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NASA NTRS1985

The spectra of Orion A and IRC + 10216 between 72.2 and 91.1 GHz

Spectral scans of Orion A and the envelope of IRC + 10216, obtained with resolution 1 MHz over the complete range from 72.2 to 91.1 GHz using the radome-enclosed 20-m mm-wave telescope at Onsala Space Observatory during 1979-1982, are presented graphically (as main-beam brightness temperature in 500-MHz bands), providing the data basis is for the discussion of Johansson et al. (1984). Observing parameters include main-beam efficiency 0.58, aperture efficiency 0.44, FHPBW 47 arcsec, and total-system noise temperature 300-500 K.

Johansson, L. E. B.↗

NASA NTRS1985

An optical technology study on large aperture telescopes

The difficult and crucial problem of selecting a suitable telescope concept for an advanced space observatory was examined. To this end two and four mirror telescopes were analyzed and compared. Both configurations are very practical and structurally similar. Parabolic primary and spherical primary four mirror telescope were compared with respect to their performance and the alignment sensitivities of the three correction mirrors. A 1 meter class afocal telescope system with lag angle compensation, to be used in a LIDAR experiment, was examined.

Korsch, D.↗

NASA NTRS1986

Proceedings of the Second Infrared Detector Technology Workshop

The workshop focused on infrared detector, detector array, and cryogenic electronic technologies relevant to low-background space astronomy. Papers are organized into the following categories: discrete infrared detectors and readout electronics; advanced bolometers; intrinsic integrated infrared arrays; and extrinsic integrated infrared arrays. Status reports on the Space Infrared Telescope Facility (SIRTF) and Infrared Space Observatory (ISO) programs are also included.

Mccreight, C. R.↗

NASA NTRS1986

Dark current measurement in photoconductors

The Space Infrared Telescope Facility (SIRTF) is envisioned as a next generation space observatory for observations between 2 and 700 microns. In order to address many of the important scientific questions in areas such as cosmology, star formation, and galaxy evolution, infrared detectors of unparalleled sensitivity will be required. Dark current measurements are described for a number of different discrete photoconductive detectors that may be of importance at the very low backgrounds expected with SIRTF.

Young, E. T.↗

NASA NTRS1986

Detector systems for ISO's photometer ISOPHOT

One of the four focal plane instruments of the Infrared Space Observatory (ISO) is ISOPHOT, a photopolarimeter for the wavelength region 3 to 200 microns. Each experiment occupies a quadrant of the focal plane. The telescope beam is directed into each experiment by means of a pyramid mirror and by tilting the satellite. The diameter of the unvignetted field of view is 3 arcmin or 7.85 mm in the focal plane (1 mm = 23 arcsec). The temperatures provided are 3 K for cooling the detector systems and 8 K for the experiment structure. Available detectors are described along with the current status of the experiment.

Wolf, J.↗

NASA NTRS1986

Development of InSb and Si:Ga arrays for ISO camera

The Infrared Space Observatory (ISO) satellite will contain a 60 cm telescope. A 4 faces pyramid mirror feeds each experiment with a 3 arc minute part of the telescope field of view. The camera system is described. The arrays for the 3 to 5 and 5 to 17 micron channel are also discussed.

Sibille, F.↗

NASA NTRS1987

The first radio astronomy from space - RAE

The spacecraft design, instrumentation, and performance of the Radio Astronomy Explorer (RAE) satellites (RAE-1 launched to earth orbit in 1968 and RAE-2 launched to lunar orbit in 1972) are reviewed and illustrated with drawings, diagrams, and graphs of typical data. Consideration is given to the three pairs of antennas, the Ryle-Vonberg and burst radiometers, and problems encountered with antenna deployment and observing patterns. Results summarized include observations of type III solar bursts, the spectral distribution of cosmic noise in broad sky regions, Jupiter at low frequencies, and auroral kilometric radiation (AKR) from the earth. The importance of avoiding the AKR bands in designing future space observatories is stressed.

Kaiser, M. L.↗

NASA NTRS1988

Space and lunar-based optical telescopes

The growth of space observatories, especially at optical wavelengths, during the next several decades is considered. It is concluded that large aperture optical telescopes on the Moon, possibly constructed of lunar glasses, will be very competitive with and in some instances superior to Earth orbiting telescopes.

Stockman, H. S.↗

NASA NTRS1988

Methods of correction for the 'wet' atmosphere in estimating baseline lengths from VLBI

The error in VLBI estimates of baseline length caused by unmodelled variations in the propagation path through the atmosphere is greater for longer baselines. Series of estimates of baseline lengths obtained using different methods to correct for the propagation delay caused by atmospheric water vapor are presented and discussed. The main methods are use of data from: a water-vapor radiometer (WVR) and Kalman-filtering of the VLBI data themselves to estimate the propagation delay. Since the longest timespan of WVR data associated with geodetic VLBI experiments was obtained at the Onsala Space Observatory in Sweden, results are presented for the following three baselines: (1) Onsala-Wettzell, FRG (920 km), (2) Onsala-Haystack/Westford, MA (5600 km), and (3) Onsala-Owens Valley (7914 km).

Elgered, G.↗

NASA NTRS1988

Hot stars

Theoretical models developed to explain the emission of hot stars are examined, summarizing and analyzing the results of ground-based and space observations obtained at different wavelengths. The physical processes responsible for emission in the radio, IR, visible, UV, and X-ray bands are reviewed, and particular attention is given to observations of OB-star winds, B-emission stars, compact stellar cores, and hot stars in binary systems. The importance of the UV and EUV spectral regions and the need for a space observatory to replace the IUE when it becomes inoperative are stressed.

Snow, Theodore P.↗

NASA NTRS1989

Status of the isophot detector development

ISOPHOT is one of the four focal plane experiments of the European Space Agency's Infrared Space Observatory (ISO). Scheduled for a 1993 launch, it will operate extrinsic silicon and germanium photoconductors at low temperature and low background during the longer than 18 month mission. These detectors cover the wavelength range from 2.5 to 200 microns and are used as single elements and in arrays. A cryogenic preamplifier was developed to read out a total number of 223 detector pixels.

Wolf, J.↗

NASA NTRS1989

ISO/LWS: Detector status

The aim of the long wavelength spectrometer (LWS) of the Infrared Space Observatory is to perform spectrometry in the wavelength range 45 to 200 microns using two resolution modes. The resolution will be around 200 in the medium resolution mode while it will reach 10(exp 4) in the high resolution mode. The sensitivity of this instrument will be close to 10(exp -18) W/sq. root Hz. A schematic view of the focal plane unit is presented. The detectors divide the wavelength range into ten spectral channels. The spectral range and position of each detector is indicated. Each detector will cover approximately a spectral bandwidth sufficient to allow for a 50 percent redundancy in the case of detector failure. There are three types of detectors. SW1 is a Ge:Be photoconductor covering the 45 to 55 micron region. LW1, SW2, SW3, SW4, SW5 are unstressed Ge:Ga photoconductors which cover the 50 to 120 micron region. LW2, LW3, LW4, LW5 are uniaxially stressed Ge:GA photoconductors covering the range from 100 to 200 microns. The stress applied to each detector will be adjusted in order to get the peak response in the corresponding wavelength range, and to minimize the dark current of the shorter wavelength stressed detectors. Stressed and unstressed detectors are located alternatively in order to receive the first and second order of the diffracted beam.

Lenaour, C.↗

NASA NTRS1990

The determination of maximum deep space station slew rates for a high Earth orbiter

As developing national and international space ventures, which seek to employ NASA's Deep Space Network (DSN) for tracking and data acquisition, evolve, it is essential for navigation and tracking system analysts to evaluate the operational capability of Deep Space Station antennas. To commission the DSN for use in tracking a highly eccentric Earth orbiter could quite possibly yield the greatest challenges in terms of slewing capability; certainly more so than with a deep-space probe. The focus here is on the determination of the maximum slew rates needed to track a specific high Earth orbiter, namely the Japanese MUSES-B spacecraft of the Very Long Baseline Interferometry Space Observatory Program. The results suggest that DSN 34-m antennas are capable of meeting the slew rate requirements for the nominal MUSES-B orbital geometries currently being considered.

Estefan, J. A.↗

NASA NTRS1989

X-ray/EUV optics for astronomy and microscopy; Proceedings of the Meeting, San Diego, CA, Aug. 7-11, 1989

Topics included in these proceedings are on X-ray/EUV zone plates, filters, and windows; X-ray/EUV microscopes, telescopes, and monochromators; the design, characterization, and test of multilayer optics; the fabrication of X-ray/EUV multilayer optics; and the design, characterization, and test of grazing incidence X-ray optics. Other topics are on the fabrication of grazing incidence X-ray optics, X-ray/EUV space observatories and missions, the test and calibration of X-ray/EUV instruments, X-ray polarimetry, and X-ray/EUV spectroscopy and instruments. Papers are presented on 8-keV X-ray zone plates, a cylindrical X-ray multilayer monochromator, multilayer mirrors for 182 A, advanced flow polishing of exotic optical materials, and optical analysis of grazing incidence ring resonators for free-electron lasers. Attention is also given to X-ray mirrors for the European Synchrotron Radiation Facility, the XUV wide-field camera for Rosat, an optical test and alignment method for the XMM mirror module, Bragg crystal polarimeters, and a liftoff process for multilayer phase gratings.

Hoover, Richard B.↗

NASA NTRS1990

High-precision orbit determination for high-earth elliptical orbiters using the Global Positioning System

Orbit covariance analyses pertaining to the Japanese VLBI Space Observatory Program (VSOP) MUSES-B satellite and to the International VLBI Satellite are presented. It is determined that a combination of Doppler and GPS measurements can provide the orbit accuracy required to support advanced radio interferometric experiments. For the VSOP, the required orbit accuracy of 130 m is easily met with two-way Doppler as the primary type of data; the 0.4 cm/s VSOP velocity requirement is also feasible provided that precise ground calibrations of tropospheric delays and station coordinates are available. It is concluded that combining the data from a VSOP GPS flight instrument with the ground GPS and two-way Doppler data will significantly enhance orbit determination accuracy in position and velocity.

Lichten, S. M.↗

NASA NTRS1991

Cryogenic mechanisms for scanning and interchange of the Fabry-Perot interferometers in the ISO long wavelength spectrometer

The Infrared Space Observatory (ISO) is an ESA cornerstone mission for infrared astronomy. Schedules for launch in 1993, its four scientific instruments will provide unprecedented sensitivity and spectral resolution at wavelengths which are inaccessible using ground-based techniques. One of these, the Long Wavelength Spectrometer (LWS), will operate in the 45 to 180 micron region (Emery et. al., 1985) and features two Fabry-Perot interferometers mounted on an interchange mechanism. The entire payload module of the spacecraft, comprising the 60 cm telescope and the four focal plane instruments, is maintained at 2 to 4 K by an onboard supply of liquid helium. The mechanical design and testing of the cryogenic interferometer and interchange mechanisms are described.

Davis, G. R.↗

NASA NTRS1990

Mission to Planet Earth

The rationale behind Mission to Planet Earth is presented, and the program plan is described in detail. NASA and its interagency and international partners will place satellites carrying advanced sensors in strategic earth orbits to collect muultidisciplinary data. A sophisticated data system will process and archive an unprecedented large amount of information about the earth and how it functions as a system. Attention is given to the space observatories, the data and information systems, and the interdisciplinary research.

Wilson, Gregory S.↗

NASA NTRS1990

Optical surface refurbishment in space environment

The potential use of the vacuum environment of space to clean contaminated mirror surfaces or generate Al mirror surfaces with high reflectance in the 80-200-nm region is discussed and illustrated with diagrams and graphs, reviewing previous studies and current experiment proposals. Consideration is given to (1) applying the atomic oxygen plasma environment of LEO to clean coated mirrors and (2) depositing freshly evaporated Al onto a mirror surface in vacuum, providing relatively long periods of high EUV reflectance before oxidation of the surface degrades performance: such a procedure could be performed as a maintenance measure or even incorporated into the design of a space observatory. A free-flying experiment is described which would produce and maintain an Al surface with controlled exposure to OH, H2O, and O2; demonstrate directed-beam Al deposition onto a simulated telescope/spectrometer surface; monitor instrument reflectance/sensitivity over time; and demonstrate in situ refurbishment of the degraded surface.

Heaney, James B.↗