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The concept of a satellite capable of multiwavelength observations of GRBs was discussed at the Santa Cruz meeting on GRBs in 1981. In 1986, the first realistic implementation of the HETE concept by an MIT-led International Team was proposed. This concept, which was adopted, emphasized accurate locations and multiwavelength coverage as the primary scientific goals for a sharply-focused small satellite mission which would ultimately solve the gamma-ray burst mystery.In 1986, the first realistic implementation of the HETE concept by an MIT-led International Team was proposed. This concept, which was adopted, emphasized accurate locations and multiwavelength coverage as the primary scientific goals for a sharply-focused small satellite mission which would ultimately solve the gamma-ray burst mystery.
In 1989, NASA approved funding for a low-cost "University Class" explorer satellite to search for GRBs. In 1992, the HETE-1 program was funded, and the design and construction of HETE-1 began.
The original spacecraft contractor for HETE-1 was AeroAstro, Inc., of Herndon, VA. AeroAstro was responsible for the spacecraft bus, including power, communications, attitude control, and computers.
The instrument complement for HETE-1 consisted of
- Four wide-field gamma-ray detectors, supplied by the CESR of Toulouse, France
- A wide-field coded-aperture X-ray imager, supplied by a collaboration of Los Alamos National Laboratory and the Institute of Chemistry and Physics (RIKEN) of Tokyo, Japan.
- Four wide-field near-UV CCD cameras, supplied by the Center for Space Research at the Massachusetts Institute of Techology.
The HETE-1 satellite was launched on November 4, 1996, along with the Argentine satellite SAC-B, on a Pegasus rocket from Wallops Island, VA. The Pegasus rocket achieved a good orbit, but the third stage failed to release the two satellites. As a result, SAC-B and HETE-1 were unable to function as designed and both died due to lack of solar power within a day of launch.
Due to the tragic fate of HETE-1 and the continuing timeliness of GRB science (see below), NASA agreed to a reflight of the HETE-1 satellite, using flight spare hardware from the first satellite. In July, 1997, funding for a second HETE satellite was granted, with a target launch date of late 1999 or early 2000.
Construction of the HETE-2 satellite began in mid-1997. The HETE-2 satellite bus was built entirely at MIT.
The results of observations of GRBs in early 1997 by BeppoSAX and ground-based telescopes made it clear that a) we should not expect copious UV or optical radiation from the GRB and b) the ratio of X-ray to gamma-ray flux from GRBs could be significantly higher that previously believed. As a result, the HETE team decided to remove the UV cameras from the spacecraft and replace two of them with a CCD-based coded-aperture imager sensitive to soft X-rays (the Soft X-ray Camera, or SXC). The other two cameras were replaced with optical CCD cameras, which serve as star trackers on HETE-2.
The experience of the BeppoSAX and RXTE satellites, the former in an equatorial orbit and the latter in a 28 degree orbit, made clear that the effect of background electrons and protons would have a profound effect on the observing efficiency and lifetime of HETE-2's X-ray instruments. In 1998, NASA agreed to flying HETE-2 in an equatorial orbit.
As of January, 2000, the HETE-2 satellite is fully complete and being prepared for launch from Kwajalein Atoll in the Republic of the Marshall Islands.