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
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