In order to understand how to achieve a low scatter coating on an 82" diameter mirror, three different coatings, several cleaning processes, and four different coating chambers were utilized. Microphotographs documented many phases of the analysis, including some taken with an electron microscope at 15000X. Xray analysis of the surface particulates were also made. The results of the many experiments led to the careful cleaning of the 82" mirror surface before aluminizing the surface. The post-coating cleaning process used compensated for the inevitable degradation in the surface scattering characteristics due to shipping and storage. The desired mirror Bidirectional Reflectance Distribution Function was achieved with all the measured values being below 5x10^-5 sr^-1.

The previously reported Aerojet Mass Analyzer Program (AMAP-I) for on-orbit satellite contamination prediction has been refined (1.kMAP-II), and its capabilities expanded. The program development is based on a rigorous treatment of surface outgassing kinetics and a molecular transport mechanism. The upgraded AMAP-II Program has a transient analysis capability with a built-in stability criterion for automatic time stepping and incorporates an analytical thruster plume model. The results of an analysis performed on an operational geosynchronous satellite using the AMAP-II Program have shown good agreement with the flight temperature data.

The Shuttle/Payload Contamination Evaluation (SPACE) computer program was designed to three dimensionally synthesize the dynamics of the induced on-orbit molecular contaminant environment of the Shuttle Orbiter and a number of Spacelab payload carrier configurations. The concept of the SPACE computer program originated during the Skylab Program where extensive contamination control activities were conducted. SPACE has the capability to accept any instrument or spacecraft configuration for contamination evaluation through manipulation of program input data . It represents a significant advancement over previous analytical or modeling techniques in that it is the first integrated systems level model of its type to collectively consider geometry (emphasizing surface shadowing), any arbitrary contaminant source(s) and the contaminant transport mechanisms of: 1) direct source-to-surface; 2) return flux due to molecular collisions with the ambient atmosphere and other contaminant molecules and 3) reflection/reemission from structural surfaces. SPACE Program outputs include: 1) the molecular density or thickness of the contaminant cloud through which a scientific instru-ment might view; 2) the contaminant flux to spacecraft or payload surfaces and 3) the level of deposition accumulated on sensitive surfaces. The SPACE Program is operational on CDC 6500 and UNIVAC 1108/1110 computer systems. This paper provides an overview of the SPACE Program, its capabilities and applications.

The ultimate test of the validity of the Martin Marietta Aerospace Shuttle/Payload Contamination Evaluation Computer Program utilized to analyze the induced optical environment of sensitive instruments and systems will be through comparison of model predictions with acquired flight data. A prime opportunity will occur during the early Shuttle and Spacelab missions which will carry the Induced Environment Contamination Monitor (IECM) package. This paper presents the applicable IECM instrument descriptions, an assessment of the applicable IECM parametric measurements and a synopsis of the systematic approach to be employed in verifying the computer model methodology and the significant influencing model parameters.

The Infrared Astronomical Satellite, to be launched in August 1981, will perform an all-sky survey in the 8-120 μm wavelength region. High sensitivity to thermal radiation and the low operating temperature of optics and thermal control surfaces make the IRAS telescope extremely vulnerable to contamination. Four special topics of importance are discussed in this paper: (a) deposition of atmospheric gases, (b) sighting of particles released from the satellite, (c) functions of a deployable aperture cover, and (d) degradation of a radiatively cooled sunshade from spacecraft outgassing. These topics demonstrate how mission strategy, ground cleaning and handling, and hardware design are used to avoid contamination which would degrade telescope performance.

Exhaust products from rocket engine firings can produce undesirable effects on sensitive satellite surfaces, such as optical systems, solar cells, and thermal control surfaces. The Air Force has an objective of minimizing the effect of rocket plume contamination on space-craft mission effectiveness. Plume contamination can result from solid rocket motors, liquid propellant engines, and electric thrusters. To solve the plume contamination problem, the Air Force Rocket Propulsion Laboratory (AFRPL) has developed a plume contamination computer model which predicts the production, transport, and deposition of rocket exhaust products. In addition, an experimental data base is being obtained through ground-based vacuum chamber experiments and in-flight measurements with which to compare the analytical results. Finally, the experimental data is being used to verify and improve the analytical model. The plume contamination model, known as CONTAM, has been used to make contamination predictions for various engines. The experimental programs have yielded quantitative data, such as species concentrations and temperatures, in all regions of the plume. The result of the modelling and experimental programs will ultimately be computer models which can be used by the satellite designer to analyze and to minimize the effect plume contamination will have on a particular spacecraft system.

The accuracy, lifetime, and mission effectiveness of a spacecraft is affected adversely by any degradation of sensitive spacecraft surfaces. With a trend towards more sophisticated and complex spacecraft systems capable of performing multimissions over longer time periods, there is increasing concern about the effects of plume contamination. Analytical tools in concert with a good data base are necessary to predict the transport of plume contaminants and their effects on spacecraft surfaces. This paper describes an assessment of bipropel-lant thrusters, the production and transport of plume contaminants from these thrusters and the use of the JPL Contamination Analysis Program to assess the effects of plume contamination on the Galileo spacecraft.

Spacecraft operating at geosynchronous altitude are subject to sporadic bursts of energetic electrons that can charge vehicle surfaces to multi-kilovolt potentials. Electric fields emanating from these surfaces attract ions and charged particulates from vehicle outgassing and propellant exhausts, which substantially enhance the collection of contaminants. Solar arrays, second-surface mirrors, thermal control paints, and other dielectric surfaces are especially vulnerable because their charge dissipation requires solar photoemission. This study is particularly concerned with sensor contamination from rocket exhaust during geosynchronous orbit insertion. The Inertial Upper Stage and its payloads have been analyzed with three dimensional finite-element models to obtain electrostatic field configurations and with lumped-constant electric circuits for dynamic charging and arcing response. Results indicate these natural charging events seriously contaminate payloads if they occur during orbit insertion maneuvers. Preventive actions are suggested to alleviate the charging and avoid such contamination.

Contamination from. plumes of solid rocket motors has been suspect over the years for the anomalous temperature behavior of many spacecraft systems and subsystems. The presence of contamination only can t determined positively when the vehicle is manned, returned to Earth, or by incontrovertible instrument response. An instrument package has been designed and fabricated to monitor any condensible contamination that occurs during the ignition and burn of a TE-M-7i64-15 apogee kick motor. The results of this experiment will be particularly moaningful to those concerned with. modeling the flow fields and subsequent contamlnation effects of solid rocket motors on critical spacecraft surfaces or on the optics of scientific experiments.

Due to the more demanding and stringent requirements of detectability, the importance of stray light rejection has become a major driver in many instances. In the last ten years, great strides have been made in developing techniques for achieving higher stray light rejection, including analytical computer programs for analysis and experimental facilities for the measurement of these low light levels. The status of some of the problems, techniques, and experiences with the stray light problem is presented in this paper. One area of recent study is the effect of cryodeposition on scattering. The definitions of surface scattering, vital to the standardization of results are shown. Presently available analytical techniques including the software packages GUERAP and APART and the few experimental facilities capable of measuring the stray light rejection of a total sensor are summarized. A comparative study of the analytical and experimental tools is made by means of two specific examples of aerospace application.

A brief descriptive review of the General Unwanted Energy Rejection Analysis Program (GUERAP) is given. Two generic optical sensors are discussed, showing the use of the GUERAP as an analysis program for predicting stray light levels, as well as an aid to the design of baffles for the suppression of stray light. The predictions of the program are shown to agree with measured values of the point source rejection ratio.

This paper reviews those aspects of the near-earth space environment that could have potentially adverse effects on electro-optical systems and their operations in space. As such systems have grown in complexity, their susceptibility to damage by the space environment has grown comparably. As the mission lifetimes have increased, the long term effects of radiation damage, spacecraft charging, and surface contamination have become significant concerns. Current models of the charged particle environment responsible for these effects are presented from the standpoint of their applicability to design needs. Although much still needs to be done, these models are sufficiently accurate that significant improvements can be made in system survivability if the models are employed early in the design phase.

Satellites in geosynchronous orbits have been found to be charged to significant negative voltages during encounters with geomagnetic substorms. When satellite surfaces are charged, there is a probability of enhanced contamination from charged particles attracted back to the satellite by electrostatic forces. This could be particularily disturbing to large satellites using sensitive optical systems. In this study the NASA Charging Analyzer Program (NASCAP) is used to evaluate qualitatively the possibility of such enhanced contamination on a conceptual version of a large satellite. The evaluation is made by computing surface voltages on the satellite due to encounters with substorm environments and then com-puting charged-particle trajectories in the electric fields around the satellite. Particular attention is paid to the possibility of contaminants reaching a mirror surface inside a dielectric tube because this mirror represents a shielded optical surface in the satellite model used. Deposition of low energy charged particles from other parts of the spacecraft onto the mirror was found to be possible in the assumed moderate substorm environment condition. In the assumed severe substorm environment condition, however, voltage build up on the inside and edges of the dielectric tube in which the mirror is located prevents contaminants from reaching the mirror surface.

The ML12 experiment was launched on January 30, 1979, on the United States Air Force (USAF) Space Test Program P78-2 spacecraft, which is sometimes called SCATHA. It was designed to determine if spacecraft charging contributes significantly to the rate that contaminants arrive at exterior spacecraft surfaces, and to establish some of the characteristics and effects of these contaminants. Two sensor types are used in the experiment. One type is a combination retarding potential analyzer (RPA) and temperature controlled quartz crystal microbalance (TQCM). With it, distinction can be made between charged and uncharged arriving molecules, and information can be obtained concerning the temperature dependence of contaminant adsorption and desorption rates. The other sensor type is a tray of calorimetrically mounted thermal control coating (TCC) samples. Samples of different spacecraft surface materials are exposed to arriving contaminants, and the solar absorptances (as) of these materials are continuously measured. The two RPA/TQCMs are both accumulating mass, but the accumulation rates and characteristics of the mass differ, probably because of the locations of the RPA/TQCMs on the spacecraft. Of the 16 TCC samples, two quartz fabric samples showed .01 to .05 increases in as during the first 50 days on orbit.

A simple and inexpensive optical system is described which can be used to focus a laser beam to provide a very fast f# diffraction-limited point source, for use in optical testing, experiments, etc. The design is characterized by an extremely low sensitivity of its performance to uniform temperature changes (thermal soaks). A temperature change of several hundred degrees centigrade - from cryogenic temperatures up to near the melting point of the optics, has essentially no effect on the predicted performance. Since the system has no aspheric surfaces, it is substantially less expensive than a fast f# parabolic mirror, which would also provide a point source. The system is also less alignment sensitive than a parabola of the same f#.

A 36-inch f/5 lens and a 24-inch f/3.5 lens used for aerial reconnaissance missions are described. The two lenses are analyzed over their operating temperature ranges, and their performance at ambient conditions and over the operating temperature range is reported. The results indicated that at steady-state the performance of the two lenses is affected only modestly over the operating temperature range when the back focus is compensated by a thermal compensating lens mount.

An optical system is described which is corrected for spherical aberration, coma, astigmatism, Petzval curvature, longitudinal and lateral color, secondary color, spherochromatism and chromatic variation of all the field aberrations. It has very good performance on a flat image over an extremely broad spectral range, from the ultraviolet to the infrared. It has also been designed to cover a very broad temperature range. All spherical surfaces are used, and only one glass type. With BK-7 glass, the catadioptric design has a spot size of four arc-seconds over a 3 degree diameter field of view flat image at f/2.5, over the whole spectral range of 0.3650 μ to 2.0 μ. Predicted performance is essentially unchanged over a temperature range of 1000^oC.

The Teal Ruby Experiment is an infrared telescope designed to passively operate in a cryogenic and orbital environment. As such, it had to be shown capable of maintaining integrity under a severe set of design criteria. Spacecraft payload capabilities required minimum optical element and structure weight while sufficient support strength was required to resist stresses developed under severe launch loading. Good stiffness characteristics were necessary to preclude excessive dynamic excursions as well as to minimize optical element motions caused by gravity release. Heat loss through supports which connect assemblies at different temperatures had to be kept to an extremely low value to assure life expectancy of the operational mission. Finally, low thermal expansion characteristics were a must if subassembly relative motions and cryogenic mirror distortions were to be held to the optical tolerances required. The recently completed telescope design satisfies these criteria and is presented in the paragraphs below. Here, a woven graphite epoxy composite structure houses lightweight fused silica mirrors. Variations in the coefficient of thermal expansion within the optical elements and structures are duly considered. The structural design and analysis, optical resolution capability, fabrication and manufacturing processes, and optical test results are discussed in detail.

The SIRE sensor is scheduled for use in orbital experiments aboard the Shuttle Orbiter vehicle during 1983. Sources of gas phase contaminants and how they affect the cryogenic optics have been studied and the results are summarized in this paper. A helium gas purging system has been designed on the basis of ion beam experiments carried out in the laboratory. Flow rates on the order of 10^-4 grams/second are indicated for orbital altitudes of about 250 n. mi. Analytical computations that include the effects of the detailed scattering geometry indicate the need for higher purge gas flow rates than those based on the laboratory data.

ATMOS is a Fourier transform spectrometer to measure atmospheric trace molecules over a spectral range of 2-16 μm. Assessment of the system performance of ATMOS includes evaluations of optical system errors induced by thermal and structural effects. In order to assess the optical systemerrors induced from thermal and structural effects, error budgets are assembled during system engineering tasks and line of sight and wavefront deformations predictions (using operational thermal and vibration environments and computer models) are subsequently compared to the error budgets. This paper discusses the thermal/structural error budgets, modelling and analysis methods used to predict thermal/ structural induced errors and the comparisons that show that predictions are within the error budgets and thus the system is predicted to meet requirements.

Many organizations presently are evaluating the potential loss to plant, equipment and production capability in event of a major earthquake in their area. Often it is found that equipment can be protected at a fraction of the replacement cost. The paper discusses ground accelerations, seismic probability and certain characteristics of earthquake ground motion. Methods for determining loads from the Uniform Building Code and acceleration response spectrums are explained. Protection techniques for optical equipment are presented including rigid anchors, snubbers and sensing systems. The paper is for optical engineers and managers, with no particular background in seismology or structural engineering required.

High-energy laser (HEL) systems involve an optical train consisting of mirrors and windows, which may compromise the system's operation because of unavoidable irradiance-mapping aberrations resulting from the absorption of some fraction of the incident laser-beam energy. This paper describes an analytic investigation of relevant processes and discusses how laser-driven mirror/window distortions may affect the performance of HEL systems with regard to focal intensities and on-target fluences. An approximate expression for the brightness at the Gaussian focus is derived on the basis of the AFWL far-field degradation model and shown to be simple enough to allow HEL system designers to assess the capability of a contemplated optical train and to evaluate its behavior as a function of beam-power level and laser run-time. Two figures of merit are introduced for the purpose of characterizing the response of power-optics mirrors and windows in terms of thermally induced wavefront errors. On using these figures of merit (FoMm and FoMw), an important result emerges: If the window-pane and the mirror-faceplate material both have positive distortion coefficients, window lensing suppresses the steady-state mirror-related phase aberration at time tc = N (D /d)² FoM_W/FoM_M, where N is the number of relay mirrors and D /d is the telescope magnification. In applying these considerations to a model system operating at chemical laser wavelengths, we find that CVD-ZnSe output windows can be quite beneficial in maximizing either the peak irradiance on target or the short-pulse energy delivery capability of contemporary HEL systems.

A laser system employing acousto-optic deflectors and a Bi₁₂S10₂₀ Pockels readout optical modulator (PROM) has been assembled for imaging with ionizing radiation. A primary motivation was to produce a remotely operable imaging device relatively impervious to electromagnetic disturbances and to high levels of background radiation--effects commonly plaguing our TV systems. The laser beam raster-scans the image imprinted on the PROM and the transmitted light is sensed by a high-current photomultiplier. The detector output can be cast into a TV format for display convenience, or can be digitized, independent of scanning format, for storage and processing. The information is directly imprinted on the PROM by an x-ray, gamma-ray, or neutron field. This sensing technique resulted from efforts to understand the background radiation effects on the PROM. The system has proved stable and background insensitive. In a recent experiment at the Nevada Test Site the scanner suffered no adverse effects while a parallel TV system lost some data. Advan-tages other than background immunity include (1) long image integration/storage time, (2) random or programmed, nondestructive sampling of the accumulating image, and (3) scan format versatility.

The design of equipment for measuring temperature and strain in a rapidly heated and pressurized cylinder of stainless steel is discussed. Simultaneous cinematography of the full circumference of the cylinder without interference with temperature and strain measurements is also illustrated. The integrated system uses a reflective chamber for the sample and requires careful consideration of the spectral energy distribution utilized by each instrument.

A laser system has been designed for use in longwall coal mining operations to monitor the height of the last cut. This coal mine environment is particularly adverse to optics because of low reflectivity and surface inconsistency of the coal, as well as vibration, debris and explosion hazards.

A number of on-line infrared process signature measurements have been made through combustion atmospheres. Examples include signature studies of jet engines, piston engines and coal gasification reactors. Typical problems include operation in the presence of pressure as high as 1800 psi, temperatures as high as 3200°F, and explosive, corrosive and dust-laden atmospheres. Other problems have required the use of long viewing tubes of small diameter which sometimes become distorted as the temperature of the observed process increases. Calibration problems have resulted from the use of purge gases to clear viewing tubes, and the obscuration of view ports by combustion products. The paper describes solutions that have been employed to counteract many of these problems and reviews the areas in which better solutions are required.

A coordinated national program is being formulated to adapt and develop optical materials to support a goal of meeting 20% of our national energy needs with solar by the year 2000. The program contains elements covering absorber, reflector, and transmitter materials but not photovoltaic materials. These elements include research on glass and polymer materials for glazing and reflector components, environmental testing, and long-term reliability modeling. Program subelements that support R&D and encourage commercialization of new products are also discussed. An overview of the proposed funding levels is presented.

A laboratory bidirectional reflectometer and a field. portable reilectometer have been used to determine' the effects, of environmental exposure and consequent dust buildup on the reflectance of mirrors located. in the heliostat field of the Central Receiver Test, Facility (CRTF). Surprisingly low rates of reflectance degradation have been observed in 64 weeks of sample mirror exposure and in two and one-half years of CF heliostat exposure,

Experimental techniques have been employed to characterize aging mechanisms in second surface mirrors for solar applications. Initial studies were focused on weathering (changes in the front surface of the glass due to exposure to moisture and pollutants in the environ-ment) and on solarization (changes in the optical absorption in the bulk of the glass due to incident sunlight). A newly initiated program is concerned with adhesion and corrosion at the silver-glass interface. The intent of all three studies is to provide sufficient understanding of the aging mechanisms to contribute to (a) the design of accelerated testing procedures, and (b) the selection of optimized solar materials. Experimental results and proposed aging mechanisms will be presented.