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Statistical Analysis of Aquarius Radiometer Radio Frequency Interference (RFI) and Implications on RFI Detection and Mitigation

The Aquarius/SAC-D mission operated between August 2011 and June 2015 with the main goal of providing global estimates of sea surface salinity (SSS). It comprised both active and passive microwave sensors operating at L-band to observe the same surface area almost simultaneously. Measurements from both instruments underwent subsequent filtering to mitigate the effect of Radio Frequency Interference (RFI). This report describes the analysis of statistics of RFI in samples acquired by the Aquarius radiometers, and its results could be used to improve the performance of the interference detection algorithm.

De Matthaeis, Paolo↗

Changes in the Optical Properties of Materials Are Observed After 18 Months in Low Earth Orbit

Materials located on the exterior of spacecraft in low Earth orbit are subjected to a number of environmental threats, including atomic oxygen, ultraviolet radiation, thermal cycling, and micrometeroid and debris impact. Atomic oxygen attacks materials vulnerable to oxidation. Ultraviolet radiation can break chemical bonds and cause undesirable changes in optical properties. Thermal cycling can cause cracking, and micrometeroid and debris impacts can damage protective coatings. Another threat is contamination. The outgassing of volatile chemicals can contaminate nearby surfaces, changing their thermal control properties. Contaminated surfaces may undergo further change as a result of atomic oxygen and ultraviolet radiation exposure. The Passive Optical Sample Assembly (POSA) experiment was designed as a risk mitigation experiment for the International Space Station. Samples were characterized before launch, exposed for 18 months on the exterior of Mir, and characterized upon their return. Lessons learned from POSA about the durability of material properties can be applied to the space station and other long-duration missions.

Jaworske, Donald A.↗

Engineering Polymers as Structural Materials in Spacecraft Water Systems

The novel application of structural materials, surface treatments, and barrier coatings is desired to mitigate the rapid loss of ionic silver (Ag+) biocide observed with passive metal alloys, improve reliability, and reduce system mass. In this work, we provide an initial look at the potential replacement of these heritage alloys in spacecraft water systems with high-performance thermoplastic engineering polymers, including PEEK, PEI, and PVDF. Such materials have found increasing use as structural materials in a broad array of performance-critical applications, including in the aerospace, medical implant, and chemical processing fields. We selected a number of promising materials for investigation, compiled mechanical behavior data, and conducted theoretical performance analyses. We also identified and began to address numerous material suitability concerns as well as design requirements for pressurized components in human-rated spacecraft hardware. These include material flammability, offgassing, leaching, chemical resistance, radiation tolerance, prevention of fracture/yielding, and others. We find that there is significant potential for use of engineering polymers in spacecraft water systems, and suggest some directions for future research.

Lance Dean Delzeit↗

Engineering the Interface: Advanced Surface Technologies for Lunar Dust Management and Equipment Longevity

Through the Artemis program, NASA intends to develop a sustainable human foothold on the Moon, ultimately paving the way for crewed exploration of Mars. The Moon's hostile environment poses numerous obstacles, including exposure to radiation, temperature extremes, micrometeoroid threats, and particularly the persistent problem of lunar dust. Lunar dust impacts nearly every aspect of surface operations through adhesion and abrasion mechanisms, with contamination from anthropogenic activities (landing, rovers) far outweighing natural phenomena. Multiple adhesion pathways contribute to surface contamination in the lunar environment, including van der Waals forces, electrostatic forces, chemical reaction, and magnetic forces from elemental iron deposits. Sharp asperities from micrometeoroid bombardment and atmospheric absence increase interaction potential and enable mechanical interlocking. Low cohesion between dust particles exacerbates these challenges, as minimal interaction potential between dust and nearby surfaces overcomes particle cohesion, causing contamination. Lunar dust adhesion mitigation technologies can be categorized as either active, requiring external energy, or passive, relying on intrinsic material properties. Ultrasonic and electrodynamic technologies have been developed to the highest technology readiness level for active approaches. Passive strategies primarily focus on surface chemistry and topography modifications. At NASA Langley Research Center, approaches include surface migration agents to reduce surface energy, topographical modification using laser ablation patterning, and tailored surface conductivity to reduce intrinsic adhesion force. Performance has been evaluated using custom-built ultrasonic and centrifuge instruments. Plume-surface interactions from lunar landers can propel micrometer-sized particles at velocities up to 1000 m s-1.8 These particles pose risks to landers, habitats and infrastructure, leading to erosion, degradation, and reduced component lifespan. A panel recovered from Surveyor III was determined to have been severely abraded because of lunar dust displaced from the Apollo 12 lunar module that landed 160 m away. The performance of metallic surfaces has been evaluated via high velocity single particle impact using the laser-induced project impact test (LIPIT) facility at the University of Utah. Peridynamics modeling, a form of continuum mechanics that uses a nonlocal approach enabling greater simulation capabilities of crack initiation and fracture, has also been utilized to gain greater insight into material response during impact events. Lunar dust contamination challenges extend to power generation systems and moving equipment. Cables, rotation stages, and other mechanisms may experience limited range of motion and reduced lifetime due to dust infiltration. NASA Langley Research Center has evaluated traditional aerospace alloys, softgoods, wear resistant ceramics, and several polymer and polymer composite materials. Test methods have included traditional techniques like Taber abrasion testing, as well as designed test configurations developed in the DUSTE (dust, ultraviolet radiation, and space thermal environmental) chamber that reproduce mechanism functions in operational environment. Beyond laboratory experiments, several flight experiments have been conducted. Materials were exposed to the low Earth orbit environment on the Materials International Space Station Experiment (MISSE) and to the lunar surface environment through the Aegis Aerospace Regolith Adherence Characterization (RAC) payload and the Honeybee Robotics PlanetVac payload. Determining lunar dust's impact on surface exploration and habitation requires comprehensive experimental and computational capabilities combined with lessons learned from initial lunar activities. Identifying the greatest environmental challenges and developing mitigation technologies provides the clearest path toward successfully, expeditiously, and efficaciously completing NASA's mission. This presentation will discuss ongoing efforts at NASA Langley Research Center and collaborator contributions to these critical objectives.

Surface Engineering↗

Analysis of RFI Statistics for Aquarius RFI Detection and Mitigation Improvements

Aquarius is an L-band active/passive sensor designed to globally map sea surface salinity from space. Two instruments, a radar scatterometer and a radiometer, observe the same surface footprint almost simultaneously. The radiometer is the primary instrument for sensing sea surface salinity (SSS), while the scatterometer is included to provide a correction for sea surface roughness, which is a primary source of error in the salinity retrieval. Although the primary objective is the measurement of SSS, the instrument combination operates continuously, acquiring data over land and sea ice as well. An important feature of the data processing includes detection and mitigation of Radio Frequency Interference (RFI) which is done separately for both active and passive instruments. Correcting for RFI is particularly critical over ocean because of the high accuracy required in the brightness temperature measurements for SSS retrieval. It is also necessary for applications of the Aquarius data over land, where man-made interference is widespread, even though less accuracy is required in this case. This paper will provide an overview of the current status of the Aquarius RFI processing and an update on the ongoing work on the improvement of the RFI detection and mitigation performance.

Microwave remote sensing↗

Shunted Piezoelectric Vibration Damping Analysis Including Centrifugal Loading Effects

Excessive vibration of turbomachinery blades causes high cycle fatigue problems which require damping treatments to mitigate vibration levels. One method is the use of piezoelectric materials as passive or active dampers. Based on the technical challenges and requirements learned from previous turbomachinery rotor blades research, an effort has been made to investigate the effectiveness of a shunted piezoelectric for the turbomachinery rotor blades vibration control, specifically for a condition with centrifugal rotation. While ample research has been performed on the use of a piezoelectric material with electric circuits to attempt to control the structural vibration damping, very little study has been done regarding rotational effects. The present study attempts to fill this void. Specifically, the objectives of this study are: (a) to create and analyze finite element models for harmonic forced response vibration analysis coupled with shunted piezoelectric circuits for engine blade operational conditions, (b) to validate the experimental test approaches with numerical results and vice versa, and (c) to establish a numerical modeling capability for vibration control using shunted piezoelectric circuits under rotation. Study has focused on a resonant damping control using shunted piezoelectric patches on plate specimens. Tests and analyses were performed for both non-spinning and spinning conditions. The finite element (FE) shunted piezoelectric circuit damping simulations were performed using the ANSYS Multiphysics code for the resistive and inductive circuit piezoelectric simulations of both conditions. The FE results showed a good correlation with experimental test results. Tests and analyses of shunted piezoelectric damping control, demonstrating with plate specimens, show a great potential to reduce blade vibrations under centrifugal loading.

Min, James B.↗

Effect of Molecular Flexibility upon Ice Adhesion Shear Strength

Ice formation on aircraft surfaces effects aircraft performance by increasing weight and drag leading to loss of lift. Current active alleviation strategies involve pneumatic boots, heated surfaces, and usage of glycol based de-icing fluids. Mitigation or reduction of in-flight icing by means of a passive approach may enable retention of aircraft capabilities, i.e., no reduction in lift, while reducing the aircraft weight and mechanical complexity. Under a NASA Aeronautics Research Institute Seedling activity, the effect of end group functionality and chain length upon ice adhesion shear strength (IASS) was evaluated with the results indicating that chemical functionality and chain length (i.e. molecular flexibility) affected IASS. Based on experimental and modeling results, diamine monomers incorporating molecular flexibility as either a side chain or in between diamine functionalities were prepared, incorporated into epoxy resins that were subsequently used to fabricate coatings on aluminum substrates, and tested in a simulated icing environment. The IASS was found to be lower when molecular flexibility was incorporated in the polymer chain as opposed to a side chain.

Smith, Joseph G.↗

Radio Frequency Interference Detection for Passive Remote Sensing Using Eigenvalue Analysis

Radio frequency interference (RFI) can corrupt passive remote sensing measurements taken with microwave radiometers. With the increasingly utilized spectrum and the push for larger bandwidth radiometers, the likelihood of RFI contamination has grown significantly. In this work, an eigenvalue-based algorithm is developed to detect the presence of RFI and provide estimates of RFI-free radiation levels. Simulated tests show that the proposed detector outperforms conventional kurtosis-based RFI detectors in the low-to-medium interferece-to-noise-power-ratio (INR) regime under continuous wave (CW) and quadrature phase shift keying (QPSK) RFIs.

Passive remote sensing↗

NASA and ESA Collaboration on Alternative to Nitric Acid Passivation: Parameter Optimization of Citric Acid Passivation for Stainless Steel Alloys

National Aeronautics and Space Administration (NASA) Headquarters chartered the Technology Evaluation for Environmental Risk Mitigation Principal Center (TEERM) to coordinate agency activities affecting pollution prevention issues identified during system and component acquisition and sustainment processes. The primary objectives of NASA TEERM are to: Reduce or eliminate the use of hazardous materials or hazardous processes at manufacturing, remanufacturing, and sustainment locations. Avoid duplication of effort in actions required to reduce or eliminate hazardous materials through joint center cooperation and technology sharing. Corrosion is an extensive problem that affects the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The damaging effects of corrosion result in steep costs, asset downtime affecting mission readiness, and safety risks to personnel. Consequently, it is vital to reduce corrosion costs and risks in a sustainable manner. NASA and ESA have numerous structures and equipment that are fabricated from stainless steel. The standard practice for protection of stainless steel is a process called passivation. Passivation is defined by The American Heritage Dictionary of the English Language as to treat or coat (a metal) in order to reduce the chemical reactivity of its surface. Passivation works by forming a shielding outer (metal oxide) layer that reduces the impact of destructive environmental factors such as air or water. Consequently, this process necessitates a final product that is very clean and free of iron and other contaminants. Typical passivation procedures call for the use of nitric acid; however, there are a number of environmental, worker safety, and operational issues associated with its use. Citric acid is an alternative to nitric acid for the passivation of stainless steels. Citric acid offers a variety of benefits including increased safety for personnel, reduced environmental impact, and reduced operational cost. The primary objective of this effort is to qualify citric acid as an environmentally-preferable alternative to nitric acid for the passivation of stainless steel alloys. While citric acid use has become more prominent in industry, there is little evidence that citric acid is a technically sound passivation agent, especially for the unique and critical applications encountered by NASA and ESA.

citric acid passivation↗

Bio-inspired Surface Structures to Mitigate Interfacial Particle Adhesion and Erosion - A Review

Lunar dust known as regolith is a huge challenge for lunar exploration missions. Formed over millennia by a complex process involving impacts of meteoroids and micrometeoroids on the lunar surface, lunar dust is porous, highly abrasive with sharp jagged edges, chemically reactive, electrostatically charged and sometimes magnetic. The chemical composition and thickness of the dust layer also varies in different regions of the lunar surface. From samples obtained by previous lunar missions, the average particle size is below 100 microns. This dust has the tendency to strongly adhere to any exposed surfaces, and often degrades the material functionality to eventually cause failure. Any material on the lunar surface is also subject to harsh temperature cycles ranging from -178 ̊C to + 123 ̊C and extreme ultraviolet radiation. While on the lunar surface, different classes of materials would be required for different applications. Advanced materials have been and will be used throughout the lunar lander, habitat, and mission equipment. Examples include: polymeric materials for astronaut protective clothing; metals and ceramics for the lunar lander legs and habitats, and excavating equipment; and semiconductors for solar panels and on-board electronics. In all these applications, the surfaces of the materials are expected or understood to be exposed to the extreme lunar environment condition that includes the regolith dust. During the Apollo missions, the dust clung to and abraded the astronaut’s suits, degraded seals, optics, clogged sensors and reduced performance of thermal radiators. The lunar dust adheres to the surface by various mechanisms, which include electrostatic and Coulombic interactions, Van-der-Waals forces, magnetic forces, mechanical interlocking, chemical bonding and donor-acceptor interactions. There are three primary strategies for developing technologies to minimize the lunar dust adhesion: active, passive and a combination of active and passive. In the active approach, an external energy is needed to prevent or remove particles from collecting on the surface. Mechanically powered brushes and electrodynamic dust screens are two examples. In the passive approach, no external power is needed, and the material surface properties are able to mitigate dust adhesion. A well-known example of this strategy is the low work function coatings for non-stick surfaces. In most cases a combination of active and passive methods might be needed to optimally manage the lunar regolith. The passive method is significantly more attractive as it does not require any external power or an additional control subsystem. These approaches optimize the mission payload and reduce risk. Surface modification to minimize the dust adhesion is thus very important to lunar missions. Here, naturally evolved surface structures might provide guidance for solutions. There are several factors that have to be considered for minimizing particle adhesion to a surface. These include the substrate material properties, surface topography, chemistry, and the characteristics of the adhering particles. When engineering a surface, the substrate material chosen would be dependent on the needs of the application. Tailoring the surface microstructure or chemistry opens up more possibilities for its optimal utilization

Lunar Dust↗

An Assessment of Environmental Health Needs

Environmental health fundamentally addresses the physical, chemical, and biological risks external to the human body that can impact the health of a person by assessing and controlling these risks in order to generate and maintain a health-supportive environment. In manned spacecraft, environmental health risks are mitigated by a multi-disciplinary effort, employing several measures including active and passive controls, by establishing environmental standards (SMACs, SWEGs, microbial and acoustics limits), and through environmental monitoring. Human Health and Performance (HHP) scientists and Environmental Control and Life Support (ECLS) engineers consider environmental monitoring a vital component to an environmental health management strategy for maintaining a healthy crew and achieving mission success. ECLS engineers use environmental monitoring data to monitor and confirm the health of ECLS systems, whereas HHP scientists use the data to manage the health of the human system. Because risks can vary between missions and change over time, environmental monitoring is critical. Crew health risks associated with the environment were reviewed by agency experts with the goal of determining risk-based environmental monitoring needs for future NASA manned missions. Once determined, gaps in environmental health knowledge and technology, required to address those risks, were identified for various types of exploration missions. This agency-wide assessment of environmental health needs will help guide the activities/hardware development efforts to close those gaps and advance the knowledge required to meet NASA manned space exploration objectives. Details of the roadmap development and findings are presented in this paper.

Macatangay, Ariel V.↗

RFI Statistical Distribution and Missed Detection in Aquarius Radiometer Measurements

Aquarius is an microwave active/passive sensor whose main goal is to globally estimate sea surface salinity from space. Two instruments, a radar scatterometer and a radiometer, operate at L-band observing the same surface footprint almost simultaneously. The sensitivity to sea surface salinity (SSS) is given by the radiometer, while the scatterometer measurements provide a correction for sea surface roughness. Although the primary objective is the measurement of SSS, the instrument combination operates continuously, acquiring data over land and sea ice as well. Radio Frequency Interference (RFI) can occur in both the radiometer and the scatterometer bands of operation, and for this reason detection and mitigation of RFI was included in the data processing of both active and passive instruments. This paper will focus on the RFI processing for the Aquarius radiometer only and provide an update on the efforts to reduce the amount of missed RFI detection.

RFI↗

Development and Validation of The SMAP Enhanced Passive Soil Moisture Product

Since the beginning of its routine science operation in March 2015, the NASA SMAP observatory has been returning interference-mitigated brightness temperature observations at L-band (1.41 GHz) frequency from space. The resulting data enable frequent global mapping of soil moisture with a retrieval uncertainty below 0.040 cu m/cu m at a 36 km spatial scale. This paper describes the development and validation of an enhanced version of the current standard soil moisture product. Compared with the standard product that is posted on a 36 km grid, the new enhanced product is posted on a 9 km grid. Derived from the same time-ordered brightness temperature observations that feed the current standard passive soil moisture product, the enhanced passive soil moisture product leverages on the Backus-Gilbert optimal interpolation technique that more fully utilizes the additional information from the original radiometer observations to achieve global mapping of soil moisture with enhanced clarity. The resulting enhanced soil moisture product was assessed using long-term in situ soil moisture observations from core validation sites located in diverse biomes and was found to exhibit an average retrieval uncertainty below 0.040 cu m/cu m. As of December 2016, the enhanced soil moisture product has been made available to the public from the NASA Distributed Active Archive Center at the National Snow and Ice Data Center.

SMAP Enhanced↗

Incorporation of Functionalized Polyhedral Oligomeric Silsesquioxane Nanomaterials as Reinforcing Agents for Impact Ice Mitigating Coatings

In-flight, aircraft are exposed to a wide range of environments. One commonly exposed environment are clouds containing super-cooled water droplets. These water drop- lets exist in a metastable state below the freezing point of water, in the range of 0 to -20°C. As the vehicle impacts the droplets, latent heat is released and within milliseconds the droplets convert to ice. This process is referred to as impact icing or in-flight icing.1 Impact icing is a major concern for aircraft since it can lead to degraded aerodynamic performance and, if left un- treated, can lead to loss of the vehicle. Active approaches (i.e., pneumatic boots, heated air ducts) typically utilized in mitigating in-flight ice accretion significantly increases vehicle weight and cannot be applied to all aircraft.1-3 A passive approach based on coatings is desired, but durability issues are a concern, especially on the wing leading edge.3 Nanomaterials have been shown to afford significant improvement in coating and composite physical properties at low loading levels.4 In this study, Polyhedral Oligomeric Silsesquioxane (POSS) nanomaterials have been shown to increase coating durability. Also, with wide variety of functionalities present on the arm structure, POSS nanomaterials have been shown to readily alter coating surface chemistry to mitigate impact ice adhesion from -16 to -8°C in a simulated in-flight icing environment.

Beck, Devon M.↗

Implementation of Active Thermal Control (ATC) for the Soil Moisture Active and Passive (SMAP) Radiometer

NASA's Earth Observing Soil Moisture Active and Passive (SMAP) Mission is scheduled to launch in November 2014 into a 685 kilometer near-polar, sun-synchronous orbit. SMAP will provide comprehensive global mapping measurements of soil moisture and freeze/thaw state in order to enhance understanding of the processes that link the water, energy, and carbon cycles. The primary objectives of SMAP are to improve worldwide weather and flood forecasting, enhance climate prediction, and refine drought and agriculture monitoring during its three year mission. The SMAP instrument architecture incorporates an L-band radar and an L-band radiometer which share a common feed horn and parabolic mesh reflector. The instrument rotates about the nadir axis at approximately 15 revolutions per minute, thereby providing a conically scanning wide swath antenna beam that is capable of achieving global coverage within three days. In order to make the necessary precise surface emission measurements from space, the electronics and hardware associated with the radiometer must meet tight short-term (instantaneous and orbital) and long-term (monthly and mission) thermal stabilities. Maintaining these tight thermal stabilities is quite challenging because the sensitive electronics are located on a fast spinning platform that can either be in full sunlight or total eclipse, thus exposing them to a highly transient environment. A passive design approach was first adopted early in the design cycle as a low-cost solution. With careful thermal design efforts to cocoon and protect all sensitive components, all stability requirements were met passively. Active thermal control (ATC) was later added after the instrument Preliminary Design Review (PDR) to mitigate the threat of undetected gain glitches, not for thermal-stability reasons. Gain glitches are common problems with radiometers during missions, and one simple way to avoid gain glitches is to use the in-flight set point programmability that ATC affords to operate the radiometer component away from the problematic temperature zone. A simple ThermXL model (10 nodes) was developed to exercise quick trade studies among various proposed control algorithms: Modified P control vs. PI control. The ThermXL results were then compared with the detailed Thermal Desktop (TD) model for corroboration. Once done, the simple ThermXL model was used to evaluate parameter effects such as temperature digitization, heater size and gain margin, time step, and voltage variation of power supply on the ATC performance. A Modified P control algorithm was implemented into the instrument flight electronics based on the ThermXL results. The thermal short-term stability margin decreased by 10 percent with ATC and a wide temperature error band (plus or minus 0.1 degrees Centigrade) compared to the original passive thermal design. However, a tighter temperature error band (plus or minus 0.1 degrees Centigrade) increased the thermal short-term stability margin by a factor of three over the passive thermal design. The current ATC design provides robust thermal control, tighter stability, and greater in-flight flexibility even though its implementation was prompted by non-thermal performance concerns.

Mikhaylov, Rebecca↗

RFI Detection and Mitigation using Independent Component Analysis as a Pre-Processor

Radio-frequency interference (RFI) has negatively impacted scientific measurements of passive remote sensing satellites. This has been observed in the L-band radiometers Soil Moisture and Ocean Salinity (SMOS), Aquarius and more recently, Soil Moisture Active Passive (SMAP). RFI has also been observed at higher frequencies such as K band. Improvements in technology have allowed wider bandwidth digital back ends for passive microwave radiometry. A complex signal kurtosis radio frequency interference detector was developed to help identify corrupted measurements. This work explores the use of Independent Component Analysis (ICA) as a blind source separation (BSS) technique to pre-process radiometric signals for use with the previously developed real and complex signal kurtosis detectors.

independent component analysis↗

Investigating the Feasibility of Utilizing Carbon Nanotube Fibers for Spacesuit Dust Mitigation

Historical data from the Apollo missions has compelled NASA to identify dust mitigation of spacesuits and other components as a critical path prior to sending humans on potential future lunar exploration missions. Several studies thus far have proposed passive and active countermeasures to address this challenge. However, these technologies have been primarily developed and proven for rigid surfaces such as solar cells and thermal radiators. Integration of these technologies for spacesuit dust mitigation has remained an open challenge due to the complexity of suit design. Current research investigates novel methods to enhance integration of the Electrodynamic Dust Shield (EDS) concept for spacesuits. We leverage previously proven EDS concept developed by NASA for rigid surfaces and apply new techniques to integrate the technology into spacesuits to mitigate dust contamination. The study specifically examines the feasibility of utilizing Carbon Nanotube (CNT) yarns manufactured by Rice University as electrodes in spacesuit material. Proof of concept testing was conducted at NASA Kennedy Space Center using lunar regolith simulant to understand the feasibility of the proposed techniques for spacesuit application. Results from the experiments are detailed in this paper. Potential challenges of applying this technology for spacesuits are also identified.

Electrodynamic Dust Shield↗

Evaluation of Space Power Materials Flown on the Passive Optical Sample Assembly

Evaluating the performance of materials on the exterior of spacecraft is of continuing interest, particularly in anticipation of those applications that will require a long duration in low Earth orbit. The Passive Optical Sample Assembly (POSA) experiment flown on the exterior of Mir as a risk mitigation experiment for the International Space Station was designed to better understand the interaction of materials with the low Earth orbit environment and to better understand the potential contamination threats that may be present in the vicinity of spacecraft. Deterioration in the optical performance of candidate space power materials due to the low Earth orbit environment, the contamination environment, or both, must be evaluated in order to propose measures to mitigate such deterioration. The thirty two samples of space power materials studied here include solar array blanket materials such as polyimide Kapton H and SiO(x) coated polyimide Kapton H, front surface aluminized sapphire, solar dynamic concentrator materials such as silver on spin coated polyimide and aluminum on spin coated polyimide, CV 1144 silicone, and the thermal control paint Z-93-P. The physical and optical properties that were evaluated prior to and after the POSA flight include mass, total, diffuse, and specular reflectance, solar absorptance, and infrared emittance. Additional post flight evaluation included scanning electron microscopy to observe surface features caused by the low Earth orbit environment and the contamination environment, and variable angle spectroscopic ellipsometry to identify contaminant type and thickness. This paper summarizes the results of pre- and post-flight measurements, identifies the mechanisms responsible for optical properties deterioration, and suggests improvements for the durability of materials in future missions.

Jaworske, Donald A.↗