only with great effort and the services of a huge IBM 7090 computer.
The hypervelocity ballistic ranges were obviously well suited for impact research, but the reasons Ames originally entered this field of research are slightly obscure. Explanations involving practical applications appeared a little thin; indeed, the reasons may have been more deeply based in the inherent urge of boys to throw rocks at things and see them smash. With the coming of the space age, an excuse fortuitously appeared in the need to study the effects of meteoroid impacts on spacecraft. Later, in view of NASA's liberal attitude toward pure research, even this reason was largely abandoned and the impact work accelerated on the basis of sheer interest. One could hope that fun, as it often does, might become profitable.
One of the first NASA impact studies was reported in TN D-94 (ref. C-23), "Investigation of High-Speed Impact: Regions of Impact and Impact at Oblique Angles," by James L. Summers. In this investigation, small metal spheres of widely varying densities were fired into lead and copper targets at speeds up to 11,000 feet per second. At low impact speeds, it was found that a sphere of hard, strong material (tungsten carbide) would enter the target and remain largely intact. At higher speeds, it would penetrate and shatter into pieces. Finally, as the impact speed increased still further, both it and the target material would melt and splash. The resulting crater would be large and its surface would be plated with the material of the sphere.
One of the first investigations of the effect of meteoroid impact on a space vehicle is reported in TN D-1039 (ref. C-24), "Preliminary Investigation of Impact on Multiple-Sheet Structures and an Evaluation of the Meteoroid Hazard to Space Vehicles," by C. Robert Nysmith and James L. Summers. Though some meteoroids are composed of metal, most are formed of stony material. Meteoroid velocities in general range from 36,000 to 236,000 feet per second and fortunately most of the meteoroids are very small. In the design of spacecraft structures best calculated to resist the effects of meteoroid hits, a question had arisen as to whether to use a skin composed of one thick sheet or of two or more thin sheets, perhaps with a filler of some kind in between. It was a question that had to be answered in the laboratory. From their study of this problem, Nysmith and Summers found that, for resisting meteoroid impacts, a multiple-skin structure was much better than a single-skin structure of the same weight though even it was not proof against penetration.
As gun development advanced, higher launching speeds were available for impact tests. In a study reported in TN D-1210 by Pat Denardo, plastic projectiles were launched at speeds up to 25,600 feet per second at massive...
....aluminum targets mounted on a ballistic pendulum. The use of the ballistic pendulum in this case allowed measurements to be made of the transfer of momentum from the projectile to the target. The penetration, crater volume, and material splashed from the crater were also observed. The basic character of the crater changed noticeably with the impact speed. In general, the crater rapidly increased in size and irregularity with speed as the materials in the impact area became more fluid and, at the highest speeds, quantities of fluid material were ejected clear of the target.
The best source of evidence on impact cratering was, of course, the moon. Through a telescope, the breadth and depth of lunar craters could be readily measured and the radial rays of ejected material easily observed. It was appropriate therefore that Ames, as part of its impact research program, should undertake a study of the mechanics of meteor impacts on the moon. From this study, it was hoped, might come information useful in the preparations for man's first lunar visit. The investigation was undertaken as a joint project with the U.S. Geological Survey. Principal investigators were Donald E. Gault for NASA and E. M. Shoemaker and H. J. Moore for USGS.
The first phase of the joint program was to conduct, in Ames range facilities, several series of impact tests using assumed lunar material (sand and rock) as the target. Such investigations were duly carried out and their results published in various technical journals. Finally the results of these experimental investigations were used as the basis for the analysis reported in TN D-1767 (ref. C-25),"Spray Ejected From the Lunar Surface by Meteoroid Impact," by Donald E. Gault, Eugene M. Shoemaker, and Henry J. Moore. This study made use of available statistical data on the size, [381] frequency, and velocity of impacting meteoroids to determine the mass and size distribution, the velocities and trajectories of solid material ejected from the crater on impact. It was shown that, although the bulk of the material splashed from the craters reaches an altitude of no more than 6 miles, some relatively small portion is ejected at sufficiently high velocity (7800 feet per second) to escape from the moon's gravitational field.
In the impact tests they had conducted on rock and sand, Gault and his colleagues had been astonished at the volume of material ejected from the craters. In their subsequent lunar analysis, they estimated that the mass of rock and sand thrown up by a meteor striking the moon might be as much as a thousand times that of the meteor itself. Thus they conceded the possibility that the lunar surface might be permanently shrouded in a very thin dust cloud arising from its continuous bombardment by meteorites and falling lunar debris. Gault also estimated that as much as 10 tons of ejected material escapes from the moon each day. Of this, about 85 percent goes into orbit around the sun while the remainder forms a "cloud" of lunar material circling the earth.
Harvey Allen's interest in aerodynamic heating had led him, quite early, to a study of the heating and ablation of meteoroids as they ripped into the earth's atmosphere at speeds ranging from 7 to 50 miles per second. One of his early studies of this subject was recorded in a paper entitled "On the Motion and Ablation of Meteoric Bodies," which he presented at the Durand Centennial Conference at Stanford in August 1959. In this paper he attempted to correlate the information on meteors that astronomers and astrophysicists had collected with what had been learned in the relatively new, laboratory-developed science of aerodynamic heating. Allen's continuing interest in meteors was evidenced by his inclusion of a discussion of the subject in his 1962 paper on "Hypersonic Aerodynamic Problems of the Future" (ref. C-21) .
In one of the last uses of the 1- by 3-foot blowdown tunnel before it was dismantled, Dean Chapman in early 1959 exposed a ball of "glycerin glass" (frozen glycerin) to the tunnel's Mach 3 airstream. As confirmed by photographs, the glass quickly softened and, as its surface melted into a viscous fluid, a system of surface waves appeared that were concentric about the stagnation point. Shortly after this, Dean departed for England for the year at the University of Manchester that constituted the Rockefeller Public Service Award with which he had been honored.
En route to England, Dean stopped off at the U.S. Museum of Natural History in Washington and while there told the Museum's curator, Dr. E. P. Henderson, about the wave patterns he had observed on the glycerin-glass models. Henderson immediately recognized the likeness between the wave pattern Dean described and the wave pattern on certain buttonlike pellets of black glass which, over several centuries, had been picked up at various [382] places, notably Australia, on the surface of the earth. Even though the tektites, as the pellets were called, had been observed for hundreds of years, their origin was still most uncertain and the subject of much speculation in scientific circles. The Australian aborigines pointed to the sky when asked where the pellets came from. The Museum had a collection of meteorites which Dean examined with interest, and Henderson mentioned a fine collection of tektites in the British Museum in London. Dean's interest was vastly aroused. Although he did not recognize it at the time, these events had brought him to a major turning point in his scientific career. It was for the purpose of learning the nature and origin of tektites that Chapman at this point set forth on a scientific sleuthing task that would occupy his full attention for years. The hunt was an exciting exercise in pure research.
During his year at Manchester, Dean took the opportunity to study tektite collections in the museums of Europe, and a couple of years later he and Howard Larson, his colleague at Ames, went around the world visiting tektite collectors, obtaining specimens, and making measurements and molds of specimens in existing collections. The tektites found in different parts of the world were not all of the same shape, but those found in Australia were commonly of a small (1/2-inch diameter) button shape and some of these, despite millenniums of weathering and erosion on the earth's surface, still revealed annular, or ring, waves similar to those which had appeared on the glycerin-glass models.
An important part of Chapman's detective work on tektites was performed with the arc-jet facilities of the Ames Research Center. Earlier tektite studies, of which there had been many, had been made by chemists, geologists, naturalists, geochemists, petrologists, mineralogists, and physicists -but none by aerodynamicists and none by scientists equipped with the special knowledge of aerodynamic heating and ablation that only recently had been developed at Ames. To Dean it was fairly obvious that one face of the button tektites had been melted by aerodynamic heating and the viscous liquid surface thus formed had been swept back, like the waves of the sea, by aerodynamic forces. Indeed, in an arc-jet tunnel, using actual tektite material, he was able to produce a tektite button, complete with ring waves, that was almost identical with the better preserved of the natural specimens found in Australia. Natural tektites, cut in half, revealed flow lines in the surface material from which flight speed could be deduced; and it also became clear that, for the most part, the buttons had originally been spheres, a shape acquired following a previous melting.
Quite early, Chapman began to suspect an extraterrestrial origin for tektites and later, by systematically eliminating each alternate posssibility, he concluded that the most likely origin was the moon. Tektites were composed, he believed, of material splashed from the moon's surface many thousands of years ago by one or more huge meteors. The material splashed....
....up in such an impact would be molten, and the hotter and faster-moving portions would tend to break up into spherical drops. Some drops would escape from the moon, harden in the cold of outer space, and be drawn into orbit around the sun. Others, ejected from the moon with just the right speed and angle, would be captured by the earth's gravitational field and land on the surface of the earth. On entry into the earth's atmosphere, their front face would melt and flow back, thus forming the shape and surface waves of the Australian button tektite. The buttons, flattened-face forward, would be statically stable and the pseudostability, provided by increasing air density, would damp out oscillations during the ablation (heating) period.
Dean Chapman and Howard Larson prepared a number of scientific papers on tektites during this period, one of which was the fascinating document (ref. C-26) entitIed "On the Lunar Origin of Tektites," which in 1963 was published in the Journal of Geophysical Research.
A few of the scientists who had earlier studied tektites were in agreement with Dean concerning the origin of these geological curiosities. More of them, however, including one Nobel Laureate, were strongly opposed to Chapman's theory. Among the prevalent ideas regarding the source of [385] tektites were the ones that they had been produced by lightning or volcanoes, had come from comets, or had been splashed over Australia by a huge meteor which long ago had impacted in Antarctica. Indeed the years of speculation on the subject had allowed time for many experts to go out on limbs from which retreat was embarrassingly difficult.
Some of the more serious objections to Chapman's theory were based on preconceived opinions or, in Dean's words, "intuitive expectations" regarding the origin, structure, and materials of the moon. In these cases, the sweeping approach of the cosmologist was at odds with the ability of a research specialist to wring the truth out of tiny scraps of physical evidence.
The opinions of world-famous scientists in the objecting group were not to be taken lightly: but neither was the carefully studied opinion of Dean Chapman. Dean had the temerity to disagree with the "experts" and proceeded with penetrating analytic power to disassemble their arguments one by one. As 1962 ended, the matter was far from settled; but the Ames staff, at least, was backing Dean Chapman.
Space research after 195X was notably augmented by direct on-the-spot observations made by instruments sent aloft in spacecraft. The simulation of spatial phenomena in earthbound laboratories was difficult, if not impossible, and would remain so at least until much more had been learned about the phenomena from direct observation. This technique was a frightfully expensive one, it was appreciated, and the greatest care had to be exercised in planning the experiments, designing the instruments, and, of course, in recovering and analyzing the data. All these activities were the assigned function of the new Space Sciences Division, headed by Dr. Charles P. Sonett, at the Ames Research Center. The first member of the Ames staff to transfer to the new division was John Wolfe, who later became chief of the Electrodynamics Branch. However, one of the first units of the division to commence operations, late in 1962, was the Theoretical Studies Branch under John Spreiter.
Spreiter and Wolfe had, in fact, been working in the space-science field well before the division was formed. In the course of this work both had developed a considerable interest in the interaction between the earth's magnetic field and the continuous flow of charged particles (nuclei of hydrogen and helium atoms and electrons) emanating from the sun. It had been suggested that, at a distance of about 10 earth radii, the geomagnetic field formed a blunt-nosed, egg-shaped boundary that fended off the oncoming particles. The limited experimental evidence then available revealed no sign of a boundary at 10 earth radii but did show a termination of the geomagnetic field at about 14 earth radii. A question thus remained concerning....
....the location and nature of the boundary that defined the limits of the magnetic field, or magnetosphere.
John Spreiter and Ben Briggs decided that this problem was a good one on which to exercise their analytical abilities. Their first studies of the subject are contained in the paper, "Theoretical Determination of the Form of the Boundary of the Solar Corpuscular Stream Produced by Interaction with the Magnetic Dipole Field of the Earth," by John R. Spreiter and Benjamin R. Briggs, published in the January 1962 issue of the Journal of Geophysical Research (henceforth, for convenience, to be designated JGR) .
The theoretical study by Spreiter and Briggs also indicated a boundary at from 8 to 10 earth radii. Efforts were made in scientific circles to explain the discrepancy between theory and space measurements. The existence of a weak interplanetary magnetic field working perhaps at cross purposes to the geomagnetic field was postulated. Theoretical studies of this possibility suggested that a tenuous collision-free shock wave would form at some distance ahead of the geomagnetic boundary, and between the shock wave and the boundary the magnetic field would be irregular. The situation would thus be similar to the blunt-body flow patterns encountered in conventional aerodynamics except that the flow would be extremely tenuous. The interplanetary-field idea was investigated theoretically by a number of people including John Spreiter and William Prichard Jones, whose paper (ref. C-27), "On the Effect of a Weak Interplanetary Magnetic Field on the Interaction Between the Solar Wind and the Geomagnetic Field," was published in the June 1963 issue of the JGR.
While Spreiter and his colleagues were carrying on their initial theoret-[387] ical attack on the space flow-field problem, Michel Bader of the Physics Branch was also investigating the problem through the Center's first space experiment, carried out in 1961. With the help of T. B. Fryer of the Instrument Research Division and F. C. Witteborn of the Physics Branch, Bader developed an instrument for measuring solar-particle flux. The instrument was carried aloft as one of the experiments in the Explorer Xll satellite, which was launched on August 16 of that year. The data obtained with the instruments aboard Explorer XII revealed no sharp boundary between the geomagnetic field and the "solar wind" but did suggest the existence of a broad interference zone between the two. This indication seemed reasonably compatible with the shock-wave concept. The results of Bader's experiment are contained in his paper, "Preliminary Explorer 12 Data on Protons below 20 KEV," which was published in the JGR, December 1962. After this work had been completed, the Space Sciences Division was formed and solar-wind experimentation was taken over by Charles Sonett and John Wolfe.
It might be mentioned that during this period, Bob Jones was dabbling in relativity theory. Typical of his work was the paper "Conformal Coordinates Associated with Uniformly Accelerated Motion," which in 1961 was published in the American Journal of Physics. Another fairly abstruse study, relating perhaps to space physics, was made by Vernon Rossow and published as TR R-161, "Theoretical and Experimental Study of the Interaction of Free-Surface Waves on Liquid Metals with Transverse Magnetic Fields (One Dimensional Unsteady Waves) ''
1 From the moon, about 7800 fps; from Mars, about 16,500
fps; and from Jupiter. about 196,500 fps.
2 Advisory Group on Aeronautical Research and Development (NATO).
