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NASA NTRS1992

Characteristics of hypervelocity impact craters on LDEF experiment S1003 and implications of small particle impacts on reflective surfaces

The Ion Beam Textured and Coated Surfaces Experiment (IBEX) was designated S1003 on the Long Duration Exposure Facility (LDEF) at a location of 98 degrees relative to the ram direction. Thirty-six diverse materials were exposed to the micrometeoroid (and some debris) environment for 5.8 years. Optical property measurements indicated no changes for almost all of the materials except S-13G, Kapton, and Kapton-coated surfaces, and these changes can be explained by other environmental effects. From the predicted micrometeoroid flux of NASA SP-8013, no changes in optical properties of the surfaces due to micrometeoroids were expected. However, there were hypervelocity impacts on the various diverse materials flown on IBEX. The characteristics of these craters were documented using scanning electron microscopy (SEM) and are presented. Interest in placing large solar concentrator/solar dynamic systems in space for power generation has again brought up a concern for maintaining the integrity of the optical properties of highly specular reflecting surfaces in the near-Earth space environment. It has been shown that highly reflective polished metals and thin film coatings degrade when exposed to simulated micrometeoroids in the laboratory. At LeRC, a shock tube was used to simulate the phenomenon of micrometeoroid optical properties of surfaces exposed to this impact were then evaluated. A calibrated sensor, 2000 A Al/stainless steel, was developed to not only detect the small size micrometeoroid environment, but also to evaluate the degradation of the optical properties of thin aluminum films in space. This sensor was flown on LDEF experiment S1003 and also on the OSO 3 and SERT 2 satellites that were launched in 1967 and 1970, respectively. No changes in the optical properties of the highly reflective surface sensor on SERT 2 were measured during 20 years in space. The results, as determined by the accuracy of the sensor, indicate that a highly reflective surface should lose less than 1 percent of its specular reflectance in near-Earth orbit during 20 years.

Mirtich, Michael J.↗
NASA NTRS1993

Characteristics of hypervelocity impact craters on LDEF experiment S1003 and implications of small particle impacts on reflective surfaces

The Ion Beam textured and coated surfaces EXperiment (IBEX), designated S1003, was flown on LDEF at a location 98 deg in a north facing direction relative to the ram direction. Thirty-six diverse materials were exposed to the micrometeoroid (and some debris) environment for 5.8 years. Optical property measurements indicated no changes for almost all of the materials except S-13G, Kapton, and Kapton-coated surfaces, and these changes can be explained by other environmental effects. From the predicted micrometeoroid flux of NASA SP-8013, no significant changes in optical properties of the surfaces due to micrometeoroids were expected. There were hypervelocity impacts on the various diverse materials flown on IBEX, and the characteristics of these craters were documented using scanning electron microscopy (SEM). The S1003 alumigold-coated aluminum cover tray was sectioned into 2 cm x 2 cm pieces for crater documentation. The flux curve generated from this crater data fits well between the 1969 micrometeoroid model and the Kessler debris model for particles less than 10(exp -9) gm which were corrected for the S1003 positions (98 deg to ram). As the particle mass increases, the S1003 impact data is greater than that predicted by even the debris model. This, however, is consistent with data taken on intercostal F07 by the Micrometeoroid/Debris Special Investigating Group (M/D SIG). The mirrored surface micrometeoroid detector flown on IBEX showed no change in solar reflectance and corroborated the S1003 flux curve, as well as results of this surface flown on SERT 2 and OSO 3 for as long as 21 years.

Mirtich, Michael J.↗
NASA NTRS1989

The effects of atomic oxygen on the thermal emittance of high temperature radiator surfaces

Radiator surfaces on high temperature space power systems such as SP-100 space nuclear power system must maintain a high emittance level in order to reject waste heat effectively. One of the primary materials under consideration for the radiators is carbon-carbon composite. Since carbon is susceptible to attack by atomic oxygen in the low earth orbital environment, it is important to determine the durability of carbon composites in this environment as well as the effect atomic oxygen has on the thermal emittance of the surface if it is to be considered for use as a radiator. Results indicate that the thermal emittance of carbon-carbon composite (as low as 0.42) can be enhanced by exposure to a directed beam of atomic oxygen to levels above 0.85 at 800 K. This emittance enhancement is due to a change in the surface morphology as a result of oxidation. High aspect ratio cones are formed on the surface which allow more efficient trapping of incident radiation. Erosion of the surface due to oxidation is similar to that for carbon, so that at altitudes less than approximately 600 km, thickness loss of the radiator could be significant (as much as 0.1 cm/year). A protective coating or oxidation barrier forming additive may be needed to prevent atomic oxygen attack after the initial high emittance surface is formed. Textured surfaces can be formed in ground based facilities or possibly in space if emittance is not sensitive to the orientation of the atomic oxygen arrival that forms the texture.

Rutledge, Sharon K.↗
NASA NTRS1984

Manifestation of the Fermi resonance in surface polariton spectra

The method of disturbed full internal reflection (DFIR) is used to detect and interpret the resonance splitting of the surface polariton. The effect in the spectra of oscillatory SP which are reflected by the DFIR method in Otto geometry was experimentally recorded. It is concluded that the resonance splitting of the dispersion branch of SP may serve as an effective method for detecting weak oscillations and for measuring their parameters.

Puchkovskaya, G. A.↗
NASA NTRS1994

Identification of surface-exposed domains on the reducing side of photosystem I

Photosystem I (PSI) is a multisubunit enzyme that catalyzes the light-driven oxidation of plastocyanin or cytochrome c6 and the concomitant photoreduction of ferredoxin or flavodoxin. To identify the surface-exposed domains in PSI of the cyanobacterium Synechocystis sp. PCC 6803, we mapped the regions in PsaE, PsaD, and PsaF that are accessible to proteases and N-hydroxysuccinimidobiotin (NHS-biotin). Upon exposure of PSI complexes to a low concentration of endoproteinase glutamic acid (Glu)-C, PsaE was cleaved to 7.1- and 6.6-kD N-terminal fragments without significant cleavage of other subunits. Glu63 and Glu67, located near the C terminus of PsaE, were the most likely cleavage sites. At higher protease concentrations, the PsaE fragments were further cleaved and an N-terminal 9.8-kD PsaD fragment accumulated, demonstrating the accessibility of Glu residue(s) in the C-terminal domain of PsaD to the protease. Besides these major, primary cleavage products, several secondary cleavage sites on PsaD, PsaE, and PsaF were also identified. PsaF resisted proteolysis when PsaD and PsaE were intact. Glu88 and Glu124 of PsaF became susceptible to endoproteinase Glu-C upon extensive cleavage of PsaD and PsaE. Modification of PSI proteins with NHS-biotin and subsequent cleavage by endoproteinase Glu-C or thermolysin showed that the intact PsaE and PsaD, but not their major degradation products lacking C-terminal domains, were heavily biotinylated. Therefore, lysine-74 at the C terminus of PsaE was accessible for biotinylation. Similarly, lysine-107, or lysine-118, or both in PsaD could be modified by NHS-biotin.

Non-NASA Center↗
NASA NTRS1994

Nuclear electric propulsion: A better, safer, cheaper transportation system for human exploration of Mars

NASA has completed a preliminary mission and systems study of nuclear electric propulsion (NEP) systems for 'split-sprint' human exploration and related robotic cargo missions to Mars. This paper describes the study, the mission architecture selected, the NEP system and technology development needs, proposed development schedules, and estimated development costs. Since current administration policy makers have delayed funding for key technology development activities that could make Mars exploration missions a reality in the near future, NASA will have time to evaluate various alternate mission options, and it appears prudent to ensure that Mars mission plans focus on astronaut and mission safety, while reducing costs to acceptable levels. The split-sprint nuclear electric propulsion system offers trip times comparable to nuclear thermal propulsion (NTP) systems, while providing mission abort opportunities that are not possible with 'reference' mission architectures. Thus, NEP systems offer short transit times for the astronauts, reducing the exposure of the crew to intergalactic cosmic radiation. The high specific impulse of the NEP system, which leads to very low propellant requirements, results in significantly lower 'initial mass in low earth orbit' (IMLEO). Launch vehicle packaging studies show that the NEP system can be launched, assembled, and deployed, with about one less 240-metric-ton heavy lift launch vehicle (HLLV) per mission opportunity - a very Technology development cost of the nuclear reactor for an NEP system would be shared with the proposed nuclear surface power systems, since nuclear systems will be required to provide substantial electrical power on the surface of Mars. The NEP development project plan proposed includes evolutionary technology development for nuclear electric propulsion systems that expands upon SP-100 (Space Power - 100 kw(e)) technology that has been developed for lunar and Mars surface nuclear power, and small NEP systems for interplanetary probes. System upgrades are expected to evolve that will result in even shorter trip times, improved payload capabilities, and enhanced safety and reliability.

Clark, John S.↗
NASA NTRS2012

Detecting Organic Compounds Released from Iron Oxidizing Bacteria using Sample Analysis at Mars (SAM) Like Instrument Protocols

Mars is a planet of great interest for Astrobiology since its past environmental conditions are thought to have been favourable for the emergence life. At present, the Red Planet is extremely cold and dry and the surface is exposed to intense UV and ionizing radiation, conditions generally considered to be incompatible with life as we know it on Earth. It was proposed that the shallow subsurface of Mars, where temperatures can be above freezing and liquid water can exist on rock surfaces, could harbor chemolithoautotrophic bacteria such as the iron oxidizing microorganism Pseudomonas sp. HerB. The Mars Science Laboratory (MSL) mission will provide the next opportunity to carry out in situ measurements for organic compounds of possible biological origin on Mars. One instrument onboard MSL, called the Sample Analysis at Mars (SAM) instrument suite, will carry out a broad and sensitive search for organic compounds in surface samples using either high temperature pyrolysis or chemical extraction followed by gas chromatography mass spectrometry. We present gas chromatograph mass spectrometer (GC/MS) data on crushed olivine rock powders that have been inoculated with Pseudomonas sp. HerB at different concentrations ranging from approx 10(exp 2) to 10(exp 7) cells per gram. The inoculated olivine samples were heated under helium carrier gas flow at 500 C and the pyrolysis products concentrated using a SAM-like hydrocarbon trap set at -20 C followed by trap heating and analysis by GC/Ms. In addition, the samples were also extracted using a low temperature "one-pot" chemical extraction technique using N-methyl, N-(tert-butyldimethylsilyl) trifluoroacetamide (MTBSTFA) as the silylating agent prior to GC/MS analysis. We identified several aldehydes, thiols, and alkene nitriles after pyrolysis GC/MS analysis of the bacteria that were not found in the olivine control samples that had not been inoculated with bacteria. The distribution of pyrolysis products extracted from the bacteria was clearly distinct from similar GC/MS analyses of the carbonaceous meteorite Murchison that was dominated by sulfur containing aromatic compounds. A similar comparison, if organic compounds are detected by SAM on Mars, could be useful to help discriminate between meteoritic or biological origins.

Glavin, D. P.↗
NASA NTRS2024

Bumper Implementation of LMEEM

The Hypervelocity Impact Technology (HVIT) group at the NASA Johnson Space Center (JSC) maintains the Bumper 3 computer program (referred to as “Bumper”) to perform Micrometeoroid and Orbital Debris (MMOD) risk assessments for spacecraft. To perform its calculations, this program requires detailed mathematical models of the space environments and can include those models representing orbital debris, micrometeoroids, and lunar ejecta. The lunar ejecta environment is a projectile environment specific to the lunar surface. Due to the Moon’s lack of an atmosphere, meteoroids frequently strike the lunar surface. When this happens, the impact ejects material radially away from the impact point, which can pose a potential impact hazard to surface-based hardware. This lunar ejecta environment was previously described in 1969, in NASA Special Publication SP-8013, which was used as the basis for a model that will be referred to in this document as the “SP-8013 environment model,” or simply, “SP-8013.” Since around 2020, this model has been used in MMOD risk assessments for the Human Landing System (HLS) program and other lunar surface programs. A new lunar meteoroid ejecta environment was developed via a computer code named Lunar Meteoroid Ejecta Engineering Model (LMEEM), produced by the Natural Environments Branch (NEB) at Marshall Space Flight Center (MSFC). A global lunar surface environment definition using LMEEM is to be provided in the Cross-Program Design Specification for Natural Environments (DSNE) Revision J in 2024. Contact the NASA MSFC Natural Environments Branch for an in-depth discussion of the LMEEM environment model and its derivation. This environment model will supersede SP-8013 for MMOD risk assessments. To perform such assessments, Bumper must read data from text files output by LMEEM and use that data in risk calculations. The purpose of this document is to: •Demonstrate verification that the Bumper code has properly implemented the LMEEM environment model (Section 3) •Discuss the LMEEM environment as understood through an initial environment file (Section 4) •Compare the calculated risk due to the SP-8013 and LMEEM models (Section 5)

Bumper↗
NASA NTRS1989

SP-100 power system conceptual design for lunar base applications

A conceptual design is presented for a nuclear power system utilizing an SP-100 reactor and multiple Stirling cycle engines for operation on the lunar surface. Based on the results of this study, it was concluded that this power plant could be a viable option for an evolutionary lunar base. The design concept consists of a 2500 kWt (kilowatt thermal) SP-100 reactor coupled to eight free-piston Stirling engines. Two of the engines are held in reserve to provide conversion system redundancy. The remaining engines operate at 91.7 percent of their rated capacity of 150 kWe. The design power level for this system is 825 kWe. Each engine has a pumped heat-rejection loop connected to a heat pipe radiator. Power system performance, sizing, layout configurations, shielding options, and transmission line characteristics are described. System components and integration options are compared for safety, high performance, low mass, and ease of assembly. The power plant was integrated with a proposed human lunar base concept to ensure mission compatibility. This study should be considered a preliminary investigation; further studies are planned to investigate the effect of different technologies on this baseline design.

Mason, Lee S.↗
NASA NTRS2018

Advantages of a Modular Mars Surface Habitat Approach

Early crewed Mars mission concepts developed by the National Aeronautics and Space Administration (NASA) assumed a single, large habitat would house six crew members for a 500-day Mars surface stay. At the end of the first mission, all surface equipment, including the habitat, -would be abandoned and the process would be repeated at a different Martian landing site. This work was documented in a series of NASA publications culminating with the Mars Design Reference Mission 5.0 (NASA-SP-2009-566). The Evolvable Mars Campaign (EMC) explored whether re-using surface equipment at a single landing site could be more affordable than the Apollo-style explore-abandon-repeat mission cadence. Initial EMC assumptions preserved the single, monolithic habitat, the only difference being a new requirement to reuse the surface habitat for multiple expedition crews. A trade study comparing a single large habitat versus smaller, modular habitats leaned towards the monolithic approach as more mass-efficient. More recent work has focused on the operational aspects of building up Mars surface infrastructure over multiple missions, and has identified compelling advantages of the modular approach that should be considered before making a final decision. This paper explores Mars surface mission operational concepts and integrated system analysis, and presents an argument for the modular habitat approach.

Rucker, Michelle A.↗
NASA NTRS2018

Advantages of a Modular Mars Surface Habitat Approach

Early crewed Mars mission concepts developed by the National Aeronautics and Space Administration (NASA) assumed a single, large habitat would house six crew members for a 500-day Mars surface stay. At the end of the first mission, all surface equipment?including the habitat--would be abandoned and the process would be repeated at a different Martian landing site. This work was documented in a series of NASA publications culminating with the Mars Design Reference Mission 5.0 (NASA-SP-2009-566). The Evolvable Mars Campaign (EMC) explored whether re-using surface equipment at a single landing site could be more affordable than the Apollo-style explore-abandon-repeat mission cadence. Initial EMC assumptions preserved the single, monolithic habitat?the only difference being a new requirement to reuse the surface habitat for multiple expedition crews. A trade study comparing a single large habitat versus smaller, modular habitats leaned towards the monolithic approach as more mass-efficient. More recent work has focused on the operational aspects of building up Mars surface infrastructure over multiple missions, and has identified compelling advantages of the modular approach that should be considered before making a final decision. This paper explores Mars surface mission operational concepts and integrated system analysis, and presents an argument for the modular habitat approach.

Rucker, Michelle↗
NASA NTRS2008

Comparison of Ejecta Distributions from Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

The National Aeronautics and Space Administration (NASA) is progressing toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013, was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice and unconsolidated JSC-1A Lunar Mare Regolith stimulant (JSC-1A) targets. The Ames Vertical Gun Range (AVGR) was used to accelerate projectiles to velocities in excess of 5 km/s and impact the targets at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the impact site and angular distributions were determined for ejecta. Comparison of ejecta angular distribution with previous works will be presented. A simplistic technique to characterize the ejected particles was formulated and improvements to this technique will be discussed for implementation in future tests.

Edwards, David L.↗
NASA NTRS2007

Measurement of Primary Ejecta From Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar primary ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the primary ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar primary ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface primary ejecta environment. This paper reports the results of experiments on projectile impact into pumice targets, simulating lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 km/s and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.

Edwards, David L.↗
NASA NTRSDate not supplied

An Updated Secondary Lunar Meteoroid Ejecta Model for Engineering Design

Introduction: The surface of the Moon is constantly being bombarded by a flux of meteoroids of various sizes. Impacts due to these meteoroids produce secondary ejecta material at much lower speeds but with a total mass larger than the original impactor. Details about the secondary ejecta are important for planning missions on the lunar surface. In this work, an updated ejecta model is presented called the Meteoroid Model of Secondary Ejecta (MeMoSeE), to re-place the Apollo-era ejecta model, NASA SP-8013 [1], in the SLS-SPEC 159 Design Specification for Natural Environments (DSNE) [2]. The model pro-duces secondary ejecta flux environments for a user-specified location on the lunar surface, and sorts the incoming secondary flux by angular direction and speed. Methods: MeMoSeE is separated into three parts: the inputs, the conversion step, and the integration of fluxes. Inputs to the model include the primary meteoroid fluxes and the primary near-Earth object (NEO) fluxes. Meteoroid fluxes, both asteroidal and cometary, are calculated using the Meteoroid Engineering Model (MEM3) [3] for different locations on the Moon. For each surface location, an ephemeris is generated using the JPL HORIZONS System [4] that feeds into MEM3. The NEO fluxes are approximated by the high-density population of MEM3 (i.e., only the directionality), where the speed distribution of the NEO fluxes is renormalized to match observations [5]. The regolith properties are used as defined in the DSNE [2]. The conversion step utilizes scaling laws given by Housen & Holsapple 2011 [6] to convert the primary impactor flux to the total mass of secondary ejecta. The ejecta distribution, at the point-of-impact (POI), is separated into a zenith angle and azimuthal angle distribution. The zenith angle distribution follows a beta distribution where the peak depends on the impact altitude angle and the impact azimuth [7]. We employ an ejecta azimuth distribution that is based on Rival & Mandeville 1999 [8] which focuses ejecta in the downstream direction for more oblique impacts. Finally, during the integration step, we sum secondary ejecta number fluxes at a particular region-of-interest (ROI) that originated from many POI locations over the entire surface of the Moon. We keep track of both altitude and azimuth angle bins as well as a range of speed bins, following the igloo gridding as done in MEM3 [9]. The ejecta particle size distribution and density is assumed to be the same as the lunar regolith [10, 2]. Results: The primary fluxes are computed for one Metonic cycle (19 years) for various locations over the lunar surface with a fixed orientation. Both the angular and speed distributions of the primary fluxes are dependent on the latitude and longitude. The over-all primary fluxes show a roughly 13% increase from the eastern limb to the western limb. In general, the speed distribution of the secondary fluxes span from a user-defined minimum speed to the escape speed of the Moon (2.38 km/s), roughly following a power-law relation [6]. Different parts of the speed distribution come from different primary impact locations on the Moon. The secondary ejecta is dominated by the slowest speeds, where these particles originate nearby the ROI. For speeds around 71% of the escape speed, the secondary ejecta originates from locations near the antipodal point. On the other hand, for secondary ejecta speeds that exceed roughly 90% the escape speed, the ejecta particles come from all over the lunar surface to the ROI. Comparing the secondary ejecta fluxes from MeMoSeE with NASA SP-8013 [1], there is a reduction by about 2-3 orders of magnitude for secondary ejecta particles greater than 1 µg. These estimates agree with recent findings from Bjorkman & Christiansen 2019 [11]. The secondary ejecta fluxes are also compared with the primary fluxes, where the ejecta fluxes are roughly an order of magnitude greater than the primary fluxes. References: [1] Cour-Palais, B. G., (1969) NASA SP-8013. [2] NASA SLS-SPEC-159 Rev. H (2020). [3] Moorhead, A. V., et al. (2019) JS&R, 1-17. [4] Giorgini, J. D., (2015) IAUGA, 29, 2256293. [5] Moorhead, A. V., (2020) Memo OSMA/MEO/Lunar-001. [6] Housen, K. R., and Holsapple, K. A., (2011) Icarus, 211(1), 856-875. [7] Gault, D. E., and Wedekind, J. A., (1978) L&PSCP, 9, 3843-3875. [8] Rival, M., and Mandeville, J., (1999) Space Debris, 1(1), 45-57. [9] Moorhead, A. V., (2019) MEM3 User Guide. [10] Carrier, W. D., (1973) The Moon, 6(3-4), 250-263. [11] Bjorkman, M. D. & Christiansen, E. L., (2019) ODC

impacts↗
NASA NTRS2026

Fatigue Behavior of Laser Powder Bed Fused HAYNES 214: Effects of Different Surface Treatments

In this study, under NASA’s Rapid and Analysis Manufacturing Propulsion Technology (RAMPT) project, effects of different surface post-treatments on surface texture and fatigue behavior of L-PBF Alloy 214 were investigated. Various subtractive SPTs including abrasive flow machining (AFM), machining (M), shot peening (SP), vapormatt (VM), dry electropolishing (DE), chemical milling (CM), chemical-mechanical polishing (CMP), electro chemical (ECP) were applied to study the variations of the surface texture, microstructure and uniaxial fatigue behavior under fully reversed strain-controlled condition at four different strain amplitudes of 0.005, 0.004, 0.003, and 0.0025 mm/mm. The insights gained regarding the relationship between structural and mechanical properties for different SPTs can help establish guidelines for selecting the most effective process to enhance the performance of Laser Powder Bed Fusion (L-PBF) Alloy 214, especially for critical aerospace applications.

Post-Processing↗
NASA NTRS1993

Environmental interactions and the SP-100 power system

Interactions of the SP-100 power system with its expected ambient environments are defined. SP-100 payloads will float 100 V negative of the low Earth orbit (LEO) plasma. Choice of proper geometries and materials will prevent arcing at conductor-insulator junctions in LEO. Care in selecting surface coatings will prevent dielectric breakdown. Sputtering is a concern for long-duration LEO missions. Atomic oxygen durability of SP-100 materials will be tested in ground and flight tests. Evaluation of SP-100 in lunar and planetary environments has begun. The report of a recent workshop on Chemical and Electrical Interactions on Mars identified many of the primary interactions.

Ferguson, Dale C.↗
NASA NTRS1971

The Effect of Temperature on the Survival of Microorganisms in a Deep Space Vacuum

A space molecular sink research facility (Molsink) was used to evaluate the ability of microorganisms to survive the vacuum of outer space. This facility could be programmed to simulate flight spacecraft vacuum environments at pressures in the .1 nanotorr range and thermal gradients (30 to 60 C) closely associated to surface temperatures of inflight spacecraft. Initial populations of Staphylococcus epidermidis and a Micrococcus sp. were reduced approximately 1 log while exposed to -105 and 34 C, and approximately 2 logs while exposed to 59 C for 14 days in the vacuum environment. Spores of Bacillus subtilis var. niger were less affected by the environment. Initial spore populations were reduced 0.2, 0.3, and 0.8 log during the 14-day vacuum exposure at -124, 34, and 59 C, respectively.

Hagen, C. A.↗
NASA NTRS1987

Atmospheric reentry of the in-core thermionic SP-100 reactor system

Presumed end-of-life atmospheric reentry of the GA SP-100 system was studied to assess dispersal feasibility and associated hazards. Reentry was studied by sequential use of an orbital trajectory and a heat analysis computer program. Two heating models were used. The first model assumed a thermal equilibrium condition between the stagnation point aerodynamic heating and the radiative cooling of the skin material surface. The second model allowed for infinite conductivity of the skin material. Four reentering configurations were studied representing stages of increased SP-100 breakup: (1) radiator, shield and reactor, (2) shield and reactor, (3) reactor with control drums, and (4) reactor without control drums. Each reentering configuration was started from a circular orbit at 116 km having an inertial velocity near Mach 25. The assumed failing criterion was the attainment of melting temperature of a critical system component. The reentry analysis revealed breakup of the vessel in the neighborhood of 61 km altitude and scattering of the fuel elements. Subsequent breakup of the fuel elements was not predicted. Oxidation of the niobium skin material was calculated to cause an increase in surface temperature of less than ten percent. The concept of thermite analogs for enhancing reactor reentry dispersal was assessed and found to be feasible in principle. A conservative worst-case hazards analysis was performed for radioactive and nonradioactive toxic SP-100 materials assumed to be dispersed during end-of-life reentry. The hazards associated with this phase of the SP-100 mission were calculated to be insignificant.

Stamatelatos, M. G.↗