Years Of Space Exposure Research Articles

DNA Damage and Survival Time Course of Deinococcal Cell Pellets During 3 Years of Exposure to Outer Space.

The hypothesis called “panspermia” proposes an interplanetary transfer of life. Experiments have exposed extremophilic organisms to outer space to test microbe survivability and the panspermia hypothesis. Microbes inside shielding material with sufficient thickness to protect them from UV-irradiation can survive in space. This process has been called “lithopanspermia,” meaning rocky panspermia. We previously proposed sub-millimeter cell pellets (aggregates) could survive in the harsh space environment based on an on-ground laboratory experiment. To test our hypothesis, we placed dried cell pellets of the radioresistant bacteria Deinococcus spp. in aluminum plate wells in exposure panels attached to the outside of the International Space Station (ISS). We exposed microbial cell pellets with different thickness to space environments. The results indicated the importance of the aggregated form of cells for surviving in harsh space environment. We also analyzed the samples exposed to space from 1 to 3 years. The experimental design enabled us to get and extrapolate the survival time course to predict the survival time of Deinococcus radiodurans. Dried deinococcal cell pellets of 500 μm thickness were alive after 3 years of space exposure and repaired DNA damage at cultivation. Thus, cell pellets 1 mm in diameter have sufficient protection from UV and are estimated to endure the space environment for 2–8 years, extrapolating the survival curve and considering the illumination efficiency of the space experiment. Comparison of the survival of different DNA repair-deficient mutants suggested that cell aggregates exposed in space for 3 years suffered DNA damage, which is most efficiently repaired by the uvrA gene and uvdE gene products, which are responsible for nucleotide excision repair and UV-damage excision repair. Collectively, these results support the possibility of microbial cell aggregates (pellets) as an ark for interplanetary transfer of microbes within several years.

Effect of 1.5 Years of Space Exposure on Tensile Properties of Teflon

Materials on the exterior of spacecraft in low Earth orbit are subject to extremely harsh environmental conditions, including exposure to various forms of radiation, temperature extremes, thermal cycling, and atomic oxygen. These environmental exposures can result in erosion and optical and mechanical property degradation of susceptible materials, threatening spacecraft performance and durability. In an effort to better understand the effect of space exposure on the mechanical property degradation of Teflon insulation, 19 tensile samples were exposed to the space environment for 1.5 years on the exterior of the International Space Station. The samples were flown in ram, wake, zenith, or nadir orientations as part of three Materials International Space Station Experiment 7 mission experiments. This paper provides an overview of the flight mission, an introduction to the experiments, and compares the Teflon property degradation in the various orientations. The reduction in ductility of the samples correlates with the amount of solar radiation. Samples with high solar exposure (zenith orientation) experienced a 76% reduction in elongation relative to controls, whereas samples in the shadowed nadir orientation only experienced a 4% reduction. Additionally, thickness loss measurements show that erosion is significant in the ram orientation, but negligible in other orientations.

Results of the Komplast experiment on the long-term exposure of materials specimens on the ISS surface

The Komplast materials experiment was designed by Khrunichev State Research and Production Space Center together with Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University and other Russian scientific institutes, and has been carried out by Mission Control Moscow since 1998. The purpose of this experiment is to study the complex effect of the low Earth orbit environment on samples of various spacecraft materials. On November 20, 1998 the Komplast experiment began with the launch of the first International Space Station module Zarya, or Functional Cargo Block (FGB). Eight Komplast panels with samples of materials and sensors were installed on the outer surface of FGB module. Two of eight experiment panels were retrieved during Russian extravehicular activity in February 2011 after 12years of space exposure and were subsequently returned to Earth by Space Shuttle “Discovery” on the STS-133/ULF-5 mission in March 2011.The article presents the results obtained from this unique long-duration experiment on board of the International Space Station.

Degradation of Hubble Space Telescope Aluminized-Teflon Bi-Stem Thermal Shields

A section of retrieved Hubble Space Telescope (HST) bi-stem thermal shields (BSTS), which experienced 8.25 years of space exposure, was analyzed for space environmental durability. The shields were comprised of 2 mil (0.051 mm) aluminized-Teflon® fluorinated ethylene propylene (Al-FEP) rings fused together into a circular bellows shape. As the circular thermal shields had solar, anti-solar and solar-grazing surfaces and were exposed to the space environment for a long duration, it provided a unique opportunity to study solar effects on the environmental degradation of Al-FEP, a commonly used spacecraft thermal control material. Therefore, the objective of this research was to characterize the degradation of retrieved HST BSTS Al-FEP with particular emphasis on solar effects. Data obtained included tensile properties, density (as-retrieved and after 200 3C heating), solar absorptance, and surface morphology and chemistry. The solar-facing surfaces of the thermal shields were found to be extremely embrittled and contained numerous through-thickness cracks. Tensile testing verified that near solar-facing surfaces lost their mechanical strength and elasticity, whereas the anti-solar-facing surfaces maintained their ductility. The density of the as-retrieved BSTS insulation was similar to pristine FEP. Heating at 200 3C resulted in significant increases in density for the solar-facing BSTS indicating chain scission damage, consistent with the loss of mechanical strength and elongation. The solar absorptance of the solar-grazing and the anti-solar-facing surfaces were found to be similar to pristine BSTS, whereas the solar-facing surfaces were found to have significantly increased solar absorptance. Both solar- and anti-solar-facing surfaces were microscopically textured from sweeping atomic oxygen erosion with the solar-facing surface appearing to have a more pronounced texture in spite of being exposed to a lower atomic oxygen fluence indicating a possible solar/atomic oxygen synergistic effect. These results provide valuable information on space environmental degradation of Al-FEP, particularly with respect to solar radiation effects on embrittlement.

Impact effects from small size meteoroids and space debris

When the impact risk from meteoroids and orbital debris is assessed the main concern is usually structural damage. With their high impact velocities of typically 10–20 km/s millimeter or centimeter sized objects can puncture pressure vessels and other walls or lead to destruction of complete subsystems or even whole spacecraft. Fortunately chances of collisions with such larger objects are small (at least at present). However, particles in the size range 1–100 μm are far more abundant than larger objects and every orbiting spacecraft will encounter them with certainty. Every solar cell (8 cm 2 area) of the Hubble Space Telescope encountered on average 12 impacts during its 8.25 years of space exposure. Most were from micron sized particles. Micron sized particles are believed to have permanently damaged pixels of Charge Coupled Devices (CCDs) of the XMM-Newton telescope on at least five occasions. Many shuttle windows have been replaced when showing impact craters, which resulted from sub-millimeter sized particles. Impacts from small sized particles can lead to momentum transfer sufficient to disrupt accurate formation flying as is planned for several future space missions. Numerous small impacts lead to degradation of sensors and of surface properties. Even small punctures of protective layers can lead to much larger damage by subsequent penetration of reactive plasma or gases. Future large sensors, which are freely exposed to space or just shielded by foils, like e.g. on the XEUS and GAIA space missions, will have to cope with frequent impacts from small particles. In addition, impacts by sub-millimeter sized particles can cause indirect disturbances or damage by e.g. creation of impact ionisation plasma or by triggering electrostatic discharges of pre-charged surfaces. The paper presents on overview and discussion of the various effects of hypervelocity impacts from small particles.

Solar Effects on Tensile and Optical Properties of Hubble Space Telescope Silver-Teflon Insulation

ABSTRACTDuring the fourth servicing mission of the Hubble Space Telescope (HST), the second set of solar arrays (SA-II) was replaced with a third set and the SA-II was brought back to Earth. A section of the retrieved SA-II solar array drive arm (SADA) multilayer insulation (MLI), which experienced 8.25 years of space exposure, was provided to NASA Glenn Research Center for environmental durability analyses of the top layer of silver-Teflon fluorinated ethylene propylene (Ag-FEP). Because the SADA MLI had solar and anti-solar facing surfaces and was exposed to the space environment for a long duration, it provided a unique opportunity to study solar effects on environmental degradation of Ag-FEP, a commonly used spacecraft thermal control material. Therefore, the objective of this research was to characterize the degradation of retrieved HST SADA Ag-FEP with particular emphasis on solar radiation effects. Data obtained included tensile properties, solar absorptance, surface morphology and chemistry. The solar facing surface of the SADA was found to be extremely embrittled and contained numerous through-thickness cracks. Tensile testing indicated that the solar facing surface lost 60% of its mechanical strength and 90% of its elasticity while the anti-solar facing surface had ductility similar to pristine FEP. The solar absorptance of both the solar facing surface (0.155 ± 0.032) and the anti-solar facing surface (0.208 ± 0.012) were found to be greater than pristine Ag-FEP (0.074). Solar facing and anti-solar facing surfaces were microscopically textured, and locations of isolated contamination were present on the anti-solar surface resulting in increased localized texturing. Yet, the overall texture was significantly more pronounced on the solar facing surface indicating a synergistic effect of combined solar exposure and increased heating with atomic oxygen erosion. The results indicate a very strong dependence of degradation, particularly embrittlement, upon solar exposure with orbital thermal cycling having a significant effect.

The collection of micrometeoroid remnants from low earth orbit

The solar array panel returned from the Hubble Space Telescope after 3.62 years of space exposure offered the opportunity to study individual solar cells for hypervelocity impact damage and residue. A detailed electron microscope investigation of impact craters (100–1000μm diameters) has identified that most are residue-rich and by digitised x-ray elemental mapping and semi-quantitative micro-spot analysis the original precursor composition of the impactor can almost unambiguously be identified. The residues contain diverse elemental compositions that can be associated with known meteorite mineralogies and directly compared with interplanetary dust particles and micrometeorites, possibly the most likely source object. The observation of a magnesium-rich residue with (Mg+Fe)/Si ratio similar to that of forsterite (end-member Mg-olivine identified in meteorites), indicates that it is possible in favourable conditions to define clearly the compsitional nature of the impactor. The identification of near-intact calcium-rich fragments, that are neither artefacts nor contamination, indicates that volatile chemistries can survive hypervelocity impacts in brittle glass substrates. The abundance of micrometeoroid residues in the individual solar cells has highlighted that valuable information can be retained from impact craters in returned space hardware which are essentially not designed as a dust collectors.

Natural and simulated hypervelocity impacts into solar cells.

The solar array which was returned to Earth from the Hubble Space Telescope (HST) in 1993, after 3.62 years of space exposure in low Earth orbit (LEO), has offered the opportunity to document populations of natural micrometeoroids and artificial “space debris”. Residues from the hypervelocity impact (HVI) of material deposited in 25 individual solar cells from the array have been investigated herein by scanning electron microscopy. The observations have been compared with the results of simulated HVIs into solar cells using known meteorite mineralogies. This has permitted assessment of the probability of retention for residue materials derived from HVI by well-characterised mineral species. The simulation experiments have thus far suggested that some of the textural features observed in impact residues are dependent on the nature of the individual mineral components within the original impactor. Furthermore it transpires that compounds containing volatile elements, such as Ca (from calcium carbonate), can be preserved as near-intact fragments explosively emplaced in an impact crater. Such unusual particles should not always be dismissed as simply contamination products if observed in LEO-derived HVIs.

Oxygen plasma asher contamination: An analysis of sources and remedies

The low Earth orbit (LEO) environment is commonly simulated using oxygen plasma ashers to determine the effects of LEO on spacecraft materials. However, plasma ashers can also contaminate samples during plasma exposure, making them less than ideal for space simulation. This study results from attempts to minimize or eliminate contamination. Optical methods of variable angle spectroscopic ellipsometry and reflectance spectrophotometry were used to quantify contaminant stoichiometry and deposition rate. Auger electron spectroscopy identified deposited contaminants and their surface coverage. Contamination results from etching of the rubber chamber seals by the plasma. The deposited contaminant was nearly indistinguishable from fully stoichiometric SiO2. Contaminant deposition rates up to 0.27 nm/min have been observed, and these layers effectively passivate the surface by depositing an overcoat of SiOx. Placing metal into the path of the plasma before it can reach the chamber seals greatly reduces contamination. A newly designed chamber confines the plasma to a small volume away from the chamber seals. For fluences as high as 3.5×1022 atoms/cm2, equivalent to 7.5 years of space exposure for the International Space Station, the redesigned asher showed less than one monolayer of deposited contaminant.