The induced molecular environment of a spacecraft and the contamination of instruments and surfaces are largely dependent on the molecular outgassing of its materials. The materials are selected in accordance with the criteria that when a sample of that material is held in vacuum for 24 hours at 125°C, it will not lose more than 1 percent of its mass nor will it deposit more than .1 percent of its mass on a 25°C collecting surface. Many materials have been tested for these criteria and other spacecraft materials are being routinely tested. The results are readily available in the literature. Unfortunately, the criteria and the test results neither indicate mass losses at other temperatures, nor do they provide data on mass loss as a function of time. Both of these parameters are needed to evaluate the induced environment and to estimate surface degradations. In this paper a large number of normalized plots of material mass losses versus time have been prepared based on theoretical and experimental behavior of materials under vacuum. They cover a range of temperatures up to 125°C and outgassing activation energies up to 40 kcal/mole. The plots are intended to provide a description of the outgassing kinetics of the material given the results of the criteria test and some additional data from the same type of test carried out at other temperatures and/or for different testing time. This approach can add to the present characterization of materials and avoid, in many cases, the costly long term tests which measure continuously the mass loss of a sample at a specific temperature.

Contamination mechanisms such as particulate accretion, molecular film accretion, and impact cratering can degrade the quality of an optical surface by decreasing its throughput (transmissivity or reflectivity) and/or by increasing its total integrated scatter (TIS). The sensitivity of an optical sensor to a given contaminant species depends upon a number of factors, including the spectral passband of the sensor, the type of surface (mirror or lens, coated or uncoated, etc.), the relative intensities of signal and stray light, and the desired output of the system. A precise analysis of an instrument's contamination sensitivity must consider all of these factors. It is possible, however, to define "acceptable" levels of contamination as those which produce small throughput and TIS degradations in comparison to manufacturing defects and unavoidable environmental conditions. These criteria may be used to calculate a conservative value for the minimum separation between a spaceborne optical sensor and a contamination source such as a solid fuel rocket motor or a chemical release module.

The weight loss of twenty different typical Shuttle materials was measured with a thermogravimetric analyzer as the material temperature was increased from ambient to 300°C. An additional ten tests were performed where conditioning of the material varied. The materials were selected from each general grouping such as adhesives, coatings, lubricants, encapsulants, elastomers, and resins. Care was taken in the preparation, curing, and preconditioning of the materials to simulate flight use. Making the assumption that the weight loss follows first order rate theory, the source outgassing parameters for these thirty materials is presented.

As the DOD makes the transition into the Shuttle era, experimenters are becoming more concerned about the environmental contamination of the Shuttle Orbiter. Their concern is that Shuttle contamination could prevent major planned experiments from obtaining required data, particularly sensitive infrared systems (e.g., Talon Gold, SIRE, STMP). The performance of optical experiments could be limited by the natural background, by light scattering and emissions from particulates and molecules, and by molecular absorption. Deposition and optical surface degradation may prove to be extensive problems, particularly for cryogenic optics. Other experiments such as communications and space environment tests may also be affected by deposition as well as electromagnetic interference. It has been known that the Shuttle's environment could cause contamination problems during water dumps, thruster firings, paint outgassing and other sources. Predictions have been made, but the contamination species and extent of these problems will not be known definitely until space measurements are made. This paper identifies the contamination types, sources, and their possible effect on particular types of space experiments. The paper also discusses NASA's plans for contamination measurements and the Space Test experiments which could contribute to early resolution of the contamination questions.

The ultraviolet light coronagraph being developed for Shuttle by the Harvard-Smithsonian Center for Astrophysics is described. Effects of Shuttle contaminants on ultraviolet coronagraphic observations are discussed and column densities for acceptable attenuation are provided which are generally applicable to high spectral resolution measurements in the 600 Å -1700 Å spectral range.

Diffusion of outgassed shuttle bay materials is of concern to payloads especially if optics and sensitive instrumentation are not protected. Contamination can occur which will reduce data collection ability and lifetime of shuttle launched spacecraft. Therefore, prediction and prevention of such contamination is of concern. A diffusion solution is discussed which is capable of making such predictions. Use of a protective cover and/or a purge is also discussed as methods of contamination prevention and their effectiveness is analyzed as a function of cover vent size and flow rate.

As part of the development of the Space Shuttle, a payload integration system has been established. This integration system or process encompasses several technical disciplines, one of which is concerned with the control of molecular and particulate contamination. Specific integration procedures and documentation have evolved that reflect the incorporation of payload/Space Transportation System contamination requirements and capabilities. Of the 38 payloads in the payload integration system currently, about 20% are considered sensitive to contamination in that special precautions must be taken to ensure that contamination from the Space Shuttle Orbiter does not impair payload function. Most of these payload requirements have been satisfied by the incorporation of controlled ground operations discipline and installation of a payload bay liner, which isolates the payload from the Orbiter systems. Some payloads, however, provide covers for sensitive payload instrumentation.

With inception of the Space Shuttle Program and the evolution of payload systems and instruments to ultrasensitive levels, the vulnerability of payload systems and instruments to the induced contamination environment has become a prime consideration in mission operations and hardware design. This paper presents the current management philosophies and the systems level approach being applied to payload integration to address the discipline of contamination and insure its control. Applicable documentation and the status of the current contamination data base are discussed. Existing analytical tools and their applicability to integration analysis are presented, and typical analysis results are provided. All program phases from initial concept design through ground operations and on-orbit activities are addressed as related to state-of-the-art technology and management philosophy. The status of this approach as applied to current Shuttle integration activities with NASA, DOD, and spacecraft contractors is presented to reveal basic problems which exist in such areas as spacecraft contamination requirements, KSC ground facility cleanliness control and weaknesses in analytical tools and related data bases. Ultimately, recommendations are provided for improvements deemed necessary to refine the technology of payload contamination integration.

The Shuttle Payload Integration Facility (SPIF) is a payload processing facility at the Eastern Launch Site (ELS), Cape Canaveral Air Force Station (CCAFS) which has been designed to accommodate assembly, test, and checkout operations for a number of Shuttle payloads, many of which are contamination sensitive. In general, the SPIF was designed to meet class 100,000, per Fed. Std. 209B (Reference 1), cleanliness requirements and operate as a class 100,000 clean area. However, due to the expansiveness of the building (which includes several airlocks, a transfer aisle, and integration cells), the variety of hardware to be processed through the facility (payloads, upper states, and support equipment), and the variety of operations to be performed for these hardware, many different contamination control methods must be carefully integrated and implemented to maintain an overall clean environment. In instances where the operation being performed is not generally compatible with the clean environment, uniaue and innovative contamination control methods must be developed with respect to ease of implementation as well as effectiveness of contamination control.

The Space Computer program is a systems level analytical model designed to three-dimensionally synthesize the dynamics of the induced on-orbit molecular contaminant environment of the Shuttle Orbiter (SO), Spacelab (SL), and various payloads. The SPACE code is the first systems level code to consider: 1) detailed spacecraft geometry with surface shadowing; 2) a complex mixture of arbitrary contamination sources including both point sources (RCS engines, overboard vents) and extended sources (surfaces), and; 3) a variety of contamination transport mechanisms including direct source-to-surface mass transfer, and impingement flux from scattering due to intermolecular collisions. Significant improvements to the model have resulted from contract activities with MSFC and JSC. These improvements include: 1) an evaluation of the multiple reflection option to determine the significance of this phenomenon for a typical Shuttle Orbiter/Payload configuration; 2) the design and development of new logic to accumulate predicted deposition levels for consecutive orbital time slices and thus provide the capability for automated full mission simulations; and, 3) the development of a simplified version of the SPACE code (Mini-SPACE) to provide a quick-look analysis capability for mission planning purposes circumventing the complex procedures required to model a configuration and prepare the detailed input data files needed for analysis with SPACE; and 4) an interface with the DISSPLA system utility plot package to provide an enhanced presentation of SPACE output data. This paper provides an overview of SPACE program capabilities, a detailed description of recent improvements, and a summary of the anticipated future activities.

A program for analyzing the flowfield parameters in the neighborhood of the Space Shuttle Orbiter (herein referred to as Shuttle) has been developed. The program uses the Direct Simulation Monte Carlo Method, which is a completely probabilistic Monte Carlo technique capable of analyzing 3-dimensional steady or unsteady flow with prescribed internal and external boundary conditions. The freestream flux densities incident on the external flow-field boundaries are calculated from the drifting Maxwellian gas properties of the freestream. The flux entering the flowfield from the internal boundary is calculated from the outgassing flux density distribution over the Shuttle external surface and the prescribed discrete source fluxes. This technique produces a numerical flowfield solution which is the probabilistic equivalent of a complete solution of the time-dependent, 3-dimensional Boltzmann equation. Flowfield results are presented for the following configurations: (1) Shuttle angles of attack of 0° and 90°, (2) freestream density from 10⁹ to 10¹¹ cm^-3, (3) Shuttle out-gassing flux density from 10¹³ to 10¹⁶ cm^-2 s^-1, and (4) operation of the aft downfiring vernier Reaction Control System (RCS) engine. Results are presented for column density distribution of outgassed and engine species and for the flux density of outgassed and engine species incident on the Shuttle bay and the windshield.

The solid propellant apogee insertion motor (AIM) on board the United States Air Force P78-2 SCATHA (spacecraft charging at high altitudes) satellite is of the same general design as that of the inertial upper stage (IUS) that will raise payloads from space shuttle orbits to higher altitudes. Therefore, contamination effects arising from the firing of the AIM would be of interest to those concerned with the IUS or other solid propellant rockets as possible sources of contamination. Several of the contamination detectors on the P78-2 satellite were operating prior to, during, and following the AIM burn. These detectors consist of (1) two trays of eight calorimetrically mounted thermal control coatings (TCCs), (2) a temperature controlled quartz crystal microbalance (TQCM), and (3) a retarding potential analyzer (RPA). The data from these sensors have been analyzed to look for contamination due to the firing of the AIM. No contamination was detected with either the TCCs or the TQCM. Some anomalies were noted in the data from the RPA. However, these anomalies, if they actually correspond to AIM-related contamination, represent an upper limit of only 0.8 ng/cm² at the detector location. Although these instruments are sensitive to molecular contamination, they are relatively insensitive to contamination in the form of particulates. Furthermore, the instruments were not optimally located on the vehicle to detect AIM products. The data do set upper bounds on the condensable molecular contamination that reached two locations on a typically configured satellite during the firing of an intermediate sized solid propellant motor.

The Space Shuttle is planned as a major DOD space capability through the 1990 time frame. Since many of the DOD programs involve electro-optical sensors there is concern that contamination of the shuttle environment may be a serious problem for experiments using sensitive infrared technology. This paper describes the AFGL CIRRIS experiment a it relates to this problem. CIRRIS (Cyrogenic Infrared Radiance Instrumention for Shuttle) is a high spectral resolution cyrogenic Michelson interferometer-spectrometer coupled to a high straylight rejection telescope with coaligned photometer and cameras. The instrument's features and mission objectives will be described as they pertain to characterization of Shuttle contamination and measurements of the infrared earthlimb background in the 2.5 - 25um region.

This paper presents the results of a contamination analysis and computer modeling study performed for the Space Infrared Experiment (SIRE) using the Space Transport System (STS) Shuttle Orbiter as the launch vehicle for the proposed seven-day sortie mission. These results will provide an accurate description of the deposition levels on the telescope primary mirror and of the molecular number column density (NCD) along the telescope line-of-sight. The planned Helium Purge System was assumed not to be operating. The contribution to the contamination environment of any cargo element, other than SIRE and its pallet, was not considered in this study. The study considers five potential contamination sources, including the flash evaporator vent effluents and the vernier reaction control system (VCS) engines plume constituents.

A new volatile condensable materials (VCM) facility has been constructed. The facility features a unique in situ Fourier transform infrared spectrophotometric system in addition to a quartz crystal microbalance and quadrupole mass spectrometer. Contaminants can be collected and subjected to infrared spectroscopy at the collection temperature, circumventing problems associated with ex situ infrared measurements. Preliminary results indicate that VCM, with deposition thicknesses less than 200 Å, can be identified.