Astronomical Techniques - Space Astronomy Missions


Hubble Space Telescope. Deployed 25 April 1990. Two cameras, two spectrometers originally required, changing complement in flight. Simultaneous parallel observations possible with multiple instruments. Sensitivity to 1150 Å , spatial resolution to < 0.05 arcseconds, optical aberration fixed late 1993. Instrument complement updated, including at various times near-IR detectors and sensitive UV spectrographs as well as imagers. Still operating, past nominal 20-year lifetime, continued servicnig became political football after the Columbia disaster. Instrument complements have been as follows:


Hubble has been unique in having servicing by astronauts built in as part of the initial plan, which has been both blessing and curse. It has also been the public flagship for space astronomy. HST experience has provided the models for proposal review, scheduling, operations, and archiving for other instruments on and off Earth.

Hipparcos - ESA's specialized astrometric satellite with two telescopes scanning sky 1 radian apart. Operated August 1989 -- August 1993 in suboptimal orbit. Yielded a catalog of about 250,000 stellar parallaxes to milliarcsecond precision, which required a simultaneous global solution of the entire mission data stream. The products include the Hipparcos and Tycho catalogs, with Tycho covering more stars at reduced precision (118,000 stars at 1 mas versus 1.05 X 106 stars at 20 mas; beware Tycho parallaxes!).

MOST- Microvariability and Oscillations of STars. Canadian smallsat orbited by converted Russian sub-launched ICBM. Magnetic pointing, precision photometry for asteroseismology and planetary transits.

COROT - French-led program for asteroseismology and planetary transits. Faster/cheaper counterpart to Kepler.

Kepler - designed to approach detection of terrestrial-size planets by stellar transits. Using the very stable photometric environment of space, high-precision photometry shows transits of those planets which happen to be aligned with our viewing direction. 1.5m Schmidt optics for 3° field of view, defocussing to spread starlight over multiple pixels, sophisticated pipeline. Needed to limit systematic effects to well below 0.01% for goal of Earth-sized planets around Sun-sized stars.


Some of the earliest results were measurements of bright stars and the diffuse light of the Milky Way from spinning satellites, often with after-the-fact attitude reconstruction: USN 1964 83C, Cosmos 51. Cameras were flown on the three highest X-15 flights to cross-check photography and early electronic detectors.

OAO-2. Low-resolution stellar UV spectra (15 Å resolution).

OAO-4 (Copernicus). Launched 21 Aug 1972 - 80-cm telescope, stepped grating spectrometer with photomultiplier for high-resolution hot-star spectra and interstellar absorption lines. Operated until 15 February 1981.

Astronomical Netherlands Satellite (ANS) - 22-cm telescope, broad-band UV photometry from 1550-3300 Å. Launched 30 August 1974 into a sun-synchronous orbit.

Orion systems on Salyut 1 and Soyuz 13. Objective-prism telescopes for UV spectroscopy.

Apollo 16 (UV Schmidt on lunar surface) - multiband images of Earth, LMC, deep fields. Slow lunar rotation meant they could get away with a fixed mount. Stellar surveys, LMC. A backup camera was modified for use on the final Skylab flight, mostly to observe Comet Kohoutek.

International Ultraviolet Explorer (IUE). NASA-ESA-UK. Launched 26 Jan 1978 - geosynchronous orbit, 45-cm telescope with vidicon (TV) detectors on low- and high-dispersion spectrometers in two ranges 1200-2000 and 2000-3200 Å. Over 100,000 astronomical spectra archived in its 18-year lifetime. Winds from hot stars, coronae of cool stars, hot stars in cold galaxies, variability mapping of AGN emission regions.

Astro 1 and 2: UV Intensified Telescope (UIT), Hopkins UV Telescope (HUT), Wisconsin UV Photopolarimetry Experiment (WUPPE). In orbit 2-10 December 1990 (STS-35) and 2-18 March 1995 (STS-67). UIT results given in ApJLetters 395, number 1, 1992 Aug 10. The UIT used film and image intensifier, because of field size and storage constraints. HUT included range from 912-1200 Å - results featured in ApJL 454, no. 1, 20 Nov. 1995. Some greatest hits include the nature of hot stars in elliptical galaxies and high-ionization lines in supernova remnants and Seyfert galaxies, plus its design goal of the Gunn-Peterson test for the hot intergalactic medium using QSOs as background probes of redshifted He II absorption.

Extreme Ultraviolet Explorer (EUVE). Launched 7 June 1992 - grazing-incidence optics, multiband all-sky survey, deep ecliptic survey looking along Earth's shadow through geocorona. Spectroscopy possible. Operated a program of pointed observations following sky survey, through January 2001.

Far-Ultraviolet Spectroscopic Explorer (FUSE) - high-resolution spectroscopy from 912--1150 Å. Uses four coaligned telescopes to cover the whole range with optimal coatings. Launched 24 June 1999, operating into 2007 using geomagnetic field for pointing and tracking as gyros failed.

Astron - Soviet-French UV spectrometer, very high orbit (2000 X 200,000 km). Functioned March 1983-June 1989. The associated X-ray detectors seem to have been the most fruitful part of the mission.

Glazar (Kvant/Mir) - wide-field UV photography, hot star survey in galaxy. Low sensitivity due to corrector-plate material; augmented by Glazar 2, which in turn suffered from mechanical problems sometimes brought on by human servicing, eventually fell out of use with dissolution of USSR. Kvant also carried four X-ray instruments, used)for coded-mask observations of the galactic center and X-ray pulsars.

Incidental deep-space use of Voyager UV spectrometers - low point-source sensitivity due to small optics, but sensitive into deep UV, and very long exposures were possible (so that, for example, 3C 273 and M33 could be detected). Beyond zodiacal dust contribution.

GALEX - all-sky UV imaging and objective-grating survey, except where there are stars bright enough to damage the anode arrays. Very good at finding unexpected star-forming regions in the galactic boondocks, aimed to trace the cosmic history of star formation at modest redshifts as well as fill in that annoying wavelength gap in available surveys. Launched by a Pegasus booster on 28 April 2003, still at work and paying some of the bills around here. Uses two sets of MAMA detectors.

X- and γ-rays

A complete list of early missions was given by Bradt, Ohashi and Pounds, ARAA 30, 391, 1992)

SAS-1 (Uhuru). Launched 12 Dec 1970 - spin-stabilized, all-sky survey. Cluster X-ray sources. End of mission March 1973.

ROSAT - all-sky survey, soft sensitivity. Piggyback wide-field EUV survey. 1 June 1990 - 12 February 1999. Carried Position-Sensitive Proportional Counter (PSPC, did the survey) and High-Resolution Imager (HRI) with 5" resolution. Deliberately dithered pointing to fill in shadows of support wires for detector window - at low event rates, it's not so important that the telescope be very stable as that you know exactly where it's pointing at each instant.

Exosat (ESA). May 26, 1983 - April 9, 1986. Low-energy X-rays, high-accuracy background determination. Variability of AGN, quasiperiodic oscillations of stellar X-ray sources. High 90-hour orbit.

Einstein (HEAO-B). 13 November 1978 - April 1981. First useful X-ray imaging - clusters, stellar sources, AGN. Carried Imaging Proportional Counter (IPC) and High-Resolution Imager (HRI) plus focal-plane spectrometer.

HEAO-1 - sky survey with modulation collimator, carried spectrometer. 12 August 1977 - 9 January 1979. Spanned 0.2 keV- 10 MeV.

HEAO-3. 20 Sept 1979 - 29 May 1981. Gamma-ray spectroscopy.

SAS-2. 19 Nov 1972 - 8 June 1973. Early γ-ray survey.

Compton Gamma-Ray Observatory (CGRO). Deployed (with manual assistance) by Atlantis 5 April 1991. Compton Telescope, EGRET, OSSE, BATSE burst detector. Isotropy and log N - log S for gamma-ray bursts, gamma-ray quasars, pulsars. Deorbited into Pacific while functional, due to gyro flakiness.

Astro-1/Shuttle Columbia: Broad-Band X-ray Telescope (BBXRT). In orbit 2-10 December 1990. High-resolution spectroscopy.

Granat - Dec 1989 - Nov. 27, 1998. X-ray and γ-ray observatory. Identity and variations of galactic center high-energy sources; picked out several galactic microquasars. Carries Sigma coded-mask imaging system described by Paul et al 1991, Adv. Space Res. 11, no. 8, 289.

Kvant/Mir - multipurpose astrophysics module attached to space station.

ASCA. Launched 20 Feb. 1993. Reasonable angular resolution, excellent spectral resolution X-ray spectroscopy. Abundances in cluster gas, line features in AGN.

Rossi X-ray Timing Explorer (RXTE). Launched 30 December 1995. Designed for large collecting area, high time resolution on variable targets.

BeppoSAX. Launched 30 April 1996. Most notable for finding the X-ray counterparts to gamma-ray bursts and facilitating their optical identification and redshifts.

Chandra (formerly AXAF), launched 23 July 1999. Angular resolution 0.5", high-resolution spectroscopy as well as imaging. High 4-day 10000 X 139000-km orbit.

X-ray Multi-Mirror Mission (XMM-Newton), launched 10 December 1999 by ESA. Great light-gathering power, few arcseconds resolution. High orbit, 7365 X 114000 km. One will notice a certain affinity between the orbits of Chandra and Newton.



Swift - coordinated suite of GRB detectors, imaging X-ray telescope, and optical/UV systems tailored to "catch gamma-ray bursts on the fly". Has already delivered one burst counterpart at z > 6.

INTEGRAL (INTErnational Gamma-RAy Laboratory).

Gamma-ray Large Area Space Telescope (GLAST) now Fermi.

Long wavelengths

Infrared Astronomical Satellite (IRAS). Launched 25 Jan 1983 - all-sky survey at 12,25,60,100 μ m. Some pointed observations, diffraction-limited to arcminute resolution. Low-resolution spectra of bright sources. Used 60-cm telescope in a liquid He bath, which lasted almost 11 months. First results in ApJLett vol 278, no. 1. Galactic structure, infrared cirrus, starburst galaxies. Source catalogs available.

Infrared Space Observatory (ISO). Carried cameras and spectrometers from 2-200 microns. Targeted and some survey observations. Operated November 1995 - May 1998 (at exhaustion of the liquid He).

IRTS (Infrared Telescope in Space) - Japan. Surveyed 7% of the sky from 1-1000 μm from 18 March - 15 April 1995.

Submillimeter Wave Astronomical Satellite (SWAS). Especially aimed at [C II] 158 μm lines and oxygen fine-structure emission. Launched from Pegasus booster 5 December 1998. Woken from hibernation to watch the Deep Impact finale.

Cosmic Background Explorer (COBE). Launched 18 November 1989 - all-sky mapping at far-IR to submm wavelengths. Cosmic and galactic backgrounds, properties of galactic dust.

Wilkinson Microwave Anisotropy Probe (WMAP) - followon CMB mission, using two oppositely-pointed detectors on a spinning platform to measure the angular power fluctuations in the microwave background. This power spectrum can yield the Hubble constant, densities of dark matter and the overall cosmos, and the age of the Universe independent of the traditional "ladder" approaches.

Midcourse Space Experiment (MSX) - a strategic-defense testbed which incidentally obtained high-quality data on mid-IR astronomical radiation.

Spitzer (once SIRTF). Fourth of the "Great Observatories". 0.9m cryogenic telescope with cameras and spectrometers, in Earth-trailing heliocentric orbit to facilitate passive cooling. Science module has only one moving part (a scanning mirror for MIPS).

Akari, similar in concept to IRAS with 25 years' better detectors.

WISE (Wide-Field INfrared Explorer), just completed all-sky survey in bands at 3.4, 46, 12, and 22 μm. Asteroids, brown dwarf, luminous IR galaxies (among many other things).

Radio Astronomy Explorer 2 (Explorer 49) - lunar orbit, long radio wavelengths with very little angular resolution. Used two 230-m long dipole antennae.

VLBI test using TDRSS antenna. Described by Levy et al 1986, Science 234, 187 and Linfield et al 1989, ApJ 336, 1098.

Highly Advanced Laboratory for Communication and Astrophysics (HALCA) - Japan. Dedicated 8-meter orbiting VLBI antenna, in 560 X 21000-km orbit for a wide range of baselines to Earthbound antennas, since 12 February 1997. Has yielded very high-resolution maps of QSO cores and jets.

Herschel, formerly FIRST (Far Infrared and Submillimeter Telescope) - ESA. 3.5m far-IR telescope operating in the L2 region.

Planck - ESA. Successor to COBE and WMAP.

Planned missions

James Webb Space Telescope (JWST) (formerly Next-Generation Space Telescope or NGST). 6.5-meter class IR-optimized successor to HST, in a halo orbit around the Sun-Earth outer Lagrange point.

Space Interferometry Mission (SIM) - largely a testbed for astrometry and simple optical imaging over ~20m baseline. Part of the roadmap to TPF.

Terrestrial Planet Finder (TPF). Multiple 1.5m cooled telescopes on a single structure, designed for nulling interferometry to reduce starlight and find extrasolar planets down to Earth mass (plus get low-resolution IR spectra to seek ozone and water bands in atmospheres). May need to be boosted to a Jupiter swingby orbit in order to reduce zodiacal light background. An alternative approach involves a single-aperture "catseye" pupil to act as a nulling interferometer. At one point, both approaches were in the budget pipeline; this number may have just been declared to be zero.

Global Astrometry Interferometer for Astrophysics (GAIA) - ESA. Followup to Hipparcos. Parallaxes across the Milky Way to 20th magnitude!


Public data archives are maintained for many of these - IRAS, IUE, HST, HEAO, Einstein, Voyager, COBE, UIT, OAO, early X-ray missions, ROSAT. Virtually the entire Einstein and IRAS datasets are avalable on CD-ROM as well as by WWW search. Space astronomy missions often incorporate open data access and proposal processes, both because of public funding and because of the demonstrated science advantages of such operations. The major starting points for space-based data are MAST at STScI, HEASARC at NASA-GSFC for high-energy data, and IPAC at Caltech for IR products.

Airborne astronomy

Some of these science issues can be addressed more economically from aircraft, including balloons. There have been notable successes with early UV surveys from balloons, and IR work from the 0.9m Kuiper Airborne Observatory. These have led to the development (and current testing) of the Stratospheric Observatory for Infared Astronomy (SOFIA), a US/German project placing a 2.5m telescope in a long-range Boeing 747 airframe. Long-duration balloons have proven effective for some FIR and submillimeter projects.

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