We report results pertinent to the high total dose tolerance of Si nanocrystal non-volatile memory cells. The nc-Si FETs made by ion implantation retained virtually unchanged write / erase characteristics, typical for the two-state devices, to cumulative doses exceeding 15 Mrad(Si).

Polymeric materials undergo rapid erosion when exposed to the harsh low-earth-orbit (LEO) environment. Coatings can reduce the erosion rate of polyimide Kapton from atomic oxygen (AO) attack. Specifically, we are investigating how thin Al coatings can protect Kapton. Protective Al layers with variations in layer thickness and growth conditions were deposited on Kapton H. The quality of these protective coatings were evaluated by mass loss measurement and compared to Kapton alone and the SiO2 coating, where dramatically decreased erosion rate was noted. To understand how these coatings protect Kapton as well as how the AO interacts with the coatings, we are investigating the microstructure of these coated materials by plane view and cross-sectional transmission electron microscopy (TEM) methods. To understand the AO degradation mechanism, we attempted to correlate the mass loss with growth conditions and microstructures. We noted a slight improvement in erosion resistance of the Al coating due to the presence of the dendrimer, but a major improvement when the Al coating is deposited under ultrahigh vacuum conditions.

The challenges posed by long duration human space flight have made regenerable air revitalization a critical technology. Current systems using disposable lithium hydroxide do not address the difficulties presented by long duration missions. Solid amine systems offer the capability to regeneratively adsorb CO2 using an amine—impregnated porous substrate. Desorption of CO2 is then achieved by exposing the system to vacuum or by increasing temperature. However, thermal inefficiencies and system size constraints prevent adoption of regenerable systems on current and future space vehicles. A key challenge is the thermal management of the adsorbing bed. The adsorbing surface increases in temperature which reduces adsorbing efficiency. The removal of CO2 reduces temperature, which in turn produces a loss in regeneration efficiency. These thermal inefficiencies necessitate prohibitively large volumes of traditional solid-amine materials, which do not have optimized surface areas and pore distributions. Single-wall carbon nanotubes (SWCNTs) may provide a means to increase surface area of the amine support and thermal efficiency. Recent work by Cinke et. al. provided a method of functionalizing SWCNTs and increasing the surface area to the order of 1500 m2/g [1]. We will report on the production of free standing, high surface area carbon nanotube structures currently being impregnated with amines. This novel SWCNT/amine approach will be compared with the current state of the art polymer structure-based system and characterized using SEM, TEM, surface area analysis through Brunauer-Emmett-Teller (BET), and also thermogravimetric equilibrium absorption. Results of SWCNT material improvements from processing modifications will also be presented.

Siloxanes have a wide variety of applications throughout the aerospace industry which take advantage of their exceptional insulating and adhesive properties and general resilience. They also offer a wide range of tailorable engineering properties with changes in composition and filler content. They are, however, subject to degradation in radiatively and thermally harsh environments. We are using solid state nuclear magnetic resonance techniques to investigate changes in network and interfacial structure in siloxane elastomers and their correlations to changes in engineering performance in a series of degraded materials. Nuclear magnetic resonance (NMR) parameters such as transverse (T2) relaxation times, cross relaxation rates, and residual dipolar coupling constants provide excellent probes of changes crosslink density and motional dynamics of the polymers caused by multi-mechanism degradation. The results of NMR studies on aged siloxanes are being used in conjunction with other mechanical tests to provide insight into component failure and degradation kinetics necessary for preliminary lifetime assessments of these materials as well as into the structure-property relationships of the polymers. NMR and magnetic resonance imaging (MRI) results obtained both from high resolution NMR spectrometers as well as low resolution benchtop NMR screening tools will be presented.

Atomic oxygen, formed in Earth's thermosphere, interacts readily with many materials on spacecraft flying in low Earth orbit (LEO). All hydrocarbon based polymers and graphite are easily oxidized upon the impact of ∼4.5 eV atomic oxygen as the spacecraft ram into the residual atmosphere. The resulting interactions can change the morphology and reduce the thickness of these materials. Directed atomic oxygen erosion will result in the development of textured surfaces on all materials with volatile oxidation products. Examples from space flight samples are provided. As a result of the erosive properties of atomic oxygen on polymers and composites, protective coatings have been developed and are used to increase the functional life of polymer films and composites that are exposed to the LEO environment. The atomic oxygen erosion yields for actual and predicted LEO exposure of numerous materials are presented. Results of in-space exposure of vacuum deposited aluminum protective coatings on polyimide Kapton indicate high rates of degradation are associated with aluminum coatings on both surfaces of the Kapton. Computational modeling predictions indicate that less trapping of the atomic oxygen occurs, with less resulting damage, if only the space-exposed surface is coated with vapor deposited aluminum rather than having both surfaces coated.

Uniform single-walled carbon nanotube (SWNT) polycarbonate composites were fabricated using noncovalently functionalized, soluble SWNTs. These composites showed dramatic improvements in the electrical conductivity and mechanical tensile strength at low SWNT loading. We also observed a stress-induced SWNT alignment in polycarbonate film, which is very difficult to achieve with pristine SWNTs.

Radiation resistant ferrite materials have potential applications in space station. Mg-Mn spinel ferrite was choosen for this study because of its radiation resistance and potential for use as an insulator in radiation environments. The radiation damage expected in these environments can be quickly and conveniently simulated using ion irradiation. The results of swift heavy ion irradiation induced modifications in the magnetization behavior of the Mg-Mn ferrite nanoparticles have been investigated using 100 MeV Ni8+ ion irradiation. To ensure the singlephase spinel structure of the system powder x-ray diffraction patterns has been performed. The powder samples were irradiated at three different fluences in the range 1×1012-5×1013 ions/cm2. Isothermal dc magnetization studies have been performed using SQUID and vibration sample magnetometer (VSM) on the pristine as well as on the irradiated samples at 20 K and 300 K. With irradiation saturation magnetization remains almost constant with ions irradiation. The coercivity values of the materials decreased about 5% with the fluence 1×1013 ions/cm2 as compare to the pristine nanoparticles. The results have been explained on the basis of the existence of surface defects produced by swift heavy ions, which generate orientational disorder of surface spins. The behavior of saturation magnetization with irradiations makes these nanoparticles suitable for memory devices in the space research.

A novel micro-scale electrostatic actuator has been designed and fabricated to study fatigue properties of low-stress LPCVD silicon nitride thin films, which are the structural materials of microshutter arrays to be used in NASA's James Webb Space Telescope (JWST). To obtain different stress levels without high applied voltages, the electrostatic actuator was designed based on a resonant technique to achieve mechanical amplification. All fabricated devices were tested inside a focused-ion-beam (FIB) system with pressure of 10-6 torr at room temperature (23 ± 1 °C) and with the test duration ranging from 5 seconds to 8.5 hours, 105 to 109 cycles, respectively. From the experiment, no fatigue failure of low-stress LPCVD silicon nitride thin films has been observed up to 109 testing cycles, four orders of magnitude higher than the expected lifetime of the microshutter arrays. The presented test device and experimental technique can be extended to characterize fatigue properties for other thin film materials.

Transient ionizing radiation fields have been observed to cause substantial optical loss in undoped LiNbO3 crystals operating at 1.06 microns. This loss is slow to recover and makes the selection of this material for Q-switch applications in radiation environments unfeasible. We have studied the effects of Mg doping on the radiation response of LiNbO3 crystals and have investigated the optical luminescence of doped and undoped samples. Our results indicate a strong correlation between crystal defects, formed primarily during crystal growth, and the radiation-induced optical loss exhibited by these materials. These findings have enabled us to produce radiation-hard LiNbO3 crystals for use in high gamma-field environments.

Many organic-based materials exposed to low Earth orbit (LEO) environment undergo dramatic changes and irreversible degradation of physical characteristics. While many protective schemes are used to reduce the effects of LEO environment, protection of such materials in LEO still remains a major challenge, especially for future long duration missions or space stations.

In addition to the traditional protective coating approaches, surface modification processes were proposed and successfully used as an approach to protect polymers, thermal control paints and other components and structures from LEO environment. Among them two surface modification processes, the Photosil™ and the Implantox™ that used new approaches in silicon functionalization, as in the Photosil™, and a modified ion implantation process, as in the Implantox™ allowed to incorporate up to 36 at.% of Si into the upper surface layer regions of the treated polymers, composite materials, thermal control paints and other high-performance organic materials.

The tests conducted in plasma and fast atomic oxygen (FAO) beam facilities at comparable to LEO fluencies (∼ (1–2)·1020 at.O/cm2 ) demonstrated erosion yields lower than −10−26 cm3at, unchanged thermal optical properties, where important, and excellent thermal match between the treated layers and the bulk of the treated materials. After FAO testing, the Implantox™ treated samples were clear and transparent, with a glassy-like shiny surface with no signs of any surface erosion.

Cubic boron nitride (c-BN) is a synthetic material which exhibits exceptional physicochemical properties such as: hardness, thermal conductivity, thermo-chemical stability, semiconducting properties and radiations resistance. Such outstanding properties make it a promising multifunctional material for applications in extreme conditions, as those found in the outer space environment. Its further use for such applications requires, however, a much better understanding of the lattice defects and radiation damage properties. Here we present the results of multifrequency ESR studies concerning the native and radiation induced point defects in crystalline c-BN under irradiation with high intensity 1MeV electron beams.

In this paper the ESA internal approach regarding the assessment of materials for inner solar system missions is presented. A main part of the work is devoted to the assessment of thermal control materials and space environmental testing at elevated temperature. As these materials are the most exposed it is important to understand how they will interact with the relevant space environment at elevated temperature. Driving parameters for materials degradation are discussed and on-going testing efforts are described. An important input parameter for thermal models is the knowledge of the end of life values for the thermo-optical properties as these determine the equilibrium temperatures. In certain cases end of life testing needs to be done when the uncertainty of extrapolation is too high.

Radiation-induced modifications in polymeric materials are briefly reviewed. The attention is paid to the effect of ionizing radiation on the mechanical properties of polymers. The competition between several parallel degradation processes in the harsh conditions of the space environment is analyzed. The need for a complex analysis of the effect of polymeric materials in simulated space environments is demonstrated.

Radiation doses from galactic cosmic rays (GCR) are a significant issue for spacecraft crew exposures in deep space. We report initial work to evaluate a range of materials for GCR shielding. Earlier work has shown that conventional spacecraft materials, aluminum and higher atomic number structural alloys, provide relatively little shielding and, under certain conditions, may increase radiation risk. Materials containing high proportions of hydrogen and other low atomic mass nuclei provide improved GCR shielding. Polyethylene (PE) is generally considered a good performance benchmark shield material. However, PE shielding occupies volume and adds mass to the spacecraft. In this work we investigate several materials that are shown to provide shielding similar to PE, but which could furnish additional spacecraft functions, possibly eliminating the need for materials currently used for structural support or thermal management. Carbon forms that can incorporate a large mass of hydrogen, as well as polymers and polymer composites are being explored. Calculations of shielding effectiveness in GCR spectra have been carried out. Experiments to measure shielding properties recently have been completed at the NASA Space Radiation Laboratory (NSRL) located at Brookhaven National Laboratory (BNL) using high energy beans of O16. In this paper we report preliminary shielding results.

The reasons to develop a nanodosimetry theory are critically reviewed. The necessity of such an approach is proved. The main features of nanodosimetry are analyzed. The predicted enhanced sensitivity of nanomaterials to ionizing radiation is demonstrated. It is concluded that the lifetime of nanomaterials in the harsh conditions of the space environment has to be accurately estimated.

Two-types of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) are evaluated as the protective coatings against ion erosion in electric propulsion systems. A series of experiments have been conducted to understand the erosion rate and erosion mechanism of these VA-MWNTs. These experiments were carried out with Xe propellant at an ion current density of 5 mA/cm2. We found that the erosion rates of both types of VA-MWNTs were changing with time. Such a nonlinear erosion process is explained according to a possible erosion mechanism.

The present work reports phase transformations of thin films of C60 irradiated with 100 MeV 197Au8+ ions. This work is in continuation with our earlier work using 58Ni10+ and 16O6+ ions, to study the modification in C60 thin films. The study of C60 thin films using 197Au8+ ions, provides us enough additional data to investigate thoroughly the role of Se in causing phase transformations under different ion fluences. The Raman spectra indicate that swift heavy ion (SHI) irradiation results in several transformations of crystalline C60. At low fluences along with the fragmentation of C60 there is dimer/polymer formation. As fluence increases the dimer/polymer content first rises, optimizes, decreases and finally vanishes at very high fluences. At high fluences, all the C60 molecules as well as the polymer C60 break up, possibly resulting in nano-crystalline graphite embedded in amorphous carbon (a-C).

Piezoelectric polymers based on polyvinylidene fluoride (PVDF) are of interest for large aperture space-based telescopes. Dimensional adjustments of adaptive polymer films are achieved via charge deposition and require a detailed understanding of the piezoelectric material responses which are expected to suffer due to strong vacuum UV, λ-, X-ray, energetic particles and atomic oxygen under low earth orbit exposure conditions. The degradation of PVDF and its copolymers under various stress environments has been investigated. Initial radiation aging studies using λ- and e-beam irradiation have shown complex material changes with significant crosslinking, lowered melting and Curie points (where observable), effects on crystallinity, but little influence on overall piezoelectric properties. Surprisingly, complex aging processes have also been observed in elevated temperature environments with annealing phenomena and cyclic stresses resulting in thermal depoling of domains. Overall materials performance appears to be governed by a combination of chemical and physical degradation processes. Molecular changes are primarily induced via radiative damage, and physical damage from temperature and AO exposure is evident as depoling and surface erosion. Major differences between individual copolymers have been observed providing feedback on material selection strategies.

Future science missions of the European Space Agency (ESA) to the inner part of the solar system will require the use of materials at an extreme radiation and temperature environment. A major concern regarding the selection of these materials is the thermal behaviour and the thermal stability. In this paper ways are shown to assess the thermal endurance of polymers by kinetic modelling. Two commonly used kinetic models, the one following the ASTM E 1641 and ASTM E 1877 standards and the other following the Model Free Kinetics (MFK) approach, are presented and compared to each other with the given example of two competing polyimide films, Kapton HN® of DuPont and Upilex S® of Ube Industries1, which were tested within ESA's critical materials technology program.

The thermodynamic efficiency of the Brayton cycle, upon which all gas turbines (aeropropulsion and power generation) are based on scales with the peak operating temperature. However, the peak temperature is limited by the turbine blades and the temperature they can withstand. The highest temperatures in the gas turbine occur in the combustor region but these temperatures are often too high for turbine blades. As a result, the combustion products must be diluted with relatively cooler air from the compressor to reduce the temperature to tolerable levels for the turbine blades. This research suggests placing a ring of high temperature open cell metal foam between the combustors and turbine sections of the jet engine to mix and average the difference in temperatures resulting from the cooling schemes in combustor cans. Temperature mixing effect was tested using a special setup with the application of an infrared camera and streams of hot and cold air passing through the foam. High speed flow pressure drop around Mach 1 (340 m/s) was done on the same foam samples to understand pressure drop in the compressible regime of air. Infrared imaging showed that open cell metal foams successfully mixed and averaged the difference in temperatures of the hot and cold gasses thus creating a more uniform temperature profile while pressure drop testing revealed that open cell metal foams result in minimal pressure drop at high flows especially when the increase in temperature in taken into consideration.