High Energy Transient Explorer
|Operator||NASA with significant contributions from Japan and France|
|Major contractors||AeroAstro, Inc.|
|Launch date||November 4, 1996 at 17:08:56 UTC|
|Launch site||Wallops Flight Facility, Virginia|
|Orbital insertion date||November 4, 1996 at 17:08:56 UTC|
|Mass||128 kilograms (282 lb)|
|Apoapsis||555 kilometres (345 mi)|
|Periapsis||487 kilometres (303 mi)|
|Major contractors||Massachusetts Institute of Technology|
|Launch date||October 09, 2000 at 05:38:00 UTC|
|Launch site||Bucholz Army Airfield, Kwajalein, Marshall Islands|
|Orbital insertion date||October 09, 2000|
|Mass||124 kilograms (273 lb)|
|Semimajor axis||6,932 kilometres (4,307 mi)|
|Apoapsis||650 kilometres (400 mi)|
|Periapsis||590 kilometres (370 mi)|
|Orbital period||95.7 minutes|
The High Energy Transient Explorer (abbreviated HETE; also known as Explorer 79) was an American astronomical satellite with international participation (mainly Japan and France). 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. A unique feature of the HETE mission was its capability to localize GRBs with ~10 arc second accuracy in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories enabling rapid, sensitive follow-up studies in the radio, IR, and optical bands. The satellite bus for the first HETE was designed and built by AeroAstro, Inc. of Herndon, VA; the replacement satellite, HETE-2, was built by MIT based on the original HETE design.
The first HETE was lost during the launch on Nov.4, 1996. The Pegasus rocket achieved a good orbit, but explosive bolts releasing HETE from another satellite (Argentina's SAC-B) and from its DPAF envelope failed to charge, dooming both satellites. A battery on the third stage of the rocket and responsible for these bolts cracked during the ascent.
A second HETE satellite, HETE-2, was launched on October 9, 2000 in a follow-up mission. It was similar to the first HETE, but replaced the UV camera with an additional X-ray camera (Soft X-ray Camera or SXC) capable of higher localization accuracy than the original X-ray instrument (Wide-Field X-ray Monitor or WXM).
HETE-2 was placed in a 625 km altitude Earth orbit with an inclination of 0-2 degrees.
Among the achievements of the HETE-2 mission are:
- The discovery of GRB 030329, a widely observed, nearby gamma ray burst, firmly connecting GRBs with supernovas.
- The discovery of GRB 050709, which was the first short/hard GRB to be found with an optical counterpart, leading to a firm establishment of the cosmological origin of this subclass of GRBs.
- Dark bursts, or GRBs previously thought to have no optical counterparts, are not completely optically dark. Some of these dark GRBs fade in the optical very rapidly, others are dimmer but detectable with large (meter class) telescopes.
- The establishment of another subclass of GRBs, the less energetic X-Ray Flashes (XRF), and its first optical counterpart.
- The first to send out arcminute positions of GRBs to the observation community within tens of seconds of the onset of GRB (and in a few instances, while the burst was ongoing).
The HETE website  lists 6 in 2001, 19 in 2002, 25 in 2003, 19 in 2004, 12 in 2005, 3 in 2006 - the last reported being in March 2006.
The trigger summaries lists 2 GRBs in May 2006 and an XRB in Jan 2007.
As of March 2007 "The operational efficiency of the HETE spacecraft and instruments has decreased due to the advanced age of the NiCd batteries on board."
- HETE-2 at MIT
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