High Energy Transient Explorer

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-1 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.

High Energy Transient Explorer 1
NamesHETE-1
Mission typeHigh-energy astronomy
OperatorNASA
COSPAR ID1996-061A
SATCAT no.24645a
Spacecraft properties
ManufacturerAeroAstro, Inc
Launch mass128 kilograms (282 lb)
End of mission
DisposalLaunch failure
DestroyedNovember 4, 1996 (1996-11-04)
Decay dateApril 7, 2002
Orbital parameters
Reference systemGeocentric
Eccentricity0.0
Perigee altitude487 kilometres (303 mi)
Apogee altitude555 kilometres (345 mi)
Inclination38.0°
EpochNovember 4, 1996
 
High Energy Transient Explorer 2 (HETE 2)
HETE 2
Mission typeAstronomy
OperatorNASA
COSPAR ID2000-061A
SATCAT no.26561
Mission durationOctober 2000 - March 2008
Spacecraft properties
BusHETE
ManufacturerMassachusetts Institute of Technology
Launch mass124 kilograms (273 lb)
Power4 deployable fixed solar arrays
Start of mission
Launch dateOctober 9, 2000, 05:38:00 (2000-10-09UTC05:38Z) UTC
RocketPegasus-H
Launch siteKwajalein
Orbital parameters
Reference systemGeocentric
RegimeLEO
Semi-major axis6,932 kilometers (4,307 mi)
Eccentricity0.0018587
Perigee altitude534 kilometers (332 mi)
Apogee altitude559 kilometers (347 mi)
Inclination1.9485°
Period95.7 minutes
RAAN207.197 degrees
Argument of perigee13.7551 degrees
Mean anomaly346.2996 degrees
Mean motion85387
EpochMay 9, 2016 at 15:49:27 UTC
 

Launch attempts

The first HETE was lost during the launch on November 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 (Dual Payload Attach Fitting) 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.

Pegasus XL rocket carrying the SAC-B and HETE satellites.

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.[1]

Originally planned operational life was 18 months.[2] The mission continued until March 2008.[3]

Achievements

Among the achievements of the HETE-2 mission are:

  1. The discovery of GRB 030329, a widely observed, nearby gamma ray burst, firmly connecting GRBs with supernovas.
  2. 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.
  3. 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.
  4. The establishment of another subclass of GRBs, the less energetic X-Ray Flashes (XRF), and its first optical counterpart.
  5. 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).

Burst alert summary

The HETE website lists 6 GRBs in 2001, 19 in 2002, 25 in 2003, 19 in 2004, 12 in 2005, and 3 in 2006 - the last reported being in March 2006.[4]

The trigger summaries list 2 GRBs in May 2006 and an XRB in Jan 2007.[5]

Latest status

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."[6]

The mission ended in March 2008.[3]

  • HETE under test
  • HETE-2 attached to its Pegasus launcher
  • Implementation of the launcher fairing
  • FREGATE instrument
  • WXM instrument
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References
  1. "HETE-2 Spacecraft". MIT School of Science. Retrieved February 18, 2019.
  2. "HETE 1, 2". Gunter's Space Page. Retrieved February 18, 2019.
  3. "The HETE-2 Satellite". Goddard Space Flight Center. January 29, 2014. Retrieved February 18, 2019.
  4. "HETE Bursts". MIT School of Science. Retrieved February 18, 2019.
  5. "HETE Trigger Summaries: H40xx". MIT School of Science. January 6, 2009. Retrieved February 18, 2019.
  6. "HETE Mission Status". MIT School of Science. March 28, 2007. Retrieved February 18, 2019.

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