X-ray detecting satellites

Other X-ray detecting satellites

• The SOLar RADiation satellite program (SOLRAD) was conceived in the late 1950s to study the Sun's effects on Earth, particularly during periods of heightened solar activity.^[10] Solrad 1 is launched on June 22, 1960, aboard a Thor Able from Cape Canaveral at 1:54 a.m. EDT.^[11] As the world's first orbiting astronomical observatory, Solrad 1 determined that radio fade-outs were caused by solar X-ray emissions.^[10]
• The first in a series of 8 successfully launched Orbiting Solar Observatories (OSO 1, launched on March 7, 1963) had as its primary mission to measure solar electromagnetic radiation in the UV, X-ray, and gamma-ray regions.
• OGO 1, the first of the Orbiting Geophysical Observatories (OGOs), was successfully launched from Cape Kennedy on September 5, 1964, and placed into an initial orbit of 281 × 149,385 km at 31° inclination. A secondary objective was to detect gamma-ray bursts from the Sun in the energy range 80 keV - 1 MeV. The experiment consisted of 3 CsI crystals surrounded by a plastic anti-coincidence shield. Once every 18.5 seconds, integral intensity measurements were made in each of 16 energy channels which were equally spaced over the 0.08-1 MeV range. OGO 1 was completely terminated on November 1, 1971. Although the satellite did not achieve its goals due to electrical interference and secular degradation, searching back through the data after the discovery of cosmic gamma-ray bursts by the Vela satellites revealed the detection of one or more such events in the OGO 1 data.
• Solar X-ray bursts were observed by OSO 2 and an effort was made to map the entire celestial sphere for direction and intensity of X-radiation.

This is a display model of the GRAB 1 satellite, which carried two sets of instruments: Solrad 1 and Tattletale.

• The first USA satellite which detected cosmic X-rays was the third Orbiting Solar Observatory, or OSO-3, launched on March 8, 1967. It was intended primarily to observe the Sun, which it did very well during its 2-year lifetime, but it also detected a flaring episode from the source Sco X-1 and measured the diffuse cosmic X-ray background.
• The fourth successful Orbiting Solar Observatory, OSO 4, was launched on October 18, 1967. The objectives of the OSO 4 satellite were to perform solar physics experiments above the atmosphere and to measure the direction and intensity over the entire celestial sphere in UV, X, and gamma radiation. The OSO 4 platform consisted of a sail section (which pointed 2 instruments continuously toward the Sun) and a wheel section which spun about an axis perpendicular to the pointing direction of the sail (which contained 7 experiments). The spacecraft performed normally until a second tape recorder failed in May 1968. OSO 4 was put into a "standby" mode in November 1969. It could be turned on only for recording special events in real-time. One such event occurred on March 7, 1970, during a solar eclipse. The spacecraft became totally inoperable on December 7, 1971.
• OGO 5 was launched on March 4, 1968. The satellite, primarily devoted to Earth observation, was in a highly elliptical initial orbit with a 272 km perigee and a 148,228 km apogee. The orbital inclination was 31.1°. The satellite took 3796 minutes to complete one orbit. The Energetic Radiations from Solar Flares experiment was operational from March 1968 - June 1971. Primarily devoted to solar observations, it detected at least 11 cosmic X-ray bursts in time coincidence with gamma-ray bursts seen by other instruments. The detector was a 0.5 cm thick NaI(Tl) crystal with a 9.5 cm² area. Data were accumulated into energy ranges of: 9.6-19.2, 19.2-32, 32-48, 48-64, 64-80, 80-104, 104-128, and > 128 keV. The data were sampled for 1.15 seconds once every 2.3 seconds.
• Cosmos 215 was launched April 19, 1968 and contained an X-ray experiment. Orbit characteristics: 261 × 426 km, at an inclination of 48.5°. The orbital period was ~ 91 minutes. It was intended primarily to perform solar studies, but did detect some non-solar X-ray events. It reentered the atmosphere on June 30, 1968.
• The Soviet Union's Intercosmos series began in 1969.
• OSO 5 was launched on January 22, 1969, and lasted until July 1975. It was the 5th satellite put into orbit as part of the Orbiting Solar Observatory program. This program was intended to launch a series of nearly identical satellites to cover an entire 11-year solar cycle. The circular orbit had an altitude of 555 km and an inclination of 33°. The spin rate of the satellite was 1.8 s. The data produced a spectrum of the diffuse background over the energy range 14-200 keV.
• OSO 6 was launched on August 9, 1969.^[12] Its orbital period was ~95 min.^[13] The spacecraft had a spin rate of 0.5 rps. On board was a hard X-ray detector (27-189 keV) with a 5.1 cm² NaI(Tl) scintillator, collimated to 17° × 23° FWHM. The system had 4 energy channels (separated 27-49-75-118-189 keV). The detector spun with the spacecraft on a plane containing the Sun direction within ± 3.5°. Data were read with alternate 70 ms and 30 ms integrations for 5 intervals every 320 ms.^[13]

Vela-5A/B satellites sit in the clean room at TRW. The two satellites, A and B, are separated after launch on May 23, 1969.

• The Vela satellites 5A and 5B, launched on May 23, 1969, are responsible for significant discoveries of gamma-ray bursts and astronomical X-ray sources including V 0332+53.
• Like the previous Vela 5 satellites, the Vela 6 nuclear test detection satellites were part of a program run jointly by the Advanced Research Projects of the U. S. Department of Defense and the U. S. Atomic Energy Commission, managed by the U. S. Air Force. The twin spacecraft, Vela 6A and 6B, were launched on April 8, 1970. Data from the Vela 6 satellites were used to look for correlations between gamma-ray bursts and X-ray events. At least 2 good candidates were found, GB720514 and GB740723. The X-ray detectors failed on Vela 6A on March 12, 1972, and on Vela 6B on January 27, 1972.
• Cosmos 428 was launched by the USSR into Earth orbit on June 24, 1971, and recovered July 6, 1971. The orbit characteristics: apogee/perigee/inclination 208 km, 271 km, and 51.8°, respectively. It was a military satellite on which X-ray astronomy experiments had been added. There was a scintillation spectrometer sensitive to X-rays >30 keV, with a 2° × 17° field of view. In addition, there was an X-ray telescope which operated in the range 2-30 keV. Cosmos 428 detected several X-ray sources which were correlated to already identified Uhuru point sources.
• Following on the success of Uhuru (SAS 1), NASA launched the Second Small Astronomy Satellite SAS 2. It was launched from the San Marco platform off the coast of Kenya, Africa, into a nearly equatorial orbit.

The satellites launched with the Thor-Delta rocket system became known as the TD satellites. TD-1A was successfully launched on March 11, 1972, from Vandenberg Air Force Base (March 12 in Europe).

• TD-1A was put in a nearly circular polar Sun-synchronous orbit, with apogee 545 km, perigee 533 km, and inclination 97.6°. It was ESRO's first 3-axis stabilized satellite, with one axis pointing to the Sun to within ±5°. The optical axis was maintained perpendicular to the solar pointing axis and to the orbital plane. It scanned the entire celestial sphere every 6 months, with a great circle being scanned every satellite revolution. After about 2 months of operation, both of the satellite's tape recorders failed. A network of ground stations was put together so that real-time telemetry from the satellite was recorded for about 60% of the time. After 6 months in orbit, the satellite entered a period of regular eclipses as the satellite passed behind the Earth—cutting off sunlight to the solar panels. The satellite was put into hibernation for 4 months, until the eclipse period passed, after which systems were turned back on and another 6 months of observations were made. TD-1A was primarily a UV mission however it carried both a cosmic X-ray and a gamma-ray detector. TD-1A reentered on January 9, 1980.
• To continue the intensive X-ray investigation of the Sun and the cosmic X-ray background, OSO 7 was launched on September 29, 1971. OSO 7 made the first observation of solar gamma-ray line emission, due to electron/positron annihilation at 511 keV, from a solar flare in April 1972.
• To conduct experiments in X-ray astronomy and solar physics among others the Indian Space Research Organization (ISRO) built Aryabhata. It was launched by the Soviet Union on April 19, 1975, from Kapustin Yar. A power failure halted experiments after 4 days in orbit.
• The third US Small Astronomy Satellite (SAS-3) was launched on May 7, 1975, with 3 major scientific objectives: 1) determine bright X-ray source locations to an accuracy of 15 arcseconds; 2) study selected sources over the energy range 0.1-55 keV; and 3) continuously search the sky for X-ray novae, flares, and other transient phenomena. It was a spinning satellite with pointing capability. SAS 3 was the first to discover X-rays from a highly magnetic WD binary system, AM Her, discovered X-rays from Algol and HZ 43, and surveyed the soft X-ray background (0.1-0.28 keV).
• Orbiting Solar Observatory (OSO 8) was launched on June 21, 1975. While OSO 8's primary objective was to observe the Sun, four instruments were dedicated to observations of other celestial X-ray sources brighter than a few milliCrab. A sensitivity of 0.001 of the Crab nebula source (= 1 "mCrab"). OSO 8 ceased operations on October 1, 1978.

The Signe 3 spacecraft is operated by the Centre D'Etude Spatiale des Rayonnements, Toulouse, France.

• Signe 3 (launched on June 17, 1977) was part of the Soviet Union's Intercosmos program.
• Bhaskara was the second Indian Space Research Organization (ISRO) satellite. It was launched on June 7, 1979, with a modified SS-5 Skean IRBM plus upper stage from Kapustin Yar in the Soviet Union. A secondary objective was to conduct X-ray astronomy investigations. Bhaskara 2 was launched on November 20, 1981, from Kapustin Yar like its predecessor also in size, mass and design may have conducted X-ray astronomy investigations.
• On March 23, 1983, at 12:45:06 UTC, the Astron spacecraft is launched into an orbit around the Earth with an apogee of 185,000 km allowing it to make observations with an onboard X-ray spectroscope outside the Earth's umbra and radiation belt. Observations of Hercules X-1 are made from 1983 to 1987 in both the prolonged low state ("off" state) and "high on" state.^[14]

The Polar satellite (line drawing) is the sister ship of the WIND satellite.

• The Global Geospace Science (GGS) Polar Satellite was a NASA science spacecraft launched at 06:23:59.997 EST on February 24, 1996, aboard a McDonnell Douglas Delta II 7925-10 rocket from launch pad 2W at Vandenberg Air Force Base in Lompoc, California, to observe the Earth's polar magnetosphere. Polar is in a highly elliptical orbit, at an 86° inclination with an orbital period of ~18 hrs. It gathers multi-wavelength imaging (including X-ray) of the aurora, and measures the entry of plasma into the polar magnetosphere and the geomagnetic tail, the flow of plasma to and from the ionosphere, and the deposition of particle energy in the ionosphere and upper atmosphere. Polar Mission Operations were terminated at 14:54:41 EDT on April 28, 2008.^[15]

The Astron spacecraft is based on Venera.

• A later satellite of the Intercosmos series, Intercosmos 26, (launched on March 2, 1994) as part of the Coronas-I international project may have conducted X-ray studies of the Sun.
• Hitomi, formerly known as Astro-H, was a Japanese satellite which attempted to re-fly the microcalorimeter that failed on the Suzaku mission, along with hard-X-ray and soft-gamma instruments. It launched successfully on February 17, 2016. However, spacecraft controllers lost communications with Hitomi on March 26, and declared the spacecraft lost April 28.

Proposed (future) X-ray observatory satellites

ATHENA

Advanced Telescope for High Energy Astrophysics was selected in 2013 as a second large mission of the Cosmic Vision programme.^[16] It will be one hundred times more sensitive than the best of existing X-ray telescopes.^[17]

International X-ray Observatory

International X-ray Observatory (IXO) was a cancelled observatory. A result of the merging of NASA's Constellation-X and ESA/JAXA's XEUS mission concepts, it was planned to feature a single large X-ray mirror with a 3 m² collecting area and 5" angular resolution, and a suite of instrumentation, including a wide field imaging detector, a hard X-ray imaging detector, a high-spectral-resolution imaging spectrometer (calorimeter), a grating spectrometer, a high timing resolution spectrometer, and a polarimeter.

Constellation-X

Constellation-X was early proposal that was superseded by IXO. It was to provide high resolution X-ray spectroscopy to probe matter as it falls into a black hole, as well as probe the nature of dark matter and dark energy by observing the formation of clusters of galaxies.

See also

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