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Very large telescopes will be needed for the future of space science, space laser-com, and other interstellar or interplanetary applications. However, as telescopes’ diameters increase, their weight and cost increase dramatically. An approximation for ground-based observatories is that their cost increases to the power of 2.7 of its diameter [SAO, Special Report #385 (1979), p. 9]. Large space-based telescopes become limited by the rocket size and power. Multiple telescopes are also needed for very long baseline interferometry (VLBI), which further increases cost. A solution to overcome these issues is the use of inflatable telescopes. A thin mirror material clearly has much lower mass; however, controlling its surface error or wavefront can be a challenge. Intensity interferometry is an imaging method that has a much looser sensitivity to wavefront error (WFE), and thus is an ideal match for very large inflatable telescopes. A spherical inflatable mirror is the most practical; however, it suffers from spherical aberration. This paper presents new optical designs and simulations for intensity interferometry in support of large inflatable spherical telescopes. The optical system design includes a novel five-mirror off-axis, free-form, spherical aberration corrector. The system design shown is a 10 m diameter f/1 spherical primary mirror with 1.2 arcmin (0.02°) field of view (FOV). MATLAB simulations of intensity interferometry combine signal with noise and WFE. Visibility-based VLBI image simulations are shown based on various telescope arrays. Simulations show that with a 1 GHz detector, a 1 cm RMS WFE is tolerable. So the challenge of the optical design is then more about gathering and concentrating the light down to a reasonable size detector. Further simulations of signal combined with noise indicate that the signal rate must be about 100 times higher than the noise rate for an adequate intensity interferometry measurement. Visibility-based image simulations reveal that many telescopes (5–20 per axis) are needed in a 2D array out to the first visibility minimum to adequately resolve unknown features of a distant object.

Two disruptive space telescope concepts are being designed and developed at the University of Arizona; these are the 20-meter OASIS (Orbiting Astronomical Satellite for Investigating Stellar Systems) and 8.5-meter Nautilus. OASIS combines break-through inflatable aperture and adaptive optics techniques to realize the dream of a 20+ meter class spaceborne terahertz/far-infrared telescope. In the Nautilus visible/near-infrared telescope concept, conventional primary mirrors are replaced by an ~8.5-meter MODE (Multi-order diffractive engineered) lens with 10 times lower areal density and up to 100 times lower mis-alignment sensitivity over traditional systems, enabling large-diameter optical space telescopes. The OASIS and Nautilus concepts have the potential to greatly reduce mission costs and risks compared to the current state of the art.

The Imager for Mars Pathfinder returned over 16,000 high-quality images from the surface of Mars. The camera was well-calibrated in the laboratory, with

The imager for Mars Pathfinder (IMP), a stereoscopic, multispectral camera, is described in terms of its capabilities for studying the Martian environment. The camera's two eyes, separated by 15.0 cm, provide the camera with range-finding ability. Each eye illuminates half of a single CCD detector with a field of view of 14.4×14.0° and has 12 selectable filters. The ƒ/18 optics have a large depth of field, and no focussing mechanism is required; a mechanical shutter is avoided by using the frame transfer capability of the 512×512 CCD. The resolving power of the camera, 0.98 mrad/pixel, is approximately the same as the Viking Lander cameras; however, the signal-to-noise ratio for IMP greatly exceeds Viking, approaching 350. This feature along with the stable calibration of the filters between 440 and 1000 nm distinguishes IMP from Viking. Specially designed targets are positioned on the Lander; they provide information on the magnetic properties of wind-blown dust, measure the wind vectors, and provide radiometric standard reflectors for calibration. Also, eight low-transmission filters are included for imaging the Sun directly at multiple wavelengths, giving IMP the ability to measure dust opacity and potentially the water vapor content. Several experiments beyond the requisite color panorama are described in detail: contour mapping of the local terrain, multispectral imaging of the surrounding rock and soil to study local mineralogy, viewing of three wind socks, measuring atmospheric opacity and water vapor content, and estimating the magnetic properties of wind-blown dust. This paper is intended to serve as a guide to understanding the scientific integrity of the IMP data that will be returned from Mars starting on July 4, 1997.

A fog chamber, developed to support measurement of the performance of electrooptical devices in the presence of fog, is discussed. Rationale for the fog chamber concept is presented. Emphasis is placed on the theory of operation of the chamber, an optical method for assessing fog particle characteristics, and the optical properties of the different types of fog produced.

The authors have previously called attention to the importance of atmospheric and aerosol emission in IR imaging device performance. The present paper derives a more precise and general result than the empirically derived expressions in the earlier paper. The same general conclusion, that atmospheric and aerosol emissions are an important factor in IR imaging performance, is supported, assuming that the system is photon noise-limited.

The Mars Surveyor Spacecraft's Robotic Arm Camera (RAC) is a CCD imager designed to enhance the capability of studyingboth trenched areas and material collected by the craft's Robotic Arm. Because of the wide range of object distances/imagescales desired, an active focus mechanism will be used, capable of imaging from a magnification of 1 : 1 to infinity focus, witha maximum resolution of 23 microns/pixel for Mars surface material samples in the mouth of the scoop. This paper willdiscuss the optomechanical design of the optics, mechanism, and actuator, operational scenarios for the most efficientcollection of the necessary images, and algorithms for selection of images to be returned to earth.Keywords:Optomechanical, camera, autofocus, instrument, Mars 1. INTRODUCTION The Mars Volatiles and Climate Surveyor (MVACS) instrument package to be flown on the Mars SurveyorSpacecraft scheduled for launch in January, 1999, includes a Robotic Arm for collecting and delivering samples to a thermalanalysis instrument. The Robotic Arm Camera, to be mounted at the wrist, will be capable of imaging the contents of thescoop, the interior of the trench and surrounding areas, and even the horizon. Figure 1 .

Using a layered atmospheric turbulence model, it is shown that substantial extension of the compensated field of view is possible by employing a number of adaptive mirrors and guide stars. In large astronomical telescopes additional extension of the compensated field of view can be achieved at the expense of effective aperture size available for diffraction limited resolution.

A wave-front sensor based on pseudo-phase-conjugate interferometry is presented. We show that a pseudo-phase-conjugate interferometer is suitable for the measurement of phase distribution on a propagating wave. This new method may be employed for optical workshop applications and wave-front sensing for adaptive optics. The theoretical sensitivity of the interferometer is twice that of the Hartmann-Shack wave-front sensor. Preliminary laboratory experiments demonstrate excellent performance and consistency with computer simulations.

Optical wave-front propagation in a layered model for the atmosphere is analyzed by the use of diffraction theory, leading to a novel approach for utilizing artificial guide stars. Considering recent observations of layering in the atmospheric turbulence, the results of this paper indicate that, even for very large telescopes, a substantial enlargement of the compensated angular field of view is possible when two adaptive mirrors and four or five artificial guide stars are employed. The required number of guide stars increases as the thickness of the turbulent layers increases, converging to the conventional results at the limit of continuously turbulent atmosphere.

A general procedure is introduced for sidelobe and noise reduction in optical or digital signal processing. Specific examples of sidelobe reduction in imaging are presented. It is demonstrated that the new method provides superior spatial resolution to previously proposed sidelobe-reduction techniques.

The use of subwavelength near-field apertures opens the possibility of optical dish data density increases in excess of 4 orders of magnitude.

One of the limiting factors in the operation of highly energy-efficient optical computers is the fluctuation in the rate of photon detection events. Squeezed light technology, which appeared to be a possible way to mitigate this fluctuation, is shown to be of limited utility in this field.

A projection system is described which can simulate emissions from flares, muzzleflashes, shellbursts, and other emissive agents which may degrade the performance of electrooptical systems in the 0.5–15 μm spectral range. The simulation capability obtained will allow the apparent radiance and temporal characteristics of muzzleflashes and shellbursts to be mimicked at simulated ranges as close as 23 m within the Electro-Optical Test Facility. This demonstrates that tests of electro-optical system performance in the presence of interferers can be performed under laboratory conditions with higher repeatability and lower cost than field tests.

Details are presented for terrain and sky backgrounds and targets which give realistic signatures in the visible and infrared spectral regions. Characteristics of these targets and backgrounds include: (i) The targets and backgrounds have realistic emission spectra in the thermal infrared, (ii) It is relatively easy to vary the viewing angle of the targets and to provide target motion, (iii) The radiances of the background and target signatures are independently variable, (iv) The target signature can be controlled in spatial distribution as well as radiance. These visible and infrared signatures are sufficiently accurate to allow low cost simulation of field tests under repeatable laboratory conditions.

Fog spectral transmission data generated in the Electro-Optical Test Facility and propagation models usedm by the authors are presented. Preliminary results of a modeling effort are presented that support the following conclusions: (1) atmosphere emission is a major factor in IR system performance despite the fact it is commonly omitted; (2) the 3.5-4.1-microm interval offers superior performance to the 3-5 band at both relatively short and long ranges; and (3) the longer wavelength 9.5-11.5-microm band is superior to either the 3-5 or 3.5-4.1 bands in the presence of fog.