Launched November 3, 1994
Authors:
Melissa J.B. Rogers and Richard DeLombard
TABLE OF CONTENTS
Experiments flown in the middeck of Atlantis during the STS-66 mission were supported by the Space Acceleration Measurement System (SAMS). In particular, the three triaxial SAMS sensor heads collected data in support of protein crystal growth experiments. Data collected during STS-66 are reviewed in this report. The STS-66 SAMS data represent the microgravity environment in the 0.01 Hz to 10 Hz range. Variations in the environment related to differing levels of crew activity are discussed in the report. A comparison is made among times when the crew was quiet during a public affairs conference, working quietly, and exercising. These levels of activity are also compared to levels recorded by a SAMS unit in the Spacelab on Columbia during the STS-65 mission.
Fluid physics, materials sciences, combustion, fundamental sciences, and life sciences experiments are conducted on the NASA Space Shuttle Orbiters to take advantage of the reduced gravity environment resulting from the continuous free fall state of low earth orbit. Accelerometer systems are flown on the Orbiters to record the microgravity environment which is composed of quasi-steady accelerations and vibrations of the Orbiter, equipment, and local structures.
The third Atmospheric Laboratory for Applications and Science (ATLAS-3) payload flew on the Orbiter Atlantis on mission STS-66 in November 1994. The ATLAS-3 payload on STS-66 studied the energy of the sun and how it affects the Earth's climate and environment. Two protein crystal growth experiments were operated in the middeck: Protein Crystal Growth-Thermal Enclosure (PCG-TES) and Protein Crystal Growth-Single Locker (PCG-STES). The NASA Lewis Research Center (LeRC) managed Space Acceleration Measurement System (SAMS) recorded acceleration data in the middeck to support the protein crystal growth experiments.
The Principal Investigator Microgravity Services (PIMS) project at NASA LeRC supports principal investigators of microgravity experiments as they evaluate the effects of varying acceleration levels on their experiments. This report is provided by PIMS to furnish interested experiment investigators with a guide to evaluating the acceleration environment during STS-66 and as a means of identifying areas which require further study. To achieve this purpose, various pieces of information are presented. Section 2 of this report provides an overview of the STS-66 payloads and the experiments manifested on the payloads. Section 3 describes the SAMS unit flown on STS-66. Section 4 discusses some specific analysis of the accelerometer data in relation to the various activities which occurred during the mission. Appendix A describes how SAMS data can be accessed through the internet. Appendices B and C contain SAMS data plots to provide an overview of the microgravity environment during the entire mission. Appendix D contains a user comment sheet. Users are encouraged to complete this form and return it to the authors.
At 11:59:43 am EST on 3 November 1994 the Space Shuttle Atlantis launched on the STS-66 mission from NASA Kennedy Space Center. Landing was at Edwards Air Force Base on 14 November at 10:33:45 am EST. In terms of other time conventions used in this report, launch was at Greenwich Mean Time (GMT) 307/16:59:43 or Mission Elapsed Time (MET) 000/00:00 and landing was at GMT 318/15:33:45 or MET 10/22:34:02. Both GMT and MET are recorded in day/hour:minute:second format. The primary objective of the STS-66 mission was to perform science experiments using the ATLAS-3 primary payload. The ATLAS-3 experiments studied the Northern Hemisphere's middle atmosphere and investigated the Antarctic ozone hole.
During STS-66, the Cryogenic Infrared Spectrometer Telescope for Atmosphere, or CRISTA, payload explored the variability of the atmosphere and provided measurements that will complement those obtained by the Upper Atmosphere Research Satellite launched aboard Discovery in 1991. CRISTA is a joint U.S./German experiment that was deployed from the cargo bay and later retrieved and returned to the cargo bay. Other payloads in the Atlantis cargo bay were the Shuttle Solar Backscatter Ultraviolet payload and the Experiment on the Sun Complementing ATLAS. Payloads located in the middeck were the Physiological & Anatomical Rodent Experiment, PCG-TES, PCG-STES, Space Tissue Loss/National Institute of Health, SAMS, and the Heat Pipe Performance-2 Experiment (HPP-2). Seventeen development test objectives (DTO) and sixteen detailed supplementary objectives (DSO) were performed on STS-66; they are listed in Tables 1 and 2.
The Space Acceleration Measurement System measured the microgravity environment of the Orbiter Atlantis during the STS-66 mission. SAMS was developed to measure the low-gravity environment of Orbiters in support of science payloads sponsored by the NASA Headquarters Microgravity Science and Applications Division [1-4]. STS-66 marked the eleventh shuttle flight of a SAMS unit; one SAMS unit is used to collect data on the Mir space station.
A SAMS unit typically consists of three remote triaxial sensor heads, connecting cables, and a controlling data acquisition unit with a digital data recording system using write once, read many optical disks with 200 megabytes of storage capacity per side. On STS-66, a SAMS unit and three remote triaxial sensor heads were located in the Orbiter middeck in support of protein crystal growth experiments. All three sensor heads recorded data at 50 samples per second after lowpass filters were applied to the data with cutoffs at 10 Hz. The sign convention used when reporting SAMS data is such that when there is a forward acceleration of the Orbiter (such as the OMS firing), then this is reported as a positive Xb (negative X0) acceleration, where the subscript b denotes the Orbiter body coordinate system and the subscript 0 denotes the Orbiter structural coordinate system. The locations and orientations of the SAMS heads, with respect to the Orbiter structural coordinate system, are given in Table 3 and Fig. 1.
On STS-66, 1.02 gigabytes of SAMS data, representing the middeck microgravity environment, are available between MET 000/16:00 and 010/08:00. The raw SAMS data were processed to correct for pre-mission bias calibration offsets and to compensate for temperature and gain related errors of bias, scale factor, and axis misalignment. The data were orthogonally transformed from the SAMS TSH coordinate system to the Orbiter structural coordinate system. SAMS data for STS-66 are available on CD-ROM from the PIMS group at LeRC. Appendix A describes how these data can be accessed via the internet.
The acceleration environment measured by an accelerometer system on the Orbiter is contributed to by numerous sources. All ongoing operations of crew life support systems and activities and operations of the Orbiter, crew, carrier and experiments tend to have vibratory and/or oscillatory components that contribute to the background acceleration environment. In this report we are concerned with the identification of activities and the contributions to the acceleration environment. The Appendices provide an overview of the microgravity environment during the STS-66 mission. Appendix B shows time history plots of SAMS Head A (10 Hz filter) data. Appendix C provides a frequency domain representation of the SAMS Head A data. The remainder of this section discusses the environment related to varying levels of crew activity. The overall microgravity environment of this mission is also compared to the environment during a mission dedicated to microgravity experiments.
The six member crew of STS-66 worked on a dual shift schedule, with their activities confined to the middeck and flight deck areas. For this mission configuration, several examples of the environment related to crew activity are explained in the remainder of this section.
Fig. 2 shows an example of the vibration environment of the middeck as recorded by SAMS during a period when the entire crew was participating in a public affairs conference. All crew members were quietly situated in the flight deck for this time. This is a typical activity for a mission and the time was confirmed by downlink video. The data plots in column a) of Fig. 2 are time histories of the three axes of SAMS Head A data from MET 004/20:10:00 to 004/20:15:27. The data plots in column b) of Fig. 2 show power spectral density (PSD) representations of the column a) data. For each axis the PSD is calculated according to Parseval's theorem to give an indication of the frequency distribution of power in the acceleration signal.
During STS-66, the crew noted two times during which they made a concerted effort to work quietly (MET 2/03:00-2/05:00 and 4/00:00-4/04:30). This activity was performed to demonstrate to experiment investigators that quiet microgravity conditions can be maintained even as the crew is working. A summary of the microgravity environment during these time periods is provided by Figs. B-21, B-22, B-44, B-45, C-11, C-12, and C-23. Comparison of these plots to other survey plots in the Appendices shows that the environment during these times was somewhat reduced. A shift in the mean acceleration at MET 002/04:05 is under investigation at this time, but is not considered to be related to crew activity. An increase in acceleration rms level at MET 004/00:25, also seen in the color spectrogram C-23, appears to be related to Mission Specialist 2 exercising on the ergometer in the flight deck. Fig. 3 shows SAMS Head A data for a five minute period starting at MET 002/04:00. This figure shows the environment per Orbiter axis during this limited section of a quiet work period.
Fig. 4 shows SAMS Head A data for an eleven minute period of nominal crew activity starting at MET 009/06:19. The members of one crew shift were asleep while the members of the other crew were performing daily activities, conducting experiments, but not exercising.
During a video crew conference, the SAMS team in the LeRC User Operations Facility noticed that a crew member touched the SAMS Head A box a few times between 004/20:24 and 004/20:25. Fig. 5 shows SAMS Head A data for an eleven minute period starting at 004/20:19:02. The PIMS team is currently attempting to correlate the spikes in this data window with the recorded downlink video of the crew conference. Note that the acceleration transients in this time window are of relatively low magnitude, compared to the on-going crew exercise excitation discussed in section 4.1.5, and the direct contact with the SAMS head does not excite Orbiter structural modes that propagate throughout the Orbiter.
Crew exercise on STS-66 was performed with two separate systems: the bicycle ergometer and the interlimb resistance device (ILRD). A list of crew exercise times is given in Table 4. The ergometer was used hard-mounted to the flight deck during HPP-2 experiment operations (~ MET 002/12 to 006/18). At other times the ergometer was hard-mounted to the middeck. The vibration environment related to ergometer exercise is consistent with that observed on previous missions. Ergometer exercise is characterized by excitation of frequency components related to the pedalling frequency of the crew member. Fig. 6 shows SAMS Head A data taken when the Pilot was exercising on the hard-mounted ergometer in the flight deck (MET 003/20:18:00).
The ILRD provides variable resistance exercise, using the resistance of one limb against another. To use the ILRD, the crew used bungee tethers to suspend a low-mass harness in the middle of the middeck. The crew member was then secured in the harness and exercised. SAMS Head A data shown in Fig. 7 (MET 009/05:28:00) indicate that both the non-dynamic nature of the resistance exercise and the isolation afforded by the tether system meant that the ILRD contributed very little disturbance to the microgravity environment.
The microgravity environment of the STS-65 mission is discussed in a report in print [6]. The STS-65 crew worked on a dual-shift schedule. The primary payload was the second International Microgravity Laboratory (IML-2) which was dedicated to microgravity experiments. Performance of the IML-2 experiments required a low-level microgravity environment that was achieved by orbiting in a stable gravity gradient attitude to minimize thruster firings. During some experiment operations, thruster activity was completely inhibited but the crew was required to perform the experiments, so crew activity could not be completely restricted. Figs. 8, 9 and 10 show the microgravity environment related to various activities on STS-65. The STS-65 SAMS data presented here were collected in the Spacelab module at fifty samples per second after a 10 Hz lowpass filter was applied to the data. Fig. 8 data represent the environment when the entire crew was in the flight deck for a public affairs conference. Fig. 9 data represent the environment when nominal IML-2 experiment operations were ongoing in the Spacelab module. Fig. 10 data represent the environment when a crew member was exercising on an isolated ergometer in the middeck.
The STS-65 environment may be compared to the STS-66 environment discussed in 4.1. Fig. 11 shows the cumulative RMS acceleration levels versus frequency up to 10 Hz for all the STS-66 and STS-65 events presented here. The variability of the microgravity environment is related to the combined effect of crew activity, experiment operations, and Orbiter operations. Note that significant steps in the cumulative rms plot represent the increases in acceleration power content at a particular frequency. With the exception of the STS-66 crew public affairs conference, the STS-65 isolated exercise and the STS-66 hardmounted exercise, the microgravity environments of the middeck of Atlantis on STS-66 and the Spacelab of Columbia on STS-65 are comparable for the frequency range 0.05 to 10 Hz.
This report serves as a road map to the SAMS data acquired in the middeck of Atlantis during the STS-66 mission. Further analysis of specific events and comparisons with other missions will be performed and published in future documents.
The primary payload on the STS-66 mission was ATLAS-3 with experiments which studied the Northern Hemisphere's middle atmosphere and investigated the Antarctic ozone hole. Other payloads on STS-66 were the Cryogenic Infrared Spectrometer Telescope for Atmosphere payload, the Shuttle Solar Backscatter Ultraviolet payload, and the Experiment on the Sun Complementing ATLAS. Payloads located in the middeck were the Physiological & Anatomical Rodent Experiment, Protein Crystal Growth-Thermal Enclosure, Protein Crystal Growth-Single Locker, Space Tissue Loss/National Institute of Health SAMS, and the Heat Pipe Performance-2 Experiment. The SAMS unit installed in the middeck had three triaxial sensor heads mounted near experiments in and on middeck lockers.
A range of crew activity levels was documented during the mission. and the microgravity environment that existed during these activities is summarized. The environment was also compared to that experienced in the Spacelab module during STS-65. The variability of the microgravity environment evident on both of these missions is related to the combined effect of crew activity, experiment operations, and Orbiter operations.
A summary of the vector magnitude rms and average accelerations for the entire mission was produced for the SAMS Head A (10 Hz) data. Spectrograms were also produced to give a frequency domain summary for the entire mission. These plots are presented in the Appendices B and C.