Important physical, optical, thermal, and mechanical properties of cubic (β) silicon carbide produced via a bulk chemical vapor deposition (CVD) process, developed at CVD Incorporated, are presented in this paper. The material's properties make it an ideal candidate material for optical components for LIDAR mirrors, solar collectors and concentrators, and astronomical telescopes. The CVD process has been scaled to produce large monolithic pieces of bulk SiC, i.e. disks up to 60-cm (24-in) diameter and plates up to 76-cm (30-in) long by 46-cm (18-in) wide with thickness up to 13 mm (0.5 in).

Small models (7.5-cm dia.) of lightweight Si/SiC mirrors have been fabricated via a scalable chemical vapor deposition process. These mirrors consist of a low f-number (f/1.6), concave faceplate of SiC coated with CVD Si, and a lightweight back-up structure made of SiC. The lightweight structure consists of an outer hexagonal cell with six triangular inner cells. The complete lightweight mirror substrate was fabricated directly in a CVD chamber, and no bonding agent was used to attach the SiC back-up structure to the faceplate. The Si/SiC mirrors were polished to a figure of 1/5th of a wave and a surface finish of 10 Å RMS. The CVD mirror fabrication process was scaled from a small horizontal research furnace to a vertical pilot-plant size CVD reactor. Silicon carbide depositions were successfully performed to fabricate 40-cm-diameter f/1.6 concave mirror faceplates. Currently, experiments are under way to fabricate a SiC lightweight structure on the backside of the SiC faceplate. Experimental results and important issues concerning the large scale fabrication of mirrors via CVD are discussed.

NASA and the international atmospheric science community are committed to the careful and protracted study of the problems associated with global changes in the ecosystem [1-3]. Remote sounding of the atmosphere from space is a nesessary part of this effort. Active remote sensors, those using lasers as a source of probing radiation in light detection and ranging (lidar) measurements, will play a central role in atmospheric sounding [4]. Lidar instruments enable measurements not possible by passive measurement systems and significantly improve upon the accuracy and resolution of passive measurements. The development of these instruments depends, in turn, on the identification and characterization of new materials, on the incorporation of these materials into laser systems and on the development of innovative measurement strategies. The technological products of this research are versatile and can be utilized by other NASA programs. For example, lidar instruments can also be used for doppler lidar measurements of windshear.

Large optical-quality T13AsSe3 (TAS) single crystals were grown by the vertical Bridgman-Stockbarger method. Optical quality of the TAS boules was observed to depend on the purity of source materials and thermal gradient applied at the solidifying interface. Crystal quality was verified by etchpit studies and optical evaluation. Several TAS crystals were fabricated into a collinear acousto-optic tunable filter (AOTF) for use as an all-electronic intracavity laser-tuning element. Electronic tuning was demonstrated with a pulsed CO2 laser on both the P and R branches of the (001)-(100) CO2 band. Observed tuning properties, including exact RF drive frequency, matched modelling predictions. With some modification, such collinear AOTFs can tune over the entire 9-11 μm range by selection of RF drive frequency. Random access of any wavelength in the 9-11 μm range is possible at rates up to 50 kHz.

Clear fused silicon dioxide (quartzglass) is one of the simplest but most valuable compounds available to the optical industry. It offers a unique combination of optical, thermal, mechanical, and chemical properties which makes it a very favourable material for a wide variety of space optical applications. Selection of raw material and control of manufacturing processes allow to modify the quartzglass properties within certain limits. The most relevant properties are discussed from a material supplier's point of view, also indicating limitations and constraints, e.g. due to the manufacturing process, and taking into account the typical requirements for space optical material (i.e. functional requirements and specifications for a given application, requirements due to the adverse environment, reliability, and safety requirements). The discussion is based on selected examples of existing space related hardware covering such different fields of applications as transmissive optics (corner cubes for laser ranging, optical windows for space crafts, and space simulation chambers), reflective optics (lightweight mirror blanks, cryogenic mirrors, X-ray telescope), components for micro-gravity experiments (ampoules, calibration standard for mirror furnace).

Coarse and fine variants and standard grades of I-70A beryllium powder manufactured by Brush Wellman were consolidated by vacuum hot pressing (VHP) and by direct hot isostatic pressing (HIP) techniques. Five cm diameter flat mirrors were fabricated from 7.5 cm diameter by 7.5 cm long billets. All billets had densities of essentially 100% after HIP'ing. The mirror blanks were polished bare and the resulting surface evaluated for surface roughness and surface scatter at 0.51, 3.39, and 10.6 μm. The general trend noted was that better optical properties were obtained with direct HIP'ed coarse powder (since designated as 0-50 material). Surface roughnesses of 15 to 20 angstroms rms were obtained. The coarse powder was then used to fabricate a 0.5 meter diameter solid HIP'ed blank. This blank was polished as an F/1.5 sphere, scatter measurements taken, and the figure evaluated at cryogenic temperatures. Distortion of 0.19 waves rms @0.63 μm was seen at 97 K, corresponding to a homogeneity of ~ 26 ppb/K rms.

The severe environmental conditions in low Earth orbit (LEO) have a detrimental effect on the performance and longevity of some thermal control coatings. Commonly used thermal control materials such as silver-Teflon, Kapton, and organic paints have shown significant mass loss and changes in optical properties after exposure in LEO. Sulfuric acid anodized aluminum has been evaluated as a thermal control coating for the radiators of the Space Station Freedom. The evaluation included: study of processing parameters necessary to achieve suitable solar absorptance (a) and thermal emittance (c) properties; study of temperature effects on the stability of the aluminum oxide produced by sulfuric acid anodizing; ultraviolet radiation, and electron radiation testing of sulfuric acid anodized aluminum; and characterization of surface chemistry and morphology before and after environmental testing to determine the cause of degradation. Results show that sulfuric acid anodized aluminum may be a satisfactory thermal control coating for the radiators of the Space Station Freedom.

Thin Al and Ag coatings (20 nm-100 nm) have been deposited on Be substrates using an ion beam enhanced deposition (IBED) process. Optical characterization was carried out by measuring the total hemispherical reflectance (THR) of these films over a wavelength range of 400-1000 nm and renorrnalizing the THR values to the solar spectrum (AM0). Al and Ag films laid down on polished sintered Be substrates had THR values below calculated theoretical values of 5-8% while Ag films laid down on sputtered Be substrates had THR values of only 1-3% below the calculated values. High coating adherency was demonstrated through the use of pulsed (65 ns) electron beam irradiations up to 0.45 cal/cm2. At this fluence, the Ag coatings melted and the Al coatings were unaffected.

Optical systems intended for use in the near-space environment have special requirements for their light-controlling baffle systems; to date these requirements have not been fully met. A program of work to produce and evaluate new, all-metal, baffle materials which are optically effective, radiation hardened, and immune to the challenges of near-space is described and a very promising baffle material is identified.

Beryllium is probably the most frequently used material for spaceborne system scan mirrors. Beryllium's properties include lightweightedness, high Young's modulus, high stiffness value, high resonance value. As an optical surface, beryllium is usually nickel plated in order to produce a higher quality surface. This process leads to the beryllium mirror acting like a bimetallic device. The mirror's deformation due to the bimetallic property can possibly degrade the performance of the associated optical system. As larger space borne systems are designed and as temperature considerations become more crucial in the instruments, the concern about temporal deformation of the scan mirrors becomes a prime consideration. Therefore, two sets of tests have been conducted in order to ascertain the thermal effects on nickel plated beryllium mirrors. These tests are categorized as follows: 1. On seven small samples of nickel plated beryllium, the bimetallic effect was measured under very controlled conditions. 2. On a large (20" diameter) nickel plated beryllium space quality mirror, the bending of the mirror as a function of temperature was determined. The purpose of this paper is to present the values of the bimetallic effect on typical nickel plated beryllium mirrors.

The test results of the IBSS Optical Subsystem are presented. The newly developed instrument consists of a spectrometer and a radiometer together with a diffraction-limited telescope. The instrument is designed for remote measurements of infrared emissions aboard spacecraft and is cooled with supercritical helium to temperatures down to 5-20 K in order to suppress the self-emission of the instrument. The optical layout of the telescope is optimized for high straylight rejection of the earth's radiation and for for good image quality, which is required for spatial observations. The performance data of the instrument, i.e. image quality, detector performance data, and spectral resolution were verified by several cooling cycles.

High efficiency silver based reflective coatings useful in the visible and infrared regions have been developed. These coatings have been found to withstand both terrestrial and space environment. The durability characteristics of the coatings are presented.

Deposition behavior of thin films of contaminants (less than 10 Å) has been studied under vacuum conditions. Dependence of deposition behavior on the composition of the contaminant and of the condensing surface was considered. Quartz crystal microbalances (QCMs) were used to measure the mass accumulation rates of contaminants. Experimental results indicate that rough surfaces have higher mass accumulation than smooth surfaces and that polar attraction between the contaminant and the condensing surface affect deposition behavior.

Indium tin oxide thin films (650 Å) were prepared by dc sputtering onto room temperature substrates. The films were exposed to an rf excited oxygen plasma, to qualitatively simulate the effects of atomic oxygen. Changes in optical, electrical, and structural properties were characterized as a function of exposure time.

We present a contamination control program that has been developed for the optical components of the Extreme Ultraviolet Explorer (EUVE) satellite, whose performance in the 80-900 Å wavelength range is highly sensitive to particulate and molecular contamination. The specification for the optical components has been set at less than 10 particles greater than 25 microns (μm), and less than 1.0 microgram non-volatile residue (NVR) per square centimeter at instrument end-of-life. We discuss a variety of contamination control approaches and monitoring methods used throughout our project to characterize possible causes of contamination of EUV optics, and to develop cleanliness requirements for use during the design, fabrication, and test phases of the EUVE instrumentation. The contamination control approach includes isolating the sensitive optical components in an 'o'-ring sealed optics cavity that is kept sealed from the time of delivery to NASA until deployment on orbit. Monitoring methods and devices used prior to launch include thermal quartz crystal microbalances, particle and NVR witness plates, direct sampling from flight hardware, and optical witness samples to monitor EUV reflectivity and scattering. A mass transfer model which has been used to predict instrument contamination trends during the two-year mission in a 500-km altitude space environment is also discussed.

Spaceborne containerless materials processing will require efficient heating systems. The technique described here makes use of lamp systems with power conversion efficiencies that are as high as 65 percent. The effectiveness of these systems is enhanced by multipassing the lamp beam to re-use the lamp flux that is not absorbed by the sample on the initial pass. We believe that these systems have a great deal of merit when compared with more conventional tungsten furnaces or laser systems. We have evaluated the effectiveness of an optical multipass radiation system, OMRS, used in conjunction with a high intensity light source as a means of heating levitated samples.

Of significant importance to the field of protein crystallography is the preparation of single crystals suitable for x-ray diffraction studies. Recent experiments have been conducted on the Space Shuttle to study in detail the effects of microgravity on protein crystallization. The device used on these Shuttle missions, the Protein Crystal Growth Apparatus (PCGA), utilizes the vapor diffusion crystallization method and has yielded extremely favorable results. We describe here our efforts to modify the PCGA in order to incorporate an automated CCD-based video system, the Video Monitoring and Analysis Subsystem (VMAS) for direct monitoring of crystallization experiments. The video system discussed allows frequent monitoring and observation of crystal growth. In addition, images of crystallization experiments obtained with the VMAS will be processed and analyzed on-board with a dedicated microcomputer to automatically determine the presence and rate of crystal growth.

Several different optical position sensing techniques have been used in sample levitation systems. In experiments that have an optically clean environment, electro-optical position transducers have been found to yield accurate results. This paper describes and compares charge coupled device (CCD) sensors, and two dimensional and one dimensional position detectors (PSD's) which have been used in electrostatic sample levitation. Of these the one-dimensional PSD had the best position resolution viz., better than one micron.

ILC's involvement in aerospace lighting will be discussed, detailing the pitfalls and problems associated with the design development and qualification of space suitable hardware. A recent project will be investigated and a brief opinion of the requirements for future space lighting issues will be presented. ILC's history in the aerospace lighting field began in 1977 with a project for a xenon short arc lamp for the Mars Viking Lander biological experiments. This lamp required the design and fabrication of a 5 watt device that would withstand lift-off and on-orbit conditions and function once landed on Mars. This first ILC product was an outgrowth of on-going work at Varian in Palo Alto. Next came lighting for the Space Shuttle both the interiors and exteriors; fluorescent tubes for the European Spacelab; beacon lights for the manned maneuverable unit; light sources for several shuttle experiment packages and currently, projects to provide pilot lights for a tethered satellite, beacons for rockets, and the general illumination for the proposed Space Station. ILC has grown with the US space program, and now has a dedicated division to respond to the expanding lighting needs of the space related community. The problems encountered and solutions for these problems for the luminaires for the Space Shuttle are well documented in the papers by Evans, et.al.,and in the papers Since these publications are almost 10 years old it is a tribute to their initial designs that to date the only failures that have occurred to space hardware are 6 lamp failures to Pay Load Bay Lights (PLB's) and 3 lamp failures to Remote Manipulator Arm Lights (RMA's), no fluorescent luminaire has failed. Technical issues that have provided the most challenge include: o Developing a highly efficient metal halide lamp that would withstand the vibration and thermal specifications. o Designing fluorescent luminaires that can withstand the balldrop test. o Identifying materials that provide the correct thermal and mechanical stability (RMA, Overhead Docking Light [OHD], PLB). o Dimming of fluorescent tubes.