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An overview of radiation effects on spacecraft materials is given in this paper. Specifically, the environment of the Jupiter Orbiting Spacecraft, Galileo, is treated along with analysis methods and simulated testing. Summaries of previous and present material test results are given. Preliminary results of surface erosion on insulation from a Space Shuttle experiment are summarized.
Thermal characteristics and offgas products from nonmetallic spacecraft materials
Outgassing data, derived from tests at 398 K (125 C) for 24 hours in vacuum as per ASTM E-595-90, have been compiled for numerous materials designed for spacecraft use. The data presented are the total mass loss (TML) and the collected volatile condensable materials (CVCM). The various materials are compiled by likely usage, and then in alphabetical order.
In this study, we have extensively tested various cleaning protocols. The variant parameters included the type and concentration of solvent, type of wipe, pretreatment conditions, and various rinsing systems. Taguchi statistical method was used to design and evaluate various cleaning conditions on ten common spacecraft materials.
Solid propellant rocket exhaust impingement effect on spacecraft materials
This tenth compilation of outgassing data of materials intended for spacecraft use supersedes Reference Publication 1124, Revision 2, November 1990. The data were obtained at the Goddard Space Flight Center (GSFC), utilizing equipment developed at Stanford Research Institute (SRI) under contract to the Jet Propulsion Laboratory (JPL). SRI personnel developed an apparatus for determining the mass loss in vacuum and for collecting the outgassed products. The outgassing data have been presented in three different ways in order to facilitate material selection. In Section A, the materials are divided by category into the 18 probable uses, such as adhesives, greases, paints, potting compounds, and so forth. In Section B, all the materials contained in Section A are listed in alphabetical order by the manufacturer's identification. In Section C, the only materials listed are those having 'Total Mass Loss' (TML) and Collected Volatile Condensable Materials (CVCM) equal to or lower than a maximum 1.0 percent TML and a maximum 0.10 percent CVCM. These are grouped by use, as in Section A.
This slide presentation reviews the concerns regarding qualifiying materials used in spacecraft construction for harsh radiation environments, defined as a high flux charged particle environment in space. This environment consists of high surface doses at low energy and low doses at high energies. The concept phase of the Europa Flagship mission is used as an example.
In the execution of this proposal, we will first examine current and developing spacecraft materials and evaluate their ability to attenuate adverse biological mutational events in mammalian cell systems and reduce the rate of cancer induction in mice harderian glands as a measure of their protective qualities. The HZETRN code system will be used to generate a database on GCR attenuation in each material. If a third year of funding is granted, the most promising and mission-specific materials will be used to study the impact on mission cost for a typical Mars mission scenario as was planned in our original two year proposal at the original funding level. The most promising candidate materials will be further tested as to their transmission characteristics in Fe and Si ion beams to evaluate the accuracy of the HZETRN transmission factors. Materials deemed critical to mission success may also require testing as well as materials developed by industry for their radiation protective qualities (e.g., Physical Sciences Inc.) A study will be made of designing polymeric materials and composite materials with improved radiation shielding properties as well as the possible improvement of mission-specific materials.
The harsh space environment imposes stringent requirements upon spacecraft materials, especially those located on exterior surfaces of space objects in low Earth orbit (LEO). As humankind moves from space exploration to space commercialization, these polymers may have to last for 15–20 years without considerable degradation of their material properties. Hence, we must understand the effects of the space environment on materials currently in use as well as on untested materials. In the presented study authors exposed several space-relevant polymers to the simulated space weather comprised by electrons and atomic oxygen irradiation. First, materials were thoroughly characterized in their pristine state to create a baseline for the ground- and space-based experiments. Next, alteration of optical, surface, and charge transport properties of the same materials were studied under space-simulated environment.
Photoyields and secondary electron emission (SEE) characteristics were determined under UHV conditions for a group of insulating materials used in spacecraft applications. The SEE studies were carried out with a pulsed primary beam while photoyields were obtained with a chopped photon beam from a Kr resonance source with major emission at 123.6 nm. This provides a photon flux close to that of the Lyman alpha in the space environment. Yields per incident photon are obtained relative to those from a freshly evaporated and air oxidized Al surface. Results are presented for Kapton, FEP Teflon, the borosilicate glass covering of a shuttle tile, and spacesuit outer fabric.
Effects of low Earth orbit (LEO) atomic oxygen were measured on a variety of spacecraft materials which obtained exposure on STS-5. Material degradation dependency on temperature was found in one material. Of the five paints flown, only S13GLO was unaffected. Generally, the glossy paints became Lambertian and the diffuse coatings improved. Scanning electron microscope examinations indicated removal of urethane and epoxy paint binder materials. Reaction products were evident on the surfaces of Z302 paint and Mylar. Thin films showed thickness losses ranging from negligible loss in Teflon to considerable loss in Mylar and Kapton. Glossy films such as black Kapton and white Tedlar became diffused. Kevlar 29 rope lost tensile strength and silver solar cell interconnect material oxidized. Oxidation on the backside of an elevated specimen indicated that reflections of oxygen atoms were occurring and that reflecting surfaces, probably Kapton, were not fully accommodating the incident atoms.
The effect of atomic oxygen interaction experienced by polymeric-based spacecraft materials is described. An experimental package (ACOMEX) flown on shuttle mission STS-41G carried out the investigation of advanced composite specimens such as carbon-epoxy and Kevlar-epoxy both with and without protective coatings added to thermal protective paints and films. Information on the exposure environment of the specimens was provided by a carbon coated atomic oxygen fluence monitor together with a photographic record. Mass loss measurements and photomicrographs made possible the analysis of the effect of interaction. After a total of about 38 hours of equivalent normal exposure at 225 km altitude the results showed that unprotected exposed surfaces exhibited severe erosion and mass loss with the possibility of seriously degrading structural and thermal performance. However, the specimens with a thin fluorocarbon overcoat showed promise of providing a protective barrier to the attack without altering the base properties of the material.
Spacecraft structures and surface materials exposed to the space environment for extended periods, up to thirty years, have increased potential for damage from long term exposure to the combined space environment including solar ultraviolet radiation, electrons, and protons and orbiting space debris. The space environment in which the Space Station Freedom and other space platforms will orbit is truly a hostile environment. For example, the currently estimated integral fluence for electrons above 1 Mev at 2000 nautical miles is above 2 x 10(exp 10) electrons/cm(sup 2)/day and the proton integral fluence is above 1 x 10(exp 9) protons/cm(sup 2)/day. At the 200 - 400 nautical miles, which is more representative of the altitude which will provide the environment for the Space Station, each of these fluences will be proportionately less; however, the data indicates that the radiation environment will obviously have an effect on structural materials exposed to the environment for long durations. The effects of ultraviolet radiation, particularly in the vacuum ultraviolet (less than 200 nm wavelength) is more difficult to characterize at this time. Very little data is available in the literature which can be used for determining the life cycle of a material placed in space for extended durations of time. In order to obtain critical data for planning and designing of spacecraft systems, use of a small vacuum system at the Environmental Effects Facility at MSFC, which can be used for these purposes was used. A special effort was made to build up this capability during the course of this research effort and perform a variety of experiments on materials proposed for the Space Station. A description of the apparatus and the procedure devised to process potential spacecraft materials is included.
Sixteen materials consisting of metallizations, silicones, and FEP Teflon were applied as protective coatings to selected spacecraft material surfaces and exposed on STS-41G to the LEO atomic oxygen environment. Evaluations of their protective effectiveness were made through assessing their mass loss/gain characteristics, maintenance of base material optical properties, and imperviousness to atomic oxygen attack. Generally, all coatings provided some degree of protection for the underlying material. In some cases the overcoat appeared to be too thin thereby providing inadequate protection.
In situ determination of effects of ultraviolet radiation, solar wind protons, and temperature on thermophysical properties of solar cell filters and other spacecraft materials
The 5.8-year exposure data from the Long Duration Experiment Facility (LDEF) has demonstrated the benefits of long-term exposure in low Earth orbit (LEO) for understanding the behavior of spacecraft materials and coatings for use in extended space missions. The Space Station Freedom represents the next large area spacecraft available in NASA planned missions for obtaining this long term space exposure data. The advantages of using the Space Station Freedom for these studies are presented. Discrepancies between short-term flight exposure result from Shuttle Orbiter experiments and the long-term LDEF results are shown. The major objectives and benefits of conducting materials and coatings experiments on Space Station Freedom are emphasized.
The Advanced Composite Materials Exposure to Space Experiment flown on shuttle mission STS-41G was designed to investigate the effect of low Earth orbit space environment on polymeric spacecraft materials. The effect of the phenomenon attributed to atomic oxygen on Kapton and advanced composite materials of carbon-epoxy and kevlar epoxy is described. The results of true space exposure are compared to duplicate specimens subjected to a simulated environment in an Earth-based nozzle beam test facility utilizing microwave discharge to form atomic oxygen. Although the energy level for atomic oxygen in the beam facility did not achieve the orbital energy level of 5 eV, similar effects of surface erosion and degradation are observed after equivalent exposure times.
NASA-STD-6001B, Determination of Offgassed Products (Test 7), provides the offgassing characteristics under standardized conditions for materials and assembled articles to be located within habitable spacecraft environments. Experience with Test 7 has found certain material types to be of higher risk for offgassing undesirable compounds aboard spacecraft than others. Formaldehyde and acrolein are historically high T value offgassed components of the offgassed compound target list because they have low spacecraft maximum allowable concentration (SMAC) values assigned by the JSC Toxicology Group. Carbon disulfide, benzene, acrylonitrile, and furan are additional target compounds of concern due to their lower thresholds of toxicity as determined by the JSC Toxicology Group. Materials offgassing siloxanes are also of concern due to their degradation effects on environmental control and life support system (ECLSS) components and performance. Spacecraft materials and articles defined in this manuscript as high risk were identified after examining and condensing data for these compounds of concern from approximately 3000 tests performed over 30 years. Summaries of high risk material and article types based on highest Multi-Purpose Crew Vehicle (MPCV) T values are also presented. Historical analysis shows high risk components are produced largely from test materials and articles in the general categories of electronic/powered components, foams, paints/coatings/films, adhesives/tapes, epoxy/resins, liquids/gels, Nomex® with surface treatments, markers/pens/inks, dry film lubricants, thermoplastics, hygiene items (deodorants, lip balms), and silicone rubber. These data are intended to be a resource for spacecraft materials and processes managers, designers, and toxicologists. High risk materials and articles intended for use aboard spacecraft should be tested in accordance with NASA-STD-6001B Test 7.