The Midcourse Space Experiment (MSX) satellite was launched on April 24, 1996. This paper provides an update of the quartz crystal microbalance (QCM) data accumulated over these last four years in space. The MSX is the only known experiment that has provided continuous contamination monitoring for such an extended length of time. The five QCMs on board the satellite have provided on-orbit data that have been invaluable in characterizing contamination levels around the spacecraft and inside the cryogenic Spatial Infrared Imaging Telescope (SPIRIT 3). One of the QCMs, the cryogenic QCM (CQCM), located internal to SPIRIT 3, was mounted adjacent to the primary mirror and provided contamination accretion measurements during the 10-month lifetime of SPIRIT 3. Real- time monitoring of contaminant mass deposition on the primary mirror was provided by this CQCM which was cooled to the same temperature as the mirror - approximately 20K. Thermogravimetric analyses (TGAs) on the CQCM provided insight into the amount and species of contaminants condensed on the SPIRIT 3 primary mirror during various spacecraft activities. The four temperature-controlled QCMs (TQCMs) were mounted on external surfaces of the spacecraft for monitoring spacecraft contamination deposition. The TQCMs operated at approximately -50$DEGC and were positioned strategically to monitor the silicone and organic contaminant flux arriving at specific locations. Updated time histories of contaminant thickness deposition for each of the QCMs are presented. Gradual contaminant thickness increase was observed during the first year in space. During the second year, the QCM frequencies (contaminant film thickness) began to decrease, with the time of onset depending on QCM location. Possible explanationsfor this interesting behavior are discussed.

Outgassing experiments in space were conducted during the critical period in the cryogen lifetime of the large infrared telescope called Spatial Infrared Imager and Telescope (SPIRIT III) on the Midcourse Space Experiment (MSX) spacecraft. This was the period when the solid hydrogen in the dewar was being depleted and the optical components were warming up to evaporate previously condensed volatile materials. The volatile condensable materials were collected on the cryogenically cooled surfaces during the 4 months of prelaunch testing and the 10 months in orbit. The contamination instruments on board the spacecraft were used to monitor the outgassing of these materials. Besides contamination monitoring, it was also desired to control the heating or warm-up process without contaminating the still functioning UV and visible sensors. After considering several scenarios via thermal modeling, it was decided to conduct the warm-up period into two phases, with the first phase intended to approach but not exceed the sublimation point of ice on the primary mirror. Solar radiation was used to heat the SPIRIT III baffle and parts of the +Y face of the spacecraft while the contamination instruments were monitored the outgassing event. Ice redistribution from the baffle to the much colder primary mirror, as well as external pressure bursts and slight film depositions on quartz crystal microbalances were observed. The second phase of warm-up experiments again used solar heating to drive the telescope optics through the 150 K range for final sublimation of any ice remaining as well as condensed hydrocarbons from the cold primary mirror. The results of these end-of-cryo experiments are discussed in terms of the measured film deposits on the cryogenic quartz crystal microbalance and the pressures from the total pressure sensor.

We present a summary of the particle environment surrounding the Midcourse Space Experiment (MSX) satellite after 32 months on orbit, including two discrete particle releases produced by micrometeoroid or debris impact. We report on the characteristics of that environment, including particle occurrence rates, velocities, size distributions and trends in the environment. To our knowledge, the long term particle contamination observations that we have made on MSX are the first of their kind. The particle occurrence rate decreased steadily during the first year on orbit, but then remained at a constant level after 32 months on orbit. Our estimate of the total number of particles on the spacecraft surfaces at launch. We conclude that environmental effects such as UV, radiation, thermal cycling, and micrometeoroid impacts are a significant and continuing source of particles on orbit.

The Midcourse Space Experiment (MSX) spacecraft was specifically designed and processed to minimize contamination. This spacecraft represents a best case scenario of spacecraft induced environment. The contamination instrument suite consisted of 10 sensors for monitoring the gaseous and particulate environment. The Total Pressure Sensor (TPS) has continuously measured the ambient local pressure surrounding MSX since its launch on April 24, 1996. The sensor's primary goal was to monitor the early mission (less than one week) ambient pressure surrounding the spacecraft's optical telescopes and to indicate when environmental conditions were acceptable for opening the protective covers. However, the instrument has illustrated that it is quite robust and has successfully measured the long-term decay of the pressure environment. The primary constituent of the atmosphere is water outgassed from the thermal blankets of the spacecraft. The water-induced environment was expected to rapidly decay over the first few months to levels more closely approaching the natural environment. The data generally shows decay toward this level, however, the pressure is quite variable with time and can be influenced by discrete illumination and spacecraft orbital events. Several experiments conducted yearly indicate that the thermal blankets retain significant quantities of water. The local pressure due to water vapor is shown to increase by a factor of 100 from direct solar illumination. Moreover, the multi-layer construction of the blankets causes them to form a deep reservoir that continues to be a source of water vapor 3+ years into the mission. We will present pressure data from several experiments, each separated by one orbital year, that exhibit these water vapor induced pressure busts. The decay and longevity of these bursts will also be discussed.

A solar panel with more than ten years space exposure was returned to Earth in January 1998. Several types of residues were deposited or transported onto the solar cell coverglasses during the space exposure. Self-contamination of SiO_x films from the silicone potting compound was a major contamination of the coverglasses. A second type of contamination was thick, detergent-like residues of the order of a millimeter diameter on many, but not most of the coverglasses. A third, prevalent type of contamination was very thin irregular shaped films or patterns of a millimeter size which are readily visible in brilliant colors when the coverglasses are viewed with a 50x brightfield microscope. These prolific, overlapping, and almost ubiquitous patterns strongly suggest wetting on the surface. The probably cause of most of the wetted patterns on the returned Mir solar cell coverglasses is trace hydrazine nitrate in condensed water droplets produced as reaction products from Mir's and the Orbiters' hypergolic thrusters. This paper presents some of the wetted patterns, information regarding hypergolic reaction products, and type of thrusters associated with Mir operations.

A solar panel with more than ten years space exposure was returned to Earth in January 1998. Methy-phenyl silicone was used for both the adhesive between the coverglasses and silicon wafer, and for the potting compound between individual solar cells. Glass fiber scrim was used for structural integrity of the panel. Atomic oxygen in low-Earth-orbit interacted with the exposed silicone and converted the outermost layer (several microns thick) to oxidized silicon, i.e. SiO_x, where x~2. This brittle SiO_x served to protect underlying silicone from oxidation, unless the film was removed by some means. There is much evidence of microeruptions within the potting compound and spewing of silicone and SiO_x film debris across the solar cell coverglasses. Ten of 409 solar cells of a returned panel have been scanned with a 50x brightfield microscope. This paper presents measurements of millimeter size SiO_x particles and, glass fibers on the returned solar cell coverglasses. Erosion of the potting compound is also discussed.

A series of external contamination measurement were made on the Russian Mir Space Station. The Mir external contamination observations summarized in this paper were essential in assessing the potential system level impact of Russian Segment induced external contamination onto the Internal Space Station (ISS). Mir contamination observations include results from a series of flight experiments: CNES (Centre National d'Etudes Spatiales) Comes-Aragatz, retrieved NASA camera bracket, EuroMir '95 ICA (Instrument Comrade Active), and the Russian Astra-II. Results from these experiments were studied in detail to characterize the Mir induced contamination. In conjunction with Mir contamination observations, Russian materials samples were delivered to the U.S. for condensable outgassing rate testing. These test results were essential in the identification and characterization of Mir contamination sources. Once Mir contamination sources were identified and characterized, activities to assess the implications to ISS were implemented. As a result of these efforts, and in conjunction and collaboration with scientists at RSC-Energia in Russia, modifications in Russian materials selection and usage were implemented to control induced external contamination and mitigate risk to ISS.

Manu U.S. government standards are being replaced with nongovernmental standards, both national and international. The use of international standards is increasing as the levels of international trade increase. Contamination control is critical for many industries and has resulted in greater numbers of national and international standards on this subject with more standards in development. Some standards relate to specific industries, and others are applicable to many industries. This paper review the status of the U.S., European, and ISO (International Organization for Standardization) that are of interest to optical systems, especially those related to space systems.. Items taht are discussed include the following: The revision to MIL-STD-1246 (Product Cleanliness Levels and Contamination Control Program) will be published by the IEST (Institute of Environmental Sciences and Technology) as a nongovernmental standard; ISO 14644-1 and 14644-2 will replace FED-STD-209 (Airborne Particle Cleanliness Classes in Cleanroom and Clean Zones); ISO 15388 (Space Systems - Contamination and cleanliness Control) is under development; IEST-RP-CC016 (The Rate of Deposition of Nonvolatile Residue in Cleanrooms) is now being revised; ASTM E 595 (outgassing screening test) is used internationally; the ASTM E 1559 outgassing test has been revised; and ASTM E 490 (Standard Solar Constant and Zero Air Mass Solar Spectral Irradiance Tables) has been revised. Other standards from ASTM, IEST, ECSS (European Cooperation for Space Standardization), and ISO are discussed. Lists of standards, points of contact, and information available on the Internet are included.

An inflatable structural system to deploy a space system such as a solar shield, an antenna or another similar instrument, requires a stiffening element after it is extended by the inflated gas pressure. The stiffening element has to be packaged in a folded configuration before the deployment. It must be relatively small, lightweight, non-damaging to the inflated system, and be able to become stiff in a short time. One stiffening method is to use a flexible material inserted in the deployable system, which, upon a temperature curing, can become stiff and is capable of supporting the entire structure. There are two conditions during the space operations when the inflated volume could be damaged: during the transonic region of the launch phase and when the curing of the rigidizing element occurs. In both cases, an excess of pressure within the volume containing the rigid element could burst the walls of the low-pressure gas inflated portion of the system. This paper investigates these two conditions and indicates the vents, which will prevent those damaging overpressures. Vent openings at the non-inflated volumes have been calculated for the conditions existing during the launch. Those vents allow the initially folded volume to exhaust the trapped atmospheric gas at approximately the same rate as the ambient pressure drops. That will prevent pressure gradients across the container walls which otherwise could be as high as 14.7 psi. The other condition occurring during the curling of the stiffening element has been investigated. This has required the testing of the element to obtain the gas generation during the curing and the transformation from a pliable material to a rigid one. The tested material is a composite graphite/epoxy weave. The outgassing of the uncured sample at 121$DEGC was carried with the Cahn Microbalance and with other outgassing facilities, including the micro-CVCM ASTM E-595 facility. The tests provided the mass of gas evolved during the test. That data, including the chemical nature of the evoloved gas, provided the data for the calculation of the pressure produced within the volume. The evaluation of the areas of the vents that would prevent excessive pressures and provide a rapid release of the gas away from contamination sensitive surfaces has been carried out. The pressure decay with time has been indicated.

Cleaning large optics with carbon dioxide snowflakes is a process that has achieved general acceptance as a maintenance technique at astronomical observatories over the past decade. The technique is slowly spreading into the general optics community where smaller optics need to be cleaned, but removal and washing of precisely positioned, or deeply embedded, optics is time consuming and impractical. One obstacle preventing the more widespread use of CO₂ snow cleaning has been the fact that the more inexpensive lower grades of liquid CO₂, the source material used to produce the snowflakes, are often contaminated with oil. The origin of this oil is believe to be the lubricant used in the compressor that liquefies the CO₂ gas. Since liquid CO₂ is an excellent solvent for oil, the contaminants eventually turn up in the liquid. Recent development of an inexpensive zeolite based filtering system, allows removal of oil contaminants with nearly 100% efficiency. The data presented in this report show the result of decontamination experiments for a variety of oil components. The snowflakes made from the purified liquid CO₂ are capable of producing surfaces that are nearly atomically clean. This level of cleanliness can be important for the successful operation of some ultraviolet and infrared optical systems.

The goal is the Active Cleaning for Space-systems (ACES) project is to develop and demonstrate a new means for on-orbit cleaning of particle contaminants from optical surfaces on satellites. This paper describes the rationale for on-orbit cleaning, a carbon dioxide (CO₂) snow cleaning system, and a future Space Shuttle experiment with that system. The experiment and hardware designs are described in some detail to show how all experiment objectives will be met.

Real-time instruments based on surface acoustic wave (SAW) resonators are now seeing greater application for measuring the accumulation of nonvolatile residues (NVRs) on contamination sensitive surfaces. In this paper, we study the use of a desiccant, or dry GN+-2) to remove volatile films from the SAW sensing surfaces, with the intent of leaving the NVR behind. Using water as moderately volatile model material, the SAW device was capable of indicating monolayer growth in agreement with the expected frequency change. The drying agent was successful in removing all water from the SAW device. Additionally, the SAW device was capable of detecting different regimes of desorption kinetics. In trials of several candidates, only one example of NVR could be deposited, most likely a phthalate from flexible tubing heated beyond its working temperature. The deposit was so large that it overwhelmed subsequent observations of water desorption.

This paper presents the results of an experimental investigation of Aeroglaze Z306 black paint used as a functional coating in a cryogenic telescope for the Space Based Infrared System (SBIRS) program. During ground testing of a DBIRS infrared sensor engineering test model (ETM), degradation of optical transmission was observed. Analysis showed that the degradation was caused by water vapor condensing onto sensor collection optics, which were operating at 120 to 130 K. Root cause analysis identified Aeroglaze Z306 black pain as a likely candidate source of the water vapor. Prior to ETM testing, the painted telescope housing was vacuum baked for 100 hours at 100 $DEGC. However ASTM E 595 test data show that significant water vapor regain occurs within 24 hours after vacuum bake-out. To obtain a detailed characterization of the black paint with respect to water vapor regain and subsequent removal under vacuum conditions, a test plan was developed involving a series of ASTM E 1559 test measurements. These tests improve our understanding of the processes involved and provide the basis for design of an on-orbit H₂ bakeout capability for the SBIRS infrared sensor payload.

This paper provides a progress report on the development of a new contamination prediction code, the Aerospace Satellite Contamination Model Evaluator (ASCME). In this development, we intend to exploit the growing ASTM E1559 database for outgassing and desorption measurements and to incorporate realistic physical and kinetic models of condensation and photochemical deposition.

A numerical procedure is presented to calculate transmittance degradation caused by contaminant films on spacecraft surfaces produced through the interaction of orbital atomic oxygen (AO) with volatile silicones and hydrocarbons from spacecraft components. In the model, contaminant accretion is dependent on the adsorption of species, depletion reactions due to gas-surface collisions, desorption, and surface reactions between AO and silicon producing SiO_x (where x is near 2). A detailed description of the procedure used to calculate the constituents of the contaminant layer is presented, including the equations that govern the evolution of fractional coverage by specie type. As an illustrative example of film growth, calculation results using a prototype code that calculates the evolution of surface coverage by specie type is presented and discussed. An example of the transmittance degradation caused by surface interaction of AO with deposited contaminant is presented for the case of exponentially decaying contaminant flux. These examples are performed using hypothetical values for the process parameters.

This paper describes two modeling approaches developed at Lockheed Martin Missiles and Space Operations for analysis of the sputter erosion of spacecraft surfaces due to the use of Hall thrusters. The PIC-DSMC (Particle in Cell-Direct Simulation Monte Carlo) plume model developed at Massachusetts Institute of Technology was successfully modified to model the BPT-4000 thruster (4,5 kW, 350 V) plumes. In addition to modeling the complicated plume features using the PIC-DSMC codes, we also developed a semi-empirical plume model that requires less computational time for modeling the sputter erosion of spacecraft surfaces. The approach uses PLIMP (Plume Impingement) code as a ray- tracing tool to determine the plume distances from the exit to impinged objects (e.g. solar arrays), plume divergence angles, and impingement angles. Measured ion current flux and sputter rates were then used to examine the sputtering erosion for solar arrays on a representative geostationary spacecraft. This semi-empirical model allows one to perform a quick spacecraft-plume interaction investigation. Moreover, contamination deposition of eroded thruster products and sputtered spacecraft materials was examined.

A new computer model for the outgassing and potential contamination of S/C surfaces in orbit is described. It calculates the redistribution of contaminants on internal surfaces with time and their escape into space with time, based on the calculation of the various vapour pressures generated by the contaminated surfaces. These vapour pressures are a function of the type of the contaminant, of surface temperatures and of surface coverage. Different vapour pressures over different surfaces generate net flows of contaminants from higher to lower pressure, limited by the venting resistance between these surfaces. Calculating these net flows with time results in change of contamination layer thickness of all surfaces, as a function of temperature and size of vent holes. The advantage of this new model is that it is not limited to few wall collisions of a molecule, as it is the case in models calculating the movement of individual molecules by statistical methods. The model mainly was developed for the X-ray satellite XMM-Newton, to estimate the contamination with time of its cold experiments within the telescope tube. At the date of this publication, XMM-Newton results were not yet available, and therefore the model also was tested by comparison to results gained from a former outgassing test made for ROSAT. The coincidence between experimental results here can be made remarkably good, by assuming certain initial conditions.

The presence of contaminants in optical interfaces modifies their optical properties. In the presence of contaminants, the organization of the molecules within the medium is no longer the same for the interior and the surface. Such an interface becomes a region of some finite thickness in which there is a gradual change of physical properties. In this case, a step refractive index profile cannot be used to describe this region, as is generally used in refractometry. In general, the refractive index at a surface or an interface should be presented as a gradient. The profile of the refractive index distribution at an interface is defined by the physical-chemical properties of the base medium and the contaminant. From the thermodynamic models developed for interfaces, a refractive index distribution can be proposed. The description of the interface in terms of a refractive index profile allows the use of optical testing methods developed for the characterization of optical materials. In particular, geometrical and interferometric testing procedures can be used. Ray tracing is required become the analysis of interferograms and light distribution in the outcome of geometrical test relays on an a-priori knowledge of the optical path followed by light. In this work we propose refractive index distributions based on the thermodynamic potentials of typical interfaces. Making use of the mathematical forumlism based on Fermat's principle, the ray tracing equation associated to each case is presented. The information about these light trajectories is necessary to determine the thickness, concentration, as well as the type of contaminant in the contaminated region.

Molecular contaminants degrade the optical or thermal properties of spacecraft systems. In the case of grazing incidence mirrors, they may even increase the system throughput at certain wavelengths. Theoretical calculations using a semi-imprircal model developed by Henke, Davis and Gullickson at the Lawrence Berkeley National Laboratory show the effect of varying film thickness' on mirror reflectivity.² The reflectivity is a product of the base material and any thin films, including molecular contaminants. The effect on nickel, gold, and Zerodur substrates are evaluated with polycarbonate, polypropylene and poly(dimenthyl silicone) contaminants in the range of 5 to 100 Angstroms x-ray wavelength. X-rays pass through the film until they meet an atom; they are then scattered elastically or absorbed. Photoabsorption occurs when the photon energy is equal to or greater than the energy required to promote an inner shell electron out of the atom. Strategies for evaluating contaminant effects with different light sources are included, taking into account the scattering cross section, expressed as mirror reflectance, of the materials involved.

The Space Infrared Telescope Facility (SIRTF) is designed to explore the infrared universe. It will be placed into a heliocentric orbit and will perform background-limited imaging and spectroscopic measurements of celestial objects in the 3-180micrometers spectral range. Because the main components are operating at cryogenic temperatures, SIRTF has several unique contamination control drivers. This paper describes the analytical approaches to verify the requirements and to show that the requirements can be met. The particulate contamination analysis uses measured surface particle removal data and analytical random vibration surface interaction models to predict the particle distribution in an enclosure, such as the payload fairing, in an ascent vibroacoustic environment. The prediction shows an increase of percent area coverage (PAC) of the S tar Tracker front aperture window from 0.004$ (Level 200) to 0.475% (Level 572), assuming a surface random vibration level of 23 g-rms. The low-(epsilon) thermal control surface shows an increase of emissivity of 0.005 to 0.035, which meets the required value of 0.05 at end-of-life. In the molecular contamination analysis, the molecular transport kinetic (MTK) model was used with the cool-down temperature profiles to predict the molecular deposit during the early orbit period. An innovative sticking coefficient model that is a function of both the surface temperature and the mean dwell time, was used in the calculation. The results show that deposits of water condensation during this cool-down period are 18A on the exterior of the Cryogenic Telescope Assembly (CTA), 77A on the bus-side spacecraft shield, and negligible on the solar array shield and on the CTA-side spacecraft shield. Other molecular contamination sources, such as returned flux, interior molecular source, and nitrogen thruster plume, were also examined. The effects from these sources were found to be insignificant to the operations.