ORFEUS (Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer) is a 1 m normal incidence telescope for spectroscopic investigations of cosmic sources in the far and extreme ultraviolet spectral range. The instrument will be integrated into the freeflyer platform ASTRO-SPAS. ORFEUS-SPAS is scheduled with STS ENDEAVOUR in September 1992. We describe the telescope with its two spectrometers and their capabilities i.e. spectral range, resolution and overall sensitivity. The main classes of objects to be observed with the instrument are discussed and two examples of simulated spectra for the white dwarf HZ43 and an O9-star in the LMC are shown.

The Ultra-Violet Space Telescope “SPECTRUM-UV” consists of a 170-cm diffraction limited telescope for spectroscopy and imaging at λ ≥ 912 Å and a co-aligned assembly of two 50-cm telescopes for imaging and spectroscopy in the 400 to 1200 Å range and of four 20-cm, multilayer coated telescopes for narrow band imaging in the 100 to 400 Å range. The Observatory is an international facility to be launched in a highly eccentric orbit in the mid-1990s.

The Space Infrared Telescope Facility (SIRTF) is a one-meter class observatory for infrared astronomy that will be launched into high earth orbit by NASA in the late 1990’s. SIRTF’s three focal plane instruments will permit imaging and spectroscopy over most of the infrared spectrum with sensitivities of 100 to 10,000 times their predecessors. This paper briefly reviews SIRTF’s capabilities, science objectives, and current status.

The Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), is an astronomical satellite, which will operate at wavelengths from 3–200 μm. ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to distant extragalactic sources. The satellite essentially consists of a large cryostat containing at launch about 2300 litres of superfluid helium to maintain the Ritchey-Chrétien telescope, the scientific instruments and the optical baffles at temperatures between 2K and 8K. The telescope has a 60-cm diameter primary mirror and is diffraction-limited at a wavelength of 5μm. A pointing accuracy of a few arc seconds is provided by a three-axis-stabilisation system consisting of reaction wheels, gyros and optical sensors. ISO’s instrument complement consists of four instruments, namely: a photo-polarimeter (3–200μm), a camera (3–17μm), a short wavelength spectrometer (3–45μm) and a long wavelength spectrometer (45–180μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. ISO will be launched in 1993 by an Ariane 4 into an elliptical orbit (apogee 70000km and perigee 1000km) and will be operational for at least 18 months. In keeping with ISO’s role as an observatory, two-thirds of its observing time will be made available to the european and american astronomical community.

IRTS is a small cryogenically cooled telescope onboard the small space platform SFU (Space Flyer Unit). SFU will be launched with the new Japanese HII rocket on January 1994 and retrieved by the space shuttle.

The IRTS telescope has an aperture of only 15 cm diameter, but is optimized to observe diffuse extended infrared sources. Four focal plane instruments are being developed under collaboration between Japan and the U.S.A. IRTS covers a wide wavelength range from near-infrared to submillimeter region, and has a capability for the spectroscopic measurement. Due to newly developed detectors, the sky will be surveyed with very high sensitivities. IRTS will provide valuable data on cosmology, galactic structure, cosmic dust, etc.

First is an element of the ESA long term science program. Currently in a detailed study phase it is foreseen as a large (4.5–8 m) diameter passively cooled telescope equipped with a combination of photometer/camera and very high resolution spectrometers. The spectrometers will utilize both direct detection and heterodyne techniques to cover the wavelength band 85–600 micron. The photometers will have both bolometer and photoconductor detector arrays. FIRST is foreseen to be launched shortly after the year 2000 and will be operated as a facility open to the wide scientific community.

Submillimeter wavelengths hold the key to some of the most important aspects of astronomy. These range from star-forming molecular clouds and proto-planetary disks in our galaxy to infrared emitting galaxies at cosmological distances. Indeed, the essential problems of star-formation and galaxy-formation will be directly probed by the submillimeter spectral lines and continuum radiation emitted by these objects. Other fascinating topics falling into the submillimeter band include the Wien component of the cosmic background radiation, containing information on the nature of the early universe, and nearer to home, the spectroscopy of planetary atmospheres. Since the submillimeter contains fundamental information on the physics and chemistry of so many aspects of our universe, every effort should be made to provide the very best instrumentation for these astronomical studies. We should be capable of detection and analysis of even the most distant objects yet conceived.

Telescopes specifically designed for submillimeter astronomy are now operating on high mountain sites and the field is developing in an exciting and rapid fashion. NASA’s airborne program has been in operation for some time and has been of the greatest importance in getting the field started. Both ground and airborne programs will continue to be essential because of their flexibility for implementing new investigations, for instrument development and to support the growth of an active science community, especially students. However, it is now essential to move forward on a space program.

The Submillimeter Wave Astronomy Satellite (SWAS) is a NASA Small-Explorer Class experiment whose objective is to study both the chemical composition and the thermal balance in dense (NH2 > 103 cm−3) molecular clouds and, by observing many clouds throughout our galaxy, relate these conditions to the processes of star formation. To conduct this study SWAS will be capable of carrying out both pointed and scanning observations simultaneously in the lines of four important species: (1) the H2O (110–101) 556.963 GHz ground-state ortho transition, (2) the O2 (3,3–1,2) 487.249 GHz transition, (3) the CI (3P1 – 3P0) 492.162 GHz ground-state fine structure transition, and (4) the 13CO (J = 5–4) 550.926 GHz rotational transition. These atoms and molecules are predicted to be among the most abundant within molecular clouds and, because they possess low-lying transitions with energy differences (ΔE/k) between 15 and 30K (temperatures typical of many molecular clouds), these species are believed to be dominant coolants of the gas as it collapses to form stars and planets. A large-scale survey in these lines is virtually impossible from any platform within the atmosphere due to telluric absorption.

IVS is under study in ESA as a second generation space VLBI observatory. The mission concept calls for a 25 m diameter radio telescope in space funded by the principal space agencies. Orbiting the Earth and observing in concert with the established ground-based VLBI arrays in Europe, USA, USSR and Australia, IVS will provide high quality images of galactic and extragalactic radio sources at wavelengths spanning the radio band from decimetres to millimetres with resolution as high as 10 micro arcseconds and sensitivity equal to those of ground-based images. New features of IVS compared to the first generation missions are: a more than order of magnitude increase in sensitivity; an order of magnitude increase in maximum angular resolution; extension of the wavelength range to the millimetre band; and the capability to operate as a stand-alone radio telescope enabling it to explore new frontiers in spectral line and microwave background research, in particular the distribution of galactic molecular oxygen and Compton scattering of the microwave background by foreground cluster gas.

VSOP, VLBI Space Observatory Programme, is an approved space VLBI programme of ISAS for the study of very compact radio sources with the synthesized aperture of 30,000 km diameter, by connecting an orbiting radio observatory with ground radiotelescopes. The VSOP satellite carrying 10 m antenna with 1.6, 5, and 22 GHz band receivers will be launched in early 1995 by M-V rocket of ISAS into an eccentric orbit with 20,000 km in apogee height. The tracking network will be formed for the satellite orbit determination, phase transfer and IF down-link. VSOP aims imaging capability with best resolution of 0.0001 arc second in 22 GHz band. Imaging of active galactic nuclei, star forming regions and stellar objects, and radioastrometry are main scientific targets.

VLBI observations using a satellite in earth orbit and ground antennas in Japan and Australia were conducted in 1986, 1987, and 1988. Sources were detected on space-ground baselines at both observing frequencies: 2.3 and 15 GHz. The coherence on space-ground baselines for 340 s was 90% at 2.3 GHz and 76% at 15 GHz. Brightness temperatures in the range 1–4×1012 K were measured for 10 sources at 2.3 GHz and 6 sources at 15 GHz.

The Solar and Heliospheric Observatory, Soho, is a joint venture of ESA and NASA. The main objectives of Soho are: a) the study and understanding of solar coronal phenomena; and b) the study of the solar structure and interior dynamics from its core to the photosphere. The primary goals of the coronal and solar wind studies are to understand the coronal heating mechanism and its expansion into the solar wind.

These goal will be achieved both by remote sensing of the solar atmosphere with high resolution spectrometers and telescopes and by “in situ” measurement of the composition and energy of the resulting solar wind and the energetic particles that propagate through it. The structure and interior dynamics will be studied by helio-seismological methods and the measurement of solar irradiance variations. The Soho spacecraft will be three-axis stabilized and located in a halo orbit around the L1 Lagrangian point (approximately 1% of the distance from the Earth to the Sun). It is currently scheduled for launch in July 1995.

The Orbiting Solar Laboratory (OSL), which is a joint NASA/BMFT/ASI/ AFGL program, will be a free flying, polar orbiting complement of five scientific instruments operating as a facility and designed to observe the surface and upper atmosphere of the sun with high spatial and temporal resolution over a spectral range from the soft X-ray to the near Infrared. OSL’s primary scientific objectives are to study the coupling of velocity, magnetic, and radiation fields in the photosphere and chromosphere and to causally relate this coupling to activity in the overlying regions.

To study the photosphere and chromosphere with a spatial resolution approaching 75 km OSL will utilize a 1 meter telescope, optimized for 2000–11,000 Å, to feed a narrow band tunable filter, a set of fixed broad-band filters, and a spectrograph. These three instruments share a common structure, share a unified science data and control system, and use a single-image stabilization system for their common fields of view to form a Coordinated Instrument Package (CIP). To study the transition zone a stigmatic High Resolution Telescope Spectrograph (HRTS) optimized for 1175–1700 Å, will be used capable of providing both images and spectroscopic information. A X-Ray Extreme Ultraviolet Imager and Spectroheliograph (XUVI) optimized for the 40–400 Å regime, will allow study of the corona and of multimillion degree solar transient events such as flares. Both the HRTS and the XUVI instruments will possess image stabilization systems and have a resolving power of 350 km. All OSL instruments will operate overlapping fields of view and be co-aligned. To achieve its goals the OSL will provide a total data stream of 20 M bits/s, nominally 4 M bits/s per instrument and has a planned operational lifetime of three years.

The scientific focus of the Planetenteleskop project will be on time-variable solar system phenomena (planet-magnetosphere-satellite interactions, active processes of cometary nuclei, atmospheric circulation and dynamics), on time-invariant solar system phenomena (geochemical provinces on planetary and satellite surfaces, global characteristics of primitive bodies), on planetary environments of other stars, and on general astronomical and astrophysical applications. The proposed Planetenteleskop in elliptical 24 h earth orbit will combine near-simultaneous, high-resolution spectroscopic observations, diffraction-limited imaging quality, long integration times (< 10 h) and excellent target tracking accuracy (nominally 0.05 arc sec/10 h, up to 0.02 arc sec). The excellent tracking accuracy and stability on extended objects and features is provided by a novel real-time on-board image correlation scheme. The Planetenteleskop has been studied in prephase A and phase A by industry and the involved science community in Germany in cooperation with American colleagues.

The Astrometric Imaging Telescope (AIT) is a space-based 1.5 to 2 meter diameter telescope designed to discover and study planetary systems around other stars. The measurement objectives and instrument design aim at a definitive search for other planetary systems. The science program includes two planetary-system investigations, and the telescope carries two separate instruments: an astrometric instrument to measure the reflex motions of stars caused by the motions of unseen planets and an imaging coronagraph to directly image planets and other circumstellar matter.

Interstellar polarization and polarization of the sky background is predicted to be significantly smaller in the ultraviolet than in the optical region of the spectrum; while intrinsic polarization is expected to be greater. For these reasons alone ultraviolet polarimetry should provide a powerful diagnostic tool. To date such polarization measurements have not been undertaken. The Wisconsin Ultraviolet Photopolarimeter Experiment (WUPPE) will be the first to carry out a program of UV spectropolarimetry. WUPPE is one of the four ASTRO-1 payloads. It consists of a half meter aperture Cassegrain telescope feeding a spectropolarimeter capable of measuring spectral energy distribution and linear and circular polarization in the spectral region from about 3300 Å to 1400 Åwith spectral resolutions from about 4 Å to 40 Å, depending upon the mode of observation and nature of the source. The effective area of WUPPE is approximately 100 cm2 at 2000 Å and the faint stellar limit for measurement of all four Stokes parameters is about 16 magnitude. The design provides for a large dynamic range and the high precision required for accurate polarimetry. Launch of the first ASTRO Mission is expected in May of 1990.

The science goals for WUPPE include studies of ultraviolet interstellar polarization, intrinsic polarization of a wide variety of stellar types and measurements of polarization of selected extragalactic objects. A description of WUPPE and simulations of expected data will be presented. The paper will also discuss a wide field imaging survey polarimeter (WISP) now undergoing development for a sounding rocket payload at the University of Wisconsin. (This work is supported by NASA contract NAS5-26777).

The Hopkins Ultraviolet Telescope (HUT) will make pioneering observations in the far ultraviolet (912–1850 Å) and extreme ultraviolet (420–912 Å) bands during its upcoming flight aboard the Astro-1 shuttle mission, currently scheduled for launch on May 9, 1990. HUT employs an iridium-coated 0.9-meter f/2 primary mirror, an osmium-coated grating, and a CsI-coated microchannel plate intensifer to achieve a resolution of about 3 A in first order, with a peak effective area of 15 cm2 at 1100 Å, and time resolution of 2 milliseconds, HUT’s EUV response is obtained in second order, with a peak effective area of 10 cm2 at 600 Å.

HUT is expected to obtain several hundred spectra during its upcoming mission, ranging from Comet Austin to the quasar HS 1700+64 at a redshift of 2.7. The design and operation of the instrument are described, and simulated spectra are used to illustrate a sample of the problems that will be addressed during the Astro-1 mission. In order for HUT to be exploited fully, however, it would be desirable to convert it to a free-flying satellite mode

The Ultraviolet Imaging Telescope (UIT) is a 38-cm Ritchey-Chretien telescope with 2 arc-sec resolution and a 40 arc-min field of view. There are two magnetically-focused image intensifiers which record on film. One has a Cs-I photocathode and 6 filters, the other has a Cs-Te cathode with 5 filters and an objective grating. The film transports contain 1000 frames each of IIa-O film. The point source threshold is m (2200 Å) = 22.0 in a 30 min integration through the widest filter. For extended sources the corresponding mag is 26.0/sq. arc-sec. The UIT complements the instruments on the Hubble Space Telescope in that its field of view is ~ 200 times that of the Wide Field Camera, it has extremely good visible light rejection and is more sensitive to diffuse structures in the UV. The UIT is well-suited to locating interesting UV targets for HST follow-up and the study of large regions such as nearby galaxies and clusters.

Astro 1 will point the co-aligned UV instruments at ~ 200 targets during its 10 day mission. The UIT science team’s primary scientific programs include: The search and survey of the UV sky; SN1987A for the UV light echo; The helium burning and collapsing degenerate stars in star clusters; The structure of highly ionized regions in planetary nebulae and supernova remnants; The physics of massive star formation in spiral structure of galaxies; The interstellar medium of other galaxies; A search for active nuclei in ‘ normal ’ galaxies; The very faint regions surrounding galaxies that are produced by interactions, mergers, ejection, or accretion flows; The study of stellar populations of galaxies and galactic evolution, ages and chemical content of galaxies, and the study of large samples of galaxies in nearby clusters for comparison with objects at large lookback times.

BBXRT is one of four pointed instruments comprising NASA’s Astro-1 mission, currently scheduled for a 9–10 day flight in May 1990 on board the Space Shuttle Columbia. X-ray Spectra of over 150 sources will be obtained in the energy range 0.3 to 12 keV, with energy resolution of ~100 eV FWHM and timing resolution of 64 μS. BBXRT’S large throughput, broad band mirrors, coupled to segmented cooled Si(Li) detectors, give us the first opportunity to study in detail X-ray spectral features, from oxygen to the iron K band. In developing this instrument, we have made extensive use of detector background reduction techniques in order to be able to observe the many faint extra-galactic sources discovered with the Einstein observatory. Sources in our observing plan have been selected to give us in a 2–4 ks observation < 103 net counts with negligible background. Specific scientific objectives range from refinements of spectra previously obtained at lower resolution, such as a search for relativistic line shifts in compact objects, to observations of faint extragalactic sources for which spectral information is, at best, sketchy, viz. elliptical galaxies and distant quasars. High on our priorities are a search for emission from SN1987A and the first simultaneous observations in the UV and X-ray band of selected sources such as cataclysmic variables and late-type stars.

After a decade long hiatus in launches beyond Earth orbit, NASA’s planetary exploration program is again moving forward, beginning with the Magellan launch to Venus in May 1989 and the Galileo launch to Jupiter in October 1989. These spacecraft will reach their targets in August 1990 and December 1995, respectively. Both are missions of longstanding priority, Magellan to provide the first global high resolution mapping of the cloud-shrouded Venus surface, Galileo to make comprehensive measurements of the Jovian system in follow-up to the 1979/1980 Voyager flybys.

Beyond these two missions there are other already approved missions: the Mars Observer for launch in 1992, the Comet Rendezvous and Asteroid Flyby CRAF mission (Fig. 1) for launch in 1995, and the Cassini mission (Figs. 2 and 3) to Saturn and its moon Titan for launch in 1996. The very diversity of these five missions and their targets (Venus, the Jovian system, Mars, comet Kopff, asteroids Gaspra and Ida by Galileo, Hamburga by CRAF, and Maja by Cassini, and the Saturnian system, is indicative of the strategy being pursued in the program: one of deliberate breadth that seeks to explore all three main classes of solar system bodies (the terrestrial planets, the outer giants and their moons, and the primitive small bodies).