Cost and weight data for optical and radio telescopes are analysed to derive scaling laws appropriate to the design and costing of very large telescopes of the future. A scaling law exponent close to the 2.0 power of aperture diameter is found for telescopes of comparable sophistication ranging from a 0.4 m to 5.0 m aperture, in contrast to the often cited 2.7 exponent. Predicted characteristics for a 25-meter aperture steerable dish NGT are 5x10⁶ kg, 20 $/kg and a total cost of 1.3x10⁸$.

In the early 1960s farsighted astronomers recommended a study of a very large optical telescope that would provide a major advance in light gathering power over the Palomar 5-meter telescope. Large telescopes are expensive, however, and, for a time, great gains in performance were more easily obtained by developing better detectors, or more efficient diffraction gratings, or high performance reflective mirror coatings. Computers came into vogue and enabled better data extraction and analysis, as well as increasing the number of observations that could be made in a given period of time. Daytime usage of telescopes for infrared astronomy became commonplace, thus extending the available observing time.

We believe that an optical Arecibo telescope with an effective aperture diameter of 10 to 25 meters has considerable merit as a Next Generation Telescope design because of the outstanding economy inherent in its stationary mosaic spherical primary mirror. Although the aspheric secondary mirror corrects the spherical aberration of the primary mirror, the telescope itself has a useful field of view, limited by coma, of less than 1 arc second. Recognizing this deficiency, we have designed a field corrector assembly which will provide well-corrected extended images over a 1 arc minute flat field at a focal ratio of f/4.4. The extended field capability ought to significantly enhance the overall acceptability of the Arecibo design.

Very large telescopes of the future will be much more practical to build if the large primary mirror can have a spherical surface. This greatly reduces the time and expense required to optically figure a large surface. Several two-mirror designs are discussed which have a spherical primary mirror and a sub-aperture diameter aspheric secondary mirror. The light path reflects off of both mirrors twice, and the system is corrected for spherical aberration, coma, and astigmatism. Designs with small obscuration are possible if astigmatism correction is dropped. Scanning arrangements for huge Arecibo-type systems are also discussed.

A number of all-reflective large-aperture optical arrangements are described. These configurations form a group of systems whose optical surface figures can be monitored from the effective centers of curvature of the mirror elements. Design specifications are presented for the basic two-mirror f/3 system. Image size versus field angle data indicates that field performance is approximately one-half as good as the refractive corrector Schmidt of equivalent f/no. Geometrical ray trace results for a point source at infinity show an on-axis rms image diameter of 1.5x10^-7 radians for the two-mirror system. Practical difficulties of most of the optical arrangements depicted are the close physical proximity of the uncorrected and corrected foci, as well as the large departures of the aspheric corrector surfaces from a reference sphere. These problems are reduced by slowing down the system f/no. But unfortunately they do not disappear completely.

One of the designs for the University of California's ten meter telescope project has the primary mirror composed of many hexagonal segments. A total of 54 mirror segments surround the 3.6m central mirror. Each segment is supported by 3 position actuators which provide tilt and focus control. The mirror figure is maintained by a non-optical technique using edge sensors to monitor relative mirror segment displacements. Details of the project goals and the critical design characteristics, including the behavior of the control system, and the proposed mirror components will be presented.

A control system using mirror displacement sensors and position actuators to maintain proper surface control of a segmented mirror is summarized. The system is composed of three major components; a figure control computer, displacement sensors and displacement actuators. Desired positioning accuracy is 50 nm. Several methods for achieving the needed sensor sensitivity and stability are discussed. A capacitive hridge detector was chosen and its expected and measured behavior is described. Two mechanisms for positioning a mirror segment to optical tolerances, yet having a large dynamic range to compensate for mirror cell deformation are reviewed. Test results for a roller screw are given with an outline of the servo loop design.

The technique of rapidly wobbling the secondary mirror of a reflecting telescope to modulate the energy from an astronomical source by moving its image on and off of an aperture in the telescope's focal plane has been used with great success for a number of years on many ground based and airborne infrared telescopes. Such a secondary modulating system involving six synchronized secondaries of 23.5 cm diameter has been designed for use on the Multiple Mirror Telescope. One prototype mechanism using a linear servo drive system has been constructed and tested both in the laboratory and on the MMT itself. For image displacements up to about 20 arc seconds on the sky, the prototype is capable of a rise time of 2 ms and of operation at frequencies up to 80 Hz with a square wave driving signal. Larger displacements up to more than 120 arc seconds are available, but with a rise time of 4 ms. Adjustable hard stops and electronics to drive the secondary mechanism against these stops have been incorporated to provide a back up capability to the linear servo. Seven copies of the prototype are now in production and are expected to be in operation on the MMT in the spring of 1979.

While the Image Tube, Image Dissector Scanner (ITS) has been used for 8 years to take spectra of faint objects, the image tube gain is sufficient to support a larger number of pixels than is currently being used for spectroscopy. We have recently built a 32K memory and sweep control circuitry that can provide up to 128 scan lines, although only 64 have been used as yet. Initial tests of the two-dimensional capability of the ITS are encouraging; the system seems to be linear and has a wide dynamic range. Planned applications include broad band photometry and near simultaneous recording of two 64 x 256 pixel fields for polarization measurements. The equipment has been used to date to take multiple spectra from a polarimeter and of extended objects. Because the ITS outputs data continuously, the data can be used to generate error signals for telescope guiding. The ability to analyze the data in real time makes it feasible to record images in small fields in such a way that data are only stored during moments of good seeing.

A self-scanned diode array spectrophotometer, designed and constructed at the University of California, Los Angeles, Department of Astronomy, is described. Careful attention to physical properties of the detector and system noise and stability requirements has resulted in an instrument with performance closely approaching theory. In particular, system noise performance is limited by thermal and interface state noise in the detector (a Reticon Corp. RL-256A-17) rather than preamplifier noise. Advantage is taken of the dependence of dark current on diode bias voltage, as well as temperature, such that a tradeoff between leakage rate and dynamic range can be selected. This feature also allows operation of the array at higher temperatures, enhancing sensitivity in the near infrared.

For applications in faint-object spectroscopy at the Mt. Hopkins Observatory, a photon-counting detector has been built using a dual 936 Reticon diode array fibre-optically coupled to a high-gain image intensifier package. The electronic signal processing follows closely the design of Shectman; the diode array is scanned every millisecond, each frame is subtracted from the previous to minimize multiple counts from the tails of the P-20 phosphor decays, and the centroid of each photon event is located to recover much of the resolution of the first image intensifier. For each detected event, the corresponding address in a Nova computer is updated by a direct memory access, thus allowing simultaneous data collection, analysis, and display. Two different intensifier packages have been used, both sandwiching a 25-mm Gen II microchannel-plate tube fibre-optically between 40-mm Gen I tubes for the first and third stages. This has made possible a compact intensifier package at the expense of a poor pulse-height distribution. Our first version of the detector has been in use with the 60-inch telescope at Mt. Hopkins since February 1978. A new version using a custom dual RL1024SF Reticon is now under construction for use on the Multiple-Mirror Telescope.

A simple, low-cost, low-noise preamplifier has been developed for use with Reticon self-scanning diode arrays or similar devices. This design lends itself naturally to quasi-CDS (correlated double sampling) signal processing, allowing system bandwidth and noise to be effectively limited without resort to pulse shaping networks. The preamplifier seems potentially capable of approaching the fundamental noise level imposed by the detector itself. With minor modification, it can be operated from several kHz up to about 1 MHz pixel frequencies.

The Intensified Image Dissector Scanner has been in routine use at Kitt Peak National Observatory for two years and has been used by astronomers to obtain accurate sky-compensated spectrophotometry of objects ranging in brightness from V = 10-22 mag. In this instrument, the output phosphor of a three-stage image intensifier is used as a temporary storage medium for incoming photon events. An image dissector tube is used to rapidly scan this output phosphor, and the detected events are accumulated in up to 2048 channels, half of which are normally used for simultaneous night-sky observations.

A series of Self-Scanned Digicon image detectors has been constructed in which the target of the photoelectron imaging section is a Reticon type RL-1872F self-scanned photodiode array modified as a 2 X 936-element dual array. This paper describes an application in which the dual array is used for simultaneous spectroscopy of a faint object and a neighboring patch of skylight, Performance in this application has been tested using a Cassegrain spectrograph built for these tests and the 2.1 m Struve telescope at McDonald Observatory. Tests performedduring the course of several observing programs have demonstrated that subtraction of background skylight is complete to within limits set by photoelectron shot noise. Radial velocities of galaxies have been measured to a precision of ± 34 km/sec to v = 13,700 km/sec. The paper describes the detector, the spectrograph, the observing techniques, and the observational results.

The video camera system was designed specifically to meet the demanding needs of two dimensional astronomical observations. Primary consideration was given to stability, reliability, data handling, human interface, and modular flexibility. The video camera system was designed in modular fashion to satisfy several technical and scientific problems and to minimize the overall instrumentation cost for the national observatory. The system can be configured in both a direct mode using an RCA 4849 ISIT as the detector and in a spectroscopic mode using a 3-stage, magnetically focused RCA C70021 image intensifier lens coupled to an RCA 4804 SIT. In either mode, the analog data from the detector is digitized, one frame at a time and accumulated in a 20 bit digital memory at a rate of up to 30 frames/sec. The 16 bit quotient of accumulated data divided by its frame count is sampled at a rate of .625 frames/sec. by a display memory which outputs data to a display monitor at a rate of 60 frames/sec. The data passing from the display memory to the display monitor encounters both a 16 bit to 8 bit linear transform and a linear or non-linear transform via a look-up-table. Control of the display transforms is accomplished by the observer using the operator control panel. A bi-directional data link exists from the accumulation and display memories to the main computer.

The observational capability and instrumental details of a Fourier spectrometer intended for moderate to very high resolution (20 cm^-1 to 0.005 cm^-1) observations of astronomical sources in the visible and infrared (700-2800 cm^-1 i.e., 0.36μm to l4μm) are described and a few initial spectra are shown to illustrate performance achieved to date. The instrument is unusual in that it can be maintained by a moderate level of non-specialist technical support and does not require the observer to be an instrumentalist familiar with the details of the spectrometer.

A spectrometer constructed to search for extrasolar planets is connected to a telescope by a single optical fiber acting as an image scrambler. A nitrogen dioxide absorption cell is used as a wavelength standard. Either an intensified charge injection device (CID) or a pair of photomultipliers can be used as a detector.

The Fraunhofer spectrum appears to show subtle variability at the 0.1% level indicative of non-constant temperature and possibly mechanical wave flux in the solar atmosphere. Persistent or secular changes in these physical conditions on time scales of years has terrestrial climate implications. Spectrum line monitoring requires control of spectrometer scattered light, zero point, resolution, and linearity to high accuracy (< 0.05%). Inevitably system components such as filters, detectors, gratings, etc. will break or deteriorate and have to be replaced. The general problem of maintaining a time invariant instrument is discussed.

An infrared spatial interferometer has achieved an order-of-magnitude improvement in the angular resolution of ground-based telescopic observations at wavelengths from 2.2 to 20μm. Using incoherent detectors to measure fringe visibility versus baseline, this instrument has obtained an effective angular resolution of 0.1 arcsec at 10.2μm with a 3.2m baseline in 3 arcsec conditions of visual atmospheric "seeing". Observations are made at eight wavelengths to probe different levels of temperature and density in circumstellar envelopes. Twenty-three stars of various spectral types are partially resolved and upper limits placed on the sizes of 25 others. Three stars contain flattened, disk-shaped envelopes. At 10.2μm, objects as faint as zero magnitude have been measured. Significant improvements in sensitivity are expected using a composite diamond-germanium bolometer operating under low background conditions and cooled to 0.3K in a newly developed He³ cryostat. Angular resolution can be doubled using a ≥6.5m baseline provided by the Multiple Mirror Telescope. Plans to use the MMT as a multi-element spatial interferometer will be discussed.

A balloon-borne, 1.2 meter Cassegrain telescope designed for diffraction-limited imagery at 100μ is being developed for a survey of the Galactic plane at submillimeter wavelengths. The telescope pointing system is servo-controlled using a gyroscope for the primary stabilization reference. Extensive use is made of micro-processors for flight sequencing, pointing control and stabilization, and telemetry formatting. A description of the telescope, helium-cooled detectors, and the orientation subsystems are presented together with a brief discussion of the proposed astronomical observations.

A low-background balloon-borne far-infrared (30-300μ) telescope, utilizing a linear scan mode has dramatically increased the efficiency of mapping large extended areas over more conventional systems. The system consists of a 20 cm linear scanned mirror mounted as an off-axis (Herchelian) telescope designed to achieve an emissivity of 1% or less, a ten position cooled aperture-filter wheel, a cooled Pfund optical system with a composite diamond-germanium bolometer mounted in a spherical cavity, a minimum phase shift ultra-low frequency amplifier, and a 4 micron thick mylar dewar window. This system was used to produce detailed far-infrared maps of the galactic plane. The system specifications and operating parameters will be discussed and preliminary data shown.

The design and performance of the Arizona cryogenically-cooled, balloon-borne, multiband far infrared survey telescope are described. The 40 cm Cassegrain telescope is completely contained in a liquid helium dewar. The focal plane array consists of Fabry optics and four detectors which each have a 12 Aarc minute field of view. Both photoconductive and bolometer detectors are utilized at effective wavelengths of 20, 80, 100 and 150 microns. In 1977 the telescope was used to make multicolor large scale maps of 70 square degrees in the Cygnus X region and the W3 region.

An unusual, highly modified, Baker reflector-corrector class telescope has been adapted for wide field survey photography in the near infrared. This optical system uses a full field corrector plate and a field flattening lens to provide a flat field subtending about 4:5 on the sky. The small aperture telescope (20 inch primary) has been modified for use in the Newtonian focus configuration while preserving the optical elements of the Prime focus configuration. The telescope has been further modified to accept a very large format (146mm diameter photocathode) image intensifier camera to serve as a detector. The camera output is recorded photographically on film rather than glass plates. This uniqueinstrument system is used in a program of sky survey photography in the optical infrared (8000-9000Å bandpass) supplemented by visual bandpass photography. The photographs obtained with this system are of value not only for the extreme redness of the band but also because of their high resolution and their freedom from hydrogen emission.

The design, construction, and performance of state of the art germanium and germanium-diamond bolometers operated at 4.2, 2.0, 1.2, and 0.3K will be discussed. These detectors have a broad range of applications, and are particularly important for the long wavelength (far infrared to millimeter) regions. Current results may be extrapolated to lower temperatures and higher levels of performance. A system which will operate at 0.1K using a He⁴-He³ dilution refrigerator is under development.

In support of two infrared astronomy space projects, the IRAS satellite and the IRT on Spacelab 2, we have carried out low-background tests on the performance and characterization of Si:Ga, Si:As, Si:Sb and Ge:Ga photoconductive detectors. These test results represent a useful appraisal of this family of detectors when operated at 1.8-4.2K and at back-ground power levels of 10^-14 - 10^-13 W. In addition to detector performance data, results will also be presented on cryogenically cooled MOSFET amplifiers operated in the source follower and in the balanced-dc-TIA configurations.

Analyses of pyroelectric detectors have generally been limited to a sinusoidal representation of the differential response to chopped incoming energy. While often applicable to single detector/amplifier systems with prefiltering, this approach masks useful tradeoffs of thermal and electrical time constants which could be used to optimize performance when pyroelectric detector arrays are mated to sampled data systems for readout of large focal plane arrays. This paper describes a transient analysis that describes voltage response versus time as a function of thermal effects, electrical interface, detector characteristics, and chopper frequency. Results are used to perform tradeoffs between various types of detecors, their area, thickness, mounting substrates, and sampling methods to obtain maximum output signals for particular sampling frequencies. A major consideration is the need to hard-mount detectors for reduction of microphonics and to prevent thermal runaway, thus achieving performance and reliability that is suitable for spaceborne applications. The conclusions predict adequate capability of these room temperature devices to provide thermal imaging line arrays that can coexist in a focal plane with CCD visible imaging line arrays for accurate co-registration of images in earth observation systems.

The Multi-anode Microchannel Arrays (MAMA's) are a fa,Hily of photoelectric photon-counting array detectors being developed for use in instruments on both ground-based and spaceborne telescopes. MAMA. detectors can be operated in a windowless configuration at extreme-ultraviolet and soft x-ray wavelengths or in a sealed configuration at ultraviolet and visible wavelengths. Prototype MAMA detectors with up to 512 x 512 pixels are now being tested in the laboratory and telescope operation of a simple (10 x 10)-pixel visible-light detector has been initiated. In this paper the methods of construction and the modes of operation of the MAMA detectors are described and the status of the development program is reviewed.

Princeton University Observatory has developed an Intensified Charge Coupled Device (ICCD) image tube with a 200 mm diagonal S-20 photocathode and a 100 x 160 pixel Texas Instruments CCD. Measurements of the CCD's response to accelerated photoelectrons have been made with this tube, as well as other configurations. The paper presents the pulse height distribution and point spread function for single photoelectrons of 20 keV energy. These data are discussed in relation to a photon counting image system.

A Fairchild CCD211 (190X244 pixels) charge coupled device was thinned for photon and photoelectron rear-illumination experiments. Image smear due to injection of charge into the interline transfer registers was measured, and leakage current changes as a result of photoelectron irradiation were recorded. As expected, damage rates were less than 10^-4 of those measured for front side irradiation. Similar damage data were taken at UCSD on the Texas Instrument 100X160 thinned array. Nearly identical damage rates were measured for the two arrays.

We are developing a High Resolution Spectrograph (HRS) for ultraviolet astronomy with the Space Telescope. The instrument will provide a spectral resolution of ≈ 1.2 x 10⁵ over a nominal wavelength range of 110 - 320 nm, together with a spatial resolution of about 0.25 arc seconds. The two detectors will consist of 512-element Digicons with cesium telluride and cesium iodide photocathodes, respectively. Photoelectrons in transit between the photocathodes and the diodes within the Digicons can be deflected in two axes with 12-bit resolution. This feature facilitates a design that emphasizes reliability since (once a hermetic seal is opened in orbit), only two moving parts, a grating carrousel and a shutter, are required for regular operation of the HRS. The instrument will be controlled by a computer in the spacecraft. The scientific objectives of the HRS investigation relate to interstellar matter in our own and nearby galaxies, physical processes of stellar mass loss and mass transfer, chemical abundances, bright quasars and Seyfert galaxy nuclei, and solar system phenomena.

A helium cooled telescope of 15 cm aperture is being designed and constructed jointly by the University of Arizona, the Smithsonian Astrophysical Observatory and the Marshall Space Flight Center for high sensitivity infrared astronomical observations from Spacelab 2. A focal plane array of ten detectors provide a total field of view of 3° and cover the wavelength regions 4.5-8.5μm, 6-7μm, 9-16μm, 18-30μm and 80-120μm. A highly redundant all sky survey will be conducted by repeated scanning of the sky during many orbits of the spacecraft. High redundancy will allow discrimination among variable and constant celestial sources and several types of variable nearby sources. The principal astronomical result of the survey will be the absolute flux measurement of low surface brightness, large scale celestial infrared emissions but it will also extend existing IR sky surveys by a factor of 10 in point source sensitivity. The experiment will also make significant engineering measurements of contaminants in the Shuttle environment, test the technology of storage and utilization of large quantities of superfluid helium in space and test mechanical designs for future infrared telescopes for the Space Shuttle.

If the solar system were observed from afar, the sun's visible light would be about 10⁹ times stronger 4 than the light reflected from Jupiter. But in the far infrared (40 μm) the solar radiation is only 2 x 10 times the jovian. This paper proposes an orbiting infrared interferometer with its fringe null centered on a nearby star at a distance of say 10 parsecs. A large planet ("Jupiter") would have an angular separation from the star of about 0.5 arcsec. To have a fringe crest on the planet, a fringe period of 1.0 arcsec is needed and at 40 μm the required baseline is 8 m. Spinning the interferometer about the line of sight to the star results, even with pointing errors, in a relatively slowly varying but strongly suppressed stellar output and a more rapidly varying fringe-like planetary signal rich in higher harmonics. For pointing errors up to .050 arcsec the planet's fourth harmonic greatly exceeds that from the star, thereby relaxing interferometer pointing tolerances. Indeed, it appears that the limiting factor is zodiacal infrared background radiation and not the intense localized stellar flux which can effectively be eliminated by the fringe null of the spinning infrared interferometer.

The International Ultraviolet Explorer (IUE) is a scientific satellite operated in re Al time to obtain ultraviolet spectra of astronomical objects in the wavelength range 1000 Å ≤ λ ≤ 3200 Å in either of two selectable dispersion modes. IUE spectra are recorded by SEC vidicon cameras and transmitted digitally to a ground station as two-dimensional images. The reduction of these data begins with the International Ultraviolet Explorer Spectral Image Processing System (IUESIPS), an on-line interactive image processing system which has been in operation for one year. The task of IUESIPS is to remove all known instrumental effects from IUE spectral images and to provide, in a timely fashion, IUE Guest Observers with reduced data - in the form of spectral intensity as a function of wavelength - amenable to immediate astronomical analysis. The current status of this image processing system is discussed and the types of reduction operations which are routinely performed are presented along with the known existing limitations of the system.

The use of a Kron electrographic detector for wide-field, narrow-band imagery of faint emission nebulosity in the near-UV and visual (3100-6000 A) wavelength interval is de-scribed. As an example of the photometric quality of the imagery and of the sensitivity of the instrumentation to diffuse, low-contrast objects, imagery of the Cygnus Loop super-nova remnant in the high excitation line of [Ne V]λ3426 A is presented. In addition, we describe our current program to develop electrographic detectors which use cesium tellu-ride photocathodes for broad-band imagery and spectrography in the middle-UV (1650-3100 A) wavelength range.

The latest results in the NRL program of far-UV electrographic camera development, and application of these cameras to astrophysical and upper-atmospheric investigations, are presented. A new large electrographic Schmidt camera, of 15 cm aperture and f/2 focal ratio, has been successfully used in two sounding rocket flights, one for direct imagery in the 1230-2000 A wavelength range and the second for objective spectrography in the 950-20000A range, of stars and nebulae in the Cygnus region of the sky. The camera has an 11° field of view and better than 30 arc sec resolution (2 A spectral resolution with 600 line/mm objective grating). A nebular spectrograph, based on a microchannel-intensified electrographic Schmidt camera, is the payload of a May 1979 rocket flight. It will reach emission line features as faint as 5 Rayleighs in 100 second exposures in the 1050-2000 A range, with 5 A spectral resolution. Electrographic cameras with mesh-based semitransparent photocathodes, capable of observations in the extreme ultraviolet below 1050 A, are being developed for a number of space science applications. A camera with microchannel intensification is the detector in an XUV airglow/auroral spectrograph used in a February 1978 rocket flight, and cameras without microchannel intensification are proposed for various solar XUV spectrographic and spectroheliographic applications.

We have designed an imaging ultraviolet detector for use with a precision pointed telescope flown on a sounding rocket. Resolution of better than 80 microns over a field of 5 mm has been achieved. The ultraviolet image is converted to electrons at the front surface of a CsI coated chevron michochannel-plate electron multiplier. For each photoelectron, the multiplier produces a burst of about 3 x 10⁶ electrons, which impinges on a tellurium-coated resistive anode with four evaporated hyperbolic readout electrodes. The sizes of the four resulting output pulses are digitized to 10 bit accuracy and telemetered to the ground, where they are divided in pairs to give the x and y coordinates of the photoelectron event. The coordinates are used to generate a picture in real time, and are recorded for computer processing later. The detector was successfully flown in December 1978. Good images of Jupiter and Capella in hydrogen Lyman alpha emission were obtained.

A rocket payload, consisting of a Rowland circle spectrograph with a multi-anode, microchannel plate detector, located at the focus of a 40 cm mirror, has been constructed to observe faint astronomical objectsmin the 900 to 1800 A spectral region. It can obtain the spectrum of an unreddened, V = 10^m OB star with 3 A resolution and ±3% precision in a 60 second observation.

A multi-mode space flight instrument capable of remotely measuring the parameters necessary to construct a three-dimensional dynamic model of a planetary atmosphere is presented. This Photopolarimeter/ Radiometer (PPR) instrument was designed to make such measurements aboard the NASA Project Galileo spacecraft while orbiting the planet Jupiter. The PPR will use photopolarimetric techniques to determine the nature of atmospheric particles and aerosols, photometric techniques to trace the temporal properties of specific gas species, and radiometric techniques to assess the thermal and radiative energy balance of the planet and its prominent satellites. Special features of the PPR, including simultaneous measurement of polarization components to accommodate changing scene conditions and redundant internal calibration schemes for long-term accuracy and stability are emphasized. Construction techniques including lightweight metallic optics, a special magnetically-clean motor, and microprocessor control of measurement sequences are discussed. The design, basic operation, and key functional elements of the compact low-power radiation-resistant PPR instrument are summarized.

Design considerations are discussed for a ground-based high-resolution scanning spectrometer in which thermal background radiation to the detector is reduced to the level of the detector NEP by cooling the interferometers to liquid nitrogen temperature.

One of the questions that must be investigated in the planning of space-borne infrared telescope systems is that of the background flux due to discrete infrared sources, such as stars, external galaxies, and galactic nonstellar objects. For example, when performing an infrared sky survey, a knowledge of this background is necessary to optimize the choice of system parameters such as detector size, scan rate, and aperture size. For this reason we have combined the Cal Tech. Two Micron Sky Survey with a structural model of the galaxy in our computer code CELES to predict the number of stars/square degree brighter than a given limiting flux for particular lines of sight through the galaxy. Extragalactic sources are included by inference from visual galaxy counts, while main secuence stars are accounted for by using their optically determined properties and 2μm luminosity. Possible future work could include extension of the present technique to other near infrared wavelengths. Although this might be accomplished by using the AFGL 4-Color Sky Survey, our preliminary results at 4μm show that there is a problem with this approach which could be inherent in the 4μm catalog (e.g., due to lack of completeness to sufficient flux, or the heterogeneity of the catalog objects). To investigate this problem a comparison of the Cal Tech 2μm and AFGL μpm catalogs is presented. Longward of 2μm, the AFGL catalog is the only major infrared survey available for statistical studies, and the need for more sensitive surveys is discussed.

The U.T. Electrographic camera is the result of nearly 12 years of research undertaken to produce a high resolution and sensitivity detector for astronomy, yet reliable and easy and fast to operate. The Mark II experimental camera has a 5 cm useful field diameter and is equipped with a Cs₃Sb(0) photocathode with typical Q.E. of 15% at 430 nm. The highly corrected magnetic and electric fields produce sharp focus on the entire field with no image distortion. An aluminized thin plastic foil, which comes in intimate contact with the emulsion, prevents photocathode poisonning during the exposure. The camera is operated at accelerating voltages up to 60 kV with no detectable background in a 2 hour exposure. The design permits fast loading and unloading. The camera is being tested extensively at the F/13.5 cassegrain focus of the McDonald Observatory 0.76 m telescope and hundreds of excellent electrographs have been obtained under routine conditions. The high resolution and photocathode Q.E. permitted recording more rapidly and accurately the telescopic images of various astronomical objects. Testing will be continued until enough information is gained for designing and building, upon adequate support, a large field electrographic ca-mera with a roll film magazine and a higher Q.E. photocathode for both ground based and space telescopes.

The object of this paper is to show the conversion of a commercially made television camera to an intensified acquisition device used in astronomy. It will illustrate how the conversion took place and where and how the camera is used for field acquisition on telescopes at Kitt Peak National Observatory. Five such television cameras have been constructed and are being used with nine instruments on five different telescopes. The success of this approach versus another acquisition television camera will be discussed briefly.

Sky limit performance of an intensified detector acquisition system is degraded by noise that significantly exceeds the minimum detectable signal level. A digital television acquisition processor has been developed at Kitt Peak National Observatory to attenuate the noise by frame-to-frame integration and to enhance the contrast through an arithmetic mapping function. Recent experience at the 4M Mayall Telescope indicates that the new real-time Digital Processor will extend the useful range of RCA ISIT detectors by four stellar magnitudes. During the course of project development two important design principles were rediscovered: 1) Integration will improve an image if and only if the detector system generates frame-to frame pixel differences. 2) When a pixel in a stable image is perturbed by frame-to-frame spectral noise, the effective sampling frequency cannot exceed the Nyquist sampling frequency of the most significant noise component. In other words, the maximum √N signal-to-noise improvement factor depends upon the frequency of the frame-to-frame noise, not upon the fastest possible readout frame rate.

Magnetically focussed image tubes are of special value in astronomy because they have high resolution and can be made with flat ultraviolet-transmitting windows. There has, however, been a difficulty in operating such tubes with the very fast cameras required by spectrographs for large telescopes. An ideal fast camera for imaging linear spectra is the folded Schmidt design used, for example, in the Wampler-Robinson scanner at Lick Observatory (Epps 1975). This design, which can be as fast as f/1.0, involves a folding flat directly adjacent to the tube photocathode, and the incoming light would be blocked by the solenoid in any convention-al magnet design. We have explored more complex solenoid geometries which give the very open access to the cathode while maintaining high field uniformity, and present here a design which is practical in terms of power dissipation and weight, and is also screened against external transverse fields. The design may also have application in any optical system that requires large elements and clearance near the image tube cathode.

The Mariner Jupiter Saturn (Voyager) mission is a scaled down version of the tour of the Outer Planets mission. The spacecraft uses RTGs rather than solar panels for power generation, and the RTGs and radiation environment of Jupiter generates a requirement that the optical systems be designed and fabricated out of radiation stabilized optical materials. The narrow angle optical system is similar the one used on Mariner 10, but the wide angle system was designed for this spacecraft utilizing the cerium dcped glasses having the greatest blue transmittance.

The National Aeronautics and Space Administration in 1968 undertook the development of a very large and complex interplanetary spacecraft. Each spacecraft consisted of an orbiter and a lander. Each orbiter was to provide support for the landers as well as independent scientific studies. In support of these objectives each orbiter carried twin camera systems having identical 475mm f/3,5 telescopes. The telescopes were all spherical catadioptric cassegrains in in design using Mangin primary mirrors. The telescopes had high theoretical and measured performance and many high quality images of the Martian surface were obtained.

Four recently developed applications of image processing to astronomy are presented along with illustrative examples. These applications consist of: Automated location and analysis of star and galaxy images; Geometric and radiometric decalibration of vidicon spectra; Display of multiband radio images; Generation of high resolution polarization direction and magnitude maps from images.

Some applications of microprocessors at Lick Observatory are discussed. These include the use of an MOS Technology 6502 controlling a floppy disc to exactly emulate a magnetic tape (DECtape) system on our PDP-8I mini-computers. Other microprocessor applications in operation or under development include spectrograph controllers and an inexpensive control system for the Shane 3 meter Telescope. We also describe features of a new system for developing and debugging microprocessor controlled equipment. Our experience indicates that the costs of completing specialized equipment with hard-wired logic or with microprocessor logic are similar. A main advantage of the microprocessor appears to be that since the fraction of the cost devoted to hardware is so small, it will be economic to provide complete back-up systems for easy and rapid maintenance in difficult environments.

Several applications of microcomputers have been implemented at the Goethe Link Observatory of Indiana University. A dedicated microprocessor acquires encoder information on telescope position and time, processes the data, and displays time, coordinates, airmass, etc. on a video screen. An inexpensive image analysis system to aid in the reduction and interpretation of astronomical vidicon images has also been completed. Grey-scale and color image display, frame registration, image enhancement, hard-copy and other features have been implemented in 8080 FORTH for this system. Instrumentation control and data acquisition applications include a high speed photometer and a S-1 I-SIT vidicon data acquisition system.

DIDCS is an interactive image display and manipulation system that is used for a variety of astronomical image reduction and analysis operations. The hardware system consists of a PDP 11/40 main frame with 32K of 16-bit core memory; 96K of 16-bit MOS memory; two 9 track. 800 BPI tape drives; eight 2.5 million byte RK05 type disk packs, three user terminals, and a COMTAL 8000-S display system which has sufficient memory to store and display three 512 x 512 x 8 bit images along with an overlay plane and function table for each image, a psuedo color table and the capability for displaying true color. The software system is based around the language FORTH, which will permit an open ended dictionary of user level words for image analyses and display. A description of the hardware and software systems will be presented along with examples of the types of astronomical research that are being performed. Also a short discussion of the commonality and exchange of this type of image analysis system will be given.

The estimation of the low spatial frequency background signals in astronomical digital imagery is a fundamental problem of all the photometric techniques used with such imagery. This problem is particularly acute when numerous foreground sources (stars, galaxies, etc.) are present, because the statistical distribution of background pixel values is skewed. All linear lowpass filters (e.g., the running mean) produce biased estimates in this situation, and the result is biased photometry of the foreground sources, which can produce subtle errors in luminosity functions and other results derived from the photometry (e.g., the apparent number of faint sources may be inversely related to the number of bright sources). These problems can be mostly avoided in many situations by estimating the mode of the skewed distribution rather than the mean. This paper describes a lowpass-filter program which computes an estimate of the mode of the image values in a region around each pixel of an image.

A system for detecting and classifying images on astronomical plates is described. In particular, the very faint and barely resolved images of 24th magnitude galaxies are shown to be detectable and distinguishable from stellar images of similar brightness. The algorithms and other implementation con-siderations used in the construction of FOCAS are given. Detection and classification at 24th magnitude is achieved with N₂ presensitized IIIaJ plates exposed for one hour in the KPNO 4-m telescope prime focus camera. For a digital 6000x6000 pixel image made from the central square area 37' on a side approximately 16000 objects are found to 24.7 mag on such plates. Since the resulting catalog of objects is 3 or 4 magnitudes deeper than existing surveys a variety of internal tests must be used to assess the accuracy and completeness of the list of objects. The tests and simulations made to support these claims are also discussed.

A. square-array of holes forming a sampling screen is used to test the 3.2 m paraboloid primary for the Infrared. Telescope Facility that is to be installed at Mauna Kea on the island of Hawaii. A point source is used to illuminate the mirror through the screen, and the reflected light is recorded on a photographic plate. The data obtained. from measuring the spot locations on the plate are reduced to obtain surface departures from a desired surface. The data reduction is performed with the use of two different computer programs, one which uses trapezoidal, and another which uses spline-function integrations in order to obtain. the surface departures, given surface slope values obtained from the measured spot locations. Also considered is the effect of the number of holes used in the surface sampling compared to the method of analysis.

Two spectrograph configurations are considered for fast echelle spectrographs, one autocollimated and another with the camera placed at 45° to the collimator beam. An example is given where both cameras have the same focal length and gratings the same angular dispersion. The effect of different slit widths and astronomical seeing are considered. The effect of optical aberrations for the two cameras, an f/1.0 system for the 45° camera angle and 0.77 for the autocollimated configuration offsets the slit width advantage of the 45° camera angle case. The light losses due to the use of a slit re-imaging lens and double-pass through the camera are considered for the autocollimated configuration. The f/1.77 camera permits easy folding for use with an image tube, and if made of a solid block of optical material yields close to an f/1 camera with the same geometrical dimensions. All things considered, we recommend the autocollimated configuration for optimum use with echelle spectrographs.

This paper describes a method for evaluating the optical performance of optical systems consisting of large, flexible, actively controlled mirrors in the presence of thermal and dynamic disturbances. The computer simulation described here is divided into four major blocks: optics, thermal, structures, and dynamics. The control aspects are included in the various models used in each block. The output of the simulation is a dynamic point-spread function from which real-time or average quantities such as the line-of-sight error, Strehl ratio, and power in a certain area are calculated. As an example, a two-mirror system that expands a high-power collimated beam and focuses it on a distant plane is considered. The effects of heating of the mirrors are simulated and results on the point-spread function and associated quantities are presented.