There is a conspicuous gap in plans for X-ray timing after the X-ray Timing Explorer (XTE). Timing science has played a critical role in the development of X-ray astronomy. The need now is to move into a new domain of shorter timescales and weaker modulation, one that can be reached only with very large aperture instruments. XLA is an X-ray facility with an aperture substantially greater than 1 m2, nominally 100 m2. Most of this area is devoted to a large array of collimated proportional counters. There is also a ~ 1 m2 coded aperture. It extends observational parameter space by several orders of magnitude in timing resolution, sensitivity to variability, and angular resolution. This will lead to a qualitatively new kind of X-ray astrophysics that can be applied to the study of a broad range of astrophysical objects. XLA is thus both an advanced timing mission and a general purpose facility whose principal uses are in areas that are not well covered in other aspects of the planned High Energy Astrophysics program.

We describe an X-ray polarimeter which will be flown on the SPECTRUM-X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a Cesium Iodide photocathode. These three processes allow polarization measurements over an energy band of 0.3 keV to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will allow us to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

Observations of galaxies in the IR and optical (Lynden-Bell et al. 1989) suggest that the 600 km/s peculiar velocity of the LG (Local Group of galaxies) arises mainly from a foreground of anisotropically distributed mass within z = 0.013 (i.e., HR < 4000 km/s). Since the X-ray luminosity of bright extragalactic X-ray sources provides a good mass measure of the radiating objects involved and can be observed relatively free of galactic obscuration effects, such sources are likely candidates for serving as reliable tracers of the total underlying mass (i.e., dark as well as visible) responsible for the acceleration of the LG. In this connection, we note that the local gravitational dipole implied by the fifty X-ray brightest clusters of galaxies at z > 0.013 considered by Lahav et al. (1989) is relatively small compared with that inferred from the only three clusters at lower redshifts. Since the local space density of AGN (Active Galactic Nuclei) is about two orders of magnitude greater than rich clusters, however, such compact sources have the potential of providing a vastly improved statistical sample for tracing mass in the low-redshift region of particular interest. Furthermore, recent dipole analysis of the X-ray flux from bright AGN observed with HEAO-1 A2 indicates that they are indeed strong tracers of this matter (Miyaji and Boldt 1990). The implications of this for the very pronounced large-scale foreground anisotropies to be measured via low-redshift AGN resolved in more sensitive all-sky surveys are explored.

The payload of the italian/Dutch satellite SAX will include a set of four concentrators each with a geometric area of 90 cm2. Imaging GSPCs will be located at the focal planes of the concetrators. The Space Science Department of ESA will provide one of these GSPCs which will be sensitive to X-rays with energies between 0.1-10 keV. In order to achieve such a low-energy energy response, a driftless configuration and a thin plastic window have been adopted. At 6 keV the collecting area will be 50 cm2 and the energy and angular resolutions 8% and 1.6′ FWHM, respectively.

The EXOSAT database provides on-line access to the results and data products (spectra, images and lightcurves) from the EXOSAT mission as well as EINSTEIN SSS and MPC spectra, EINSTEIN HRI images and IUE spectra of X-ray sources. In addition, a number of well-known optical, infrared, and X-ray catalogs, including the HST guide star catalog are available. The complete database is located at the EXOSAT observatory at ESTEC in the Netherlands and is accessible remotely via SPAn by typing ‘set host 28703’ and logging in to account ‘XRAY’. Alternatively, a sub-set of the database is available at GSFC and may be accessed by typing ‘set host 6467’. Access is also possible via Arpanet/Internet, GTE TELENET and by direct mail.

The database management system has been specifically developed to efficiently access the database and to allow the user to perform statistical studies on large samples of astronomical objects as well as to retrieve information on single sources. The system has been written to be mission independent and includes timing, image processing and spectral analysis package as well as software to allow the easy transfer of analysis results and products to the user’s own institute.

Further information about the system including user’s guides is available from A.N. Parmar and N.E. White at ESTEC and from their colleagues J. Behnke/Code 634 and K. Arnaud/Code 666 at GSFC.

We propose an X-ray all sky monitor for Japanese Experimental Module (JEM) on the space station. Considering practical circumstances, we show as a case study that the all sky monitor with slit hole cameras is most promising for monitoring the short-term and long-term X-ray transients. We call this all sky monitor as MAXI (Monitor of All-sky X-ray Image). Position determination of gamma-ray bursts could be achieved with accuracy less than one degree observing the X-ray component of the burst. Weak X-ray sources such as active galactic nuclei could be also monitored with time resolution less than one day. The X-ray all sky monitor will work to discover X-ray novae and transient phenomena and give us the alarm for further detailed observations. The obtained data will be also used for archival study.

The Astro Mission, an attached payload dedicated to astronomy, is now scheduled to fly May 9, 1990 in the shuttle Columbia. Four instruments make up the complement. Broad Band X-Ray Telescope (BBXRT, Peter Serlemitsos, Principal Investigator GSFC) utilizes the Two Axis Pointing System (TAPS). The three ultraviolet instruments are Hopkins Ultraviolet Telescope (HUT, Arthur Davidson, JHU), Ultraviolet Imaging Telescope (UIT, Ted Steccher, GSFC) and Wisconsin Ultraviolet Photopolarimeter Experiment (WUPPE, Art Code, UWI). The instruments are co-aligned in the Spacelabs Instrument Pointing System (IPS). Five of the seven astronauts are professional astronomers. Mission Specialists Mike Lounge, Jeff Hoffman, and Robert Parker, and Payload Specialists Samuel Durrance and Ron Parise. During the planned ten-day mission, over 290 shuttle manoeuvres will enable approximately 1000 individual instrument observations of 230 separate astronomical objects. The Astro mission is designed for multiple flights.

Israel will orbit a satellite dedicated to scientific research. One of the two experiments studied for deployment on this platform is a three-channel imager in the ultraviolet proposed by Tel Aviv University and designed jointly by staff of the Wise Observatory and of El-Op (Electro-Optical Industries, Ltd.). The design provides very significant scientific returns in a small payload and for a moderate cost.

A new instrumental concept for interference spectroscopy called Spatial Heterodyne Spectroscopy (SHS) is described. This instrument as currently demonstrated could provide important information on the structure, excitation, and dynamics of the ≃ 105 K component of the interstellar medium by providing velocity-resolved (20 km s−1) maps of the faint FUV emission line background over a hemisphere of the sky within a 5-6 year observation period. We are currently studying concepts expected to reduce this time by at least an order of magnitude.

In the SHS technique, an all-reflection dispersive interferometer produces a Fourier transform of the spectrum as two-dimensional spatial frequencies on an imaging detector. The system does not require scanning, and measures its own internal alignment state. Although the system suffers the conventional Fourier transform multiplex disadvantage associated with the photon noise in the background FUV continuum, we estimate that for a broad-band survey Spatial Heterodyne Spectroscopy as currently demonstrated can provide 4-5 fold gains over practical grating spectrometers of similar dimensions and spatial and spectral resolution. Field widened methods currently being studied promise additional gains of two orders of magnitude.

We present a project of a three-reflection 1.5 m f/3 aplanatic wide-field telescope, in view of a small-satellite mission for the all-sky survey in the Ultraviolet.

SANTA MARIA is a program of international scope, being a collaboration between scientific groups in Italy, Spain and the United States. The experiment consists of a cooperative space project with the objective of designing, developing, launching, data processing and scientific exploitation of an astronomical satellite under the name of SANTA MARIA.

The three research organizations will contribute to the project with tasks shared in the most practical way to guarantee the success of SANTA MARIA.

The ROE ISOCAM optical test facility is described. The results of testing of lenses shows good agreement with theory and remarkable consistency.

EDISON is a large-aperture telescope under study for the second generation of infrared space observatories, whether in orbit or on the moon. The optics equilibrate via radiative cooling to temperatures between 40 and 80 K, depending upon, for example, telescope structure and location. At these temperatures, telescope emission is below that of the astronomical background at all wavelengths shortward of 20-40 μm. The detector components can be cooled via mechanical refrigerators now in an advanced stage of development. A mixture of radiative and mechanical cooling means that there is no natural limit to EDISON’s lifetime. In addition, the upper stage rocket fairing can be almost filled with light-collecting optics and alternative low-emissivity optical designs, such as off-axis systems, can be easily engineered. We are presently evaluating a design for a 2.5 m observatory to be launched in collaboration with European astronomers as part of the NASA Explorer program. In this presentation, we describe possible spectroscopic and spectrophotometric studies of very faint infrared sources that will require large-aperture space telescopes working at the celestial background limit.

Two dedicated space VLBI projects are currently in preparation to launch one or more VLBI radio telescopes in orbit between 1993-1996. One in the Soviet Union called RADIOASTRON is already an approved and funded mission. The second one is a Japanese orbiting VLBI mission called VSOP. There is a Western European mission with NASA participation in Phase A Study at ESA called QUASAT. Although this project was not approved by ESA at the end of 1988, it might still be taken into consideration during the next decade. In the meantime in 1986 a successful demonstration of space VLBI was made at the first attempt using the NASA TDRSS satellite.

Low frequency radio astronomy for the purpose of this discussion is defined as frequencies ≲100 MHz. Since the technology is fairly simple at these frequencies and even Jansky’s original observations were made at 20.5 MHz, there have been many years of research at these wavelengths. However, though radio astronomers have been working at low frequencies since the first days of science, the observing limitations and the move of much of the effort to ever shorter wavelengths has meant that most areas still remain to be fully exploited with modern techniques and instruments. In particular, the possibilities for pursuing the very lowest frequencies by interferometry of ground to space, in Earth orbit, or from the Moon promises a rebirth of work in this wavelength range.

We present concepts for space-ground VLBI and a fully space-based array in high Earth orbit to pursue the astrophysics which can only be probed at these frequencies. An Orbiting Low Frequency Radio Astronomy Satellite (OLFRAS) and a Low Frequency Space Array (LFSA) are two concepts which will open this last, poorly explored area of astronomy at relatively low cost and well within the limits of current technology.

HISAT, a multi-element heterodyne interferometer attached to Space Station Freedom, will provide spectroscopic images with unprecedented detail of those submillimeter lines of C,O and C+ which are critical diagnostics of UV excitation in the Galaxy. With the arcsecond angular resolution achievable from the space station, HISAT will reveal:

1. – The distribution of sources of ultraviolet radiation in the Galaxy;

2. –The effective temperature of the UV radiation as a function of galactocentric radius;

3. – The chemical and isotopic enhancement of atomic carbon and oxygen with galactic radius;

4. – The propagation of UV radiation in molecular clouds and its stimulative, or inhibitive, effect on star formation;

5. – The density structure, dumpiness or fragmentation, of molecular clouds throughout the Galaxy. HISAT has been selected by NASA for a concept-phase study.

The International Ultraviolet Explorer (IUE) is a geosynchronous orbiting telescope launched by the National Aeronautics and Space Administration (NASA) on January 26, 1978, and operated jointly by NASA and the European Space Agency. The science instrument consists of two spectrographs which span the wavelength range of 1150 to 3200 Å and offer two dispersions with resolutions of 6 Å and 0.2 Å. The spacecraft’s attitude control system originally included an inertial reference package containing 6 gyroscopes for 3-axis stabilization. The science instrument includes a prime and redundant Field Error Sensor (FES) camera for target aquisition and offset guiding. Since launch, 4 of the 6 gyroscopes have failed. The current attitude control system utilizes the remaining 2 gyros and a Fine Sun Sensor (FSS) for 3-axis stabilization. When the next gyro fails, a new attitude control system will be uplinked which will rely on the remaining gyro and the FSS for general 3-axis stabilzation. In addition to the FSS, the FES cameras will be required to assist in maintaining fine attitude control during target aquisition. This has required thoroughly determining the characteristics of the FES cameras and the spectrograph aperture plate as well as devising new target acquisition procedures. The results of this work are presented.

The IUE spacecraft was launched with prime and redundant mechanical Panoramic Attitude Sensors (PAS) to determine coarse spacecraft pointing. Attitude determination typically took at least 24 hours. After launch both systems failed. A new method was developed which required pointing the spacecraft at the antisolar position. After the failure of the 4th IUE gyro, it was no longer possible to point in the antisolar direction. A second method was developed which utilizes IUE’s ability to track the sun with a solid state two-dimensional sun sensor. Attitude determination can now be completed in several hours. An hour is required for coarse position measurement and several more hours are needed, using a small 15 arc minute square finder camera, for final attitude confirmation. These methods should be of use for other spacecraft where weight is critical or there is a desire to avoid mechanical devices.

The International Ultraviolet Explorer has been successfully operated as a real time user-interactive space observatory for twelve years. It is expected to continue operation for up to five additional years, but under increasing constraints. The option to operate IUE in a more automated, non user-interactive mode is under consideration. A sophisticated software system to support such an operation is a clear requirement. The conceptual framework of such a system is described. Results of a preliminary tests are presented for which a hypothetical four day schedule of space-craft activities at a time resolutions as low as ten minutes was generated.