This PDF file contains the front matter associated with SPIE Proceedings Volume 9952, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Contamination control plays an important role in sustaining spacecraft performance. One spacecraft degradation mechanism involves long-term on-orbit molecular outgassing from spacecraft materials. The outgassed molecules may accumulate on thermal control surfaces and/or optics, causing degradation. In this study, we performed outgassing measurements of multiple spacecraft materials, including adhesives, Nylon Velcro, and other assembly materials through a modified ASTM E595 test method. The modified ASTM E595 test had the source and receiver temperature remained at 125°C and 25°C, respectively, but with prolonged outgassing periods of two weeks. The condensable contaminants were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography/Mass Spectrometry (GC/MS) to determine their spectral transmission and chemical composition. The FTIR spectra showed several spacecraft materials, primarily adhesives and potting materials, exhibiting slight absorption from contaminants consisting of hydroxyl groups and carboxylic acids. To gain insight into molecular contaminant transport, simulations were conducted to characterize contaminant accumulation inside a hypothetical space system cavity. The simulation indicated that contaminant molecules bouncing inside the hypothetical payload cavity can lead to deposition on colder surfaces, even though large openings are available to provide venting pathways for escaping to space. The newly established molecular contaminant transport simulation capability holds the promise of providing quantitative guidance for future spacecraft and its venting design.

CTSP (Contamination Transport Simulation Program) is a simulation program for performing detailed molecular and particulate contaminant transport analyses using complex, CAD-generated geometries. CTSP concurrently traces many simulation macroparticles, allowing it to compute contaminant partial pressures. The code uses a detailed surface model that supports multiple trapped gases and a multi-component surface layer. The molecular residence time is computed by considering surface temperature and activation energies. This paper describes the implemented algorithms and demonstrates the code with several test cases. These include outgassing in a vacuum chamber, spacecraft venting, particulate transport in an air flow, and redistribution of paint flakes on an orbiting satellite. The paper is concluded by summarizing the on-going effort to parallelize the code and utilize GPUs, and to add support for electrostatic return modeling by computing space potential using Green's functions.

The notion of percent area coverage (PAC) has been used to characterize surface cleanliness levels in the spacecraft contamination control community. Due to the lack of detailed particle data, PAC has been conventionally calculated by multiplying the particle surface density in predetermined particle size bins by a set of coefficients per MIL-STD-1246C. In deriving the set of coefficients, the surface particle size distribution is assumed to follow a log-normal relation between particle density and particle size, while the cross-sectional area function is given as a combination of regular geometric shapes. For particles with irregular shapes, the cross-sectional area function cannot describe the true particle area and, therefore, may introduce error in the PAC calculation. Other errors may also be introduced by using the lognormal surface particle size distribution function that highly depends on the environmental cleanliness and cleaning process. In this paper, we present PAC measurements from silicon witness wafers that collected fallouts from a fabric material after vibration testing. PAC calculations were performed through analysis of microscope images and compare them to values derived through the MIL-STD-1246C method. Our results showed that the MIL-STD-1246C method does provide a reasonable upper bound to the PAC values determined through image analysis, in particular for PAC values below 0.1.

As a laboratory for scientific research, the International Space Station has been in Low Earth Orbit for over 17 years and is planned to be on-orbit for another 10 years. The ISS has been maintaining a relatively pristine contamination environment for science payloads. Materials outgassing induced contamination is currently the dominant source for sensitive surfaces on ISS and modelling the outgassing rate decay over a 20 to 30 year period is challenging. Using ASTM E 1559 rate data, materials outgassing is described herein as a diffusion-reaction process with the interface playing a key role. The observation of -1/2 (diffusion) or non-integers (reaction limited) as rate decay exponents for common ISS materials indicate classical reaction kinetics is unsatisfactory in modelling materials outgassing. Nonrandomness of reactant concentrations at the interface is the source of this deviation from classical reaction kinetics. A t^-1/2 decay is adopted as the result of the correlation of the contaminant layer thicknesses and composition on returned ISS hardware, the existence of high outgassing silicone exhibiting near diffusion limited decay, the confirmation of nondepleted material after ten years in Low Earth Orbit, and a potential slowdown of long term materials outgassing kinetics due to silicone contaminants at the interface.

Growing evidence was accumulated on the deleterious effects of the photofixation of contaminants on solar arrays power and on the optical properties of coatings. UV irradiation indeed promotes contamination accretion, even on surfaces on which condensation would not occur and strongly degrades the optical properties of contamination layers. Recent research conducted at ONERA enabled to implement a photofixation model in the numerical tool COMOVA. Present work aims at assessing the ability of this model to reproduce in-orbit cases and at estimating the sensitivity of the results to input parameters. Simulation results are reasonably close to the in-orbit degradations.

Molecular contaminants outgassed from organic materials used for the spacecraft degrade the performance of optical surfaces of spacecraft. The influence of contaminants outgassed from epoxy resin on the spectral transmittance of the quartz substrate was investigated with an in-situ measurement system. The system can deposit the contaminants on temperature-controlled quartz substrates and the transmittance spectra were measured immediately after deposition in vacuum ambient. We tried to obtain the optical constants of the contaminant using transmittance spectrum and simple optical models for optical calculations. The optical constants were described with a harmonic oscillator model and the effective medium approximation model. This paper reports the in-situ measurement results of transmittance spectra of the epoxy-resin-induced contaminants. In addition, the result of optical calculations using the obtained optical constants were compared to the measurement results.

Increasingly satellites are carrying on-board bipropellant thrusters, especially for interplanetary missions. Many of these spacecraft are also equipped with surface-sensitive instruments, such as telescopes and detectors, which, due to the required configuration, might be impinged by the bipropellant thruster plumes and therefore contaminated by plume exhaust products. At present, there are no European analysis tools capable of determining the effects of such propulsion systems on surfaces sensitive to contamination in the preliminary design phase. This may result into a need to modify the spacecraft design in a later development phase in order to mitigate contamination effects. The consequences are additional costs, delay on schedule and possible reductions of scientific goals. This paper emphasizes the need for a tool to be used at the preliminary stage of a satellite design to analyse the contamination effects of bipropellant thruster plume impingement on sensitive surfaces. It also describes a possible approach/architecture to be used for this tool.

Traditionally, quantification of non-volatile residue (NVR) on surfaces relevant to space systems has been performed using solvent wipes for NVR removal followed by gravimetric analysis. In this approach the detectable levels of NVR are ultimately determined by the mass sensitivity of the analytical balance employed. Unfortunately, for routine samples, gravimetric measurement requires large sampling areas, on the order of a square foot, in order to clearly distinguish sample and background levels. Diffuse Reflectance Infrared Reflectance Spectroscopy (DRIFTS) is one possible alternative to gravimetric analysis for NVR measurement. DRIFTS is an analytical technique used for the identification and quantification of organic compounds that has two primary advantages relative to gravimetric based methods: increased sensitivity and the ability to identify classes of organic species present. However, the use of DRIFTS is not without drawbacks, most notably repeatability of sample preparation and the additive quantification uncertainty arising from overlapping infrared signatures. This can result in traditional calibration methods greatly overestimating the concentration of species in mixtures. In this work, a partial least squares (PLS) regression model is shown to be an effective method for removing the over prediction error of a three component mixture of common contaminant species.

At the conclusion of cryogenic vacuum testing of the James Webb Space Telescope Optical Telescope Element Integrated Science Instrument Module (JWST-OTIS) in NASA Johnson Space Center’s (JSCs) thermal vacuum (TV) Chamber A, contamination control (CC) engineers are postulating that chamber particulate material stirred up by the repressurization process may be kept from falling into the Integrated Science Instrument Module (ISIM) interior to some degree by activating instrument purge flows over some initial period before opening the chamber valves. This manuscript describes development of a series of models designed to describe this process. The models are strung together in tandem with a fictitious set of conditions to estimate overpressure evolution from which net outflow velocity behavior may be obtained. Creeping flow assumptions are then used to determine the maximum particle size that may be kept suspended above the ISIM aperture, keeping smaller particles from settling within the instrument module.

As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground based space applications, in particular, for vacuum chamber environments. This paper describes the recent use of the MAC technology during Pathfinder testing of the Optical Ground Support Equipment (OGSE) for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap persistent outgassed contaminants, specifically silicone based diffusion pump oil, from within JSC’s cryogenic optical vacuum chamber test facility called Chamber A. This paper summarizes the sample fabrication, installation, laboratory testing, post-test chemical analysis results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.

The Molecular Adsorber Coating (MAC) is a zeolite based highly porous coating technology that was developed by NASA Goddard Space Flight Center (GSFC) to capture outgassed contaminants, such as plastics, adhesives, lubricants, silicones, epoxies, potting compounds, and other similar materials. This paper describes the use of the MAC technology to address molecular contamination concerns on NASA’s Ionospheric Connection Explorer (ICON) program led by the University of California (UC) Berkeley’s Space Sciences Laboratory. The sprayable paint technology was applied onto plates that were installed within the instrument cavity of ICON’s Far Ultraviolet Imaging Spectrograph (FUV). However, due to the instrument’s particulate sensitivity, the coating surface was vibrationally cleaned through simulated acoustics to reduce the risk of particle fall-out contamination. This paper summarizes the coating application efforts on the FUV adsorber plates, the simulated laboratory acoustic level cleaning test methods, particulation characteristics, and future plans for the MAC technology.

Mass spectrometers are valuable tools for the in situ characterization of gaseous exo- and atmospheres and have been operated at various bodies in space. Typical measurements derive the elemental composition, relative abundances, and isotopic ratios of the examined environment. To sample tenuous gas environments around comets, icy moons, and the exosphere of Mercury, efficient instrument designs with high sensitivity are mandatory while the contamination by the spacecraft and the sensor itself should be kept as low as possible. With the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), designed to characterize the coma of comet 67P/Churyumov-Gerasimenko, we were able to quantify the effects of spacecraft contamination on such measurements. By means of 3D computational modeling of a helium leak in the thruster pressurization tubing that was detected during the cruise phase we examine the physics involved leading to the measurements of contamination. 3 types of contamination can be distinguished: i) Compounds from the decomposition of the spacecraft material. ii) Contamination from thruster firing during maneuvers. iii) Adsorption and desorption of the sampled environment on and from the spacecraft. We show that even after more than ten years in space the effects of i) are still detectable by ROSINA and impose an important constraint on the lower limit of gas number densities one can examine by means of mass spectrometry. Effects from ii) act on much shorter time scales and can be avoided or minimized by proper mission planning and data analysis afterwards. iii) is the most difficult effect to quantify as it changes over time and finally carries the fingerprint of the sampled environment which makes prior calibration not possible.

In-Situ Resource Utilization (ISRU) is a key NASA initiative to exploit resources at the site of planetary exploration for mission-critical consumables, propellants, and other supplies. The Resource Prospector mission, part of ISRU, is scheduled to launch in 2020 and will include a rover and lander hosting the Regolith and Environment Science and Oxygen and Lunar Volatile Extraction (RESOLVE) payload for extracting and analyzing lunar resources, particularly low molecular weight volatiles for fuel, air, and water. RESOLVE contains the Lunar Advanced Volatile Analysis (LAVA) subsystem with a Gas Chromatograph-Mass Spectrometer (GC-MS). RESOLVE subsystems, including the RP15 rover and LAVA, are in NASA’s Engineering Test Unit (ETU) phase to assure that all vital components of the payload are space-flight rated and will perform as expected during the mission. Integration and testing of LAVA mass spectrometry verified reproducibility and accuracy of the candidate MS for detecting nitrogen, oxygen, and carbon dioxide. The RP15 testing comprised volatile analysis of water-doped simulant regolith to enhance integration of the RESOLVE payload with the rover. Multiple tests show the efficacy of the GC to detect 2% and 5% water-doped samples.

We demonstrate that acoustic field-induced forces (FIF) can detach, trap, and translate particles with no physical contact. This technology thereby shows potential for cleaning optical surfaces without introducing damage to the surface as well as allowing for scale-up to cover large areas where an atmosphere exists such as prior to launch. Experiments relying on acoustic fields created a force field landscape in the region between a transducer and the contaminated glass surface. That force field was then responsible for removing dust particles, trapping them, and translating them to a repository site. We have established proof-of-principle through experiments that removed both well-controlled particles with a narrow diameter distribution, as well as Arizona road dust, with a wide diameter distribution from a glass surface.

Mars Organic Molecule Analyzer (MOMA) is an instrument suite on the European Space Agency (ESA) ExoMars 2020 Rover, and the Mass Spectrometer (MOMA-MS) is being built at Goddard Space Flight Center (GSFC). MOMA-MS is a life-detection instrument and thus falls in the most stringent category of Planetary Protection (PP) biological cleanliness requirements. Less than 0.03 spore/m2 are allowed in the instrument sample path. In order to meet these PP requirements, MOMA-MS must be built and maintained in a low bioburden environment. The MOMA-MS project at GSFC maintains three clean rooms with varying levels of bioburden control. The Aseptic Assembly Clean room has the highest level of control, applying three different bioburden reducing methods: 70% Isopropyl Alcohol (IPA), 7.5% Hydrogen Peroxide, and Ultra-Violet C (UVC) light. The three methods are used in rotation and each kills microorganisms by a different mechanism, reducing the likelihood of microorganisms developing resistance to all three. The Integration and Mars Chamber Clean rooms use less biocidal cleaning, with the option to deploy extra techniques as necessary. To support the monitoring of clean rooms and verification that MOMA-MS hardware meets PP requirements, a new Planetary Protection lab was established that currently has the capabilities of standard growth assays for spore or vegetative bacteria, rapid bioburden analysis that detects Adenosine Triphosphate (ATP), plus autoclave and Dry Heat microbial Reduction (DHMR) verification. The clean rooms are monitored for vegetative microorganisms and by rapid ATP assay, and a clear difference in bioburden is observed between the aseptic and other clean room.

Optical instruments for space applications with improved performances (smaller pixels and spectral range extension) are becoming more and more sensitive to chemical contamination and particle sedimentation. Outgassing under vacuum conditions causes dramatic flux losses, especially in the UV bandwidth. Furthermore, it is difficult to perform physicochemical analyses of contaminated surfaces on flight models, in a clean room. Conventional analytical techniques such as FTIR (Fourier Transform Infrared interferometer) need the tool to be in contact with the studied area, which is forbidden when working on satellites. In addition, it does not give any information about the distribution of the contaminants in the field of view. The probed area is large, mono-pixel, and the sensitivity of the instrument is too low for hundred nanometer thin film deposits. A first study has shown that we could benefit from using the UV/visible fluorescence spectra to partially identify contaminants and polymer materials. The shape of the fluorescence spectra of adhesives, paints and varnishes have specific signatures that could be recorded into a designated reference database. The location of the presence of these contaminants on such sensitive optics is also relevant. To acquire both these parameters, we designed a specific compact hyperspectral instrument to remotely acquire cube images (500x500 pixels) in a 5 degree field of view, and on a wide range of continuous wavelengths from UV at 320 nm up to the near infrared at 1000 nm. This paper will present the chosen trade-off between different critical optics for a new portable version of this instrument. It is dedicated to space and cultural heritage applications and the first results on an engineering prototype will be shown.

Outgassing rate measurement, or dynamic outgassing test, is used to obtain outgassing properties of materials, i.e., Total Mass Loss, “TML,” and Collected Volatile Condensed Mass, “CVCM.” The properties are used as input parameters for executing contamination analysis, e.g., calculating a prediction of deposition mass on a surface in a spacecraft caused by outgassed substances from contaminant sources onboard. It is likely that results obtained by such calculations are affected by the input parameters. Thus, it is important to get a sufficient experimental data set of outgassing rate measurements for extract good outgassing parameters of materials for calculation. As specified in the standard, ASTM E 1559, TML is measured by a QCM sensor kept at cryogenic temperature; CVCMs are measured at certain temperatures. In the present work, the authors propose a new experimental procedure to obtain more precise VCMs from one run of the current test time with the present equipment. That is, two of four CQCMs in the equipment control the temperature to cool step-by-step during the test run. It is expected that the deposition rate, that is sticking coefficient, with respect to temperature could be discovered. As a result, the sticking coefficient can be obtained directly between -50 and 50 degrees C with 5 degrees C step. It looks like the method could be used as an improved procedure for outgassing rate measurement. The present experiment also specified some issues of the new procedure. It will be considered in future work.

Recently a real time particle deposition monitoring system is developed. After discussions with optical system engineers a new feature has been added. This enables the real time monitoring of obscuration of exposed optical components by counting the deposited particles and sizing the obscuration area of each particle. This way the Particle Obscuration Rate (POR) can be determined. The POR can be used to determine the risk of product contamination during exposure. The particle size distribution gives information on the type of potential particle sources. The deposition moments will indicate when these sources were present.

The laser induced damage is a troublesome issue in the application of optical mirrors, which is related to the robustness of the whole laser system. There are two types of mechanisms about the damage of optical mirrors: thermal effect and field effect, which are responsible for the high energy continuous wave (cw) laser induced damage and the high power pulsed laser induced damage, respectively. Under the irradiation of high energy laser, the contaminant on the mirror surface absorbs the laser energy and converts the laser energy to heat. With the heat accumulating, the optical mirror is likely to fuse and even be totally destroyed. The temperature of the contaminant was measured when it was irradiated by a cw high energy laser with power intensity 3.3kW/cm². It is found that the contaminant achieves thermal equilibrium in a few seconds and then the temperature stays at ~1700K. A physical model was established to describe the process of the thermal equilibrium. The influence of the contaminant size on the thermal damage of the optical mirror was studied theoretically. The results show that the contaminant size plays an important role in the thermal damage of the optical mirror. Only when the contaminant size is smaller than a critical size (~10μm), the contaminant may reach thermal equilibrium and the optical mirror works well in the high energy laser system. If the contaminant size is quite large (<~100μm), the optical mirror will damage under the irradiation of high energy laser.

Laser-induced contamination (LIC) is still a major risk for space based laser systems. In this paper the mitigation of LIC by oxygen is investigated. Tests were performed with a pulsed laser at 355 nm. The partial pressure of the contamination material was in the range of 10^-5 -10^-4 mbar. The mitigation effect showed a threshold behavior concerning the ratio between contamination and oxygen pressure. Also a cleaning effect was successfully demonstrated: previously created depositions were completely removed by irradiation at several tens Pa oxygen pressure without any remaining degradation of the optical surface.

We have focused on photocatalytic materials to solve contamination problem for spacecraft. We have fabricated TiO₂ thin films and measured decomposition rates of methyl orange (MO) and dioctyl phthalate (DOP) in vacuum by TiO₂ thin films as a photocatalyst. From XRD results, fabricated TiO2 thin films have anatase-type crystal structure, which is known to have stronger decomposition activities than rutile-type TiO₂. The TiO₂ thin films we made were shown to decompose methylene blue (MB) solution, which means that the TiO₂ thin films have general photocatalystic activity in atmosphere. In decomposition of MO in atmosphere and vacuum, TiO₂ shows photocatalytic activity even in vacuum although the decomposition rate in vacuum is slower than that in atmosphere. In decomposition of DOP in vacuum, DOP was effused from an effusion cell in vacuum chamber and was deposited on a TiO₂ thin film using the in-situ measurement apparatus at Tsukuba Space Center, JAXA. Transmission spectra of DOP on TiO₂ thin films after UV irradiation were measured to estimate decomposition rate from absorbance of DOP. The results show that TiO₂ thin films can decompose DOP even in vacuum. Moreover, H₂O can promote the decomposition of DOP. In order to use photocatalyst materials in vacuum for long time, the studies on the durability of photocatalystic activity of TiO₂ in vacuum and the effects of O₂ and H₂O are necessary in the future.