The new and powerful NASA Advanced X-ray Astrophysics Facility (AXAF) has entered the design and development stage and is currently scheduled for launch in the mid-1990s. AXAF will be 100 times more powerful in detecting x-rays, will double the spectral wavelength coverage, and provide ten times the resolution over its highly successful predecessor, the Einstein Observatory. To achieve these goals, AXAF will be equipped with a high resolution mirror assembly (HRMA) consisting of a nested set of six Wolter Type I, x-ray telescopes with outer diameters varying from 0.68m to 1.2m, and parfocalized at a common 10.0m focal length. The mirror mounting, assembly alignment, and orbital thermal stability requirements are nearly an order of magnitude more stringent than those of the HRMA developed for the Einstein Observatory. This paper summarizes the key design features and assembly alignment approach planned to meet these very stringent requirements.

Because particles of sizes larger than a few tenths microns adversely affect hight resolution X-ray telescopes by scattering and absorbing X-rays, we are investigating the clean-liness required to maintain the ~1% overall calibration precision desired for the Advanced X-ray Astrophysics Facility (AXAF). At the grazing angles used for the AXAF mirrors, each particle shadows a surface area ~ 10² times its geometric area, necessitating glass occlusion specifications much more stringent than typically stipulated for visible-light particulate contamination. On test fiats coated with gold, we have deposited controlled levels of contamination spanning the range from 5 x 10^-5 to 5 x 10^-3 fractional area covered and have measured the absorption component of extinction over a range of grazing angles and X-ray energies to verify the predicted effects of particulate contamination. Further tests are planned to examine a wider range of energies and to take into account sample flatness and distortions introduced by holding fixtures.

A formula for the RMS blur circle radius of Wolter telescopes has been derived using the transverse ray aberration expressions of Saha. The resulting formula for the RMS blur circle radius over an image plane and a formula for the surface of best focus are based on third, fifth, and seventh order aberration theory and predict results in very good agreement with exact ray tracing. It has also been shown that one of the two terms in the empirical formula of VanSpeybroeck and Chase for the RMS blur circle radius of a Wolter I telescope can be justified in terms of the aberration theory results. Numerical results are given comparing the RMS blur radius and the surface of best focus versus the half field angle computed by skew ray tracing and from the analytical formulas for grazing incidence Wolter I-II telescopes and a normal incidence Cassegrain telescope.

The initial results of a study on Cassegrain-type telescopes, optimized for astrometric applications, are presented. Two similar designs were optimized for minimum distortion, and the results are compared to those obtained for a one-mirror telescope with the same focal length and focal ratio. The results show that the two-mirror systems as well as the one-mirror system are virtually distortionfree, when perfectly aligned. The effects of various misalignments on the state of correction are also investgated.

The goal of imaging planets around the nearby stars has important scientific significance but requires the use of advanced methods of controlling diffracted and scattered light. Over the last three years we have undertaken a study of coronagraphic methods of controlling diffracted light and of figuring hyper-contrast optics. Progress in these two general areas have led to a proposed space-based, 1.9 meter diameter coronagraphic telescope designed specifically for very high performance in the imaging of faint objects near bright sources. This instrument, called the Circumstellar Imaging Telescope (CIT), relies on a new high efficiency coronagraph design and the careful control of scattered light by extremely smooth optics. The high efficiency coronagraph uses focal plane apodization in order to concentrate diffracted light more efficiently in the pupil. This allows convenient removal of the diffracted light by masking off parts of the telescope pupil while not sacrificing the center of the field. Reductions of diffracted light by factors exceeding 1000 are not only possible but are required in order to detect extra-solar planets. Laboratory experiments with this new design have confirmed the theoretical diffraction reductions to the limits of the optics used (factors of about 300). The extremely high efficiency of this coronagraph puts strong constraints on the narrow angle scattered light due to figure errors in the telescope mirror. Since planets orbiting nearby stars are expected at angular distances of about 1 arcsecond, it is in this small angular range in which scattering must be controlled. The figure errors responsible for scattering in this range come from mid-spatial frequencies corresponding to correlation lengths of about 10 cm on the primary mirror. A primary mirror about 15 times smoother than the Hubble Space Telescope mirror is required for the CIT. Laboratory experiments indicate that small test mirrors can be fabricated with existing technology which come within a factor of two of this requirement.

The direct detection of extrasolar planets .by imaging will require reductions in scattered and diffracted light by factors in excess of 10³ within one arcsecond of a bright source. While diffraction can be reduced by a number of approaches, small angle scatter can only be reduced by controlling mid-spatial frequency figure errors. We review the surface requirements and consider their meaning when compared to the data base of existing mirrors. We describe experiments that were successful in reducing mid-spatial frequency figure so that the scatter level was 500 times less than diffraction for a 25 cm spherical mirror.

The European Space Agency ESA has started the development of the Infrared Space Observatory (ISO), that will be launched in 1993. The TNO Institute of Applied Physics has been contracted for the major part of the optical/mechanical design of one of the 4 scientific instruments of ISO. This instrument, called the Short Wavelength Spectrometer (SWS) will measure stellar spectra in the wavelength range of 2.5 - 45 μm and will operate at a temperature of about 4K. The severe performance requirements together with weight and space limitations made a special instrument design necessary, using an all reflective grating spectrometer configuration with excotic shaped aspherical mirrors. At this moment the Qualification model of the SWS has been assembled and aligned and some optical, thermal and vibration tests have been performed with satisfying results.

The Marshall Space Flight Center is developing a thin film reflector for a Gamma Ray Imaging Telescope System (GRITS) using the Shuttle External Tank (ET). The concept is to install an inflatable reflector in the ET that could be transferred from the orbiter in orbit. This is a study of a scale model reflector for the ET GRITS application. The approach is to form 1/2 mil film into a spherical mirror mounted on a seven foot diameter metal ring. The ring mount is sealed and slightly evacuated to pressurize the film into shape. Several different fabrication techniques were investigated using seamed gore designs to form the reflector. Also studied was casting a film into a seamless circular sheet. The goal for this model was to achieve a one milliradian (RMS) surface curvature error over 90% of the reflector area. This curvature was measured by a laser scanning instrument.The results show how different reflector designs and fabrication techniques contribute to surface curvature and focusing errors.

NASA's Marshall Space Flight Center is currently investigating a concept for a Gamma Ray Imaging Telescope using the space shuttle external tank. One of the major difficulties with this concept is the construction of the 28 ft. diameter spherical reflector used to concentrate the rays onto a collector. Because the access hatch through which all components of the telescope must enter the tank is 3 ft. in diameter, a rigid glass reflector would have to be segmented into individual panels of less than 3 ft. in diamater. This would result in a reflector of substantial weight and complexity in assembly. To overcome the problems involved with a rigid reflector, a concept has been developed in which an inflatable reflector can be used. A reflector of this type, attached to an inflatable torus could be designed to be transferred into the tank through the access hatch and then inflated. ILC Dover, Inc. has designed, fabricated and tested a 1/4 scale thin film inflatable reflector for use in the External Tank Gamma Ray Imaging Telescope. The prototype reflector is a 7 ft. diameter section of a 14 ft. radius sphere. Reflector configuration and seam studies were conducted to determine the optimum configuration for the reflector. The reflector is constructed from eight gore shaped panels and a 7 inch octagon in the center as determined by the "shadow" of the collector. The gore sections are designed to account for material elongation both circumferentially and radially so that the desired shape of a sphere was achieved.

When completed, the 10-meter W.M. Keck Telescope will be the world's largest instrument for optical and infrared astronomy. It has twice the diameter and four times the light-gathering power of the famous Palomar Observatory 5-meter Hale Telescope. Because of its size and required precision, it has presented many challenges in manufacturing and transportation to site. This paper reports on the progress of the construction of the telescope structure supplied by TIW Systems. At the time of this paper approximately ninety-five percent of all fabrication is complete and all major subassemblies have been proof assembled and passed shop testing. Site installation of the azimuth bearing journal is underway.

The Prototype Telescope Subassembly (PTS) is a two-axis gimballed telescope that has been designed and built for the University of Michigan. The function of the PTS is to collect light from the earth's upper atmosphere for the High Resolution Doppler Imager (HRDI), a white light interferometer built by the University of Michigan. The PTS/HRDI instrument's mission on the Upper Atmosphere Research Satellite (UARS) is to measure upper atmosphere wind velocities. This paper describes the reflective optics design, first-order fabrication, and test of the PTS. The telescope optics consist of an off-axis Gregorian afocal telecentric design. The gimbal relay optics incorporate additional fiber optics and mirrors for image transfer to the interferometer. The telescope optics and gimbal were manufactured primarily from 5000 series aluminum with the exception of two fiber optics components and one relay lens. The reflective optics are nickel-coated diamond-turned low-scatter postpolished components. The telescope incorporates an extensive low-scatter Lyot stop baffle design.

This paper documents the design and performance of advanced reflective optical systems that have been developed for laboratory collimators. Each system is designed to meet the specific requirements of the end item test article or Unit Under Test (UUT). Four specific examples are cited and a brief description of each system is included. The Large Aperture Infrared Telescope Sensor Telescope (LAIRTS) was utilized as a laboratory collimator. This system is a four-mirror "Aft-Schmidt" configuration. The system is used off-axis to provide an unobscured aperture. M1 and M3, the large elements in the system, ,and M2 are spherical figured optics, while the M4 is a Schmidt corrector. This system provides a full 1 x 1 degree field-of-view with a flat field over a 22 inch aperture. Two reflective Schmidt configurations are reviewed. The first is a Wide Field-of-View (WFOV) collimator fabricated for McDonnell Douglas Astronautics Co. for the testing of their Mast Mounted Sight (MMS). It consists of a spherical primary, two flat mirrors, one, a fold mirror, and the second, a two-axis gimbal mounted scan mirror. The fourth element is the Schmidt corrector. The second Schmidt system is the ISTF collimator, also manufactured for McDonnell Douglas Company. This system has a large aperture, 97 cm diameter sphere, a 73 cm diameter fold flat, and a 46 cm diameter Schmidt corrector. The effective focal length is 3 meters with a 15 cm usable aperture at the unit under test through a full field-of-view of 5 degrees. The fourth system that is discussed is a wide field-of-view collimator that is presently being developed at SSG. This design consists of a three mirror off-axis configuration with a hyperbolic primary, a spherical secondary, and an oblate spheroid tertiary. This system is designed to meet a spot size specification of 150 microradians over a 12 degree field-of view.

The design of a lens for long-range oblique aerial reconnaissance demonstrates how lightweight reflective optics are effective in producing an optical system which can detect, recognize, and identify distant ground objects from an airborne platform. The lens herein described transforms an object space filled with low-contrast targets of small angular subtense to an image space having the spatial and optical characteristics best suited to an electro-optical detector designed for this application. The lens incorporates two key reflective elements: a lightweight primary mirror which provides all the optical power of the lens, and a scan mirror of cellular construction which directs light into the lens. Although the nominal design is diffraction limited, the scan mirror deflections caused by gravity induce notable wavefront errors. Finite element techniques were used to predict the deflections. The deflections were then used to predict lens performance. The lens has been built and tested, and test results agree with predictions. The lens/detector-system combination allows intelligence gathering from an airborne platform at standoff ranges up to 150 nmi.

The Landsat Thematic Mapper imagers have provided moderate resolution, multispectral imagery of the Earth for the past 7 years. Yet, the need exists for higher spatial and spectral resolution and better radiometric accuracy. Santa Barbara Research Center has been exploring technology related to the design, tolerance, and alignment of wide-field, all-reflective sensors for multispectral earth observation. The goals of this study were to design an optical system with reduced fabrication risks, to develop a detailed tolerance budget and to demonstrate precision alignment of a laboratory demonstration unit. The telescope is a three-mirror unobscured form that is telecentric and flat field over 15 degrees at F/4.5, and is diffraction-limited at visible wavelengths. A computer-aided alignment approach aligned the telescope to the budgeted tolerance of 0.05 waves rms at 0.6328 microns. Details of the design, tolerance, and alignment of this telescope are described in two earlier papers. This paper consolidates the findings of those two and emphasizes the importance of keeping the hardware in mind from very early in the design.

For many LIDAR and laser atmospheric propagation experiments, large aperture, near diffraction limited optics with very small field of view and wavelength range requirements are needed. These optics should be compact and lightweight so they may be transported to various areas of experimental interest. It is also important that the cost per unit area of aperture be low. We present an optical and mechanical design of a catadioptric telescope system that meets the above requirements. It is a Cassegrain type telescope design with a Mangin secondary mirror and a low f/#, spherical primary to achieve compactness at low expense. A slumped, lightweight, borosilicate primary mirror keeps the system light weight and inexpensive. An athermal secondary mirror support maintains primary-secondary mirror separation passively. Using this design, a 1.4 m diameter, zenith pointing LIDAR transmitter/receiver fits into a semi tractor-trailer along with all the necessary support hardware. This telescope could be built for about $100 per square inch of aperture and would weigh less than 1200 lbs.

Reflective optical systems have been developed at SSG, Inc. to satisfy a wide range of spaceborne and tactical flight applications. The key mission requirements and performance goals which dictate reflective optical designs include wide spectral coverage for multi-wavelength operation; high straylight rejection; proper exit pupil location to permit a high degree of coldshielding for improved sensitivity; cryogenic operation; and inherent athermalization under harsh flight environments. Eight telescopes that have been designed and fabricated are reviewed. These telescopes have been designed and flown on various launch platforms including rockets, the space shuttle, satellites, and aircraft. This paper will also review the SPIRIT III reflective telescope being developed for the Midcourse Space Experiment for a satellite application. The selection process of the above designs will be reviewed based on mission and sensor requirements.

The Airborne Optical Adjunct (AOA) sensor mirrors' fabrication is addressed. Also reported are the final mirror figure quality achieved and the techniques used. The primary, secondary, and tertiary mirror figures are off-axis sections of high-order aspheric surfaces. The three mirrors are used as a wide field-of-view, non reimaging IR telescope. Such a complex system had never been constructed prior to the start of the AOA project. Production of these mirrors has pushed the state-of-the-art in fabrication technology. The mirrors were figured prior to being cut to size, lightweighted, and having precision mounts machined. Mirror figures were checked both mechanically and optically. Of special importance are problems overcome and lessons learned in this endeavor.

This paper discusses a study that was performed to model and simulate the operation of an end-to-end optical fabrication process. Two models dealing with facesheet and lightweighted mirrors are presented. When provided with proper process parameters and distributions, the models offer an avenue to evaluate the aggregate performance of an end-to-end optical fabrication process such as substrate material process, blank generation, aspherizing, fine grinding, polishing, and coating. The performance measures generated by the model include production capacity, system bottleneck process(es), process cost, and resource utilization. The models provide the media for an analyst to ask 'what if' type questions to assess the resource requirements for various types of mirrors under various system configurations in order to achieve desired production goals such as 100 square meters per year. The models are implemented using SIMAN, a FORTRAN based simulation language with several modeling facilities, including FORTRAN interface and process animation capabilities. The modeling flexibility in SIMAN allows the user to model special problem situations that are not captured by the usual system built-in routines.

Quartzglass mirror blanks in the form of ultra lightweight structures offer distinct advantages, especially for cryogenic and space applications. As with all other substrate materials, however, generating and finishing of large aspherical surfaces is a costly and time consuming process. Heraeus Quarzschmelze has developed a technique which allows to produce quartzglass face sheet surfaces to nearly net shape by a precision hot forming process. Spherical and aspherical surface figures achieved with this process can be accurate to within some microns.

Ultra-lightweight (ULW) mirror structures are defined by less than 20 % equivalent weight if compared with a solid piece of the same dimensions. The final mirror performance is primarily determined by the material properties and the structural design parameters. Quartzglass is a nearly ideal material for fabrication ULW mirrors due to its excellent weldability, its high degree of material homogeneity, its superior polishability, and its low coefficient of thermal expansion. ULW quartzglass mirrors made by HERAEUS have a sandwich structure consisting of one or two face plates and an egg-crate core structure. Back and face plates can be preshaped by a precision slumping process thus avoiding gross machining of the material to its final shape. The core structure consists of extruded square tubes flame-welded together. This construction allows for a high degree of design flexibility according to the needs of special applications. Test results obtained with a polished experimental ULW mirror of 0.5 m diameter did not reveal any structural problems.

This paper provides the first public disclosure of an optical technology which makes possible important new opportunities for the construction of very large telescopes. This technology, developed by Kaman Corporation in an Independent Research and Development program extending over the past several years, is generically known as PAMELAN, an acronym for Phased Array Mirror, Extendable Large Aperture. Kaman's patented PAMELA, approach leads directly to the ability to build rugged, diffraction-limited optical telescopes or beam expanders for ground-based or orbital deployment that have unprecedentedly low weight. In addition, the entire optical system will be fault-tolerant, leading to large expected savings in overall system cost and complexity. These attributes make PAMELA_TM a prime candidate technology to benefit both civilian and military optical systems in such areas as laser applications, imaging, remote sensing, and communications. PAMELA_TM will also have broad applicability to the needs of astronomy.

This paper describes a loose abrasive grinding technique as applied to Itek's computer controlled optical surfacing (CCOS) process. The intent of the new approach is to make large optics fabrication more timely and efficient. This is done by eliminating the long polishing cycle and supplementing it with microgrinding.

A technique is presented for the automated metrology of difficult to manufacture (large, highly aspheric, very precise) optics. This technique is termed MEDO- Metrology Employing Deformable Optics. It employs an Electrostatic Membrane Reflector (EMR) as the reference surface in a Twyman-Green interferometer, in combination with a commercially-available Phase Measuring Interferometer for automated data reduction. An analysis of the useful range of this proposed instrument indicates that it would, indeed, speed the production of many currently envisioned optics.

This paper will investigate diamond turning ogive error. The equations that describe surfaces with ogive error will be derived from a simple Pythagorean model for tool offsets. The geometry of an ogive "sphere" will be reviewed and ogive form errors on aspheric surfaces will also be investigated. By considering the wavefront errors created by surfaces with ogive error the implications for optical tolerancing will be examined.

We have developed a laser surface flatness measurement system, based on a new measurement principle. It measures angular displacements at a fixed interval, then caliculates the surface profile by totaling the angular data multiplies with the measurement pitch. With calibration, our system's measurement accuracy is better than 0.01 μm at about 1 mm/s.

The alignment of an off-axis parabolic mirror can be discussed mathematically in terms of third order optics using Zernike polynomials. While this discussion can add insight to the theory of alignment, it doesn't provide an easy means of knowing what to do in a "Hands-On" laboratory situation. As can be inferred from the title of this paper, a "How-To" method of alignment will be discussed. As for the theory of alignment, let it suffice to say that it can be shown that an off-axis parabola is a surface which departs from a best fit sphere in terms of spherical aberration, coma, and astigmatism.

This paper documents and investigates the optical performance of metal mirrors at cryogenic temperatures. It also reviews the telescope system level optical performance for several telescope systems designed and fabricated at SSG. These include data on the LAIRTS Telescope (Large Aperture Infrared Telescope Sensor), the CLAES Telescope (Cryogenic Limb Array Etalon Spectrometer), and the SPIRIT II Telescope (Spatial Infrared Rocketborne Interferometer Telescope). A brief discussion of the design and fabrication of these mirrors is included along with a summary of the driving design performance constraints on cryogenic infrared optics. A review of the test techniques and cryogenic test facilities is given. Interferometric testing is the primary tool used to test these mirrors and systems. This section of the paper also discusses the data analysis methods utilized to determine the cryogenic optical performance of these mirrors.

A remote fiber optic sensor system has been developed for the measurement of diffuse reflectance, luminescence, or fluorescence. The sensor is based on the use of graded index optics coupled with an appropriate source/detector. This configuration offers a low cost system capable of monitoring signals in deep wells. Other sensor configurations are described where the detector and graded index optics are integrated into a single unit, offering potential enhancements to detection sensitivity and flexibility.

A two-mirror, off axis Cassegrain telescope was fabricated and assembled for use in making Forward Looking Infrared Receiver (FLIR) to laser boresight measurements. The collimator was designed to operate over two non-coherent bands (0.30<λ<1.10 μm and 8<λ<12 μm) and the coherent 1.06 μm line. The compact multispectral collimator applications include both static and simulated dynamic operating conditions. This paper describes the results of the element, collimator and integration tests associated with the development of this steep diamond machined system. The mirrors were diamond machined out of aluminum that was nickel plated, post polished and hard gold coated. The unobscured aperture is greater than ten inches with an effective focal length of approximately ninety four inches. The large, fast primary mirror, which is an off axis portion of an f/0.37 paraboloid, drove novel fabrication and test methods for the collimator.