This PDF file contains the front matter associated with SPIE Proceedings Volume 9196 including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

The paper will discuss recent work at ASTM and IEST to update existing standards and introduce new standards. Committee work on standards of interest to contamination control engineers will be discussed. IEST-STD-CC1246E was released in the last year, and changes from revision D will be highlighted. A new ASTM Standard Practice for Spacecraft Hardware Thermal Vacuum Bakeout will also be emphasized.

Tenacious adhesion of dust to surfaces in the vacuum environment of space is a significant obstacle to exploration and scientific discovery on the Moon, Mars and asteroids. Mitigating particle adhesion is also costly and difficult during semiconductor or optics processing on earth. Over the last eight years at Ball Aerospace and Technologies Corp (BATC), we have demonstrated the effectiveness of an ion beam process that dramatically reduces the adhesion of lunar simulant dust to quartz, glass, Kapton, Teflon and silicon surfaces in dry, ambient, and vacuum environments. Treated silvercoated Teflon coupons performed well in a space-simulated environment at NASA Glenn Research Center. Surface roughening on an Ångstrom-level scale was found to correlate well with reduced adhesion, as did contact angle hysteresis. The large difference in advancing and receding contact angles reflects topological and/or chemical heterogeneity. Differences in contact charging are not believed to be major players in dust adhesion reduction. The physical basis of the dust mitigating properties of these modified surfaces is believed to be substantially due to nanometer scale differences between treated and virgin surfaces. Lastly, because this process does not add material, unlike a lotus-like coating or the work function matching coating, nor does it require power like the electrodynamic screen, it is particularly attractive for optical or thermal control materials that cannot tolerate coatings or where power is not available.

Particle counts on tape lift samples taken from a hardware surface exceeded threshold requirements in six successive tests despite repeated cleaning of the surface. Subsequent analysis of the particle size distributions of the failed tests revealed that the handling and processing of the tape lift samples may have played a role in the test failures. In order to explore plausible causes for the observed size distribution anomalies, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were employed to perform chemical analysis on collected particulates. SEM/EDX identified Na and S containing particles on the hardware samples in a size range identified as being responsible for the test failures. ToF-SIMS was employed to further examine the Na and S containing particulates and identified the molecular signature of sodium alkylbenzene sulfonates, a common surfactant used in industrial detergent. The root cause investigation suggests that the tape lift test failures originated from detergent residue left behind on the glass slides used to mount and transport the tape following sampling and not from the hardware surface.

JAXA is developing a contamination analysis tool “J-SPICE” (Japanese Spacecraft Induced Contamination analysis software). Generally speaking, contamination analysis tools predict based on various input data and mathematical models of contaminant behavior, which means prediction accuracy depends on the validity of mathematical models as well as of input data. We investigated the validity of a diffuse reflection model applied in J-SPICE by comparing the reflection flux of contaminant molecules measured by the ground experiment and the analytical result of the J-SPICE. The result showed that the diffuse reflection model of J-SPICE reasonably explains molecule distribution reflected by a flat surface.

In this paper, we report on an experimental and numerical effort to characterize removal and infiltration of atmospheric water vapor into a cavity purged with dry GN2. Multiple miniature sensors were used to track humidity and pressure inside a cylindrical enclosure with internal obstruction and a secondary volume. These measurements were compared against the well-known model of Scialdone. Although our data indicate a similar exponential-like decay, the t parameters differed from the predicted values. In addition, a numerical model was developed to study the purge and infiltration problem in more detail. The model utilizes an Advection-Diffusion solver for the contaminant species, and an incompressible Navier-Stokes solver for the flow velocity. Comparison of preliminary numerical results with the experimental data is presented.

Polydimethylsiloxane damping fluids used for structural deployment mechanisms are not required to be low outgassing. During normal use, these damping fluids are typically encapsulated; however, an unintentional leak may occur which would cause an undesirable contamination at the leak point and form volatile condensable that could reach contamination-sensitive surfaces, degrading the performance of satellites. The collected volatile condensable material (CVCM) at 25 °C from ASTM E595 of a damping fluid, MeSi-300K, was < 0.10%, when the damping fluid was maintained at 125 °C for 24 hours under 10^-6 Torr vacuum. MeSi-300K viscosity is 300,000 cSt, which indicates an average molecular weight (MW) of 204,000. This large MW polymer would contain about 2,756 dimethyl siloxane (DMS) units in the chain. These long chains are not expected to be volatile; however, during manufacture, linear chains and cyclic compounds of a smaller number of DMS units produced are volatile. Gas chromatography mass spectrometry (GC-MS) was used to identify the CVCM. Characterization of these materials revealed that the CVCM contained higher MW siloxanes, straight chain and cyclic, in the range of 682 to 1196 (9 to 16 DMS units), whereas CVCM from spacequalified, silicone-based materials have lower MW, 222 to 542 (3 to 7 DMS units). Consequently, contamination from MeSi-300K material would produce greater amounts of higher-MW siloxanes than space-qualified silicones. These higher-MW species would be harder to remove by evaporation and could remain on sensitive surfaces.

We present a finite element model for the prediction of molecular contamination through narrow pathways in a hypothetical spaceborne instrument using the commercially available COMSOL Multiphysics software. The free molecular flow module of COMSOL uses the angular coefficient method as an alternative to particle based methods. In the angular coefficient method, the microscopic dynamical aspect of the material transport problem is reduced to a macroscopic problem by calculating emission and incident fluxes at each surface rather than the trajectories of individual molecules. The model was validated by comparing the simulated and experimentally measured pressure differential between two chambers separated by a mechanical test structure. The mechanical test structure was designed to exhibit narrow pathways with characteristic size that can be found on spaceborne optomechanical structures. It is shown that materials can slowly migrate through these pathways in a spaceborne instrument to cause noticeable performance degradation within a time scale of a few months. The model for material transport through the test structure was also verified using a stochastic method. To simulate water infiltration through narrow pathways of a hypothetical spaceborne instrument, nominal payload temperature profile was used in addition to setting empirical input parameters such as the desorption energy of water and the outgassing rate of water from multilayer insulator thermal blankets to the appropriate surfaces in the modeling domain. The rate of growth of ice films on low temperature optical components and how optical performance can be degraded over time are discussed in this paper.

Outgassing rate measurements are basically performed for fresh materials, e.g. just cured adhesives, paints, etc. and reveal a lot about how the material can behave as a contamination source. It is also important to determine the bakeout process sufficiently. In the present study, a typical silicone adhesive for use in space, RTV S-691, Wacker Chemie, was selected for the measurement. Two cured specimens, 40 × 40 mm in size, were applied for several isothermal tests under identical conditions: a specimen at 125 degrees C for 144 hours with CQCM at -193 degrees C to measure TML. Consequently, it was determined that the TML and TML rate could be reduced by bakeout as expected. It also emerged that a longer bakeout, i.e. a longer cumulative bakeout time, for the material would reduce the TML and TML rate more effectively. The results suggest that bakeout mainly affects the behavior in the “low-rate” phase, whereby the TML rate curve can be divided into two phases. The elapsed time for a specimen can also be considered the cumulative test time. Based on the cumulative elapsed time, the TML rate curve is replotted and a correlation emerges between the cumulative bakeout time and TML rate. The first measurement data of TML and the TML rate could be affected by the stored time from cure, which might result from the change in unreacted substances declining as the stored time elapsed.

The in-orbit aging of thermo-optical properties of thermal coatings critically impacts both spacecraft thermal balance and heating power consumption. Nevertheless, in-flight thermal coating aging is generally larger than the one measured on ground and the current knowledge does not allow making reliable predictions¹. As a result, a large oversizing of thermal control systems is required. To address this issue, the Centre National d’Etudes Spatiales has developed a low-cost experiment, called THERME, which enables to monitor the in-flight time-evolution of the solar absorptivity of a large variety of coatings, including commonly used coatings and new materials by measuring their temperature. This experiment has been carried out on sunsynchronous spacecrafts for more than 27 years, allowing thus the generation of a very large set of telemetry measurements. The aim of this work was to develop a model able to semi-quantitatively reproduce these data with a restraint number of parameters. The underlying objectives were to better understand the contribution of the different involved phenomena and, later on, to predict the thermal coating aging at end of life. The physical processes modeled include contamination deposition, UV aging of both contamination layers and intrinsic material and atomic oxygen erosion. Efforts were particularly focused on the satellite leading wall as this face is exposed to the highest variations in environmental conditions during the solar cycle. The non-monotonous time-evolution of the solar absorptivity of thermal coatings is shown to be due to a succession of contamination and contaminant erosion by atomic oxygen phased with the solar cycle.

On October 28, 2011, the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite launched at Vandenberg Air Force base aboard a United Launch Alliance Delta II rocket. Included among the five instruments was the Ozone Mapping and Profiler Suite (OMPS), an advanced suite of three hyperspectral instruments built by Ball Aerospace and Technologies Corporation (BATC) for the NASA Goddard Space Flight Center. Molecular transport modeling is used to predict optical throughput changes due to contaminant accumulation to ensure performance margin to End Of Life. The OMPS Nadir Profiler, operating at the lowest wavelengths of 250 – 310 nm, is most sensitive to contaminant accumulation. Geometry, thermal profile and material properties must be accurately modeled in order to have confidence in the results, yet it is well known that the complex chemistry and process dependent variability of aerospace materials presents a substantial challenge to the modeler. Assumptions about the absorption coefficients, desorption and diffusion kinetics of outgassing species from polymeric materials dramatically affect the model predictions, yet it is rare indeed that on-mission data is analyzed at a later date as a means to compare with modeling results. Optical throughput measurements for the Ozone and Mapping Profiler Suite on the Suomi NPP Satellite indicate that optical throughput degradation between day 145 and day 858 is less than 0.5%. We will show how assumptions about outgassing rates and desorption energies, in particular, dramatically affect the modeled optical throughput and what assumptions represent the on-orbit data.

The susceptibility of spacecraft materials to HCl exposure was investigated in light of concerns to potential contamination during evolved expendable launch vehicle (EELV) overflight scenarios. Overflight refers to the circumstance where one spacecraft, resident on a launch pad, may be exposed to HCl generated from an earlier solid rocket launch at an adjacent pad. One aspect of the overflight risk assessments involves spacecraft materials susceptibility to HCl exposure. This study examined a wide range of spacecraft materials after being exposed to HCl vapor in a well-characterized facility. Sample thermal/optical and electrostatic dissipation properties, as well as surface chemical and morphological features, were characterized before and after the HCl exposure. All materials tested, except for indium tin oxide (ITO) coated Kapton film, showed no significant degradation after HCl exposure of up to 4800 ppb-hr. The ITO coated Kapton sample showed slight signs of degradation after being exposed to 500 ppb-hr HCl, as the surface resistance was increased by a factor of 5. However, the potential HCl dose inside the payload fairing (PLF) was estimated to be far below 500 ppb-hr in an EELV overflight event. These results, along with other relevant laboratory test data on the HCl removal efficiency of the filtration media used on the launch sites, provide the technical rationale that properly filtered air as the PLF purge should pose little risk in terms of HCl contamination under EELV overflight scenarios.

The molecular adsorber coating is a new technology that was developed to mitigate the risk of on-orbit molecular contamination on spaceflight missions. The application of this coating would be ideal near highly sensitive, interior surfaces and instruments that are negatively impacted by outgassed molecules from materials, such as plastics, adhesives, lubricants, epoxies, and other similar compounds. This current, sprayable paint technology is comprised of inorganic white materials made from highly porous zeolite. In addition to good adhesion performance, thermal stability, and adsorptive capability, the molecular adsorber coating offers favorable thermal control characteristics. However, low reflectivity properties, which are typically offered by black thermal control coatings, are desired for some spaceflight applications. For example, black coatings are used on interior surfaces, in particular, on instrument baffles for optical stray light control. Similarly, they are also used within light paths between optical systems, such as telescopes, to absorb light. Recent efforts have been made to transform the white molecular adsorber coating into a black coating with similar adsorptive properties. This result is achieved by optimizing the current formulation with black pigments, while still maintaining its adsorption capability for outgassing control. Different binder to pigment ratios, coating thicknesses, and spray application techniques were explored to develop a black version of the molecular adsorber coating. During the development process, coating performance and adsorption characteristics were studied. The preliminary work performed on black molecular adsorber coatings thus far is very promising. Continued development and testing is necessary for its use on future contamination sensitive spaceflight missions.

It is well know that the elevated satellite operating temperature causes the unused catalyst material in the Room Temperature Vulcanized materials (RTV) to volatize, which can then re-deposit or condense onto other spacecraft surfaces. In the presence of sunlight, this Volatile Condensable Material (VCM) can photo-chemically deposit onto optically-sensitive spacecraft surfaces and significantly alter their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended performance loss of the spacecraft. This has been studied in vacuum environments simulating geosynchronous orbits, but never to our knowledge in atomic oxygen environments simulating low earth orbit. In this work we present an initial study of the effect of an atomic oxygen environment on the optical properties of previously photofixed material as well the effect of an atomic oxygen environment on the photofixing process. We will employ spectroscopic ellipsometry to characterize films deposited from the outgassing of DC93500, RTV566, SCV2590, CV2568 and SCV2590-2.

Molecular contamination by outgassing can degrade the performance of optical components. In orbit, spacecraft are exposed to various environments. UV is one of the most critical. It may also have the potential to cut the chains of organic molecules in contaminants due to its high energy, degrading optical properties and even re-emission behavior. In the present study, using two kinds of UV sources with different wavelength ranges, we compare the effect of UV lights irradiated on an optical surface with silicone contaminants. The irradiated samples were evaluated in terms of their optical properties and re-emission behavior, i.e. transmittance, and thermal desorption.

The derivation of contamination control (CC) requirements for the JWST Optical Telescope Element (OTE) was presented at the SPIE conference in 20081. Since then, much work has been done to allocate contamination at each phase of Integration and Test (IandT) and to plan for achieving the allocations. Because JWST is such a large and complicated observatory, plans for meeting the requirements are many and varied. There are primary mirror segments that must be cleaned early and maintained clean; there are four science instruments that each have tight contamination requirements but cannot be cleaned after they are integrated onto the Integrated Science Instrument Module (ISIM) structure; there is the composite ISIM structure that is fragile and must be minimally handled; there are numerous cryo-vacuum tests that must be controlled and monitored in order to minimize molecular contamination during return to ambient; … and more. An overview of plans developed to implement contamination control for JWST optics, instruments, and thermal vacuum testing for JWST will be presented.

This paper will continue from Part 1 of JWST contamination control implementation. In addition to optics, instruments, and thermal vacuum testing, JWST also requires contamination control for a spacecraft that must be vented carefully in order to maintain solar array and thermal radiator thermal properties; a tennis court-sized sunshield made with 1-2 mil Kapton™ layers that must be manufactured and maintained clean; an observatory that must be integrated, stowed and transported to South America; and a rocket that typically launches commercial payloads without contamination sensitivity. An overview of plans developed to implement contamination control for the JWST spacecraft, sunshield, observatory and launch vehicle will be presented.