InterPlanetary Network
Encyclopedia
The InterPlanetary Network (IPN) is a group of spacecraft
equipped with gamma ray burst
(GRB) detectors. By timing the arrival
of a burst at several spacecraft, its precise location can be found. The farther apart the detectors, or the greater the timing precision of each detector, the more precise the GRB location. Typical spacecraft baselines of about one AU (astronomical unit
) and time resolutions of tens of milliseconds can place a burst within an error box of several arcminutes, for followup with more powerful instruments.
In addition, gamma-ray bursts are brief flashes (often as little as 0.2 seconds) that occur randomly across the sky. Some forms of gamma-ray telescope can generate an image, but they require longer integration times, and cover only a fraction of the sky.
Once three spacecraft detect a GRB, their timings are sent to the ground for correlation. A sky position is derived, and distributed to the astronomical community for followup observations with optical, radio, or spaceborne telescopes.
Spacecraft naturally join or leave service as their missions unfold, and some modern spacecraft are far more capable than prior IPN members.
group of satellites was originally designed to detect covert nuclear tests, possibly at the Moon's altitude. Thus, the Velas were placed in high orbits, so that a time delay would occur between spacecraft triggers. In addition, each satellite had multiple gamma-ray detectors across their structures; the detectors facing a blast would register a higher gamma count than the detectors facing away.
A gamma-ray burst was detected by the Vela group on June 3, 1969, and thus referred to as GRB 690603. The location was determined to be clearly outside of the satellites' orbit, and probably outside of the Solar system. After reviewing archived Vela data, a previous burst was determined to have occurred on July 2, 1967. Public reports of initial GRBs were not disclosed until the early 1970s.
and 16
missions carried detectors to study the Moon; middle-to-late Venera
spacecraft carried detectors to Venus. The relatively long baselines of these missions again showed that bursts originated at great distances. Other spacecraft (such as the OGO, OSO, and IMP series) had detectors for Earth, Solar, or all-sky gamma radiation, and also confirmed the GRB phenomenon.
spacecraft carried a detector with fine time resolution, to a Solar orbit that took it over an AU from Earth. Helios-2 was launched in 1976.
In 1978, multiple spacecraft were launched, forming the necessary baselines for a position determination. Pioneer Venus Orbiter and its Soviet counterparts, Venera 11
and 12
, brought gamma detectors to Venus orbit. In addition, the spacecraft Prognoz-7 and ISEE-3 remained in Earth orbit. These formed an Earth-Venus-Sun triangle, and the probes at Venus formed a smaller triangle. 84 bursts were detected, until the network degraded in 1980. Pioneer Venus Orbiter continued until it entered the Venus atmosphere in 1992, but not enough other spacecraft were functioning to form the required baselines.
On March 5 and 6, 1979, two bursts of hard X-rays were detected from the same source in the constellation Dorado
by the γ-ray burst detector Konus
, on the Venera 11
and Venera 12
spacecraft. These X-ray bursts were detected by several other spacecraft. As part of the InterPlanetary Network (IPN), 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 at Venus. 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
.
in 1990. The launch of the Compton Gamma-Ray Observatory in 1991 again formed triangular baselines with PVO and Ulysses. Ulysses continued until June 2009, and the PVO mission ended in August 1992.
Compton once again brought directional discrimination with the BATSE instrument. Like the Velas, BATSE placed detectors at the spacecraft corners. Thus, Compton alone could determine a coarse burst location, to within 1.6 to 4 degrees. Baselines with other spacecraft were then used to sharpen Compton's position solutions. In addition, almost half the sky from Compton was blocked by the Earth, just as Venus blocked part of the sky for PVO. Detection or non-detection by Compton or PVO added another element to the location algorithms.
Compton also had high-precision, low-field-of-view gamma instruments. Occasionally, GRBs would occur where Compton happened to be pointing. The use of multiple, sensitive instruments would provide much more accuracy than BATSE alone.
in late 1992, before that spacecraft failed. Some feel that Compton provided sufficient continuity, and that the distinction between 2nd, 3rd, and subsequent IPNs is semantic.
in 1994. Although Wind was in Earth orbit, like Compton, its altitude was very high, thus forming a short but usable baseline. The high altitude also meant that Earth blockage was negligible. In addition, Wind carried a top and bottom detector. Interpolation between the two units usually gave a general sky direction for bursts, which in many cases could augment the IPN algorithm. The addition of RXTE in 1995 also helped. Although RXTE was an X-ray mission in Earth orbit, it could detect those gamma-ray bursts which also shone in X-rays, and give a direction (rather than merely a time trigger) for them.
Two important developments occurred in 1996. NEAR
was launched; its trajectory to an asteroid again formed a triangular IPN measured in AUs. The IPN was also joined by BeppoSAX
. BeppoSAX had wide-field gamma detectors, and narrow-field X-ray telescopes. Once a GRB was detected, operators could spin the spacecraft within hours to point the X-ray telescopes at the coarse location. The X-ray afterglow would then give a fine location. In 1997, the first fine location allowed detailed study of a GRB and its environ.
Compton was deorbited in 2000; the NEAR mission was shut down in early 2001. In late 2001, the Mars Odyssey spacecraft again formed an interplanetary triangle.
Other members of the network include or have included the Indian SROSS-C2 spacecraft, the US Air Force's Defense Meteorological Satellites, the Japanese Yohkoh
spacecraft, and the Chinese SZ-2 mission. These have all been Earth orbiters, and the Chinese and Indian detectors were operational for only a few months.
Of all the above, Ulysses is the only spacecraft whose orbit takes it large distances away from the ecliptic plane. These deviations from the ecliptic plane allow more precise 3-D measurements of the apparent positions of the GRBs.
A new generation of spacecraft are designed to produce GRB locations onboard, then relay them to the ground within minutes or even seconds. These positions are based not on time correlation, but on X-ray telescopes, as on BeppoSAX but much faster. HETE
-2, launched in 2000, stares at a large region of sky. Should a GRB trigger the gamma detectors, X-ray masks report sky coordinates to ground stations. Because HETE is in a low, consistent orbit, it can use many inexpensive ground stations. There is almost always a ground station in view of the spacecraft, which reduces latency to seconds.
The Swift
spacecraft, launched in 2004, is similar in operation but much more powerful. When a GRB triggers the gamma detectors, generating a crude position, the spacecraft spins relatively rapidly to use its focusing X-ray and optical telescopes. These refine the GRB location to within arcminutes, and often within arcseconds. The fine position is reported to the ground in approximately an hour.
INTEGRAL
is a successor to Compton. INTEGRAL can similarly determine a coarse position by comparing gamma counts from one side to another. It also possesses a gamma-ray telescope with an ability to determine positions to under a degree. INTEGRAL cannot pivot rapidly like the small HETE and Swift spacecraft. But should a burst happen to occur in its telescope field of view, its position and characteristics can be recorded with high precision.
RHESSI was launched in 2002 to perform solar studies. However, its gamma instrument could detect bright gamma sources from other regions of the sky, and produce coarse positions through differential detectors. Occasionally, a GRB would appear next to the Sun, and the RHESSI instrument would determine its properties without IPN assistance.
Note however, that all these spacecraft suffer from Earth blockage to varying degrees. Also, the more sophisticated the "staring" instrument, the lower the sky coverage. Randomly-occurring GRBs are more likely to be missed, or detected at low resolution only. The use of non-directional deep space probes, such as MESSENGER
and BepiColombo
, will continue.
was launched and on 2008 the Fermi Gamma-ray Space Telescope and although these are Earth orbiters, their instruments provide directional discrimination. The Fermi Space Telescope uses both wide-area burst detectors and a narrow-angle telescope, and will have a limited ability to spin itself to place a GRB within the telescope field. MESSENGER's gamma instrument is now fully operational, and is adding data to the IPN. Due to falling power from its RTG
, Ulysses last day was June 30, 2009.
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
equipped with gamma ray burst
Gamma ray burst
Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...
(GRB) detectors. By timing the arrival
Multilateration
Multilateration is a navigation technique based on the measurement of the difference in distance to two or more stations at known locations that broadcast signals at known times. Unlike measurements of absolute distance or angle, measuring the difference in distance results in an infinite number of...
of a burst at several spacecraft, its precise location can be found. The farther apart the detectors, or the greater the timing precision of each detector, the more precise the GRB location. Typical spacecraft baselines of about one AU (astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
) and time resolutions of tens of milliseconds can place a burst within an error box of several arcminutes, for followup with more powerful instruments.
Rationale
Gamma rays are too powerful to be focused with mirrors; rays would go through virtually all materials instead of reflecting. Because gamma rays cannot be focused into an image in the traditional sense, a unique location for a gamma ray source cannot be generated as with a radio, infrared, optical, ultraviolet, or soft-X-ray source.In addition, gamma-ray bursts are brief flashes (often as little as 0.2 seconds) that occur randomly across the sky. Some forms of gamma-ray telescope can generate an image, but they require longer integration times, and cover only a fraction of the sky.
Once three spacecraft detect a GRB, their timings are sent to the ground for correlation. A sky position is derived, and distributed to the astronomical community for followup observations with optical, radio, or spaceborne telescopes.
Iterations of the IPN
Note that, since any IPN must consist of several spacecraft, the boundaries between networks are defined differently by different commentators.Spacecraft naturally join or leave service as their missions unfold, and some modern spacecraft are far more capable than prior IPN members.
A "Planetary Network"
The VelaVela (satellite)
Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means vigil or "watch" in Spanish.Vela started out as a small...
group of satellites was originally designed to detect covert nuclear tests, possibly at the Moon's altitude. Thus, the Velas were placed in high orbits, so that a time delay would occur between spacecraft triggers. In addition, each satellite had multiple gamma-ray detectors across their structures; the detectors facing a blast would register a higher gamma count than the detectors facing away.
A gamma-ray burst was detected by the Vela group on June 3, 1969, and thus referred to as GRB 690603. The location was determined to be clearly outside of the satellites' orbit, and probably outside of the Solar system. After reviewing archived Vela data, a previous burst was determined to have occurred on July 2, 1967. Public reports of initial GRBs were not disclosed until the early 1970s.
Further Missions
Additional spacecraft were given gamma-ray detectors. The Apollo 15Apollo 15
Apollo 15 was the ninth manned mission in the American Apollo space program, the fourth to land on the Moon and the eighth successful manned mission. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous...
and 16
Apollo 16
Young and Duke served as the backup crew for Apollo 13; Mattingly was slated to be the Apollo 13 command module pilot until being pulled from the mission due to his exposure to rubella through Duke.-Backup crew:...
missions carried detectors to study the Moon; middle-to-late Venera
Venera
The Venera series probes were developed by the Soviet Union between 1961 and 1984 to gather data from Venus, Venera being the Russian name for Venus...
spacecraft carried detectors to Venus. The relatively long baselines of these missions again showed that bursts originated at great distances. Other spacecraft (such as the OGO, OSO, and IMP series) had detectors for Earth, Solar, or all-sky gamma radiation, and also confirmed the GRB phenomenon.
The First True IPN
Scientists began to tailor instruments specifically for GRBs. The Helios-2Helios probes
Helios-A and Helios-B , were a pair of probes launched into heliocentric orbit for the purpose of studying solar processes. A joint venture of the Federal Republic of Germany and NASA, the probes were launched from the John F. Kennedy Space Center at Cape Canaveral, Florida, on Dec. 10, 1974,...
spacecraft carried a detector with fine time resolution, to a Solar orbit that took it over an AU from Earth. Helios-2 was launched in 1976.
In 1978, multiple spacecraft were launched, forming the necessary baselines for a position determination. Pioneer Venus Orbiter and its Soviet counterparts, Venera 11
Venera 11
The Venera 11 was a USSR unmanned space mission part of the Venera program to explore the planet Venus. Venera 11 was launched on 9 September 1978 at 3:25:39 UTC....
and 12
Venera 12
The Venera 12 was an USSR unmanned space mission to explore the planet Venus. Venera 12 was launched on 14 September 1978 at 02:25:13 UTC. Separating from its flight platform on December 19, 1978, the lander entered the Venus atmosphere two days later at 11.2 km/s. During the descent, it...
, brought gamma detectors to Venus orbit. In addition, the spacecraft Prognoz-7 and ISEE-3 remained in Earth orbit. These formed an Earth-Venus-Sun triangle, and the probes at Venus formed a smaller triangle. 84 bursts were detected, until the network degraded in 1980. Pioneer Venus Orbiter continued until it entered the Venus atmosphere in 1992, but not enough other spacecraft were functioning to form the required baselines.
On March 5 and 6, 1979, two bursts of hard X-rays were detected from the same source in the constellation Dorado
Dorado
Dorado is a constellation in the southern sky. It was created in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish , which is known as dorado in Spanish, although it has also been depicted as a swordfish...
by the γ-ray burst detector Konus
Konuš
Koňuš is a village and municipality in the Sobrance District in the Košice Region of east Slovakia.-Geography:The village lies at an altitude of 272 metres and covers an area of 23.236 km².It has a population of about 350 people.-Culture:...
, on the Venera 11
Venera 11
The Venera 11 was a USSR unmanned space mission part of the Venera program to explore the planet Venus. Venera 11 was launched on 9 September 1978 at 3:25:39 UTC....
and Venera 12
Venera 12
The Venera 12 was an USSR unmanned space mission to explore the planet Venus. Venera 12 was launched on 14 September 1978 at 02:25:13 UTC. Separating from its flight platform on December 19, 1978, the lander entered the Venus atmosphere two days later at 11.2 km/s. During the descent, it...
spacecraft. These X-ray bursts were detected by several other spacecraft. As part of the InterPlanetary Network (IPN), Venera 11
Venera 11
The Venera 11 was a USSR unmanned space mission part of the Venera program to explore the planet Venus. Venera 11 was launched on 9 September 1978 at 3:25:39 UTC....
, Venera 12
Venera 12
The Venera 12 was an USSR unmanned space mission to explore the planet Venus. Venera 12 was launched on 14 September 1978 at 02:25:13 UTC. Separating from its flight platform on December 19, 1978, the lander entered the Venus atmosphere two days later at 11.2 km/s. During the descent, it...
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 at Venus. Seconds later the Vela satellites
Vela (satellite)
Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means vigil or "watch" in Spanish.Vela started out as a small...
, Prognoz 7, and the Einstein Observatory
Einstein Observatory
Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...
in orbit around Earth were inundated. The last satellite hit was the ISEE-3
International Cometary Explorer
The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the...
before the burst exited the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
.
The Second IPN
Pioneer Venus Orbiter was rejoined by UlyssesUlysses probe
Ulysses is a decommissioned robotic space probe that was designed to study the Sun as a joint venture of NASA and the European Space Agency . The spacecraft was originally named Odysseus, because of its lengthy and indirect trajectory to near Solar distance...
in 1990. The launch of the Compton Gamma-Ray Observatory in 1991 again formed triangular baselines with PVO and Ulysses. Ulysses continued until June 2009, and the PVO mission ended in August 1992.
Compton once again brought directional discrimination with the BATSE instrument. Like the Velas, BATSE placed detectors at the spacecraft corners. Thus, Compton alone could determine a coarse burst location, to within 1.6 to 4 degrees. Baselines with other spacecraft were then used to sharpen Compton's position solutions. In addition, almost half the sky from Compton was blocked by the Earth, just as Venus blocked part of the sky for PVO. Detection or non-detection by Compton or PVO added another element to the location algorithms.
Compton also had high-precision, low-field-of-view gamma instruments. Occasionally, GRBs would occur where Compton happened to be pointing. The use of multiple, sensitive instruments would provide much more accuracy than BATSE alone.
The "Third" IPN
Compton and Ulysses were joined briefly by Mars ObserverMars Observer
The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
in late 1992, before that spacecraft failed. Some feel that Compton provided sufficient continuity, and that the distinction between 2nd, 3rd, and subsequent IPNs is semantic.
"Additional" IPNs
Compton and Ulysses were joined by WindWIND
The Global Geospace Science WIND satellite is a NASA science spacecraft launched at 04:31:00 EST on November 1, 1994 from launch pad 17B at Cape Canaveral Air Force Station in Merritt Island, Florida aboard a McDonnell Douglas Delta II 7925-10 rocket. WIND was designed and manufactured by Martin...
in 1994. Although Wind was in Earth orbit, like Compton, its altitude was very high, thus forming a short but usable baseline. The high altitude also meant that Earth blockage was negligible. In addition, Wind carried a top and bottom detector. Interpolation between the two units usually gave a general sky direction for bursts, which in many cases could augment the IPN algorithm. The addition of RXTE in 1995 also helped. Although RXTE was an X-ray mission in Earth orbit, it could detect those gamma-ray bursts which also shone in X-rays, and give a direction (rather than merely a time trigger) for them.
Two important developments occurred in 1996. NEAR
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...
was launched; its trajectory to an asteroid again formed a triangular IPN measured in AUs. The IPN was also joined by BeppoSAX
BeppoSAX
BeppoSAX was an Italian–Dutch satellite for X-ray astronomy which played a crucial role in resolving the origin of gamma-ray bursts , the most energetic events known in the universe...
. BeppoSAX had wide-field gamma detectors, and narrow-field X-ray telescopes. Once a GRB was detected, operators could spin the spacecraft within hours to point the X-ray telescopes at the coarse location. The X-ray afterglow would then give a fine location. In 1997, the first fine location allowed detailed study of a GRB and its environ.
Compton was deorbited in 2000; the NEAR mission was shut down in early 2001. In late 2001, the Mars Odyssey spacecraft again formed an interplanetary triangle.
Other members of the network include or have included the Indian SROSS-C2 spacecraft, the US Air Force's Defense Meteorological Satellites, the Japanese Yohkoh
Yohkoh
Yohkoh , known before launch as Solar-A, was a Solar observatory spacecraft of the Institute of Space and Astronautical Science with United States and United Kingdom collaboration...
spacecraft, and the Chinese SZ-2 mission. These have all been Earth orbiters, and the Chinese and Indian detectors were operational for only a few months.
Of all the above, Ulysses is the only spacecraft whose orbit takes it large distances away from the ecliptic plane. These deviations from the ecliptic plane allow more precise 3-D measurements of the apparent positions of the GRBs.
The 21st Century: Staring Spacecraft
New techniques and designs in high-energy astronomy spacecraft are challenging the traditional operation of the IPN. Because distant probes require sensitive ground antennas for communication, they introduce a time lag into GRB studies. Large ground antennas must split time between spacecraft, rather than listen continuously for GRB notifications. Typically, GRB coordinates determined by deep space probes are distributed many hours to a day or two after the GRB. This is very frustrating for studies of events which are measured in seconds.A new generation of spacecraft are designed to produce GRB locations onboard, then relay them to the ground within minutes or even seconds. These positions are based not on time correlation, but on X-ray telescopes, as on BeppoSAX but much faster. HETE
High Energy Transient Explorer
The High Energy Transient Explorer was an American astronomical satellite with international participation . The prime objective of HETE was to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft...
-2, launched in 2000, stares at a large region of sky. Should a GRB trigger the gamma detectors, X-ray masks report sky coordinates to ground stations. Because HETE is in a low, consistent orbit, it can use many inexpensive ground stations. There is almost always a ground station in view of the spacecraft, which reduces latency to seconds.
The Swift
Swift Gamma-Ray Burst Mission
The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on 20 November 2004, 17:16:00 UTC on a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...
spacecraft, launched in 2004, is similar in operation but much more powerful. When a GRB triggers the gamma detectors, generating a crude position, the spacecraft spins relatively rapidly to use its focusing X-ray and optical telescopes. These refine the GRB location to within arcminutes, and often within arcseconds. The fine position is reported to the ground in approximately an hour.
INTEGRAL
INTEGRAL
The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory is an operational Earth satellite, launched in 2002 for detecting some of the most energetic radiation that comes from space. It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in...
is a successor to Compton. INTEGRAL can similarly determine a coarse position by comparing gamma counts from one side to another. It also possesses a gamma-ray telescope with an ability to determine positions to under a degree. INTEGRAL cannot pivot rapidly like the small HETE and Swift spacecraft. But should a burst happen to occur in its telescope field of view, its position and characteristics can be recorded with high precision.
RHESSI was launched in 2002 to perform solar studies. However, its gamma instrument could detect bright gamma sources from other regions of the sky, and produce coarse positions through differential detectors. Occasionally, a GRB would appear next to the Sun, and the RHESSI instrument would determine its properties without IPN assistance.
Note however, that all these spacecraft suffer from Earth blockage to varying degrees. Also, the more sophisticated the "staring" instrument, the lower the sky coverage. Randomly-occurring GRBs are more likely to be missed, or detected at low resolution only. The use of non-directional deep space probes, such as MESSENGER
MESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
and BepiColombo
BepiColombo
BepiColombo is a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency to the planet Mercury, due to launch in 2014. The mission is still in the planning stages so changes to the current description are likely over the next few years...
, will continue.
Current IPN Developments
In the year 2007 AGILEAGILE (spacecraft)
AGILE is an X-ray and Gamma ray astronomical satellite of the Italian Space Agency .ASI has made contact with AGILE: signals from it have been acquired by the ground station at the Broglio Space Centre near Malindi, Kenya and it has been placed in a sun-pointing mode....
was launched and on 2008 the Fermi Gamma-ray Space Telescope and although these are Earth orbiters, their instruments provide directional discrimination. The Fermi Space Telescope uses both wide-area burst detectors and a narrow-angle telescope, and will have a limited ability to spin itself to place a GRB within the telescope field. MESSENGER's gamma instrument is now fully operational, and is adding data to the IPN. Due to falling power from its RTG
Radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
, Ulysses last day was June 30, 2009.
External links
- IPN Progress Report A Quarterly Refereed Journal
- IPN Status report IPN status as of September 24, 2007.