HETE-2 is the replacement mission for the original HETE satellite that was lost in 1996 following a rocket malfunction. It will be the first satellite dedicated to the study of gamma-ray bursts.

It also will have faster reflexes than any other gamma-ray-detecting satellite currently in orbit and will be able to pinpoint burst locations within seconds for making crucial follow-up observations.

"The universe is so rich that anytime you have an instrument or a satellite with a capability several times better than ever before, you come upon completely unexpected or unpredicted phenomena that knock your socks off," said Don Lamb Jr., Professor in Astronomy & Astrophysics at the University of Chicago.

Lamb helped develop the mission concept during the 1980s and now serves as a member of HETE's international science team, which is led by George Ricker at the Massachusetts Institute of Technology.

For much of the last three decades, gamma-ray bursts have ranked among the greatest mysteries of astronomy. Only recently have scientists produced evidence linking the longest of these bursts to supernovas, which result from the collapse of massive stars.

Lasting anywhere from fractions of a second to many minutes and packing the power output of as many as 1,000 supernovas, these unpredictable bursts occur almost daily and come from any direction in the sky. The bursts are followed by afterglows that are visible for a few days at X-ray and optical wavelengths. HETE-2 was specially designed to observe these afterglows.

"In the past, mysterious and exotic phenomena have been understood by finding their optical counterparts," Lamb said. In May the Compton Gamma-ray Observatory ended a highly successful mission that began in 1991, but it was unable to precisely locate burst positions for analysis by optical telescopes.

HETE-2's onboard computers, by contrast, will rapidly calculate the position of a newly detected burst and relay the data to ground stations, where it will be available immediately to astronomers worldwide for simultaneous and follow-up observations.

HETE-2 consists of a gamma-ray instrument, a wide-field X-ray monitor and a soft X-ray camera. Each of these three instruments will provide progressively more accurate measurements of gamma-ray burst positions.

Astronomers are hoping that HETE-2 will quickly find a burst that went off when the universe was quite young, no more than a billion years old. Such bursts could help cosmologists unravel the origins of the universe, Lamb said.

"Probably the second-most important thing we hope to get out of it is a short burst, one of less than a second," said Daniel Reichart, a California Institute of Technology astronomer who completed his Ph.D. at Chicago earlier this year. "It's still a mystery what causes these things. We hope to shed some light on that. Beyond that, this mission is probably going to discover things that we can't possibly predict."

HETE-2 also promises to resolve an issue that has troubled astronomers for a decade, said University of Chicago Research Scientist Carlo Graziani.

Before the Compton Gamma Ray Observatory's launch in 1991, several spacecraft collected data that indicated the possible presence in gamma-ray bursts of a magnetic field trillions of times stronger than Earth's. Such magnetic fields are associated only with neutron stars, the extremely dense, burned out cores of dead stars.

Nagging doubts persisted that the data might not be real, but they fit nicely with the idea that gamma-ray bursts were produced by magnetic neutron stars within our own Milky Way galaxy. Astronomers expected the Compton Observatory to confirm or refute the data, but definitive measurements were beyond the satellite's capabilities.

Now astronomers know that gamma ray bursts originate in the most distant reaches of the universe, far beyond the Milky Way, and probably are related to supernovas. There is no place in this new model for data indicating the presence of a super strong magnetic field, Lamb said. "Consequently, the data are never brought up in polite conversation," he said.

HETE-2's X-ray and gamma-ray instruments are well-equipped to resolve the spectral features that would confirm the phenomenon, if it is real, Graziani said. "If it's there, I expect there'll be no ambiguity about it at all. And if that happens, it is going to kick over a serious anthill," he said.

HETE-2 will be launched via Pegasus rocket from the Kwajalein Missile Range in the Marshall Islands of the South Pacific. Planning for the original HETE began in the 1980s and served as a forerunner of the "faster, better, cheaper" type of mission advocated by NASA Administrator Daniel Goldin.

"It was an experimental mission, both in terms of how the spacecraft and instruments were designed, and also in how the project was funded, administered and managed," Lamb said. "The new way of operating, decision-making and management survived. Doing it cheaply also survived, because we actually came in on budget. Doing it quickly did not."

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