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At least 343 records · Page 19

Aqueous alteration of the Nakhla meteorite

Interior samples of three different Nakhla specimens contain an iron-rich silicate 'rust' (which includes a tentatively identified smectite), Ca-carbonate (probably calcite), Ca-sulfate (possibly gypsum or bassanite), Mg-sulfate (possibly epsomite or kieserite), and NaCl (halite); the total abundance of these phases is estimated as less than 0.01 weight percent of the bulk meteorite. Rust veins are truncated and decrepitated by fusion crust and are preserved as faulted segments in partially healed olivine crystals, indicating that the rust is preterrestrial in origin. Because Ca-carbonate and Ca-sulfate are intergrown with the rust, they are also indicated to be of preterrestrial origin. Similar textural evidence regarding origins of the NaCl and Mg-sulfate is lacking. Impure and poorly crystallized sulfates and halides on the fusion crust of the meteorite suggest leaching of interior (preterrestrial) salts from the interior after Makhla arrived on earth, but coincidental addition of these same salts by terrestrial contamination cannot be exluded. At least the clay-like silicate 'rust', Ca-carbonate, and Ca-sulfate were formed by precipitation from water-based solutions on the Nakhla parent planet, although temperature and pressure conditions of aqueous precipitation are unconstrained by currently available data. It is possible that aqueous alteration on the parent body was responsible for the previously observed disturbance of the Rb-Sr geochronometer in Nakhla at or near 1.3 Ga.

Gooding, James L.↗

Spatial Factors in the Integration of Speed Information

We reported that, for a 21FC task with multiple Gabor patches in each interval, thresholds for speed discrimination decreased with the number of patches, while simply increasing the area of a single patch produced no such effect. This result could be explained by multiple patches reducing spatial uncertainty. However, the fact that thresholds decrease with number even when the patches are in fixed positions argues against this explanation. We therefore performed additional experiments to explore the lack of an area effect. Three observers did a 21FC speed discrimination task with 6 Gabor patches in each interval, and were asked to pick the interval in which the gratings moved faster. The 50% contrast patches were placed on a circle at 4 deg. eccentricity, either equally spaced and maximally separated (hexagonal array), or closely-spaced, in consecutive positions (string of pearls). For the string-of-pearls condition, the grating phases were either random, or consistent with a full-field grating viewed through multiple Gaussian windows. When grating phases were random, the thresholds for the hexagonal and string-of-pearls layouts were indistinguishable. For the string-of-pearls layout, thresholds in the consistent-phase condition were higher by 15 +/- 6% than in the random-phase condition. (Thresholds increased by 57 +/- 7% in going from 6 patches to a single patch of equivalent area.). For random-phase patches, the lower thresholds for 6 patches does not depend on a specific spacing or spatial layout. Multiple, closely-spaced, consistent-phase patches that can be interpreted as a single grating, result in thresholds closer to that produced by a single patch. Together, our results suggest that object segmentation may play a role in the integration of speed information.

Verghese, P.↗

Clearance Analysis of CTC2 (on ELC4) to S-TRRJ HRS Radiator Rotation Envelope

In response to the planned retirement of the Space Shuttle Program, International Space Station (ISS) management began stockpiling spare parts on the ISS. Many of the larger orbital replacement units were stored on the Expedite the Processing of Experiments to Space Station (EXPRESS) Logistics Carriers (ELCs) mounted on the end of the S3 and P3 truss segments, immediately outboard of the Thermal Radiator Rotary Joints (TRRJs) and their attached radiators. In an August 2009 computer-aided design (CAD) assessment, it was determined that mounting the Cargo Transport Container (CTC) 2 on the inboard face of ELC4 as planned would create insufficient clearance between the CTC2 and the rotational envelope of the radiators when the TRRJs were rotated to a gamma angle of 35.0 degrees. The true clearance would depend on how the Unpressurized Cargo Carrier Attachment System (UCCAS) was mounted to the S3 truss and how the ELC4 was attached to it. If the plane of the UCCAS attachment points were tilted even slightly inboard, it would significantly change the clearance between CTC2 and the Starboard TRRJ (S-TRRJ) radiators. Additionally, since CTC2 would be covered in multilayer insulation (MLI), the true outer profile of CTC2 was not captured in the CAD models used for the clearance assessment. It was possible that, even if the S-TRRJ radiators cleared CTC2, they could snag the MLI covering. In the fall of 2010, the Image Science and Analysis Group (ISAG) was asked to perform an on-orbit clearance analysis to determine the location of CTC2 on ELC4 and the S-TRRJ radiators at the angle of closest approach so that a positive clearance could be assured. To provide the measurements as quickly as possible to aid in the assessment, it was decided that the clearance analysis would be broken into two phases. Phase I: The location and orientation of the UCCAS fittings, which support and hold the ELC4 in place, would be measured relative to the ISS Analytical Coordinate System (ISSACS) as defined by nine preexisting Space Vision System (SVS) targets affixed to the forward/zenith side of the S1 and S3 truss segments. The location of the outboard edge of the S-TRRJ radiator would also be measured when positioned at the angle of closest approach to CTC2 (gamma = 35.0 degrees). This data would allow the Digital Pre-Assembly Group to predict how the ELC4 would sit on the UCCAS and how that would translate into the clearance between CTC2 and the S-TRRJ radiators. Phase II: After the ELC4 was delivered and installed into the UCCAS, the position of the CTC2 mounting plate on the inboard face of ELC4, would be measured in the ISSACS coordinate system relative to the SVS control points used in Phase I. Although CTC2 would not yet be mounted on ELC4, the working envelope of CTC2 could be mathematically added to the measured position of ELC4 to produce a best estimate for CTC2's mounted location. Comparing CTC2's best estimated location to the S-TRRJ radiator (measured in Phase I); relative to the ISSACS coordinate system, would provide a direct measurement of the expected clearance. Due to the impending delivery of ELC4 (scheduled for January 2011), planning for the Phase I clearance analysis began immediately. Using the Dynamic Onboard Ubiquitous Graphics (DOUG) program, ISAG designed a way to acquire images of the SVS control points on truss segments S1 and S3, the aft facing edge of the S-TRRJ Heat Rejection Subsystem (HRS) radiator, and the three UCCAS latch mechanisms mounted on the zenith face of the S3 truss using the Space Station Remote Manipulator System (SSRMS). To minimize the number of SSRMS movements, the Special Purpose Dexterous Manipulator (SPDM) would be attached to the SSRMS. This would make it possible to park the SPDM in one position and acquire multiple images by changing the viewing orientation of the SPDM body cameras using the pan/tilt units on which they are mounted. Using this implementation concept, ISAG identified four SSRMS/SPDM positions from which the majority of the needed imagery could be acquired. Five additional images would be acquired using the CP-3 external ISS camera mounted on the S1 truss immediately inboard of ELC4. Based on a photogrammetric simulation, it was estimated that the measured location of the HRS radiator and UCCAS latch points would be accurate to about 0.3 in. in each of the three axes relative to ISSACS. Working with ROBO, ISAG collected 78 images of the ISS December 29, 2010. From this imagery, the best 40 were selected for use in the analysis process. The images were radiometrically enhanced to improve color and contrast and loaded into the FotoG analysis software along with the camera parameters and control data, which consisted of the coordinates for the nine SVS targets on the S1 and S3 trusses in the ISSACS coordinate system.

Liddle, Donn↗

Performance characteristics of phased array and thinned aperture optical telescopes

While phased telescope arrays for general-purpose broadband imaging applications suffer severe sensitivity losses and field-of-view limitations, thinned-aperture telescopes consisting of a dilute, segmented primary mirror with a common secondary mirror are viable second-generation space telescope configurational possibilities yielding resolution and sensitivity an order of magnitude greater than those of the Hubble Space Telescope. Attention is given to thinned-aperture optical systems' image quality characterization problems; the 'practical resolution limit' image quality criterion proposed is defined as the reciprocal of the spatial frequency within which no zeros occur in the modulation transfer function.

Harvey, James E.↗

ASCA measurements of the grain-scattered X-ray halos of eclipsing massive X-ray binaries: Vela X-1 and Centaurus X-3

We have measured the decaying dust-scattered X-ray halo of Cen X-3 during its binary eclipse with the ASCA solid-state imaging spectrometer (SIS). The surface brightness profile (SBP) of the image in the low-energy band (0.5-3 keV) lies substantially above the point-spread function (PSF) of the X-ray telescope, while the SBP in the high-energy band (5-10 keV) exhibits no significant deviation. By contrast, the SBPs of Vela X-1 during its eclipse are consistent with the PSF in both the low- and high-energy bands -- strong evidence that a dust halo is indeed present in Cen X-3. Accordingly, we modeled the SBP of Cen X-3 taken from six consecutive time segments under the principal assumptions that the dust is distributed uniformly along a segment of the line of sight, the grains have a power-law size distribution, and the low-energy source flux was the same function of orbital phase before as during our observation. The best-fit set of parameters included a grain density value of 1.3 g/cu cm, substanially less than the density of 'astronomical silicate.' This result supports the idea that interstellar grains are 'fluffy' aggregates of smaller solid particles. We attribute the failure to detect a halo of Vela X-1 during its eclipse phase to extended strong circumsource absorption that probably occurred before the eclipse and allowed the halo to decay away before the observation began.

Woo, Jonathan W.↗

Polar Spin Axis Anomaly

The Global Geospace Science (GGS) Polar Plasma Laboratory (POLAR) spacecraft was launched on February 24, 1996, by a Delta 2. The spacecraft, a major axis spinner, appeared to function nominally throughout the early mission phase, which included several deployments, and orbit and attitude maneuvers. Of particular interest is the fact that the spacecraft was launched with a deliberate dynamic imbalance. During a segment of early orbit operations, a pair of Lanyard Deployed Booms (LDB) were extended. These booms were not identical; the intent was that the spacecraft would be nearly dynamically balanced after they were deployed. The spacecraft contained two dynamic balance mechanisms intended to fine tune the balance on orbit. However, subsequent images taken by the science instruments on the Despun Platform during the dynamic balancing segment indicated an offset of the principal spin axis from the geometric axis. This offset produced a sinusoidal blurring of the science images sufficiently large to degrade science data below mission requirement specifications. In the end, the imbalance encountered in flight was significantly outside the correction capability of the balances. The purpose of this paper is to examine the flight data during the various deployment and maneuver stages of the early orbit operations coupled with analytical simulations to discuss some of the potential causes of the resultant imbalance.

Crouse, Patrick L.↗

Lessons Learned During Cryogenic Optical Testing of the Advanced Mirror System Demonstrators (AMSDs)

Optical testing in a cryogenic environment presents a host of challenges above and beyond those encountered during room temperature testing. The Advanced Mirror System Demonstrators (AMSDs) are 1.4 m diameter, ultra light-weight (<20 kg/mA2), off-axis parabolic segments. They are required to have 250 nm PV & 50 nm RMS surface figure error or less at 35 K. An optical testing system, consisting of an Instantaneous Phase Interferometer (PI), a diffractive null corrector (DNC), and an Absolute Distance Meter (ADM), was used to measure the surface figure & radius-of-curvature of these mirrors at the operational temperature within the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC). The Ah4SD program was designed to improve the technology related to the design, fabrication, & testing of such mirrors in support of NASA s James Webb Space Telescope (JWST). This paper will describe the lessons learned during preparation & cryogenic testing of the AMSDs.

Hadaway, James↗

Thermoelectric properties of Nb3SbxTe7-x compounds

Niobium antimony telluride, Nb3Sbx,Te7-x, was synthesized and tested for thermoelectric properties in the Thermoelectrics group at the Jet Propulsion Laboratory. The forty atoms per unit cell of Nb3Sb2Te5 and its varied mixture of atoms yield acomplicated structure, suggesting that Nb3Sb2Te5 and related compounds may exhibit low thermal conductivity and hence a higher ZT value. Nb3SbxTe7-x, compounds were synthesized and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate that Nb3Sb2Te5 is a heavily doped semiconductor whose thermoelectric properties are compromised by compensating n-type and p-type carriers. Attempts to dope in favor of either carrier by varying the Sb:Te ratio yielded samples containing secondary metallic phases that dominated the transport properties of the resulting compounds.

thermoelectric power generation segmented↗

Safety analysis for complex systems

Operational risk assessment considers hardware, environment, and human factors. Technique starts with division of postulated mission into segments which are further subdivided into separate operational steps. Consequences of steps, nonoccurrence, premature operation, out-of-sequence operation, and inadvertent execution are examined at subevent, event, and phase levels. Hazards are identified and treated individually. Analysis is well suited to application in energy and transportation fields.

Onesty, J. P.↗

Guidance studies for curved, descending approaches using the Microwave Landing System (MLS)

Results for the Microwave Landing System (MLS) guidance algorithm development conducted under the Advance Transport Operating System (ATOPS) Technology Studies (NAS1-16202) are documented. The study consisted of evaluating guidance law for vertical and lateral path control, as well as speed control, for approaches not possible with the present Instrument Landing System (ILS) equipment. Several specific approaches were simulated using the MD-80 aircraft simulation program, including curved, descending (segmented glide slope), and decelerating paths. Emphasis was placed on development of guidance algorithms specifically for approaches at Burbank, where proposed flight demonstrations are planned. Results of this simulation phase are suitable for use in future fixed base simulator evaluations employing actual hardware (autopilot and a performance management system).

Feather, J. B.↗

Advanced technology optical telescopes IV; Proceedings of the Meeting, Tucson, AZ, Feb. 12-16, 1990. Parts 1 & 2

The present conference on the current status of large, advanced-technology optical telescope development and construction projects discusses topics on such factors as their novel optical system designs, the use of phased arrays, seeing and site performance factors, mirror fabrication and testing, pointing and tracking techniques, mirror thermal control, structural design strategies, mirror supports and coatings, and the control of segmented mirrors. Attention is given to the proposed implementation of the VLT Interferometer, the first diffraction-limited astronomical images with adaptive optics, a fiber-optic telescope using a large cross-section image-transmitting bundle, the design of wide-field arrays, Hartmann test data reductions, liquid mirrors, inertial drives for telescope pointing, temperature control of large honeycomb mirrors, evaporative coatings for very large telescope mirrors, and the W. M. Keck telescope's primary mirror active control system software.

Barr, Lawrence D.↗

Optical figure testing of prototype mirrors for JPL's Precision Segmented Reflector (PSR) program

JPL's PSR program is developing enabling technologies for large space telescopes employing segmented optics, and in particular, lightweight, thermally stable mirrors for telescopes operating at sub-mm wavelengths. JPL's vacuum cryointerferometric optical test facility includes a computer-controlled phase shifting interferometer operating at 10.59 microns and laser metrology for measurement of piston and absolute radius of curvature. The optical metrology has been integrated with a large vacuum chamber including a liquid nitrogen shroud capable of radiatively cooling 1.5 meter aperture mirrors down to 150 K. The facility is now being used to characterize prototype mirrors in both their room-temperature 'as-replicated' condition, and under orbital temperature conditions. The performance and limitations of the optical metrology hardware and software components are noted. Representative test results on prototype one meter-class composite mirrors being developed for PSR and related ground-based programs are also presented.

Hochberg, Eric B.↗

Biomechanics of the Treadmill Locomotion on the International Space Station

Exercise prescriptions completed by International Space Station (ISS) crewmembers are typically based upon evidence obtained during ground-based investigations, with the assumption that the results of long-term training in weightlessness will be similar to that attained in normal gravity. Coupled with this supposition are the assumptions that exercise motions and external loading are also similar between gravitational environments. Normal control of locomotion is dependent upon learning patterns of muscular activation and requires continual monitoring of internal and external sensory input [1]. Internal sensory input includes signals that may be dependent on or independent of gravity. Bernstein hypothesized that movement strategy planning and execution must include the consideration of segmental weights and inertia [2]. Studies of arm movements in microgravity showed that individuals tend to make errors but that compensation strategies result in adaptations, suggesting that control mechanisms must include peripheral information [3-5]. To date, however, there have been no studies examining a gross motor activity such as running in weightlessness other than using microgravity analogs [6-8]. The objective of this evaluation was to collect biomechanical data from crewmembers during treadmill exercise before and during flight. The goal was to determine locomotive biomechanics similarities and differences between normal and weightless environments. The data will be used to optimize future exercise prescriptions. This project addresses the Critical Path Roadmap risks 1 (Accelerated Bone Loss and Fracture Risk) and 11 (Reduced Muscle Mass, Strength, and Endurance). Data were collected from 7 crewmembers before flight and during their ISS missions. Before launch, crewmembers performed a single data collection session at the NASA Johnson Space Center. Three-dimensional motion capture data were collected for 30 s at speeds ranging from 1.5 to 9.5 mph in 0.5 mph increments with a 12-camera system. During flight, each crewmember completed up to 6 data collection sessions spread across their missions, performing their normal exercise prescription for the test day, resulting in varying data collection protocols between sessions. Motion data were collected by a single HD video camera positioned to view the crewmembers' left side, and tape markers were placed on their feet, legs, and neck on specific landmarks. Before data collection, the crewmembers calibrated the video camera. Video data were collected during the entire exercise session at 30 Hz. Kinematic data were used to determine left leg hip, knee, and ankle range of motion and contact time, flight time, and stride time for each stride. 129 trials in weightlessness were analyzed. Mean time-normalized strides were found for each trial, and cross-correlation procedures were used to examine the strength and direction of relationships between segment movement pattern timing in each gravitational condition. Cross-correlation analyses between gravitational conditions revealed highly consistent movement patterns at each joint. Peak correlation coefficients occurred at 0% phase, indicating there were no lags in movement timing. Joint ranges of motion were similar between gravitational conditions, with some slight differences between subjects. Motion patterns in weightlessness were highly consistent at a given speed with those occurring in 1G, indicating that despite differing sensory input, subjects maintain running kinematics. The data suggest that individuals are capable of compensating for loss of limb weight when creating movement strategies. These results have important implications for creating training programs for use in weightlessness as practitioners can have greater confidence in running motions transferring across gravitational environments. Furthermore, these results have implications for use by researchers investigating motor control mechanisms and investigating hypotheses related to movement strategies when using sensory input that is dependent upon gravity.

DeWitt, John↗

Rapid Turnaround of Costing/Designing of Space Missions Operations

The Ground Segment Team (GST), at NASA's Jet Propulsion Laboratory in Pasadena, California, provides high-level mission operations concepts and cost estimates for projects that are in the formulation phase. GST has developed a tool to track costs, assumptions, and mission requirements, and to rapidly turnaround estimates for mission operations, ground data systems, and tracking for deep space and near Earth missions. Estimates that would often take several weeks to generate are now generated in minutes through the use of an integrated suite of cost models. The models were developed through interviews with domain experts in areas of Mission Operations, including but not limited to: systems engineering, payload operations, tracking resources, mission planning, navigation, telemetry and command, and ground network infrastructure. Data collected during interviews were converted into parametric cost models and integrated into one tool suite. The tool has been used on a wide range of missions from small Earth orbiters, to flagship missions like Cassini. The tool is an aid to project managers and mission planners as they consider different scenarios during the proposal and early development stages of their missions. The tool is also used for gathering cost related requirements and assumptions and for conducting integrated analysis of multiple missions.

Cost estimation↗

Phosphates at the Surface of Mars: Primary Deposits and Alteration Products

Phosphorus is an essential element in terrestrial organisms and thus characterizing the occurrences of phosphate phases at the martian surface is crucial in the assessment of habitability. The Alpha Particle X-Ray Spectrometers onboard Spirit, Opportunity and Curiosity discovered a variety of primary and secondary phosphate phases allowing direct comparisons across the three landing sites. The Spirit rover at Gusev Crater encountered the "Wishstone/Watchtower" class of P-rich (up to 5.2 wt% P2O5) rocks interpreted to be alkaline volcanic rocks with a physical admixture of approximately 10 to 20% merrillite [Usui et al 2008]. These rocks are characterized by elevated Ti and Y and anomalously low Cr and Ni, which could largely reflect the nature of the protoliths: Evolved magmatic rocks. Many of these chemical signatures are also found in pyroclastic deposits at nearby "Home Plate" and in phosphate precipitates derived from fluid interactions with these rocks ("Paso Robles" soils). The Opportunity rover at Meridiani Planum recently analyzed approximately 4 cm clast in a fine-grained matrix, one of numerous rocks of similar appearance at the rim of Endeavour Crater. This clast, "Sarcobatus," has minor enrichments in Ca and P relative to the matrix, and like the P-rich rocks at Gusev, Sarcobatus also shows elevated Al and Ti. On the same segment of the Endeavour rim, subsurface samples were found with exceptional levels of Mn (approximately 3.5 wt% MnO). These secondary and likely aqueous deposits contain strong evidence for associated Mg-sulfate and Ca-phosphate phases. Finally, the Curiosity traverse at Gale crater encountered P-rich rocks compositionally comparable to Wishstone at Gusev, including elevated Y. Phosphorous-rich rocks with similar chemical characteristics are prevalent on Mars, and the trace and minor element signatures provide constraints on whether these are primary deposits, secondary products of physical weathering or secondary products of chemical weathering.

Yen, Albert S.↗

Choice of method for discretization of continuous systems

The paper discusses and compares several common methods of discretizing the transfer function of a continuous control system so that a digital computer can be used. The discretization effect on the frequency response attenuation of the simple transfer function G(s) = 1/(s + 1) is illustrated for the Tusting, Boxer-Thaler, Madwed, linear segment approximation, and stair-step with half period advanced methods. The input frequency must be significantly lower than one-half the sampling error to have negligible discretization error. Phase differences due to discretization are also plotted, and it is seen that the zero-order hold contributes much more phase shift than that due to discretization. In situations where zero-order hold must follow a computer, the method of discretization of a continuous system is not a major factor if phase shift is important.

Mcvey, E. S.↗

System analysis study of space platform and station accommodations for life sciences research facilities. Volume 1: Executive summary. Phase A: Conceptual design and programmatics

The study was conducted in 3 parts over a 3 year period. The study schedule and the documentation associated with each study part is given. This document summarized selected study results from the conceptual design and programmatics segment of the effort. The objectives were: (1) to update requirements and tradeoffs and develop a detailed design and mission requirements document; (2) to develop conceptual designs and mission descriptions; and (3) to develop programmatic, i.e., work breakdown structure and work breakdown structure dictionary, estimated cost, and implementing plans and schedules.

Source record↗

Replication of Segments of STS-94 as a Lunar Surface Mission

The Artemis program established the goal to land the first woman and first person of color on the Moon, but that is only the beginning of the program. Artemis plans to move towards a sustainable phase, with four crew living on the lunar surface for roughly 30-day annual missions, operating from a Pressurized Rover (PR) and a Surface Habitat (SH). The crew will split up – two living and operating from the PR and the others in the SH, perhaps swapping places halfway through the surface mission. There is a significant degree of maturity surrounding PR operations due to the NASA Desert Research and Technology Studies field tests from 2007-2011. However, there is a degree of uncertainty surrounding activity in the SH, with anecdotal speculation among some Artemis lunar surface engineers that the SH crew might not be fully utilized. Contrary to this belief, there is evidence in US human spaceflight history that the SH crew may instead be extremely busy. In particular, portions of the STS-94 Microgravity Science Lab mission demonstrate a science-based use case for crew activity in the SH. Fifteen Spacelab missions (not including STS-83, which was terminated early due to a fuel cell problem and reflown as STS-94) and eight Spacehab missions used the previously mentioned modules as science labs to expand the science capability of shuttle orbital missions, most flown prior to the assembly of the International Space Station. STS-94 is selected as an example of these flights. STS-94 was a 15.7-day mission with a 7-person crew. The crew operated in split 12-hour shifts, enabling 24-hour science operations. STS-94 used the space shuttle Columbia with the Spacelab module and Extended Duration Orbiter pallet in the cargo bay. The STS-94 physical science investigations were intended to explore various physical aspects of microgravity. These same investigations can be conducted on the Moon to explore 1/6 gravity. The Spacelab module was outfitted with several key facilities to enable this research: Large Isothermal Furnace, Combustion Module-1, Droplet Combustion Experiment, EXPRESS Rack, TEMPUS, Gravity Measurement Devices, and Middeck Glovebox. The current reference concept for the SH is a hybrid inflatable in a vertical orientation. Fairly typical of hybrid inflatables, the SH has an aluminum core pressurized section and a larger inflatable volume, in this case attaching to the top of the core. Two crew will live in the SH at a time, though four can briefly occupy the habitat, such as for contingency or handover activities. This paper will discuss use of the STS-94 physical science equipment in the SH and options for the architectural layout of a resulting physics laboratory. It will also discuss how this laboratory may accompany other science facilities such as biology, human research, and geology. The person hours used by the STS-94 crew to conduct physical science research will be estimated and then mapped to a two-person SH crew, making it possible to determine how many days are required in the SH to complete the lunar gravity physical science investigations at varying levels of crew availability.

STS-94↗