Attention is given to a space-borne engine plume experiment study to fly an experiment which will both verify and quantify the reduced contamination from advanced rhenium-iridium earth-storable bipropellant rockets (hot rockets) and provide a correlation between high-fidelity, in-space measurements and theoretical plume and surface contamination models. The experiment conceptual design is based on survey results from plume and contamination technologists throughout the U.S. With respect to shuttle use, cursory investigations validate Hitchhiker availability and adaptability, adequate remote manipulator system (RMS) articulation and dynamic capability, acceptable RMS attachment capability, adequate power and telemetry capability, and adequate flight altitude and attitude/orbital capability.

Measured outgassing rates are presented and compared for several laminated carbon/epoxy and carbon/thermoplastic structural materials. Outgassing rates were measured with the samples at 298 K, with a temperature controlled quartz crystal microbalance (TQCM) collector at one of two temperatures. Mass accumulation at 175 K was used to collect primarily large polymeric molecules escaping the composite matrix. Mass accumulation at 100 K was used to collect all significant outgassed species including water. Once characterized, some samples were clad with molecular barrier coatings and retested to determine whether cladding could impede outgassing in space-like conditions. The outgassing test procedures employed are described, and a comparison of these with the ASTM E595 procedure is discussed.

Once a particle is released into the telescope field-of-view, regardless of the phenomena responsible for dislodging it from the surface, it will move through the baffle tube volume until it either leaves the open end of the tube or strikes another surface. Upon impact with a surface the particle will either stick to it or rebound at some angle and with some associated energy loss. 4BOUNCE and VBOUNCE are codes which model contamination transport in spaceborne sensors. 4BOUNCE is a fast-running code which uses a smooth cylinder and parameterizes the effects of baffle vanes. VBOUNCE models all surfaces explicitly, including vanes. Both models are intended to track particles of various materials, mass and velocity combinations as they bounce within a sensor. Trade studies were made to identify the important parameters based on the output sensitivity to the varied parameter. The results of interest for contamination impact on sensor performance is the fraction of particles remaining within the sensor view as a function of time and mass.

The 3D diffusion equation is solved for molecular outgassing from a porous layer of sample material covering an inert substrate in the form of a right circular cylinder. Expressions are derived for the time dependence of the residual concentrations of outgassable materials in the porous layer and the masses of outgassable materials that are leaving the porous layer. A separate diffusion function can be extracted from outgassing measurement data for each grouping of outgassing molecules corresponding to the mass deposited on temperature-controlled quartz crystal microbalances held at different temperatures. The different time dependences of the different diffusing species are described by individual diffusion coefficients. The analytic form of the diffusion function permits extrapolation of residual concentrations of outgassing molecules to long times for each grouping of molecular components.

Several molecular species (hydrocarbons) outgassed from spacecraft materials adhere and darken on satellite optical surfaces when exposed to solar ultraviolet (UV) radiation. This absorbing molecular film of photolyzed contamination can severely degrade spacecraft optical system performance. In the Optical Scatter and Contamination Effects Facility (OSCEF) at TRW outgassed molecular species can be photo-deposited onto witness optics and an adjacent quartz crystal microbalance with vacuum ultraviolet radiation, simulating a spacecraft UV illuminated environment. Measurement of outgassing rates and concomitant photodeposition efficiencies provides useful data required in the selection of present and new spacecraft materials and accurate predictions of platform operating lifetimes. This paper will describe the methods used to measure the molecular outgassing and photodeposition rates of species from several spacecraft materials in which the samples are used in their operational configurations (no heating or grinding of the sample as in the ASTM E595 test), thus providing data highly representative of on-orbit photodeposition conditions.

Exhaust from bipropellant rocket boosters is a potential source of contamination for cooled sensor optics. The effect of monomethyl hydrazine nitrate (MMH-nitrate) on scatter at 3.39 microns is investigated as a function of temperature in the range of 200-350 Kelvin and as a function of thickness. The space-simulated deposition of MMH-nitrate took place under high vacuum onto a bare beryllium mirror.

Exact methods have been developed for calculating light scattering from particles on a perfectly reflecting surface. The computed solutions obey Maxwell's equations and the appropriate boundary conditions. A brief discussion of the theory is followed by a presentation and discussion of selected scattering results. Comparisons are made with the predictions of Young's forward scatter Mie theory model. Under certain conditions, the exact results differ significantly from Mie theory. The exact differential cross sections exhibit large amplitude oscillations that are not predicted by Mie theory. The bidirectional reflectance distribution function (BRDF) is also calculated using exact scattering theory for both spherical and hemispherical particles that are both absorptive (complex index of refraction) and nonabsorptive (real index of refraction). These exact BRDF results are compared to the predictions of Young's model.

SPIMS is capable of detection and sizing of particles passing through a detection zone that is outside the detection system hardware. The particle detection is accomplished through the digital measurement of the shadow width of a laser source. The system is engineered as a space experiment, as a result of which the design is fully automated, solar blind, employs a robust digital detection scheme, is small and lightweight, and uses minimal power.

A particle monitor based on the near forward scattering of light from an AlGaAs laser diode was modified for space flight and proved to be robust and reliable during an actual space launch. Near-field particles could result in large extraneous signals from the IR, visible and UV telescopes on board a spacecraft because of their proximity to the sensors. It is therefore desirable to build a particle monitor to go with optical sensors in order to correlate various particulate events with spacecraft operations, so that their effects on the sensors can be corrected. This device, along with the power supply, associated analog and digital electronics, and mechanical mounting will be described. Particulate measurements during ground testing will be presented.

Spacecraft-produced contamination in the optical viewing path surrounding the sensor will obscure or degrade the far-field observations. We present the predictions of the radiances and their spectral distributions produced by particles surrounding orbital spacecraft. This paper emphasizes the composition dependence of the scattering signature. Predictions are presented for likely contaminant species and size distributions modeled and observed on previous space observations. Predictions for silver, aluminum, alumina, carbon, carbon dioxide and water ice, silicon dioxide, and titanium dioxide are presented. The wavelength-dependent scattering indices produce spectrally structured radiances. The balance between earthshine and solar illumination in their wavelength-dependent emissivity produces size-dependent temperatures and spectra.

The sensitive, high resolution CIRRIS-1A radiometers/interferometer provided a unique capability to probe the optical environment surrounding the shuttle on the STS 39 mission. Ground processing was carefully controlled to minimize the contamination levels. Early in the mission all surfaces were subjected to extended solar exposure. These efforts were successful in that most of the data showed no evidence of contamination effects. However, particulate contamination effects were occasionally observed. The range and size of discrete particles are extracted from the particle radiances, spectral distributions, and blur circles.

Results of an analysis of intensified video photographs of a twilight venting of excess water from Space Shuttle are presented. The particle sizes, densities, and temperatures derived from the visible data are applied in estimating UV and IR radiances of the ice/vapor-containing volumes near Shuttle Orbiter, using a recently developed gas-transport/excitation model. The mean radius of the fragmentation-product droplets is 0.13 +/- 0.02 cm. This radius decreases by less than 5 percent over a 2.5-km initial flight path, and these particles survive for several hr. In the UV, intensities of radiation from the fragmentation particles fall off with decreasing wavelength due to the decrease in spectral irradiance of sunlight. In the IR, the mm particles are optically thick, while ice particles not greater than 0.3 micron are inefficient scatterer-radiators, except near 2.7 microns. The large-droplet component thus dominates the radiances even in projections to distant sensors, suppressing the severe spectral structure characteristic of the small droplets.

Although most optical materials are inert to the ambient low earth orbit environment, high velocity oxygen atoms will react with adsorbates to produce optical emissions from the ultraviolet into the infrared. The adsorbates arise from chemical releases or outgassing from the spacecraft itself. We have been investigating kinetic and spectral aspects of these phenomenon by direct observation of the 0.2 to 13 micrometers chemiluminescence from the interaction of a fast atomic oxygen beam with a continuously dosed surface. The dosing gases include fuels, combustion products and outgassed species such as unsymmetrical dimethylhydrazine (UDMH), NO, H₂O and CO. The surface studied include gold and magnesium fluoride. In order to relate the results to actual spacecraft conditions these phenomena have been explored as a function of O atom velocity, dosant flux and substrate temperature. UDMH dosed surfaces exhibit spectra typical (wavelength and intensity) of carbonaceous surfaces. The primary emitters are CO, CO₂, and OH. H₂O dosed surfaces are dominated by OH and /or H₂O emission while CO dosed surfaces are dominated by CO and CO₂ emissions. The nitric oxide dosed surface produces a glow from 0.4 to 5.4 micrometers due to NO₂^* continuum emission. The emission was observed to increase by a factor of two upon cooling the surface from 20 degree(s)C to -35 degree(s)C.

The analysis of CIRRIS 1A (Cryogenic InfraRed Radiance Instrumentation for Shuttle) interferometric and radiometric data obtained during the flight of STS-39 (28 Apr - 6 May 1991) reveals the presence of IR emission in the 400-900/cm (11-25 micron) region not attributable to atmospheric emission. In this paper, data are shown which identify the signal as nearfield water vapor present during all CIRRIS IA observations. Variability of the near-field water vapor emissions is characterized and compared to mass spectrometer data also obtained on STS-39 (QINMS). Further investigation indicates that the water is excited to extremely high effective temperatures, possibly in excess of 9000 K. The data presented support the theory that water outgassed from the shuttle tiles is highly excited by collisions with atmospheric O, classifying it as a type of shuttle-induced glow never before measured in the LWIR.

Efforts to reduce or eliminate contamination and off-axis leakage for the Cryogenic Infrared Radiance Instrument for the Shuttle (CIRRIS) 1A program flown on STS-39 are examined. The question of whether the Space Shuttle is a viable platform for space measurements is addressed. Mission restrictions and system precautions are reviewed. Results obtained are compared to the current models and previous data. The data show how telescope leakage and/or contamination effects can dominate the minimum signal floor and place a limit on the weakest signal that can be measured when these undesired elements are present. The Space Shuttle is found to be an acceptable platform for high-sensitivity earthlimb background and celestial measurements if prudent clean procedures are followed. Acceptable mirror bidirection reflectance distribution function can be monitored over a considerable period of time if the sensor has been pumped for a considerable period of time and careful handling procedures are followed.

The Midcourse Space Experiment (MSX) satellite is a space-based sensor platform primarily designed to collect data on the phenomenology of target detection and tracking. Because of the possible deleterious effect of contamination on these sensors, a suite of contamination monitoring instruments are also included in the satellite. These instruments are the Total Pressure Sensor (TPS), the Contamination Experiment Mass Spectrometer (CEMS), the Ion Mass Spectrometer (IMS), the Cryogenic Quartz Crystal Microbalance (CQCM), four Temperature-controlled Quartz Crystal Microbalance (TQCM), the Xenon Flashlamp Experiment (XFE), the Krypton Flashlamp Experiment (KFE) and the Spirit III Mirror Cleaning Experiment (SMCE). The philosophy of Contamination Experiment (CE), its calibration and testing, modeling and the data to be collected will be discussed.

Chemglaze Z306 flat black polyurethane paint on Chemglaze 9922 epoxy primer is the most predominantly used optically black coating on the MSX spacecraft. All MSX surfaces painted with Chemglaze Z306/9922 were baked at 90 - 100 degree(s)C under high vacuum to reduce the potential outgassing during ground operations and on-orbit. Analytical measurements have been performed to verify the bakeout efficiency, identify the outgassing products, and assist in quantitative predictions of on-orbit outgassing rates and their effects. The bakeout of the SPIRIT III telescope main baffle was monitored using a quartz crystal microbalance (QCM) and residual gas analyzers. The apparent outgassing rates of organic species decreased significantly during the bakeout. Gas chromatography/mass spectrometry (GC/MS) and FTIR analyses of cold trap samples collected at intervals during the bakeout were conducted in order to identify the outgassing species. The outgassing products at 100 degree(s)C of individual samples of G-10 fiberglass epoxy and Chemglaze Z306/9922 were analyzed using GC/MS to determine the source of the various species observed during the bakeout of the baffle. These analyses provide baseline data which will assist in the interpretation of contamination measurements (QCM, witness mirror film accumulations, and residual gas analyses) to be performed during SPIRIT III sensor integration and test.

Experimental studies on the silicone oil-damped actuators used to deploy solar panels on satellites were performed under a variety of thermal conditions. The studies were performed in order to determined if material, detrimental to the performance of the panels or other similar equipment, emanated from the actuators. It was observed that volatile components present in the silicon oil were not released from the interior of the device during thermal cycling. It was observed, however, that the surface of the test actuator examined was contaminated with a volatile hydrocarbon(s) as a consequence of an inadequate cleaning process. This process was modified and flight actuators were found to be adequately free of this contamination.

This paper presents the results of an investigation of the operational characteristics of two cryogenically cooled quartz crystal microbalances (CQCM) which are flight units for the Midcourse Space Experiment (MSX) program. The units were operated at temperatures that ranged from 15 K up to 300 K. During the course of this investigation, the CQCMs were temperature cycled over this range for 5 complete warmup/cooldown cycles using warmup rates of 2.5 K/min and 1.0 K/min. There was concern over stop/start operations on orbit wherein the CQCM power could be turned off for some time. The CQCMs were cycled in this manner to determine the return frequency variations after power restoration. A three week drift test at 15 K was carried out to determine the drift in CQCM frequency with time. Temperature effects of the heat sink attached to the CQCM base were also determined by varying this temperature. Finally, films of nitrogen, oxygen, carbon dioxide, and water were deposited at the 15 K base temperature, and a thermogravimetric analysis was done for each of the gases condensed, both for individual gases and for gas mixtures. The results of these analyses will be used to interpret on-orbit analysis of contaminants that are condensed during operation of the SPIRIT III telescope on the MSX satellite.

Many systems contain cryogenic optical systems that operate at temperatures where gases such as nitrogen, oxygen, carbon dioxide, and water will condense. This study presents experimental results of the effects of these gases condensed on highly polished (superpolished) mirror surfaces cooled to temperatures as low as 15 K under vacuum conditions. Using these gases as contaminants, the bidirectional reflectance distribution function was obtained at a wavelength of 0.6328 micron for various contaminant film thicknesses up to 8 microns. Most of the data were obtained using as the mirror surface the superpolished sense crystal of a previously developed quartz crystal microbalance (SPQCM). The SPQCM allowed the mass of the actual contaminant layer to be measured directly.

The Bhatnagar-Gross-Krook (BGK) solution technique was used to predict molecular return flux from surface outgassing of the Mid-Course Space Experiment (MSX) spacecraft. The BGK predictions were compared to those from a Direct Simulation Monte Carlo (DSMC) study. While the DSMC solution technique provides a rigorous numerical solution of the Boltzmann equation, it requires substantially more model development time and computer resources. Conversely, the BGK method yields an approximate solution to the Boltzmann equation but is simpler to use and numerical solutions can be rapidly obtained. A comparison of the two solutions, based on MSX spacecraft's near-free-molecular contamination environment, shows that the BGK predictions are within the statistical uncertainties of the DSMC results. This favorable comparison indicates that the BGK technique for modeling return flux to the MSX spacecraft is sufficiently accurate and cost effective.

This paper describes a molecular accommodation (sticking coefficient) model for predicting molecular deposition characteristics on optical surfaces under various incident-flux and surface-temperature conditions. The model is based on the simple, but general, detailed balancing concept that the deposition flux is equal to the difference between the incident flux and the desorption/re-evaporation flux, the latter assumed to be in an Arrhenius form involving an effective activation energy (a combination of the heats of desorption, vaporization, migration, etc.). By defining sticking coefficient as the ratio of deposition flux to incident flux, a general sticking coefficient formula in terms of the incident flux, the activation energy, and the surface temperature can be derived. This model can be expressed in a functional form containing the activation energy term and two other empirically determined gas-surface interaction parameters. Hence, sticking coefficient can be used as a correlational physical quantity to determine the deposition flux. The model has been applied to the MSX (Mid-Course Space Experiment) UVISI (Ultraviolet and Visible Imager and Spectrographic Imager) internal contamination problem. The main concern here was possible molecular deposition on UVISI mirrors due to Chemglaze Z306 paint outgassing during MS mission flight. Our approach was to derive a general Chemglaze Z306 sticking coefficient formula based on correlation with Chemglaze Z306 outgassing/deposition data at high source temperatures (75 degree(s)C, 125 degree(s)C, and 300 degree(s)F). This formula was then used to predict UVISI deposit buildup under relatively low source/mirror temperature conditions (-40 degree(s)C to +20 degree(s)C) during MSX mission flight.

A system for detecting and removing contaminants from a half-meter diameter primary mirror in a simulated space telescope has been designed, fabricated, and tested under vacuum conditions. Various molecular and particulate contaminants are deposited on the mirror by special sources in the open end of the telescope, causing an increase in optical scatter which is detected at infrared wavelengths by special sensors on the wall of the telescope. Depending on the type of contaminant, either of two systems of contamination-removal hardware is activated to clean the mirror surface and restore the original scattering level.

Results of an investigation of four FOV particulate contaminant removal methods - photon flux, neutral molecular flux, ion flux and electrostatic field - are presented. Minimum detectable particle sizes are calculated for IR sensors operating under three different scenarios - ground-, limb-, and space-viewing. Trajectories of particles dislodged from spacecraft at several altitudes are calculated. The neutral molecular flux method is the fastest but suffers from the disadvantages of unwanted thrust and limited gas supply. The ion beam method seems effective but slower, as it requires rastering. The radiation pressure method is energy-inefficient; a large power supply is necessary. The electrostatic field method can be effective only if the altitude is above 10,000 km.

Molecular species outgassed from spacecraft materials adhere tenaciously to and darken spacecraft surfaces when exposed to solar ultraviolet (UV) radiation. Such deposits severely degrade the performance of optical systems operating at UV and visible wavelengths. Data is presented which demonstrates the feasibility of a UV/Ozone cleaning technique in removing such deposits in a space-compatible configuration without damage to the optical surface. The technique involves the UV irradiation of the optical surface in the presence of low pressure molecular oxygen, resulting in the photolytic formation of ozone (O₃) and subsequent photochemical removal of the contamination.

Space optical systems operating at cryogenic temperatures may have stringent contamination levels due to high off-axis rejection requirements for the optics. The extreme difficulty in launching and maintaining clean cryogenic optics on-orbit is alleviated by incorporation on-orbit cleaners. This paper describes a jet spray method for removing contaminants from space optics operating down to 30 K and the apparatus. Results of experiments performed on four substrate materials using various cleaning snows and jet spray arrangements will be discussed. Cleaning efficiencies of the jet spray were measured using an in situ bidirectional reflectance distribution function (BRDF) scatterometer built into the space simulation chamber.

The location of particulates in and about a telescope assembly after jet spray cleaning of a contaminated primary mirror surface under vacuum conditions is determined. The Pathfinder experiment described here is designed to track both the location and level of residual particulate contamination in a simulated telescope assembly after jet spray. Silicon witness plates at various positions in the telescope mockup are used to track remaining contamination after jet spray cleaning of a severely contaminated primary mirror. Scatter measurement at a wavelength of 0.5145 microns is used to determine the contamination level of the silicon witness plates before and after jet spray cleaning. Analysis of scatter and visual particle counting data demonstrated that 99.99 percent of particles are removed. Residual particles levels inside the tube are determined to be on the order of background levels.

Two methods of ion cleaning of contaminant films from spacecraft optics while on orbit are examined. The first method uses energetic electron sputtering, and the second uses low-energy oxygen ion (LEOI) reactive etching. Water, ammonia, and carbon dioxide cryofilms with electron sputtering have been successfully removed. The mirror materials being cleaned include bare beryllium and protected aluminum coated optics. No damage to these ultralow-scatter mirror materials has been observed, even when the mirrors are purposely overcleaned with electrons by any orders of magnitude. Although electron cleaning sometimes polymerizes or carbonizes organic contamination instead of removing it, LEOIs are able to clean both polymerized and unpolymerized organic material at room temperature without causing damage.

A detailed model is presented for the pulsed-laser cleaning of a gold mirror surface. Temperature dependencies of the substrate thermal and optical constants were considered since these constants are sensitive to thermal variations, particularly at cryogenic temperatures. Computations of the heating of the substrate were done in order to ascertain damage thresholds. Calculations were also done for the heating of films on the metallic substrate that were either totally absorbing or totally transparent to the laser radiation. Comparisons of theory with experiments are made.

The use of a temperature-controlled 200-MHz SAW resonator piezoelectric mass microbalance to monitor the mass of nonvolatile residue (NVR) deposited on its surface in real time is reported. The fundamental frequency of this device is mainly dependent on the configuration of the transducers and not on the thickness of the substrate. Therefore, higher operating frequencies can be achieved without reducing the thickness of the crystal. The real-time instrument was integrated onto a conventional stainless steel NVR plate and operated flawlessly over a 14-d period at Kennedy Space Center and successfully measured less than 1 ng/sq cm d NVR contamination. Contamination episodes detected by the instrument were correlated with scheduled activities on the test stand. Under the assumption of a baseline noise level of +/- 2 Hz, the absolute mass lower limit of detection would be 0.065 ng/sq cm. This would enable the detection of a daily NVR deposition rate of less than 0.1 ng/sq cm d.

The Space Based Visible sensor is a high straylight rejection telescope whose performance is driven by the low scattering surfaces of its primary and secondary mirrors. The scattering performance of these mirrors is a function of the level of particulate contamination inside the telescope housing during ground processing, launch, and flight. This report describes a test program undertaken at Lincoln Laboratory to minimize the creation and spread of metallic particulates generated from the fasteners used in telescope packaging. Issues such as fastener material, insert material, lubrication, locking methodology, and insert type are described.

A method has been developed which allows optical system designers to determine the effects at the focal plane from noise generated due to contamination in a sensor's near field-of-view and deposited on system mirrors. This method is embodied in the PEARLSS code, which allows an 'end to end' simulation of contamination generation, transport, deposition, and the resulting performance degradation for spaceborne optical systems. The code is constructed in such a way as to allow trade studies over parameters such as system materials, dimensions, operating temperatures and wavebands, pointing directions, orbital locations, and ground-processing cleanliness levels. PEARLSS outputs include a 2-D map of the scattered/emitted noise at the first mirror, the BRDF there due to particle deposition, and a map of the structured noise on the focal plane of the sensor system. All of these outputs are generated as functions of time. A simple test case is run through the code to demonstrate its various capabilities.

Formulas exist for prediction of diffusion limited outgassing rates under isothermal conditions. An algorithm has now been developed that predicts outgassing rates for material species that outgas via diffusion mechanisms for non-isothermal conditions. The algorithm uses initial species mass, diffusion coefficient, activation energy and a temperature history to determine outgassing rates at prescribed times. The algorithm accounts for bulk material temperature variations through time but does not account for thermal gradients through the material thickness. The non-isothermal mass loss equation is derived from a basic isothermal mass loss equation with the term that indicates species molecular propagation for the non-isothermal conditions. For isothermal conditions, the product of D(T) (where temperature T, is constant) and time is a measure of the species molecular propagation. This term in the isothermal mass loss equation is replaced with the term for nonisothermal molecular propagation, which is the integral over time of D(T) (where temperature, T, is time dependent). Temperature dependent outgassing rates are calculated by numerically differentiating the time and temperature dependent mass loss predictions. Mass loss rates for the non-isothermal conditions are compared to isothermal mass loss rates.