The National Aeronautics and Space Administration (NASA) is launching a bold and ambitious new space initiative.
A significant part of this new initiative includes exploration of new worlds, the development of more innovative
technologies, and expansion our presence in the solar system. A common theme to this initiative is the exploration
of space beyond Low Earth Orbit (LEO). As currently organized, NASA does not have an Agency-level office that
provides coordination of space environment research and development. This has contributed to the formation of a
gap between spaceflight environments knowledge and the application of this knowledge for multi-program use. This
paper outlines a concept to establish a NASA-level Applied Spaceflight Environments (ASE) office that will provide
coordination and funding for sustained multi-program support in three technical areas that have demonstrated these
needs through customer requests. These technical areas are natural environments characterization and modeling,
materials and systems analysis and test, and operational space environments modeling and prediction. This paper
will establish the need for the ASE, discuss a concept for organizational structure and outline the scope in the three
Degradation processes in confined polymeric films, with a thickness smaller or equal to 100 nm are of particular importance for future space missions and microelectronics applications. A simplified theoretical model for the evolution of free radicals in such films is proposed. The model takes into account the dependence of the glass transition temperature (TG) on the film thickness as well as the dependence of TG on the average molecular mass of the polymer (Fox-Flory equation), by exploiting the blob concept. It is assumed that the film thickness controls blobs' size. The time and temperature evolution of free radicals is desxcribed by dividing the main physical and chemical processes into two statistically independent steps. In the first step, the reactants diffuse towards a nanometer sized reaction volume. In the second step the proper chemical reaction between reactants occurs. Two possible chemical reactions are considered: the deactiviation of free radicals through chemical reactions with small molecules or free electrons and the recombination of free radicals. It is supposed that the diffusion of free radicals is a self-diffusion process that obeys a Williams-Landel-Ferry like temperature dependence. The temperature dependence of the diffusion coefficient of small molecules was assumed to obey a simple Arrhenius like dependence. This provides a simple theoretical approach for the modeling of the physical properties thin polymeric films subjected to degradation processes within the glass transition range and may be refined to assess the lifetime of such films in extreme environments.
The National Aeronautics and Space Administration's (NASA) Marshall Space Flight Center (MSFC) continues research into the utilization of photonic materials for spacecraft propulsion. Spacecraft propulsion, using photonic materials, will be achieved using a solar sail. A solar sail operates on the principle that photons, originating from the sun, impart pressure to the sail and therefore provide a source for spacecraft propulsion. The pressure imparted to a solar sail can be increased, up to a factor of two, if the sun-facing surface is perfectly reflective. Therefore, these solar sails are generally composed of a highly reflective metallic sun-facing layer, a thin polymeric substrate and occasionally a highly emissive back surface. Near term solar sail propelled science missions are targeting the Lagrange point 1 (L1) as well as locations sunward of L1 as destinations. These near term missions include the Solar Polar Imager and the L1 Diamond. The Environmental Effects Group at NASA's Marshall Space Flight Center (MSFC) continues to actively characterize solar sail material in preparation for these near term solar sail missions. Previous investigations indicated that space environmental effects on sail material thermo-optical properties were minimal and would not significantly affect the propulsion efficiency of the sail. These investigations also indicated that the sail material mechanical stability degrades with increasing radiation exposure. This paper will further quantify the effect of space environmental exposure on the mechanical properties of candidate sail materials. Candidate sail materials for these missions include Aluminum coated Mylar TM, TeonexTM, and CP1 (Colorless Polyimide).
These materials were subjected to uniform radiation doses of electrons and protons in individual exposures sequences. Dose values ranged from 100 Mrads to over 5 Grads. The engineering performance property responses of thermo-optical and mechanical properties were characterized. The contribution of Near Ultraviolet (NUV) radiation combined with electron and proton radiation was also investigated.
A parallel analysis of radiation-induced and thermal-induced degradation of polyethyleneterephtalate (PET) films is presented. The complexity of the degradation process is analyzed as a first step in a better understanding of the effect of combined temperature and radiation on PET. electron spin resonance spectrometry, DC electrical measurements, differential scanning calorimetry, and mechanical tests were used to analysze the effect of different ioninzing radiation (such as gamma, electrons, and accelerated ions) on thin films of PET. Data on the thermal analysis of PET are presented and analyzed. This study aims to a better understanding and modeling of complex degradation processes, required for a more reliable assessment of the behavior of polymers subjected to the space environment.
The NASA Marshall Space Flight Center is currently evaluating polymer based components for application in launch vehicle and propulsion system avionics systems. Organic polymers offer great advantages over inorganic corollaries. Unlike inorganics with crystalline structures defining their sensing characteristics, organic polymers can be engineered to provide varying degrees of sensitivity for various parameters including electro-optic response, second harmonic generation, and piezoelectric response. While great advantages in performance can be achieved with organic polymers, survivability in the operational environment is a key aspect for their practical application. The space environment in particular offers challenges that must be considered in the application of polymer based devices. These challenges include: long term thermal stability for long duration missions, extreme thermal cycling, space radiation tolerance, vacuum operation, low power operation, high operational reliability. Requirements for application of polymer based devices in space avionics systems will be presented and discussed in light of current polymer materials.
A unique ultra-light solar concentrator has recently been developed for space power applications. The concentrator comprises a flexible, 140-micron-thick, line-focus Fresnel lens, made in a continuous process from space-qualified transparent silicone rubber material. For deployment and support in space, end arches are used to tension the lens material in a lengthwise fashion, forming a cylindrical stressed membrane structure. The resultant lens provides high optical efficiency, outstanding tolerance for real-world errors and aberrations, and excellent focusing performance. The stretched lens is used to collect and focus sunlight at 8X concentration onto high-efficiency multi-junction photovoltaic cells, which directly convert the incident solar energy to electricity. The Stretched Lens Array (SLA) has been measured at over 27% net solar-to-electric conversion efficiency for space sunlight, and over 30% net solar-to-electric conversion efficiency for terrestrial sunlight. More importantly, the SLA provides over 180 W/kg specific power at a greatly reduced cost compared to conventional planar photovoltaic arrays in space. The cost savings are due to the use of 85% less of the expensive solar cell material per unit of power produced. SLA is a direct descendent of the award-winning SCARLET array which performed flawlessly on the NASA/JPL Deep Space 1 spacecraft from 1998-2001.
Silicone lens materials, baselined for space power applications, were exposed to various components of a Geosynchronous Earth Orbit (GEO) radiation environment to determine the suitability of the material for long-term missions. Sample materials were exposed to electrons, protons, Near Ultraviolet (NUV), and Vacuum Ultraviolet (VUV) radiation. The samples were exposed to individual and to various combinations of these space environmental components. The electron and proton exposure levels were determined from radiation measurements performed in GEO. NUV and VUV radiation exposures were based on solar emissions at zero air mass (AM0). Lens material degradation was determined by the change in optical spectral transmission of the silicone materials. A reduction in the transmittance of the material will reduce the power generating potential of solar cells. The spectral transmission was measured at Marshall Space Flight Center (MSFC), after exposure to space environmental elements including electrons, protons, VUV and NUV. Entech, Inc. conducted performance tests on samples exposed to short duration proton and electron radiation. Results of these tests will be discussed. Minor degradation was witnessed on samples exposed to NUV and VUV light. The largest transmission spectral degradation occurred in the wavelength range below the quantum efficiency of space qualified solar cells. Transmission degradation in the wavelength range of maximum solar cell quantum efficiency was small.
The National Aeronautics and Space Administration's (NASA) Marshall Space Flight Center (MSFC) is concentrating research into the utilization of photonic materials for spacecraft propulsion. Spacecraft propulsion, using photonic materials, will be achieved using a solar sail. A sail operates on the principle that photons, originating from the sun, impart pressure and provide a source of spacecraft propulsion. The pressure can be increased, by a factor of two if the sun-facing surface is perfectly reflective. Solar sails are generally composed of a highly reflective metallic front layer, a thin polymeric substrate, and occasionally a highly emissive back surface. The Space Environmental Effects Team at MSFC is actively characterizing candidate solar sail materials to evaluate the thermo-optical and mechanical properties after exposure to a simulated Geosynchronous Transfer Orbit (GTO) radiation environment. This study is the first known characterization of solar sail materials exposed to space simulated environments. The technique of radiation dose verses material depth profiling was used to determine the orbital equivalent exposure doses. The solar sail exposure procedures and results of the material characterization will be discussed.
Transparent polymeric materials are being designed and utilized as solar concentrating lenses for spacecraft power and propulsion systems. These polymeric lenses concentrate solar energy onto energy conversion devices such as solar cells and thermal energy systems. The conversion efficiency is directly related to the transmissivity of the polymeric lens. The Environmental Effects Group of the Marshall Space Flight Center's Materials, Processes, and Manufacturing Department exposed a variety of material to a simulated space environment and evaluated them for change in optical transmission. These materials include LexanTM, polyethylene terephalate, several formulate of TefzelTM and TeflonTM, and silicone DC 93 - 500. Samples were exposed to a minimum of 1000 equivalent sun hours of near ultraviolet radiation (250 - 400 nm wavelength). Prolonged exposure to the space environment will decrease the polymer film's transmission and thus reduce the conversion efficiency. A method was developed to normalize the transmission loss and thus rank the materials according to their tolerance to space environmental exposure. Spectral results and the material ranking according to transmission loss are presented. Power loss over time for a typical solar cell was calculated based on degraded transmission of the polymer material.
Predicting the effective life of materials for space applications has become increasingly critical with the drive to reduce mission cost. Programs have considered many solutions to reduce launch costs including novel, low mass materials and thin thermal blankets to reduce spacecraft mass. Determining the long-term survivability of these materials before launch is critical for mission success. This presentation will describe an analysis performed on the outer layer of the passive thermal control blanket of the Hubble Space Telescope. This layer had degraded for unknown reasons during the mission, however ionizing radiation (IR) induced embrittlement was suspected. A methodology was developed which allowed direct comparison between the energy deposition of the natural environment and that of the laboratory generated environment. Commercial codes were used to predict the natural space IR environment, model energy deposition in the material from both natural and laboratory IR sources, and design the most efficient test. Results were optimized for total and local energy deposition with an iterative spreadsheet. This method has been used successfully for several laboratory tests at the Marshall Space Flight Center. The study showed that the natural space IR environment, by itself, did not cause the premature degradation observed in the thermal blanket.
A test program has been implemented to evaluate candidate thin film materials for the sun-facing layer of the Next Generation Space Telescope (NGST) sunshield. Various polymers are being tested to determine if any can survive the radiation environment of the proposed NGST orbit (the second Sun-Earth lagrangian point or L2). This testing will characterize the mechanical and thermal properties before and after exposure to a simulated NGST sunshield environment. In addition, because the sunshield will be folded and stowed before launch, the candidate materials will be folded, stowed and unfolded (deployed) to determine if they can survive this type of handling and storage. Based on the results of this testing, candidates will be down selected for further development and testing. Future development will include the addition of optical coatings, rip-stop for tear resistance, and seaming techniques.