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Explorational X-ray astronomy
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Explorational X-ray astronomy is deep space X-ray astronomy performed by an astronomer/explorer or probe that has an X-ray telescope or X-ray detector aboard and leaves Earth orbit. Normally, observational astronomy is performed on Earth's surface, beneath it in neutrino astronomy, or in orbit. An observer becomes a deep space explorer upon escaping Earth's orbit. Exceptions include the Explorer 1 and Explorer 3 and the earlier satellites in the series. Deep Space Network The Deep Space Network, or DSN, is an international network of large s and communication facilities that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. DSN is part of the NASA Jet Propulsion Laboratory (JPL). Mercury orbit The MESSENGER orbiter, a robotic space probe, launched by NASA on August 3, 2004, to study the chemical composition, geology and the magnetic field of Mercury, is the first orbiting spacecraft to the planet. MESSENGER entered Mercury orbit on March 18, 2011, at 01:00 UTC. MESSENGER has on board # a gamma-ray spectrometer (GRS) to measure gamma-ray emissions from the surface of Mercury to determine composition, # an X-ray spectrometer (XRS) to map mineral composition within the top mm of the surface, and # an ultraviolet detector (MASCS) to measure emissions from the atmosphere of Mercury, when the probe enters the Mercury orbital phase. Asteroid orbit The Near Earth Asteroid Rendezvous - Shoemaker (NEAR Shoemaker) is a robotic spacecraft designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a period of a year. The probe orbited several times around Eros, then touched down on the asteroid on February 12, 2001. Orbital insertion around Eros occurred on February 14, 2000, at 15:33 UT (10:33 AM EST) after NEAR completed a 13 month heliocentric orbit which closely matched the orbit of Eros. NEAR remained in this orbit for 10 days. Following the flyby NEAR moved to a 200 km circular orbit and shifted the orbit from prograde near-polar to a retrograde near-equatorial orbit. By December 13, 2000, the orbit was shifted back to a circular 35 km low orbit. Starting on January 24, 2001, the spacecraft began a series of close passes (5 to 6 km) to the surface and on January 28 passed 2 to 3 km from the asteroid. The primary scientific objective of NEAR is to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution and magnetic field of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid spin state. To accomplish some of these goals, the spacecraft is equipped with an X-ray/gamma-ray spectrometer. The spectrometer collected data while in orbit around Eros, then collected additional data from about 10 cm from the surface after touchdown. Sun-Earth equilibrium point WIND was launched on November 1, 1994. At first, the satellite had a lunar swingby orbit around the Earth. With the assistance of the Moon's gravitational field Wind's apogee was kept over the day hemisphere of the Earth and magnetospheric observations were made. Later in the mission, the Wind spacecraft was inserted into a special "halo" orbit in the solar wind upstream from the Earth, about the sunward Sun-Earth equilibrium point (L1). The satellite has a spin period of ~ 20 seconds, with the spin axis normal to the ecliptic. WIND carries the Transient Gamma-Ray Spectrometer (TGRS) which covers the energy range 15 keV - 10 MeV, with an energy resolution of 2.0 keV @ 1.0 MeV (E/ΔE = 500). Since launch TGRS has been detecting on average ~5 gamma-ray bursts per month. The onboard experiment provides event time profiles in three energy ranges, from 10 to 770 keV, with 64-ms time resolution. Halo orbit ISEE-3 was launched on August 12, 1978. It was inserted into a "halo" orbit about the libration point some 240 Earth radii upstream between the Earth and Sun. ISEE-3 was renamed ICE (International Cometary Explorer) when, after completing its original mission in 1982, it was gravitationally maneuvered to intercept the comet P/Giacobini-Zinner. On September 11, 1985, the veteran NASA spacecraft flew through the tail of the comet. The X-ray spectrometer aboard ISEE-3 was designed to study both solar flares and cosmic gamma-ray bursts over the energy range 5-228 keV. Gravitational slingshot Ulysses was launched October 6, 1990, and reached Jupiter for its "gravitational slingshot" in February 1992. It passed the south solar pole in June 1994 and crossed the ecliptic equator in February 1995. The solar X-ray and cosmic gamma-ray burst experiment (GRB) had 3 main objectives: study and monitor solar flares, detect and localize cosmic gamma-ray bursts, and in-situ detection of Jovian aurorae. Ulysses was the first satellite carrying a gamma burst detector which went outside the orbit of Mars. The hard X-ray detectors operated in the range 15-150 keV. The detectors consisted of 23-mm thick × 51-mm diameter CsI(Tl) crystals mounted via plastic light tubes to photomultipliers. The hard detector changed its operating mode depending on (1) measured count rate, (2) ground command, or (3) change in spacecraft telemetry mode. The trigger level was generally set for 8-sigma above background and the sensitivity is ~10 erg/cm . When a burst trigger is recorded, the instrument switches to record high resolution data, recording it to a 32-kbit memory for a slow telemetry read out. Burst data consist of either 16 s of 8-ms resolution count rates or 64 s of 32-ms count rates from the sum of the 2 detectors. There were also 16 channel energy spectra from the sum of the 2 detectors (taken either in 1,2,4,16, or 32 second integrations). During 'wait' mode, the data were taken either in 0.25 or 0.5 s integrations and 4 energy channels (with shortest integration time being 8 s). Again, the outputs of the 2 detectors were summed. The Ulysses soft X-ray detectors consisted of 2.5-mm thick × 0.5 cm area Si surface barrier detectors. A 100 mg/cm beryllium foil front window rejected the low energy X-rays and defined a conical FOV of 75° (half-angle). These detectors were passively cooled and operate in the temperature range -35 to -55 °C. This detector had 6 energy channels, covering the range 5-20 keV. Interplanetary heliocentric orbit A number of deep space probes carrying X-ray or gamma-ray detectors have deliberately or upon mission failure entered into an interplanetary heliocentric orbit. Ulysses Ulysses is a robotic space probe designed to study the Sun as a joint venture of NASA and the European Space Agency (ESA). To obtain an Out-Of-The-Ecliptic (OOE) heliocentric orbit Ulysses swung by Jupiter. Between 1994 and 1995 it explored both the southern (June - October 1994) and northern (June - September 1995) solar polar regions. Between 2000 and 2001 it explored the southern solar polar region, which gave many unexpected results. In particular the southern magnetic pole was found to be much more dynamic and without any fixed clear location. It operates over the Sun's poles for the third and last time in 2007 and 2008. After it became clear that the power output from the spacecraft's RTG would be insufficient to operate science instruments and keep the attitude control fuel, hydrazine, from freezing, instrument power sharing was initiated. Up until then, the most important instruments had been kept online constantly, whilst others were deactivated. When the probe neared the Sun, its power-hungry heaters were turned off and all instruments were turned on. Phobos program The Phobos program consisted of Phobos 1 and 2 which carried X-ray telescopes with RF-15 X-ray spectrometer to conduct studies of the interplanetary environment, perform observations of the Sun, and characterize the plasma environment in the Martian vicinity. Phobos 1 was launched on July 7, 1988 and Phobos 2 on July 12, 1988. Phobos 2 operated nominally throughout its cruise and Mars orbital insertion phases on January 29, 1989, gathering data on the Sun, interplanetary medium, Mars, and Phobos. Phobos 1 operated nominally until an expected communications session on September 2, 1988, failed to occur and is likely in a heliocentric orbit. Venera Venera 14 entered heliocentric orbit on March 3, 1982. Interplanetary flyby The MESSENGER spacecraft has already completed one Earth on August 2, 2005, two Venus (1) completed on October 10, 2006, and (2) on June 5, 2007, and three Mercury flybys (1) completed on January 14, 2008, (2) on October 6, 2008, and (3) on September 29, 2009. Ulysses arrived at Jupiter on February 8, 1992, for a swing-by maneuver and is the first mission to carry an X-ray detector to the Jovian magnetosphere, and thus the first to study Jovian X-radiation. Ulysses approached aphelion in 2003/2004 and made further distant observations of Jupiter. Several of the Venera program flyby probes (Venera 11, 12 and 14) carried an X-ray/γ-ray detector that observed extrasolar X-rays, while enroute to Venus or in heliocentric orbit. Venera 14 The Venera 14 flyby probe carried a Signe-2MS3 gamma-ray burst detector which was used to provide data on solar X-ray flares. The flyby probe separated from the lander on March 3, 1982, passed Venus at a range of 36,000 km and entered heliocentric orbit. Venera 12 was the identical sister craft to Venera 11. The spacecraft performed two midcourse corrections on September 21, and December 14, 1978, and as with its twin, two days prior to the planetary encounter, the flyby probe released its lander. These X-ray bursts were detected by several other spacecraft. Venera 11, Venera 12 were hit by the March 5, 1979, hard X-ray burst at ~10:51 EST, followed 11 s later by Helios 2 in orbit around the Sun, then the Pioneer Venus Orbiter. Seconds later the Vela satellites, Prognoz 7, and the Einstein Observatory in orbit around Earth were inundated. The last satellite hit was the ISEE-3 before the burst exited the solar system. Mariner 5 Between June 14, 1967, and July 24, 1967, and again between July 24, 1967, and November 21, 1967, Mariner 5 detected soft X-ray emission of the whole Sun for the wavelength range 0.2-0.8 nm. The height structure of soft X-ray bursts were studied in detail by coupling data from the Venus-bound Mariner 5 with that from Explorers 33 and 35 near the Earth. Simultaneous observations of 607 separate flares were made with similar detectors during the 117 d period from July 28, 1967, to November 21, 1967, using Explorers 33 and 35 near Earth and Mariner 5 at a markedly different heliocentric longitude. also known as the Iowa detector, as it was provided by the University of Iowa. It is a miniature tube having a 1.2 mg/cm mica window about 0.3 cm in diameter and weighing about 60 g. It detects soft X-rays efficiently and ultraviolet inefficiently, and is previously used in Injun 1, still attached to Solrad 3 and Explorer 14. Like Ranger 3, Ranger 5 was launched from Cape Canaveral, Florida, USA, with an Atlas-Agena B on October 18, 1962. Ranger 3 Ranger 3 was launched on January 26, 1962, using an Atlas-Agena B from Cape Canaveral, Florida, USA. It carried on board a gamma-ray spectrometer designed to measure gamma radiation coming from the surface of the Moon. The first 12 hr of data were obtained with the detector close to the main spacecraft structure; then, a telescoping boom moved the detector to a position 1.8 m from the main structure and data were taken for 6 hr. Lunar excursion or installation Lunokhod 2 was carried to the Moon by Luna 21. Like Lunokhod 1, it carried on board an X-ray telescope. It had a mission to observe solar X-rays and did make observations. Luna 21 landed on the Moon on January 15, 1973, at 22:35:00 UTC, latitude 25°51' N, longitude 30°27' E. Less than 3 hr later Lunokhod 2 disembarked onto the lunar surface at 01:14 UTC on January 16, 1973. While still near the Luna 21 platform Lunokhod 2 carried out solar X-ray studies. Luna 17 was launched from an Earth parking orbit towards the Moon and entered lunar orbit on November 15, 1970. The spacecraft had dual ramps by which Lunokhod 1 descended to the lunar surface. Lunokhod 1 carried on board an X-ray telescope. This is the first astrophysical station on the Moon and it operated for 10 months. Lunar orbit Explorer 35 performed solar X-ray measurements while in an elliptical lunar orbit. The satellite was launched on July 19, 1967, at 14:19:02 UTC. The spin axis direction was nearly perpendicular to the ecliptic and the spin rate was 25.6 rpm. After successful operation for 6 yr, the spacecraft was turned off on June 24, 1973. One of the three EON type 6213 Geiger-Mueller (GM) tubes (GM1) provided measurements of solar X-rays between 0.2 and 1.2 nm in the vicinity of the Moon. Moon-like orbit Explorer 33 (IMP-4) was originally intended for a lunar orbit, but due to its trajectory and speed was instead put into an eccentric Earth orbit with a perigee of 265,679 km and an apogee of 480,762 km; thereby, reaching distances beyond the Moon's orbit, though not following or preceding the Moon in its orbit. It did succeed in measuring solar X-rays. From July 2, 1966, to September 18, 1968, some 4028 (3515 bursts and 513 secondary burst peaks) solar X-ray peaks were identified in the soft wavelength range 0.2-1.2 nm observed by Explorer 33 and Explorer 35, with an average between August 1967 and August 1968 of 8 bursts per day. There is a general tendency for larger peak X-ray fluxes to occur with both larger Hα flare areas and with brighter Hα flares. This large flare lasted about 200 min and emitted 1.4 x 10 ergs over the wavelength band 0.2-1.2 nm.<ref name=VanAllen/> See Also
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