Contamination witness plates were flown on STS-51 as part of a NASA Extravehicular Activity (EVA) Flight Test Experiment to quantify and identify particulate contamination generated in the Orbiter crew compartment which has the potential to contaminate the Extravehicular Mobility Units (EMUs) and transfer from the EMUs to mission critical hardware during EVAs. Particles, larger than 100 microns, were found on both witness plates, indicating transfer from the EMUs during EVAs. For missions such as the Hubble Space Telescope First Servicing Mission, where contamination critical optical elements were exposed during EVAs, the potential for particulate transfer from the crew compartment to these optical elements and the Hubble Space Telescope was evaluated.

The Hubble Space Telescope is the first spacecraft designed from its conception to allow for Scientific Instrument upgrading and subsystem maintenance by using the Shuttle. Regular and contingency servicing missions preserve and broaden the scientific objectives of the HST through on-orbit maintenance. To achieve mission success for the Hubble Space Telescope First Servicing Mission, a contamination control methodology was developed and instituted by ensure that scientific instrument performance was not degraded or compromised during fabrication, build-up, ground integration and test activities, on-orbit servicing including Extravehicular Activities, or through on-orbit operational activities. The cleanliness methodology considered the effects of outgassing and surface contaminants on the degradation of the sensitive components. Through plans and procedures for handling sensitive components and the development of a detailed contamination budget extending from Goddard Space Flight Center processing through launch, the preservation of the science capabilities (as affected by contamination) was achieved.

For spacecraft hardware that is contamination sensitive, it is necessary to protect the hardware from inadvertent contamination from external environments. In the case of the Hubble Space Telescope First Servicing Mission hardware, contamination due to particles or non-volatile residue depositions could cause severe degradation in optical performance. Once a hardware component is vacuum baked and certified `clean' from the outgassing perspective, it must be protected from surface contaminants. Surface contaminants such as particles and non-volatile residue will cause light scattering and ultraviolet absorptance on critical optical components. One method of protecting the hardware from contamination effects is to institute the use of protective bags. Bagging of flight hardware is most efficient during the phases that include storage, integration and test, and transportation. For bags to provide an effective barrier and minimize depositions from the environment, the bags must meet several requirements to preclude the bag material itself from becoming a source of contamination to the hardware. These requirements must satisfy cleanliness specifications, in addition to strict safety standards for spacecraft and launch facilities. During the launch site processing of the HST FSM hardware, an innovative design for a protective bag was created to facilitate removal during integration into the payload bay. The protective bag design incorporated a `ripcord' method for removal to minimize contamination on the FSM hardware from Canister handling, facility fall-out, Payload Ground Handling Mechanism transfer, and personnel induced contamination. In addition to cleanliness requirements, the `ripcord' design was required due to accessibility limitations while processed in the Payload Changeout Room.

Temperature-Controlled Quartz Crystal Microbalance (TQCM) instruments were used in a clean room (under non-vacuum conditions) as an indicator of molecular contamination deposited in optics. The Wide Field Planetary Camera II and the Corrective Optics Space Telescope Axial Replacement, which were installed in the Hubble Space Telescope during the first servicing mission in December 1993, had stringent contamination budgets. While they were in a Goddard Space Flight Center cleanroom undergoing integrated testing, two TQCMs were used to provide an early warning of excessive molecular contamination on a near real- time basis and to provide a measurement of the total contamination deposited over the 50 to 75 day test period. The TQCM frequency, which changes in direct proportion to the mass of material deposited on the exposed crystal, was recorded on a computer located outside the cleanroom and was monitored on an hourly basis with alert limits set for hourly and daily frequency increase. Frequency increase was correlated to peak personnel activity in the area. The results for the period of integrated testing were within budget. The operation of the TQCM is described and the results and analysis are presented.

During Kennedy Space Center processing of the Hubble Space Telescope First Servicing Mission, critical optical components were integrated in a Class 100,000 (M 6.5 at 0.5 micrometers and 5.0 micrometers , per Fed-Std 209E) cleanroom. A Class 10,000 (M 5.5) environment was mandated by the 400B (per Mil-Std 1246B) surface cleanliness requirement of the Scientific Instruments. To maintain a Class M 5.5 environment, a contamination control plan was implemented which addressed personnel constraints, operations, and site management. This plan limited personnel access, imposed strict gowning requirements, and increased cleanroom janitorial operations, prohibited operations known to generate contamination while sensitive hardware was exposed to the environment, and controlled roadwork, insecticide spraying, and similar activities. Facility preparations included a ceiling to floor cleaning, sealing of vents and doors, and revising the garment change room entry patterns. The cleanroom was successfully run below Class 5000 while the instruments were present; certain operations, however, were observed to cause local contamination levels to increase above Class M 5.5.

A spacecraft was instrumented with four temperature controlled quartz crystal microbalance (TQCM) contamination detectors. One TQCM, located inside the vehicle, recorded contaminant deposition that was orders of magnitude higher than did the three TQCMs located in various positions outside the vehicle. The deposition rate on the interior TQCM varied with the temperatures of interior spacecraft cavity surfaces. In particular, there is clear evidence of condensation on these surfaces and re-evaporation from these surfaces by previously outgassed contaminant molecules. The e-folding time constants of the deposition on two of the exterior TQCMs held at -50 degree(s)C are approximately 1.4 years, with extrapolated final equivalent thickness of the deposition in the 20 - 25 nm (200 - 250 angstroms) range. The third exterior TQCM, which has a significant field of view of a segmented thermal blanket, collected contamination at a greater rate. The data enable the ranking of the several contamination transport mechanisms at work and the drawing of general recommendations for spacecraft design.

The Environmental Verification Experiment for the Explorer Platform (EVEEP) was launched in June 1992 and is flying on an Explorer Platform along with the Extreme Ultraviolet Explorer (EUVE). EVEEP consists of five Temperature-Controlled Quartz Crystal Microbalances (TQCMs) and the necessary electronics to control the sensors and prepare the data for downlink. Two of EVEEP's TQCMs were coated with Teflon prior to flight for atomic oxygen studies. The remaining three TQCMs were not coated and are dedicated to contamination accretion studies. The two Teflon coated TQCMs were designed to give a transient demonstration of the erosion of Teflon material caused by atomic oxygen. One of the coated TQCMs is located on the shade side of the platform and experiences only atomic oxygen erosion. The other TQCM is located on the sun side of the platform and demonstrates the effects of ultraviolet radiation on the atomic oxygen erosion rate. An analysis of the erosion rates is presented for each situation emphasizing the differences between the two erosion rates. The three uncoated TQCMs measure contamination due to direct flux emitted on-orbit. This data has been used to verify current contamination modeling techniques. There is one TQCM on each side of the platform whose sole view is of the back of the nearest solar array. These arrays were painted with TW1300 white paint. Since there are two separate TQCMs with similar views, a redundant check on the modeling techniques for this configuration was possible. A comparison between the on-orbit data and the results from the analytic contamination model is presented.

For the Hubble Space Telescope (HST) First Servicing MIssion (FSM) Project there was a high level requirement which stated that the Endeavour would not carry extra propellant for an extra EVA after the final regularly scheduled fifth EVA. Because of this the HST FSM Project needed to assess the feasibility of redeploying the HST with its Aperture Door (AD) open from the Endeavour in order to prevent the situation that the AD may not open by radio command after separation. Contamination was one of the major concerns of the HST scientific community. The prospect that the opened AD may allow unacceptable amount of Endeavour generated contaminant to enter the HST aperture and subsequently depositing onto the Primary Mirror seemed too big a risk. To assess this potential contamination threat and to put it into proper perspective, Lockheed performed a series of comprehensive contamination analyses to predict expected Endeavour generated molecular and particulate contaminant accretions on the HST primary mirror during open-AD re-deployment. This paper describes the analysis approach and some of the conclusions reached for the HST FSM redeployment phase.

The Atmospheric Infrared Sounder (AIRS) is a high spectral resolution multispectral sounder providing nearly contiguous coverage between 3.74 and 15.4 micrometers which has been selected as a facility instrument on the Earth Observing System PM series. AIRS is designed to provide data for application in climate studies and weather prediction. The degradation of AIRS by contamination could reduce its performance capabilities, reducing the instrument's expected utility by compromising its accuracy and sensitivity. AIRS contains a number of contamination sensitive subsystems which include an exposed scan mirror, passively cooled optics, mechanically cooled detectors, on board calibrators, and thermal control surfaces. Efforts were undertaken to define the contamination sensitivities of these subsystems based upon system performance goals. A series of analyses have been performed to determine the cleanliness necessary to meet the system performance goals. From this data, a contamination control program and preliminary design guidelines have been implemented. Presented in this paper are an overview of the instrument and its contamination susceptibility, the contamination performance goals for each subsystem area, and the derived cleanliness requirements. The analysis techniques used to derive the subsystem cleanliness requirements from the optical, thermal, and calibration performance goals are included. Also included are the preliminary design concepts for contamination control and contingency decontamination features built into the AIRS design to help assure the contamination requirements are met.

A series of vacuum simulation tests were conducted to characterize the possible contamination of payload surfaces due to separation of the Pegasus fairing. This paper presents the test philosophy, experimental approach and the contaminant levels found, compared to MIL-STD- 1246B. These tests show that the Pegasus fairing separation using the frangible base joint and nose bolt nut results in Level 500 payload surfaces. The source of Zn particles near the bottom of the test payload needs to be found.

The electrodynamics of particulate contamination in an ionospheric plasma near spacecraft surfaces is being investigated by a new 2D particle-in-cell (PIC) simulation. Particulate charging in the PIC simulation is treated as a collisional event and is implemented in a Monte Carlo fashion. The simulation has been applied to dusty plasmas both in an unbounded plasma and near a bounded plasma (spacecraft surface). Results from the simulation include estimates of the charge and potential structure of finite-size dust clouds. Low-density dust clouds do not perturb the electric potential of the plasma, similar to the case for isolated particulates. In high-density dust clouds, the potential forms a sheath-like structure while the charge forms a double layer on the outer boundary of the cloud. Particulates can have negative or positive charges depending on the applied surface potential, thus raising the possibility of controlling particulate contamination by controlling the spacecraft potential.

Contamination of infrared sensor systems is an area of concern to spacecraft operators and designers. This paper describes the CALCRT mathematical model which can be used for calculating the reflectance and transmittance effects of thin contaminant films on optical surfaces. It uses an optical property data base that contains the cryogenic optical properties (refractive and absorptive indices) for satellite material outgassing products, atmospheric gases, propellants, and bipropellant plume products. The bipropellant plume data were obtained during firings of a 5 lb. thrust monomethylhydrazine/nitrogen tetroxide engine. Contaminant effects can be calculated as a function of substrate refractive index, incidence angle, film thickness, film materials, wavelength, and wavenumber. The model has been modified to treat the case when the condensate contains a mixture of molecular species or when a deposit on a surface consists of a `stack' of uniform layers, each of which has a distinct material composition. Computed transmittance spectra of selected films of mixtures are compared with transmittance spectra calculated with measured optical constants of the mixture.

An analysis has been performed to define the obscuration ratio (OR) of surface particles by considering not only the geometric cross sections of the particles but also their irradiance absorption/scattering characteristics. This analysis shows that part of the `extinct' irradiance due to interaction with the surface particles will be recovered by the surface via forward scatter of the radiant energy flux. Over-prediction of irradiance loss based on the often used assumption of opaque particles can thus be avoided. Consideration of the combined effect of absorption and forward scatter permits defining a more realistic effective OR. Sample solutions have shown that for opaque particles, the OR would be reduced by 50%, and for dust particles, the reduction would be by a factor of 10.

A method is presented that conservatively predicts long term outgassing for materials outgassing diffusely using short term test data. Accurate long term predictions require knowledge of the diffusion coefficient and initial concentrations of each species outgassed from a material which are obtainable only from often prohibitively long term testing. The method presented demonstrates how one can utilize standard 24 hour TML/CVCM data or short term outgassing rate testing data to conservatively predict long term outgassing. The method is based upon diffusion theory which predicts that the amount of material outgassing is proportional to the product of a constant, the square root of time, and a function that decays with time with maximum value of 1. The conservative approach taken is to assume that outgassing is proportional to a constant times the square root of time, replacing the decaying function with its maximum value of 1.

Spacecraft surface coatings will outgas various molecular components when the spacecraft is subjected to the vacuum of space. Some of these outgassing molecules have the potential to contaminate sensitive, critical optical surfaces on the spacecraft. Some of this outgassing can be mitigated through a thermal vacuum bakeout of the coated structures. The residual outgassing, the return flux, and the deposition of outgassing molecules for the as-flown spacecraft environment needs to be modeled to assess the vulnerability of the spacecraft to this contamination. Laboratory outgassing measurements provide the data that can be used to set the protocols for thermal vacuum bakeout procedures and to develop reasonable models of the in-flight contamination process. Several questions arise: How is the outgassing information affected by the outgassing measurement procedure? After a thermal vacuum bakeout, what happens to the outgassing properties of a sample, especially after long term interim storage? Is the rate of outgassing affected by temperature cycling? How does exposure to ultraviolet radiation affect the rate of outgassing of molecules from coatings and the rate and nature of deposition onto receptor surfaces? What is the influence of primers when used as a conditioner of the metal surface to be coated? How can laboratory outgassing information be related to the to-be-flown temperature of spacecraft outgassing? The purpose of this paper is to describe these issues and to discuss some of them with examples taken from outgassing measurements performed on a black optical paint (Chemglaze Z306).

Effects of contaminants on optical surfaces is a continuing concern for space-based systems-- especially those containing cryogenic optical systems. Effects of contaminant films on mirror bidirectional reflectance distribution function (BRDF) were studied in support of the Midcourse Space Experiment (MSX) Satellite that is scheduled for launch in 1994. This study present experimental results of infrared scattering measurements made on cryogenic optical surfaces that are cooled to temperatures as low as 15 K. At this temperature gases such as nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and water will condense. These are the gases of most concern to the MSX Program. BRDF studies have been completed to determine infrared (10.5 micrometers ) effects as functions of film thickness and angle of reflection for these gases. It has been found that the change in mirror performance depends on contaminant film species, thickness, wavelength, and mirror temperature. Results of the infrared scatter data are compared with previously obtained visible scatter data.

The Midcourse Space Experiment (MSX) ion mass spectrometer (IMS) is a Bennett radio- frequency mass spectrometer designed to measure the concentration of contaminant and ambient ionospheric ions from 1 - 60 amu. The instrument is one of a suite of six onboard contamination instruments, which also includes a neutral mass spectrometer, pressure sensor, quartz crystal microbalance, krypton water vapor monitor, and particulate flashlamp experiment. The instrument is sensitive to an incoming ion flux on the order of 1 X 10⁷ ions/cm²s, which corresponds to an ion concentration of approximately 10 ions/cm³ for ionospheric ions that move at a speed of approximately equals 8 km/s with respect to the satellite. The IMS instrument and calibration are described in the paper. The purpose of the IMS calibration is to determine the detection efficiency for ionospheric and contaminant species that the MSX satellite is likely to encounter.

Employing a quartz crystal microbalance and a quadrupole mass spectrometer in a vacuum chamber, thermogravimetric analyses (TGA) and mass spectrometer analyses have been performed at low temperature on depositions of ammonia, acetone, methanol, toluene, isopropyl alcohol, water, para-xylene, and selected combinations. Deposition of a single species yielded a TGA curve characteristic of a pure substance. Homogeneous binary mixtures, like methanol and water, exhibited a desorption curve which included structure that was intermediate to that observed for pure materials. Sequential layering of one material on top of another also altered the TGA response, and the TGA curve shape was found to be a function of top-layer thickness for the water-on-methanol system. Backfilling the chamber with nitrogen or argon at a pressure of 1 Torr shifted the sublimation temperature of water about 20 K higher.

Four temperature-controlled quartz crystal microbalance (QCM) instruments are on the Midcourse Space Experiment (MSX) spacecraft to measure the accretion of contaminants and to identify the contaminant species using the thermogravimetric analysis technique. Calibration data were used to derive equations for the performance of the thermoelectric temperature controllers in the MSX QCM sensors. The equations relate input power and the crystal temperature to the base temperature. The MSX thermal model with the QCM locations was used to predict the operating temperature of each of the radiators. On orbit, the equations can be used to calculate the QCM radiator temperature from the crystal temperature and the input power.

The certainty with which low density gas measurements can be made on a space based platform is improved by cooperative sensor calibration. The Midcourse Space Experiment (MSX) spacecraft has a suite of 10 contamination monitoring instruments for measuring particulates and gases. Two of these sensors (the Total Pressure Sensor (TPS) and the Neutral Mass Spectrometer (NMS), are specifically designed to measure pressure and are located and directed in a fashion which allows for cross characterization. By their very nature, contamination instruments are difficult to test for accuracy after launch. They are intended to provide the scientific community with a measurement of spacecraft outgassing (in order to validate MSX contamination models and the effectiveness of the contamination control plan) and environmental species. Since neither environment nor spacecraft outgassing is precisely known, an accurate calibration source is not available. Consequently, the best method of verifying flight performance is the comparison of measurements by similar instruments. The early mission environment will provide an opportunity to compare the instrument performance in Argon, Water, and Helium. The stand alone calibration and cross characterization results for the TPS and NMS will be presented.

We have designed, fabricated, and tested two flashlamp-based instruments that will characterize the particulate and water vapor contamination environments aboard the Midcourse Space Experiment (MSX) spacecraft: the Xenon Flashlamp and the Krypton Radiometer. These instruments will operate as part of suite of instruments to monitor the MSX contamination environment over its five-year mission. The Xenon Flashlamp illuminates particles in the field of view of the UVISI Wide Field of View Visible Imager, which in turn measures the scattered radiation. The particle measurement can detect particles smaller than 1 micrometers and can measure cross-field particle velocities from 0.5 cm/sec to 50 m/sec. The Krypton Radiometer measures the local water vapor density. VUV radiation from an array of RF-excited krypton lamps photodissociates H₂O in the fields of view of a filtered radiometer and one of the UVISI Spectrographic Imagers. The radiometer and the spectrograph simultaneously measure the intensity of the resulting OH chemiluminescence. The H₂O density is proportional to that intensity. The spectrograph will provide a positive identification of the radiating species. Instrument descriptions as well as ground test and simulation data are presented.

Particles generated from spacecraft surfaces will interfere with the remote sensing of emissions from objects in space, the earth, and its upper atmosphere. At Optical System Contamination-II we reviewed the sources, sizes, and composition of particles observed in local spacecraft environments and presented predictions of the optical signatures these particles would generate. In this paper we present predictions of the signatures of these nearfield particles as detected by the MSX spacecraft optical systems. Particles leaving spacecraft surfaces will be accelerated by atmospheric drag (and magnetic forces if charged). Our simulations map out the particle trajectories. Both velocities and accelerations relative to the spacecraft x,y,z coordinate system allow the particle to move through the optical sensors' fields-of-view after they leave the spacecraft surfaces. The particle's trajectory during the optical system integration time gives rise to a particle track in the detected image. Predictions of tracks for both staring and scanning systems are presented. Particles can be remotely detected across the UV-IR spectral region by their thermal emission, scattered sunlight, and earthshine. The theoretical, spectra-bandpass-integrated signatures of these particles (as a function of size and composition) is then mapped back onto the UV, visible, and IR sensor systems. At distances less than kilometers, these particles are out of focus, and their image is blurred over several pixels. The absolute irradiances from single particles in the 1 to 100 micrometers size range are added to detector array noise levels to determine detection thresholds for a variety of bandpasses. We show examples of accurate particle position and trajectory retrieval using mouse-based algorithms operating on sensor array images. Particle image blurring over several pixels affects detection sensitivity. Although the eye is excellent at feature recognition, we have developed a variety of automated algorithms for particle track enhancement and extraction to facilitate the analysis of large databases. We discuss and provide examples of the operations that successfully detected particle signatures.

The 10.6 (mu) bi-directional reflectance distribution function (BRDF) of the SPIRIT III primary mirror was measured after each major phase of sensor development and testing. The compiled BRDF history provides useful insights with respect to the cleanliness levels that may be reasonably expected for a cryogenic infrared sensor of this size and complexity. The use of nitrogen blow-off was demonstrated as an effective, low-risk option for `touching-up' critical infrared optics. The BRDF measured before integration with the MSX spacecraft was consistent with the scatter that would be produced by a surface cleanliness of near Level 100. Follow-on BRDF measurements will not be possible, since the SPIRIT III sensor will remain cold and under vacuum throughout spacecraft processing. An internal cryogenic quartz crystal microbalance has been used to monitor molecular redistribution processes that may occur when internal temperatures change during cryogen refills of other cryo-vacuum operations. The CQCM data is easily understood, and will provide a valuable diagnostic during pre-launch processing of the SPIRIT III cryostat.

Operation of thermal control and optical surfaces can be impaired by contamination deposition for space-based systems. Determining the contamination level about the spacecraft and deposition of silicones and hydrocarbons will be studied during the flight of the Midcourse Space Experiment Satellite that is scheduled for launch in 1994. The contaminants will be measured using four thermoelectrically cooled quartz crystal microbalances (TQCMs) which will be mounted on external spacecraft surfaces. Rigorous characterization and calibration measurements were made on six flight TQCMs at the Arnold Engineering Development Center at Arnold Air Force Base, TN. Since the TQCM output frequency depends on some degree on both the crystal temperature and the oscillator-mixer temperature, the magnitude of these effects and the effects of solar irradiation on the TQCMs was established. Long-term frequency drift rates were also determined. The change in TQCM output frequency expected to occur in space was, in some cases less than the magnitude of the frequency changes caused by temperature and solar fluctuations. The results of this study will allow a more accurate assessment of the contamination effects that can be expected during long-term space-flight programs.

Using a 200 MHz Surface Acoustic Wave (SAW) resonator device as a high-vacuum molecular deposition microbalance, similar to a bulk quartz crystal microbalance (QCM), and an often-used 15 MHz thermoelectric QCM (TQCM), a comparison of various parameters was made during a high-vacuum outgassing experiment. The source of molecular outgassing was a bright aluminum foil which was cooled to liquid nitrogen temperature and alternately, to ambient temperature. The two sensors, the SAW QCM and the TQCM were placed next to each other and viewed only the aluminum foil. In this high-vacuum environment, a comparison between various parameters, i.e., mass sensitivity, long term drift rate, stability, thermal effects and dynamic range of the SAW and the TQCM, was obtained.

The mass sensitivity of a 200 MHz surface acoustic wave (SAW) quartz crystal microbalance (QCM) has been determined by comparison with a 10 MHz shear wave (SW) QCM. The calibration technique consisted of exposing the SW QCM and SAW QCM to the same impinging molecular flux, assuming the same rate of deposition on both surfaces, and comparing the change of frequency for the two QCMs. Although the major objective was to determine mass sensitivity at ambient temperature sensitivity was also measured for a range of temperatures between 130 K and 300 K. The materials used to provide the molecular flux were Coray 100 mineral oil, DC 704 silicone oil, and Rheolube R2000 synthetic grease. The mass sensitivity of the SAW QCM measured at 300 K is on the order of 50 Hz.cm²/ng. Mass sensitivity was observed to decrease with temperature, with the lowest value measured being about 39 Hz.cm²/ng at 130 K for Coray 100. The theoretical expression describing the mass sensitivity of the SAW QCM contains two terms, for mass and material elasticity, respectively. The observed decrease in response at lower temperatures (i.e., reduced elasticity) confirm that the material elasticity term, typically ignored at cryogenic temperatures, must be incorporated cryogenic temperatures.

A germanium wafer from the Long Duration Exposure Facility Interplanetary Dust Experiment underwent plasma cleaning to evaluate contamination removal effectiveness for molecular layers that had accumulated over the course of the mission. Angle resolved scattering at visible wavelength was utilized to measure the change in optical performance between the as-received and cleaned portions of the test sample. Results showed a significant improvement in the sample's optical quality with reactive ion cleaning, based on laboratory measurements of bi-directional reflectance distribution. Test procedures, instrumentation, and experimental data (including computed total integrated scatter) are described. Besides detecting and removing environmental contamination from sensitive optical surfaces, these techniques could be applied to semiconductor manufacturing to increase product yield, lower production costs, and improve component reliability.

Contamination control is a critical issue to the manufacture and maintenance of optical components. Particulates and thin films (organic and inorganic) can degrade optical performance. Current cleaning methods are focusing on aqueous-based cleaning and super- critical fluids. Concurrently, environmentally-conscious manufacturing processes are becoming essential for industrial applications. These manufacturing processes emphasize the reduction of water and chemical consumption and hazardous waste production. In this paper, we will introduce a chemical-free laser assisted process that has demonstrated its capability of removing particulates and films from various surfaces including optical. Since this process works with energy flux and a flowing inert gas, it's readily adaptable and cost effective for many industrial applications.

Carbon dioxide (CO₂) gas/solid jet sprays have been proposed for replacing ozone depleting cleaning solvents and for on-orbit cleaning of satellite-borne sensors. We have performed experiments to ascertain the mechanisms of molecular contaminant film removal with commercial CO₂ gas/solid jet spray devices. Infrared measurements of germanium plates coated with various contaminant films were made before, during, and after cleaning with a CO₂ jet spray. The inferred cleaning times and overall cleaning efficiencies combined with the known solubilities of the contaminants in liquid CO₂ suggest that multiple cleaning mechanisms occur: physical removal of the film and solvation of the contaminant into the CO₂ particle. These mechanisms explain the selectivity in cleaning efficiencies of the CO₂ jet spray for different contaminants. We have also measured the electrostatic charging induced by the jet spray on ungrounded substrates, which in some cases, charge up to several kilowatts. The charging results from the difference in work functions of the CO₂ and substrate. The work function is an intrinsic material property, therefore, the extent of charging can be reduced, but not eliminated. Environmental factors that affect the charging and the resultant limitations placed on the use of this device are discussed.

Low level particulate contamination of some of the COSTAR optics during environmental testing necessitated the development of a short duration, low pressure CO₂ jet spray cleaning technique. The technique was proven to be compatible with the high reflectivity UV magnesium fluoride protected aluminum coatings applied to the COSTAR optics at the Goddard Space Flight Center (GSFC). These coatings are easily damaged by solvent flush techniques in the presence of this contamination and by conventional CO₂ jet spray cleaning methods. In addition, the technique adopted here was compatible with the geometry of the fully integrated and aligned optics on the COSTAR. Eventually, thorough testing of intentionally contaminated test mirrors and a final UV throughput test of the flight optics indicated that the instrument would still meet specifications, therefore the COSTAR flight optics were not cleaned. However, we proceeded with the qualification of the process so that it would be available for use if cleaning became necessary prior to launch. Success criteria for the cleaning included minimal degradation of reflectivity, surface roughness, near-angle scattering, minimal production of pinholes in the coating, compatibility with the polyurethane bond applied to the optics and high efficiency of particulate removal. The technique was qualified for COSTAR specific coatings and particulate contamination and should be recertified for conditions departing from those baselined in our study.

Traditional solvent-based precision cleaning methods are becoming increasingly unsatisfactory due to harsher environmental regulations and more stringent cleanliness requirements. The carbon dioxide (CO₂) solid/gas jet spray cleaning technique is a superior, environmentally compatible, nonabrasive alternative cleaning technology. Experimental results demonstrating 100% removal of submicron-size particles and several types of molecular films from a variety of substrates are presented.