During past years, there have been a substantial number of Contamination Control Plans (CCPs), which have been developed for a wide variety of space missions. These plans contain useful and generally applicable information for many current and future instrument and spacecraft missions. Often, the information contained within these CCPs is essentially lost after the mission and contamination control engineers are left to develop entirely new CCPs for each new spacecraft or instrument project. A new CCP database system, sponsored by NASA Goddard Space Flight Center (GSFC) and Swales Aerospace, is under development and is designed to encapsulate and categorize past Contamination Control Plans, in an extensive, methodically-searchable, database tool. Users will be able to compare and contrast various past CCPs, extract pertinent information, then apply this data to any new mission or project. This tool is not only useful as a baseline database for quicker development of new CCPs, but can also be used as a teaching tool for new contamination control engineers.

The SABER instrument (Sounding of the Atmosphere using Broadband Emission Spectroscopy) is a cryogenic infrared sensor on the TIMED spacecraft with stringent molecular and particulate contamination control requirements. The sensor measures infrared emissions from atmospheric constituents in the earth limb at altitudes ranging from 60 to 180 km using radiatively-cooled 240 K optics and a mechanically-refrigerated 75 K detector. The stray light performance requirements necessitate nearly pristine foreoptics. The cold detector in a warm sensor presents challenges in controlling the cryodeposition of water and other condensable vapors. Accordingly, SABER incorporates several unique design features and test strategies to control and measure the particulate and molecular contamination environment. These include internal witness mirrors, dedicated purge/depressurization manifolds, labyrinths, cold stops, and validated procedures for bakeout, cooldown, and warmup. The pre-launch and on-orbit contamination control performance for the SABER telescope will be reviewed.

The National Ignition Facility will be the highest energy laser in the world when completed. Many small optics (less than or equal to 14" in diameter) have stringent transport efficiency and some have very high laser fluence requirements. For optics to sustain high spectral efficiencies and survive high fluences for a 30-year operation, these optics have cleanliness requirements to assure optimal laser system performance. These optical components have insufficient surface areas to validate the particulate and organic contamination requirements by methods used for mechanical parts. Also, the common validation techniques require some sort of surface contact which is not compatible with handling of laser optics. This presentation describes alternate cleanliness validation methods developed for the NIF small optical components. An organic validation procedure was devised based on the spectral transmission sensitivity to contamination layers on coated and uncoated fused silica windows. Optics were scanned in the near infrared before and after an application of a specific amount of organic contamination onto the surface. Changes in transmission correlated to organic contamination levels and used to determine non-volatile organic contamination optics. A validation method for particulate contamination was demonstrated on a large window, showing that acceptable cleanliness levels could be achieved after a wet-wipe and inspection with a high intensity light. The method is similar to that used to inspect the surface quality of optical components.

Under sponsorship by the Ballistic Missile Defense Organization, now Missile Defense Agency (MDA), Raytheon designed a system that allows in-situ/on orbit cleaning of particulates from contaminated optical surfaces in a satellite sensor. The system is based on the release of CO₂ from specially designed nozzles to create a gas/snow mixture that lifts the particulates from the surfaces. The ultimate purpose of the program is to reduce the risk of optical surface contamination due to launch vibrations and, potentially, ease cleanliness requirements during the ground integration of space-based optical sensors by performing optical element cleaning while in orbit. Significant cost savings in satellite construction, integration, ground preparation and, potentially, satellite optical aperture design criteria could be realized by this method. Ground and space demonstration experiments were designed and the ground vacuum chamber demonstration was conducted and successfully cleaned using the jet spray technology. Measurements of the mirrors cleanliness levels were made prior to and after vacuum chamber cleaning demonstration. These intentionally contaminated mirrors were shown to be restored to a near- pristine condition after cleaning in each chamber test. Additionally, estimates of the particle migration after cleaning were made including an estimated level of mirror re-contamination.

The use of a high velocity stream of carbon dioxide snowflakes to clean large optics is well known, and has gained widespread acceptance in the astronomical community as a telescope maintenance technique. Ultimately, however, the success of carbon dioxide snow cleaning depends on the availability of high purity carbon dioxide. The higher the purity of the carbon dioxide, the longer will be the time interval between required mirror washings. The highest grades of commercially produced liquid carbon dioxide are often not available in the more remote regions of the world - such as where major astronomical observatories are often located. Furthermore, the purity of even the highest grades of carbon dioxide are only nominal, and wide variations are known to occur from tank to tank. Occasionally, visible deposits of organic impurities are left behind during cleaning with carbon dioxide that is believed to be 99.999% pure. A zeolite molecular sieve based filtration system has proven to be very effective in removing these organic impurities. A zeolite is a complex alumino-silicate. One example has an empirical formula of (see paper for formula). The zeolites have an open crystal structure and are capable of trapping impurities like 8-methylheptadecane (an oil) and 2,6-octadine-1-ol,3,7- dimethyl-,(E)- (a fatty acid). In fact, a zeolite can trap 29.5% of its own weight in SAE 20 lubricant at 25 degree(s)C. After filtration of liquid CO₂ through zeolites, the concentration of measured impurities was below the detection limit for state-of-the-art gas chromatography systems.

During the launch of a spacecraft, particles on the spacecraft, support structure, and the payload fairing may be removed from surfaces and move to other surfaces. Some particles may vent from the payload fairing. It is desirable to be able to predict the cleanliness of critical surfaces following launch based on hardware cleanliness before launch. Reliable prediction of post-launch contamination would help in setting hardware cleanliness and cleaning requirements during assembly and integration operation before launch. Particles are removed from surfaces by forces that result from vibro-acoustic, shock, acceleration, and aerodynamic actions. Acceleration and aerodynamic forces may transport the removed particles to other surfaces and out of the vents.

The use of MIL-STD-1246 particle distributions for calculating BRDF scatter has given unrealistic cleanliness requirements for optical systems exposed to environmental fallout. MIL-STD-1246 and fallout data were reviewed and used to generate more realistic particle distributions for use in BRDF scatter predictions.

The 1992 work by Paul Spyak and William Wolfe correlating particulate contamination scatter with the predictions of Mie scatter theory has been extended and applied to the analysis of optical systems. Spyak & Wolfe's BRDF results, as applied to Mil-Spec 1246B particle distribution have been often misunderstood and misapplied. This paper provides the application of MIE theory to the modeling of scatter from particulate contaminated optics based on the Mil-Spec 1246B particle distribution and particle distributions more commonly seen in cleanroom fallout.

Molecular surface contaminants can cause degradation of optical systems, especially if the contaminants exhibit strong absorption bands in the region of interest. Different strategies for estimation of spectral degradation responses due to uniform films for various types of systems are reviewed. One tool for calculating the effects of contaminant film thickness on signal degradation in the mid IR region is the simulation program CALCRT. The CALCRT database will be reviewed to correlate spectral n and k values associated with specific classes of organic functional groups. Various schemes are also investigated to estimate the spectral degradation in the UV-Vis region. Experimental measurements of reflectance changes in the IR to UV-Vis regions due to specific contaminants will be compared. Approaches for estimating changes in thermal emissivity and solar absorptivity will also be discussed.

For contamination effects on thermal control surfaces, changes in solar absorptance are the effect noted. Emittance of the surface is not normally affected. The SIRTF (Space InfraRed Telescope Facility) and NGST (Next Generation Space Telescope) spacecraft will fly large low emissivity surfaces (e.g. aluminized Kapton shields and gold mirrors). During the orbital missions, these surfaces will not be exposed to the sun and will be at temperatures less than 150 K. Concern is that a thick molecular film, even water, will cause a change in emittance and results in affecting the thermal performance primarily controlled by emittance alone. Although an emphasis will be placed upon examining the effects on thermal performance for low emissivity surfaces, the effects on optical performance will also be examined because changes of the optical characteristics such as reflectance and scattering are of greater concern for the NGST mission.

Space borne high efficiency triple junction solar cells are calculated to be about twice as sensitive to degradation from deposition of films of molecular species (similar to those typically outgassed by spacecraft materials) than are lower efficiency silicon cells. This is a consequence of the facts that 1) sub-cells of multijunction cells are connected in series, so that one of them limits the current through the stack, 2) the current in each sub-cell is lower in multijunction cells than in single junction cells, and 3) the absorptance of the molecular films increases rapidly as wavelength is decreased, effectively concentrating its effect in one sub-cell.

The proposed paper will describe development of a time-dependent, one-dimensional counterflow diffusion model meant to help study the issue of helium exposure of the IRU (Inertial Reference Unit) used in the Earth Observing-1 (EO-1) spacecraft. The IRU features sensitive quartz crystal hemispherical resonating gyros (HRG's). Although the IRU enclosure was purged with high-purity liquid boil-off nitrogen, the HRG's were still quite susceptible to contamination generated by exposure of the enclosure to levels of helium above atmospheric background levels. This helium would be preferentially collected by the HRG's, changing their mass, and hence the driving voltage required for operations. The paper will discuss a comparison of theoretical results with test data for an IRU enclosure, and how contaminant gases can enter vent holes despite the presence of a purge. These observations are then used to describe a possible improvement for purge effectiveness.

The Wide Field Camera 3 (WFC3), a scientific instrument being prepared for the next Hubble Space Telescope (HST) servicing mission, has two detectors providing wavelength sensitivity from 0.2 to 1.7 microns. In a departure from previous HST detector enclosure designs that required extensive bakeouts, the WFC3 enclosures are vented to space. Several contamination analyses were performed to assist in the design and validation of the vent tube, detector and enclosure bakeout requirements, and instrument operational constraints. The benefits derived from the vented enclosure configuration are discussed, and the analysis techniques and implementation are presented.

This paper describes progress in the development of a new contamination prediction code, The Aerospace Satellite Contamination Model Evaluator (ASCME). This paper provides fitted parameters for Langmuire evaporation models of contaminants from 15 materials based upon kinetic testing according to the ASTM E1559-93 procedure. It is shown that the evaporation rate parameters, p₁ and p₂, derived from the E1559 TGA testing do not always agree with corresponding parameters calculated from published vapor pressure data. The uncertainty in extracting p₁ and p₂ parameters due to experimental scatter is estimated to be about ±5.6% and ±4%, respectively. It is demonstrated that m desorption profiles can vary significantly, depending upon the originating source material. It is shown that evaporation rate parameters depend strongly on the test method, static vs. kinetic.

A parametric study is presented in which the contamination environment established to aft facing spacecraft surfaces subsequent to burnout of the Inertial Upper Stage (IUS) second stage motor is characterized. Subsequent to motor burnout, the internal motor case, insulation, and materials in the flexible nozzle seal assembly of the IUS will continue to outgas and expel large hydrocarbon molecules. By means of molecular scattering, these outgassing products may be transported to payload (spacecraft) surfaces creating a potentially severe contamination environment on sensitive components. Transport of the outgassing products is characterized using the Direct Simulation Monte Carlo (DSMC) method. Since many of the physical attributes of the outgassed products are unknown, a parametric study is performed in which the outgassing temperature, reference viscosity, and molecular weight of the products are varied. In addition, inclusion or exclusion of an extendible nozzle exit cone provides the effect of nozzle length on the contamination environment. Contour plots of the resulting flowfield number density are provided in addition to incident mass flux to aft facing surfaces of a representative spacecraft.

This paper documents the development and validation of a new return flux model for the International Space Station (ISS). This model has been developed to augment current ISS external contamination modeling tool capabilities. The model is capable of characterizing return flux from ISS molecular emission sources. These sources include materials outgassing, vacuum venting, propellant purging and thruster firings. The BGK method (named after its authors: Bhatnagar, Gross and Krook¹) was selected for modeling ambient scatter. This method was used to reduce computational times, as the ISS geometric models used for external contamination modeling may contain up to 40,000 surface elements. The model has been validated by comparison with analytical results and with results from the ESA COMOVA software. Validation with on-orbit flight experiment data will be conducted when adequate experimental data is available. Previously flown experiments (i.e., REFLEX) have not produced data with high enough fidelity to validate this model. The model has been applied to the ISS to characterize return flux from the European Columbus module onto its own payload locations. Analysis results indicate the return flux contribution to ESA payload surfaces will be small, but not negligible.

On-orbit, self-contamination of a spacecraft is a concern facing instrument and spacecraft designers. While on the Earth, gases adsorb onto spacecraft surfaces. These gases are later released when placed in the vacuum of space. The rate at which the emitted gases are returned to the spacecraft by collisions with other gaseous molecules is known as the return flux. Models predicting the amount of gas released by a spacecraft that is returned to itself do exist, but these models have had very limited experimental testing. We describe a flight experiment designed to provide a test of these models and the analysis of the data obtained by that experiment. The experiment flew on a 1996 space shuttle mission and provided in-situ testing of the return flux models. Analysis of the limited data obtained by the experiment has determined the return flux is primarily due to collisions with the ambient atmosphere and not collisions with other gases released by the spacecraft. Limited measurements of the ambient atmosphere were also made.

This paper documents thruster plume induced contamination measurements from the PIC (Plume Impingement Contamination) and SPIFEX (Shuttle Plume Impingement Flight Experiment) flight experiments. The SPIFEX flight experiment was flown on Space Shuttle mission STS-64 in 1994. Contamination measurements of molecular deposition were made by XPS (X-ray Photo Spectroscopy). Droplet impact features were also recorded with SEM (Scanning Electron Microscope) scans on Kapton and aluminum foil substrates. The PIC flight experiment was conducted during STS-74 in 1996. Quartz Crystal Microbalances (QCMs) measured contaminant deposition from U.S. and Russian thruster firings. Droplet impact observations were made with SEM scans of the Shuttle RMS (Remote Manipulator System) camera lens. These flight experiments were successful in providing measurements of plume induced contamination as well as droplet impact damage. These measurements were the basis of the plume contamination models developed for the International Space Station (ISS).

This paper documents International Space Station (ISS) external contamination observations and surface assessments covering Flights 1A/R through 6A. These observations are based on imaging from ISS missions, as active external contamination monitoring is not present in the configuration at this time. Imaging from ISS missions is a critical resource as it records the condition of ISS surfaces and helps identify visible signs of surface degradation. The observations are divided into three main sections; the first section covers the Functional Cargo Block (FGB - Russian Segment), the second section covers the Service Module (SM - Russian Segment), and the third section covers the U.S. Segment (Node 1 and Primary Mating Adapters 1 and 2). This distinction is important as materials selection, design and contamination control procedures differ between the FGB and Service Module on the Russian Segment and the U.S. Segment. Numerous observations of FGB self-contamination have been made through ISS imaging obtained during Shuttle flights. These observations were not surprising as external contamination studies conducted during the Shuttle-Mir (Phase I) Program showed extensive contamination induced by the Russian hardware. The impact of FGB induced contamination on ISS sensitive surfaces was mitigated due to FGB on-orbit time vacuum baking the Russian hardware prior to the deployment of ISS contamination sensitive hardware. Service Module impacts on ISS hardware were mitigated with a combination of changes in materials selection and on-orbit vacuum baking as there would be less on-orbit time before deployment of sensitive surfaces. While changes were made to materials selection, self-contamination observations have also been made on the Service Module. At this point, the U.S. Segment appears to be largely free of self-induced contamination. This confirms predictions made during the design and integration phase. Observed darkening and degradation of surfaces on the U.S. Segment is limited to a few areas and due to interactions with the on-orbit environment.

Currently, no accurate models or recent data exist for modeling contamination from spacecraft thrusters to meet the stringent requirements of the International Space Station (ISS). Few flight measurements of contaminant deposition from spacecraft thrusters have been made, and no measurements have been made for angles away from the plume centerline. The Plume Impingement Contamination-II (PIC-II)¹ experiment is planned to provide such measurements using quartz crystal microbalances placed into the plume of a Shuttle Orbiter RCS thruster. To this end, the Johns Hopkins University Applied Physics Laboratory (APL) has supported NASA in the development of the PIC-II experiment Flight Electronics Unit known as the Remote Arm TQCM System (RATS), which will measure the contamination in the Shuttle Obiter RCS thruster. The development was based on an ongoing effort between the APL and QCM Research to develop an inexpensive, miniature TQCM controller based on a legacy of QCM controllers developed at the APL. PIC-II will provide substantial improvements over previous systems, including higher resolution, greater flexibility, intensive housekeeping, and in-situ operational control. Details of the experiment hardware and measurement technique are given. The importance of the experiment to the ISS and the general plume contamination community is discussed.

Deposition of molecular contamination onto spacecraft surfaces changes the thermo-optical and electrical properties of those surfaces. Such changes may induce changes in the properties and performance of other spacecraft systems. Interactions with space environments may continue to change the nature of contaminant species on surfaces, causing time-varying effects on other hardware. For these reasons there is a continuing interest in the properties of deposited thin films. Spectroscopic and surface measurement results are presented for fused silica and other optically transparent specimens, as well as selected first surface mirror materials from the POSA, LDEF A0034, and EOIM-III space flight experiments. A simple empirical model was used to relate the change in optical transmission of fused silica due to contamination deposits. Transmission or reflectance measurements were taken from vacuum UV wavelengths out to the mid-IR region of the spectrum. These results show that the contamination effects are most significant at wavelengths less than 400 nm.

This paper describes the development of a facility for material outgassing measurements using quartz crystal microbalances (QCMs) operating at temperatures as low as 20K. The objective of this effort was to develop a system that operates in the 4 to 30K temperature range and that provides material outgassing data at much lower temperatures than have previously been available. The desired measurements are based on the ASTM Standard E1559 test method. Many space-based infrared sensor systems operate at temperatures much colder (i.e., 4 to 30K) than the 77K temperature commonly used in the E 1559 test method. The data collected will be used to compare material outgassing data collected at 77 and 20K to determine the differences in total mass loss (TML) measured at the two temperatures. This will provide an answer to the question that for a long time has been associated with the E1559 test method: Does the 77K QCM collect essentially all of a material's outgassed products??.

Semi-volatile residues on aerospace hardware can be analyzed using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). This method can be correlated with quantitative Mil-STD 1246 NVR measurements while simultaneously providing qualitative identification of a large variety of compounds. Its high sensitivity supports the direct sampling of small areas of critical surfaces. This method involves transferring the contaminant film to a small solvent-saturated wipe, followed by extraction of the wipe, then concentration of the solvent extract and subsequent spectroscopic analysis using an FT-IR with a diffuse reflectance accessory. A library of standard curves for different classes of typical aerospace contaminants has been established. Quantitative analysis has been proven successful over orders of magnitude and detection limits exceeding 0.1 ug/cm² are routinely achieved. Several practical applications have been performed using this analytical method and detailed discussion of analysis techniques is presented. The discussion will include: instrumentation setup, selection and preparation of sample collection materials, sample extract preparation, preparation of standard calibration curves and spectral interpretation.

Organic contamination control at ESA is based on the infrared spectroscopy method described in the PSS-01-705. The method is used to verify the organic contamination levels during integration and thermal vacuum tests. The detection limits are in the 10^-8 g/cm² range or below, depending on the equipment and sampling method. Quantification is performed with common space contaminants, with the possibility to include a new calibration standard when a specific contaminant is occurring more often. Sampling is done with witness sensors of 15 cm² or infrared transparent windows to verify the cleanliness after specific events. When no witness sensor has been used, solvent compatible surfaces can be analyzed by a solvent wash or by wiping the surface using dry or wetted tissues. Calibration curves with detection limits are presented, with an examples of a contamination event found on a retrieved space hardware.

Microbial destruction of optical and electronic materials has been studied. Contamination of materials by microorganisms may be an issue for unattended and space-based optical and electronic systems. We have investigated the process of growth and distribution of fungal elements of Aspergillus flavus and Aspergillus niger, on materials that were inoculated by spores at concentrations 2.5x10⁶, 2.15x10³ spores/mL. Different optical dielectric materials, including photorefractive crystal of LiNbO₃ crystals (LN), photosensitive polymers PMMA, doped with phenantrenequinone (PQ), and sapphire were used. It was found that spores on LiNbO₃:Fe under the same environmental conditions (temperature, humidity) germinated faster and growth of hyphal strands were more elongated and more evenly dispersed than on other materials. Our preliminary interpretation of the observed data is based on the influence of the space-charge fields (observed on the surface of LN) on fungal growth. Illuminating LN crystals by space-structured light showed the possibility of controlled redistribution of microorganisms (E-coli bacteria) on the crystal surface.