The scientific and technical challenges facing the astronomical community during the next decade are discussed within the framework of new technology and technical management issues. The astronomical telescope and instrument communities of industry, academia and government need to be prepared to meet the challenges of 21st century Astronomy. Emphasis is given to ground-based optical and infrared astronomy.

We establish the groundwork for a phase theory applicable to multiple-aperture systems. To do this, we define ideal behavior as the phase behavior of an off-axis system that has inherent rotational symmetry. Then we examine the phase behavior of a more general system that has only a single plane of symmetry. This system represents a branch of an actual synthetic aperture system. The comparison of the two systems leads to conditions for which the plane symmetric system has ideal behavior. As a result of this comparison, design rules that are commonly applied to multiple aperture systems appear naturally, including the well-known requirement that the exit pupil is a scaled copy of the entrance pupil. The theory also shows that in reflective synthetic telescopes, fewer mirrors are required to achieve ideal behavior if the mirrors are off- axis sections of an axially-symmetric parent system, rather than on-axis mirrors. The phase theory that we present is cohesive, provides useful design guidelines, and can be considered an addition to wave aberration theory.

If gossamer primary mirrors were to be constructed in a spherical form, it would be possible to arrange a simple null- test in situ. However, spherical mirrors would require correction of the large amount of spherical aberration created in pupils that generally will be greater than 2 m diameter. The design requirement is for diffraction-limited performance over a useful angular field. The otherwise excellent wide- field design solutions of the classical Schmidt and Maksutov are inapplicable in gossamer structures because of the mass and size penalty of large refractive components. However, it is possible for this mode of correction to be achieved near the prime focus by means of pupil transfer optics that minify the large entrance pupil down to more acceptable dimensions. A problem with these solutions is constraint of field coverage due to pupil aberrations created by the large spherical aberration of the primary mirror. This leads the designer towards slower primaries and the penalty of larger, heavier structures. A solution is presented here for spherical primaries with speeds up to f/4. This is based on the 'KiwiStar' principle presented here in 1997, in which a large spherical catoptric is combined by pupil-transfer with a smaller spherical catadioptric to give well corrected wide field images of high speed. This system is well suited to correction at the prime focus of large spherical mirrors, and has only one relatively small weak aspheric surface to provide zonal correction, all other surfaces being spherical. An example is presented of a 4 m diameter, f/2.5 system that is diffraction-limited over the whole of a 0.25 degree field (43 mm diameter), for a bandpass of 486 - 850 nm.

Passive imaging using mm-waves offers very significant advantages in scientific and military surveillance. However, the relatively long wavelengths mean that for the resolutions that are sought, the input aperture of the imager needs to be quite large, typically in excess of one meter. Deployment of conventional dish antennas of these dimensions on aircraft and in Low Earth Orbit is highly problematic. The use of snapshot synthetic aperture interferometric radiometry (SAIR) offers an attractive route to integrating a two-dimensional antenna array into the structure of an aircraft so that the transverse dimensions of the antenna can be almost as large as the aircraft. We report here a study into the feasibility of deployment of a SAIR on unmanned airborne vehicles and the achievable performance parameters. The critical considerations are the achievement of acceptable sensitivity and angular resolution from a SAIR that does not require excessive complexity. It is shown that traditional approaches based on fully sampling the spatial frequencies in the scene are unable to simultaneously meet all of these criteria, but a that a SAIR based on thinned sampling of the spatial frequencies shows promise.

We discuss the rationale for gossamer telescopes and why the initial ones will be used for infrared wavelengths and this necessitates a cold telescope. The sunshield presents major problems for gossamer telescopes and may limit the potential for large IR telescopes in space. Astronomical sources of heat other than sun, moon and earth would set the telescope temperature at 4.5 K. We discuss the sunshield problem and suggest that gossamer telescopes at 1 AU are more likely to be limited to approximately 10 K. We discuss the spacing of the telescope and the sunshield. The optimum spacing is 100 times the telescope size. Such spacing will require constantly firing ion engines to keep the sunshield and telescope moving around the sun with the same angular velocity. Alternatively it is possible to attach the sunshield to the telescope with a compression member. This will require the telescope and sunshield to be closer together. A single layer sunshield will bring the telescope temperature to approximately 25 K. Heat sources on the telescope will limit the cooling, and so far as possible heat sources must be off-loaded to the vicinity of the sunshield.

Telescopes and imaging interferometers with sparsely filled apertures can be lighter weight and less expensive than conventional filled-aperture telescopes. Sparse-aperture systems can be characterized by their fill factor, which is the ratio of the area of a given aperture to the area of a filled aperture having comparable theoretical resolution. We show that the modulation transfer function (MTF) at the midrange spatial frequencies tends to be proportional to the fill factor. Using signal-to-noise ratio (SNR) expressions for various sources of noise, we derive the relationship between the integration time, needed to achieve a given SNR, and the fill factor. For example, for a fixed, sparse array, the integration time is proportional to the inverse cube of the fill factor for photon noise, to the inverse square of the fill factor for readout noise, and to the inverse fourth-power of the fill factor for dark current.

The Lockheed Martin phased-array telescope developed at the Palo Alto Research Laboratory is a 0.75-m imaging system consisting of 9 separate 90-mm telescopes. One of the technology drivers behind this design is the ability to maintain the phasing of the individual telescopes to sub- wavelength tolerances. We demonstrate here the use of the focal-plane method of phase diversity for maintaining the phased-array alignment. The telescope is designed to operate with white light, so the phase diversity concept is extended to accommodate a broad optical bandwidth. A simulation of white-light phase-diverse wavefront sensing is presented as a demonstration of the robustness of the method with respect to sparse pupil and wavelength sampling. The simulation is validated with laboratory experiments using a point source. Finally, a closed-loop experiment is conducted that demonstrates the ability of phase diversity to sense piston error and maintain the alignment of the phased-array system.

Sparse aperture designs can increase the effective aperture size of a remote sensing system, thus allowing the satellite to be placed in a higher orbit without compromising the resolution. The fill factor of a sparse aperture is the total area of the telescope apertures divided by the effective aperture size of the combined telescopes. Reducing the fill factor, F, reduces the overall weight, but also reduces both the signal and the MTF (modulation transfer function). Increasing the effective integration time, t, and applying Wiener filters can gain back some of the lost image quality. This study generated image simulations of various sparse aperture designs to assess the image quality as a function of fill factor. This study found that the integration time needs to be increased by a factor of 1/F² - 1/F³ in order to maintain the image quality as the fill factor decreased. This study also found that the GIQE (Generalized Image Quality Equation) did not accurately predict the change in image quality, in (Delta) NIIRS, as the fill factor is reduced.

A novel Microelectromechanical Systems (MEMS) deformable mirror (DM) technology for large, light weight, segmented space telescopes is being proposed. This technology is reported to provide an unprecedented imaging capability in a visible and near infrared spectral range. The MEMS-DM proposed in this paper consists of a continuous membrane mirror supported by electrostatic actuators with pixel-to-pixel spacing as small as 200 micrometer. An array of 4 X 4 electrostatic actuators for the DM has been successfully fabricated by a new membrane transfer technique. The fabricated actuator membrane has been characterized by using an optical surface profiler. The actuator shows a vertical deflection of 0.37 micrometer at 55 V. This device can also address requirements for smaller size and high resolution applications involving optical transmission through aberrating mediums such as imaging and optical communications through atmospheres, high resolution biometric retina signatures through the eye and endoscopic investigation of tissues and organs.

As NASA moves forward into the 21st Century, many science missions are being considered that will require optics of unprecedented size. If the launches of these missions are to be affordable, then new technology must be developed to reduce the surface densities of the optical/mechanical systems from current hundreds of kilograms per square meter down to kilograms per square meter and tenths of kilograms per square meter. Also we must greatly increase the collecting aperture of telescope systems to hundreds and thousands of square meters without incurring current costs of mirror blank manufacture and polishing. To this end, a workshop was convened which brought together scientists and engineers to examine the optics requirements of these missions and to begin the process of identifying the technological developments required to bring these systems to reality. This paper describes the workshop, the general telescope architectures considered and identifies the initial assessment of the 'tall tent pole' technologies. Finally it gives an overview of the character of the approaches and the 'gossamer optics problems.'

The future of space-based telescopes will inevitably incorporate large apertures made from lightweight, stable materials that deploy from small volumes and actively adjust for maximum efficiency. These types of telescopes are directly applicable toward imaging and non-imaging applications. Techniques to remove wavefront error via surface correction are currently being studied and are highly applicable towards deployable telescopes. Imaging telescopes require much more sophisticated surface correction and deployment than lower frequency non-imaging telescopes. The intent of this paper is to present some concepts of deployable structures and active surface correction that perhaps enables further development of these types of structures.

In this investigation a technique was developed for depositing high reflectors of alternating layers of TiO₂ and SiO₂ with varying levels of stress. The TiO₂ layers were deposited by ion assisted electron beam evaporation, and the SiO₂ layers by modulated reactive DC magnetron sputtering. The TiO₂ layers were in tensile stress, and the stress depended on the ion beam current density. The SiO₂ layers were in compressive stress. The total stress in the high reflector coating was controlled by the ion beam current density applied during deposition of the TiO₂ films. The coatings were deposited at a substrate temperature of approximately 50 degrees Celsius. Coating stress levels were unaffected by changes in relative humidity. The stability of the coating over time depended on the density of the TiO₂ layers.

The development of ultra-light fibrous substrate mirrors allows serious contemplation of large multi-mirror space telescopes using rigid segments. Mirrors made of silica and alumina fibers have a small coefficient of thermal expansion and a density competitive with inflatable structures. Furthermore, they are without the imagery problems caused by non parabolic figures, gaseous expansion and contraction, tidal distortion of large gas filled structures, leaks, and long lived transient mirror perturbations caused by intentional pointing and tracking movements, micrometeor and space debris impacts, and mechanical vibrations. Fibrous substrate primary mirrors also have logistical advantages, since segments can be fabricated in orbit from small amounts of dense raw materials. One space shuttle flight, lifting about half its payload capacity, is adequate to transport all the material necessary to fabricate substrates for a one hundred meter telescope whose primary mirror consists of 12,086 hexagonal segments, each having a diameter of 1 meter and an area of 0.6495 square meters.

Current work concentrates on making optically flat mirrors using stretched membranes. Very lightweight mirrors can be made that only require a rigid support at the perimeter of the membrane. Contact with the membrane need not be continuous, only discrete attachment points are required to tension the material. Initial results of useable area as a function of the number of attach points will be given. Experimental fixtures demonstrating methods of forming a flat membrane are shown. The potential for nearly flat mirrors is mentioned including one method of implementation. Surface measurements are also contrasted for different materials.

Beginning with the launch of Sputnik in 1957, the United States Air Force has actively pursued the development and application of optical sensor technology for the detection, tracking, and monitoring of artificial satellites. Until the mid-1980s, these activities were conducted within various Air Force Research and development agencies which supplied data to the operational components on a 'contributing' basis. This paper traces the early evolution of the optical space surveillance technologies from the experimental sensors into the current operationally deployed systems. The contributions of the participating organizations and facilities is reviewed with special emphasis on the development of techniques for the identification and monitoring of spacecraft using optical imagery and signatures.

We seek to examine near-IR photometric signatures for geosynchronous earth orbit (GEO) communication satellites. To this end, we present a set of high quality photometric measurements for a sample of ten GEOs. The observations were made with a standard set of broad band astronomical filters (Johnson filters), using the 3.6 meter telescope at the Air Force Research Laboratory (AFRL) Directed Energy Directorate Starfire Optical Range, Kirtland AFB, NM. The results indicate that near-IR photometric signatures can be used to distinguish among different satellite classes. Other uses of the data, e.g. anomaly resolution and health status, are discussed.

The primary objective of this effort was to provide near real- time on-site analysis of optical and radar imagery to the Launch Team for the Advanced Research and Global Observation Satellite (ARGOS) located on Kirtland AFB, Albuquerque NM. The imagery was collected during the initial orbits of the ARGOS satellite after being launched from Vandenburg AFB, California on 23 Feb 1999. Secondary objectives were to demonstrate the feasibility of such support, to evaluate the usefulness of the capability, and to determine the requirements to permanently establish such a capacity.

A post-processing methodology for reconstructing undersampled image sequences with randomly varying blur is described which can provide image enhancement beyond the sampling resolution of the sensor. This method is demonstrated on simulated imagery and on adaptive optics compensated imagery taken by the Starfire Optical Range 3.5 meter telescope that has been artificially undersampled. Also shown are the results of multiframe blind deconvolution of some of the highest quality optical imagery of low earth orbit satellites collected with a ground based telescope to date. The algorithm used is a generalization of multiframe blind deconvolution techniques which includes a representation of spatial sampling by the focal plane array elements in the forward stochastic model of the imaging system. This generalization enables the random shifts and shape of the adaptive compensated PSF to be used to partially eliminate the aliasing effects associated with sub- Nyquist sampling of the image by the focal plane array. The method could be used to reduce resolution loss which occurs when imaging in wide FOV modes.

We have built a spacecraft simulator which displays realistic graphics in real-time on an inexpensive personnel computer (PC). The dynamics of the spacecraft, the positions of the sun, the moon and the earth, and the direction of stars are calculated accurately. The primary use of the simulator would be in the education of statistical signal processing. A student can try a new algorithm for each of the existing modules of the spacecraft by writing a C-code and integrating it with the rest of the simulator.

Observations of the Moon during partial lunar eclipse were conducted from the Maui Space Surveillance Site on Haleakala Mountain, Maui Hawaii. Data were obtained in both the MWIR and LWIR. Preliminary analysis of LWIR data shows unexpected features in many regions that open up a variety of lines of lunar research.

The NASA/JPL Near Earth Asteroid Tracking (NEAT) Program was in operation using the Maui GEODSS as its observing platform for about three years starting in late 1995 and continuing into 1998. In October of 1998 the NASA/AFSPC Near Earth Object Working Group (NEOWG) recommended that the NASA/JPL NEAT program be moved to the AMOS 1.2 m/B37 telescope. This paper describes the technical efforts that were required to facilitate the move. The task requirements specified that the modified 1.2 m/B37 system be capable of producing a field of view (FOV) greater than or equal to 1.4 degrees X 1.4 degrees at the NEAT camera focal plane. Further, it was specified that no modifications be made to the 1.2 m/B37 mirror or the NASA/JPL camera. Thus, activity focused on the development of suitable focal reduction optics (FRO). A new headring and spider, based on the original design, were also built to receive the NEAT FRO and the NASA/JPL camera. Operation of the NEAT system, for asteroid search and discovery, will be autonomous and remotely directed from NASA/JPL. Finally, the potential for use of the NEAT system as regards the satellite metric mission will also be presented.

The Raven optical sensor is a commercial system being developed and tested by the Air Force Research Laboratory. It allows for a low cost method for obtaining high accuracy angular observations of space objects (manmade and celestial) with a standard deviation of approximately one arcsecond or less. Presented here is an overview of the past and present successes and future projects utilizing Raven. This system has evolved into a very viable and cost effective solution for obtaining low-cost observations for satellite and asteroid catalog and follow-up maintenance. Collaborative efforts between AFRL and several space agencies (JPL, NASA, Space Battlelab, Canadian Defense Ministry, etc) have successfully demonstrated and utilized the Raven system for their missions, including improved satellite orbit determination accuracy, NEO follow-ups, and remote autonomous collecting and reporting of metric data on deep space objects.

The National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) is conducting systematic searches of the Geosynchronous Earth Orbit (GEO) environment as part of an international measurement campaign under the auspices of the Inter-Agency Space Debris Coordination Committee (IADC). The objectives for this survey are to determine the extent and character of debris in GEO, buy obtaining distributions for the brightness, inclination, Right Ascension of Ascending Node (RAAN), and mean motion of the debris. The Charged Coupled Device (CCD) Debris Telescope (CDT), an automated 0.32 meter aperture, transportable Schmidt telescope presently located at Cloudcroft, New Mexico, is used nightly to monitor the GEO debris environment. The CDT is equipped with a CCD camera capable of detecting 17th magnitude objects in a 20 second exposure. This corresponds to a 0.6 meter diameter object having a 0.2 albedo at 36000 km. Two other larger telescopes have been used for this purpose, the United States Naval Observatory's new 1.3 meter telescope located in Flagstaff Arizona and a 0.6 m Schmidt telescope located at Cerro Tololo Inter-American Observatory (CTIO) near La Serena Chile. Data reduction and analysis software used to reduce this data exploit tools developed by both the astronomical and DoD communities. These tools and data results are presented.

The idea for developing the Telescopes In Education (TIE) program began around 1990. While working with Boy Scouts, it became apparent that optical astronomy captivated the interest of more boys and their parents than any other Merit Badge that I had worked with in the past. That was the beginning of the learning curve in astronomy and optical instruments.

In 1995, the NASA Project ORION investigated the feasibility of orbital debris removal using ground-based sensors and lasers (Ref. 1). This study focused on high peak-power pulsed lasers capable of initiating plasma blow-off impulse. The conclusions drawn by this study indicated that a neodymium glass laser might represent the most cost effective and technologically viable solution. Large, repetitively pulsed neodymium glass lasers have been developed by Lawrence Livermore National Laboratory for inertial confinement fusion (ICF). However, the goal of ICF is to focus the high power laser beams on a small, stationary target at very close range. The orbital debris removal problem requires the mating of a high power laser to large diameter optics equipped with laser guide star adaptive optics. The target is a rapidly moving object located many hundreds of kilometers in distance. Since the conclusion of that study, the Air Force Airborne Laser (ABL) program, utilizing a continuous wave Chemical Oxygen- Iodine Laser (COIL), has progressed dramatically. This program integrates a high average power COIL with large diameter optics, which are adaptively controlled to correct for atmospheric turbulence. The target of the Airborne Laser is a rapidly ascending ballistic missile located hundreds of kilometers in range. The similarities between the Airborne Laser and the orbital debris removal mission motivate the examination of ABL COIL technology and its associated optical hardware for the orbital debris removal mission.

Modern microdoppler ladars systems are capable of measuring a surface displacement velocity as small as 10 micrometers per second. The Precision Targeting and Identification ACTD is transitioning microdoppler ladars onto surveillance and tactical fighter platforms. They are being used to classify and identify airborne targets based on the vibration signatures of the target's power plant at ranges beyond 20 km. Derivative uses include detection/classification of operational, camouflaged surface and buried objects and an adjunct to optical imaging for space object identification. As the cost, size, and complexity of the micro-doppler ladars is reduced with the transition from the gas laser to solid state devices, microdoppler ladars will provide an affordable, operationally effective alternative to imaging sensors. This paper will discuss the status of microdoppler ladars developments and several applications including tactical airborne combat ID, detection of surface/buried targets, and space object identification.

A micro-satellite, designed to aid ground-based laser imaging, ranging, and sensing systems as a calibration target, has been constructed and is scheduled to be launched in the fall of 2000. This low-earth orbit satellite carries a set of retro- reflectors (for visible and near-infrared wavelengths) that present a spatially extended target to sites on the ground. Several of the reflectors also impart a polarization signature to the reflected laser light. This paper discusses the specifications of the retro-reflectors, positioning of the reflectors on the satellite structure, passive control of the vehicle orientation, and ground-pattern characteristics of the reflected light.

We are currently building a custom adaptive optics system for viewing missile defense testing in Hawaii. The system will utilize natural target emission in the 3 - 5 micron MWIR for imagery, as well as for sensing the phase distortion caused by atmospheric turbulence. Use of the system with the 3.67 meter AEOS telescope will provide near-diffraction-limited performance for imaging at very long range and low elevation angle.

Numerous optical engineering applications lead to two two- dimensional difference equations for the phase of a complex field. We will demonstrate that, in general, the solution for the phase can be decomposed into a regular, single-valued function determined by the divergence of the phase gradient, as well as a multi-valued function determined by the circulation of the phase gradient; this second function has been called the 'hidden phase.' The standard least-squares solution to the two-dimensional difference equations will always miss this hidden phase. We will present a solution method that gives both the regular and hidden parts of the phase. Finally, we will demonstrate the method with several examples from both speckle imaging and shearing interferometry.

The GEO Light Imaging National Testbed (GLINT) system will image objects in geo-synchronous and semi-synchronous orbits using a synthetic aperture technique known as Fourier Telescopy. The testbed will be located in the vicinity of Socorro, New Mexico, and will form one of the most powerful imaging systems on Earth in terms of resolution, with an angular resolution of about 10 nano-radians, or 2 milli-arc seconds. Various parts of the system have strong similarities to astronomical instruments, and these similarities can be exploited to perform long-baseline interferometry, long- baseline intensity interferometry, gamma-ray observation, stellar spectrometry, and remote sensing with unprecedented sensitivities and state-of-the-art resolution.

We have investigated an obvious extension of maximum entropy imaging to use triple product data directly rather than by first decomposing the triple products into complex visibilities. This approach may have some advantages for ground-based, optical Michelson interferometry where the visibilities are usually corrupted by atmospheric turbulence. Another advantage of the method is that other a priori information from earlier observing runs or different instruments may be included readily; indeed, the total flux density of the image is required as a constraint.

Many laser imaging applications produce as outputs the phase differences between adjacent points in the digital 2-D image spatial frequency domain. A wavefront reconstruction algorithm must then be used to convert phase difference arrays to a spatial frequency global phase array. The spatial frequency domain for most applications (for example, Sheared Beam Imaging) is contained in a regular square grid. For other applications such as Fourier Telescopy, the spatial frequency domain grid points depend upon the placement of the laser illuminators. Additionally, off-axis viewing angles introduce a skew into the u-v sample space, so we need to be able to reconstruct wavefronts on non-square grid arrays. In this work we will demonstrate use of standard square grid reconstructors to reconstruct non-square grid arrays. Additionally, we compare the relative accuracy between a complex exponential wavefront reconstruction algorithm and a modified least- squares wavefront reconstruction algorithm in recovering the global phase from regular square and non-square grid arrays.

Recent interest in imaging satellites in geo-synchronous earth orbit has led to the design of a ground-based active imaging system using a concept known as Fourier Telescopy. Fourier Telescopy systems use active laser illumination, aperture synthesis, and extensive computer processing to minimize atmospheric turbulence effects and form high-resolution images of distant stationary objects. Three laser transmitters of slightly different frequency illuminate the object with varying baseline separations to temporally encode object spatial frequency information in the energy backscattered from the object. Detection and demodulation of the temporal signals and processing using phase closure and wavefront reconstruction techniques yield measurements of the object's incoherent Fourier amplitude and phase distribution. We have developed a detailed wave optics simulation to analyze and optimize the performance of this system. Wavelength dependent renderings of 3-D satellite models and the statistical variations of object illumination determine the radiometric returns received for a given scenario and the effect on imaging system performance. This work uses the simulation to examine system performance for three different illumination laser wavelengths and for realistic system design limitations. System design trade-offs based on the wavelength dependence of satellite optical cross-section, atmospheric propagation, and diffraction are discussed. Our results indicate that a near infra-red (IR) wavelength may be most suitable for this system.

GLINT is a program to image geosynchronous satellites using Fourier telescopy. The standard method of creating an image takes some time requiring the satellite to be stationary for an hour or more. Important information about the satellite's motion and orientation can be obtained by measuring a small subset of the u-v sample space. These measurements can be taken relatively quickly and can be used even if the object is moving. These motion estimates can be useful in themselves -- for instance as an aid to regaining control of the satellite. They can also be used as inputs to alternate imaging schemes that map out the u-v space synchronously with the rotating satellite.

Differential GPS (DGPS) is the system used for improving accuracy in GPS position and velocity estimation. Measurements can be obtained in real time with a high level of accuracy by means of use DGPS for task the vehicle tracking, dispatching, location, navigation, etc. In this paper we present a modified Kalman filter for DGPS to achieve an accurate estimation of the position and velocity. The proposed and realized algorithms in DGPS system can be implemented by low cost commercial C/A code GPS modules. With the help of Kalman filter the reducing of the anti-common errors between the users and reference station has been achieved. Two variants of the Kalman filters have been investigated. It is presented the experimental testing of the performance of DGPS with Kalman filtering. The used filtering procedure has shown the possibility to reduce the anti-common errors. The proposed and investigated procedures of Kalman filtering could be used for better positioning in the different navigation and positioning applications.

This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.

NASA's new optical encoders use pattern recognition for images of encoder scales to encode both rotary and linear, absolute, mechanical position with ultra-high sensitivity. These encoders have advanced beyond prototype stage and are now being used in a variety of demanding applications both in the laboratory and in optical ground support equipment for space flight instrumentation. Rotary versions of these new pattern recognition encoders have sensitivity down to 0.01 arcseconds while linear models have demonstrated sensitivity of 10 nm (0.01 micrometer) with higher sensitivities achievable in both formats. The means for encoding is a radical departure from that for conventional optical encoders and offers advantages of absolute operation, very low cost, compact form, considerable immunity to scale-damage-induced dropouts of position information, an order of magnitude or more higher sensitivity over commercially available encoders, demonstrated applicability in cryostatic and vacuum environments, and suitability for space flight. Operational details of the encoder are given. Representative sensitivity performance is presented along with several examples of uses to date. Planned future development is also discussed.

The use of all classes of space systems, whether owned by defense, civil, commercial, scientific, allied or foreign organizations, is increasing rapidly. In turn, the surveillance of such systems and activities in space are of interest to all parties. Interests will only increase in time and with the new ways to exploit the space environment. However, the current space awareness infrastructure and capabilities are not maintaining pace with the demands and advanced technologies being brought online. The use of surveillance technologies, some of which will be discussed in the conference, will provide us the eventual capability to observe and assess the environment, satellite health and status, and the uses of assets on orbit. This provides us a space awareness that is critical to the military operator and to the commercial entrepreneur for their respective successes. Thus the term 'dual-use technologies' has become a reality. For this reason we will briefly examine the background, current, and future technology trends that can lead us to some insights for future products and services.

Nowadays, membrane mirrors are being under study. They are interesting from the application standpoint in telescopes with aberration correction (by phase conjugation or real-time holography methods). To give the required spherical or parabolic shape to these mirrors to be employed in the space, the mirror surface is exposed to, for example, gas pressure. For this is the cavity between two membranes, one being transparent (canopy) and the other specular, is filled with the gas. The transparent membrane appears to be undesired in a number of cases since its possible distortions have to be compensated for that a high quality image of the object observed through the telescope to be achieved. However in a number of cases the gas pressure action may be simulated with a proper electrostatic field. In this paper results of electrostatic field effect on the shape of the mylar-film mirror with reflecting coating are presented. Here is also given an analysis of the shape of the membrane mirror exposed to both an electrostatic-field load normal to and a strain load along its surface. It is shown that in the case of the electrostatic load the surface shape can be more close to a parabolic one than that in the uniform pressure case.

Today the peak of the conventional method of telescope design is the space telescope named after Hubble (2,4 m-diameter of the primary mirror). Further increase of the input-aperture diameter of telescopes requires the application of new architectures of their design based on the recent progress in optics and the development of super-light mirrors. The paper is devoted to development of the concept of a new-generation membrane primary mirror for extra-atmospheric imaging telescopes basing on the recent progress in non-linear technique of correction for dynamic distortions.

The Air Force Research Laboratory (AFRL) is exploring the feasibility of large-aperture, deployable, space-based membrane telescopes operating in the visible and/or near- infrared spectral regions. One of the near-term goals of this work is to develop an understanding of available and achievable membrane materials, specifically concentrating on practical techniques to form large aperture membranes with the necessary surface quality and economy. When this research began a little more than three years ago, the conceptual design was based upon a totally inflatable structure. An inflatable structure has been used for space solar power collection and radio frequency antennas. This totally inflatable lenticular design is simple and relatively easy to demonstrate, but maintaining inflation during an extended lifetime in near-earth orbit may not be feasible. Recently, a new concept for a membrane telescope has emerged which does not depend on sustained inflation during operation. Thin membranes on the order of 10 to 100 micrometer thick will be packaged and deployed, maintaining their surface figure by means other than inflation. Given the fact that the sub- wavelength level surface tolerances required of imaging telescopes will probably not be practical with a membrane- based telescope, such systems will probably rely on real-time holography or some other wavefront correction or compensation technique. We will discuss the primary experimental work ongoing in the AFRL Membrane Mirror Laboratory, and in doing so, some of the issues relevant to demonstrating a practical, large-aperture membrane mirror system.