RELEASE: 00-160

HETE-2 FLIES IN SEARCH OF GAMMA-RAY BURSTS

Locating the ever-mystifying phenomena called gamma-ray  bursts and other short-lived and remarkable cosmic occurrences  will soon be the job of the High-Energy Transient Explorer 2  (HETE-2), poised for launch Oct 7.

For a brief, bright moment, gamma-ray bursts outshine the rest of  the universe, but scientists do not know what causes them. One  theory is that gamma-ray bursts come from the merger of two black  holes. Another theory suggests these bursts are from a huge star  explosion, called a hypernova, which is 1000 times more powerful  than the already potent supernova. Snapping a photograph of a  burst while it is exploding is a key goal for astronomers.

"HETE-2 may well revolutionize the field of high-energy astronomy  by alerting optical and radio observatories when gamma-ray bursts  are in progress, and precisely where observers should look," said  Dr. George R. Ricker of the Massachusetts Institute of Technology  (MIT) in Cambridge, MA, principal investigator of the HETE-2  mission.

HETE-2 is scheduled for launch at 1:45 a.m. EDT from Kwajalein  Missile Range, Marshall Islands, aboard a Hybrid Pegasus  expendable launch vehicle.

HETE-2 will detect hundreds of bursts a year during its four-year  lifetime. The spacecraft also will provide very detailed  information about the location and spectra, or light  characteristics, of many of these bursts. A key feature of HETE-2  is its superior rapid response. Within seconds, HETE-2 can catch a  burst and notify observatories both in space and on the ground of  its approximate location. In less than a minute, HETE-2 will  obtain a precise location. Previous satellites have taken many  hours or even days to notify observatories of an accurate burst  location.

HETE-2 will be placed in a 370-mile-by-400-mile (592-km x 640-km)  elliptical orbit by a three-stage rocket. The Hybrid Pegasus  launch vehicle will be carried by an L-1011 aircraft to a point  approximately 40,000 feet above the Western Pacific, near  Kwajalein Atoll. From this point, the vehicle will be released and  free-fall in a horizontal configuration for five seconds before  the first-stage rocket motor ignites. It will take a little more  than 10 minutes for HETE-2 to reach its final orbit. 

HETE-2 replaces the original HETE spacecraft that was lost due to  a rocket malfunction in November 1996. The spacecraft was built by  MIT and the technology is essentially the same as the previous  HETE, except for a new detector built by MIT. MIT is responsible  for development and integration, as well as mission and science  operations, for the satellite. NASA's Goddard Space Flight Center  in Greenbelt, MD, has project oversight. The Kennedy Space Center,  FL, is responsible for all launch operations.

The HETE-2 is a collaboration between NASA; MIT; Los Alamos  National Laboratory, New Mexico; France's Centre National d'Etudes  Spatiales (CNES), Centre d'Etude Spatiale des Rayonnements (CESR),  and Ecole Nationale Superieure de l'Aeronautique et de l'Espace  (Sup'Aero); and Japan's Institute of Physical and Chemical  Research (RIKEN). The science team includes members from the  University of California (Berkley and Santa Cruz) and the  University of Chicago. 

The spacecraft carries three main instruments and a computer  network that transmits data to other observatories. The French  Gamma Telescope (FREGATE), built by CESR, will detect gamma-ray  bursts and very bright (higher energy) X-ray transients. The Wide- Field X-ray Monitor (WXM), built by RIKEN and Los Alamos National  Laboratory, detects light slightly lower in energy than the  FREGATE does. The WXM therefore will detect fewer gamma-ray bursts  than FREGATE, but because of its superior resolution, will be able  to locate the FREGATE-detected bursts to within 10 arc minutes (an  area of sky about equal to 1/10 the size of the full Moon). The  Soft X-ray Camera (SXC), built by MIT, replaces the ultraviolet  cameras on the original HETE. The SXC covers the lowest-energy  band of the three instruments. It also provides the best angular  resolution, resulting in a location accuracy of about 10 arc  seconds, more than an order of magnitude finer that any previous  gamma-ray burst instrument.

The HETE-2 satellite will continuously broadcast the burst  information. On the ground, an array of listen-only "burst-alert"  stations receives the data and transmits it to the MIT Control  Center. From there, burst information will immediately be relayed  to the Gamma Ray Burst Coordinate Distribution Network at Goddard  for distribution to interested ground observers. 

More information on the HETE-2 mission can be found at:  http://space.mit.edu/HETE