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MIT seeks new gamma-ray probe after launch failure

The failure of the Pegasus XL rocket launch on November 4 has halted two international scientific experiments in space, including an MIT high-energy astrophysics probe into the mystery of gamma-ray bursts.

Dr. George R. Ricker Jr., senior research scientist in MIT's Center for Space Research and principal investigator on the High Energy Transient Experiment (HETE) project, said the MIT team is currently exploring with NASA the possibility of assembling an inexpensive HETE-II at MIT with the existing HETE Team using flight spares.

The two spacecraft carrying the scientific experiments were launched with Orbital Sciences Corp.'s Pegasus rocket at 12:09 p.m. EST about 100 miles east of Wallops Island, VA.

Scientists have concluded that Orbital's separation mechanisms did not free the two satellites from the Pegasus rocket's third stage as planned, halting the two experiments for now. NASA, which funded most of the project, is mounting an investigation to establish why this happened.

Dr. Ricker said he hopes to re-fly the experiment in about two years. "Our partners in Japan and France strongly support this effort," he said. "If we are successful in obtaining approval and funding for an HETE-II, we may be able to make up in part for the intense feelings of scientific and personal disappointment shared by the more than 20 members of the HETE Team, many of whom devoted more than a decade of their lives to this mission."

HETE's goal was to search for and accurately locate mysterious sources of cosmic gamma-ray bursts and other high-energy transient events in the X-ray and ultraviolet spectral bands.

The 275-pound HETE spacecraft was carrying a gamma-ray burst detector, an X-ray camera to view the sky through a coded aperture and ultraviolet cameras. A unique feature of the mission was its capability to localize bursts with several-arcsecond accuracy, almost in real time, aboard the spacecraft. Some of these positions were to be transmitted continuously, in real time, to the ground and picked up by a global network of ground stations, enabling sensitive follow-up studies.

The other experimental spacecraft, the Scientific Applications Satellite (SAC-B), sponsored by the Argentine CONAE agency and by the NASA International Projects Office, was to be studying solar flares, gamma-ray bursts, X-ray cosmic background and source plasma for auroral activity.

Dr. Ricker said explicit telemetry and ground-based radar imaging showed that the Pegasus third stage failed to deploy either of the two satellites.

"In the case of the MIT satellite, there were three separation mechanisms on Orbital's Pegasus XL which had to operate successfully in order for the satellite to be freed, and none were activated," he said. The entire assembly is now circling the earth at an altitude of approximately 550 kilometers.

Although the HETE and SAC-B satellites were trapped on the third stage, both managed to be powered on after third-stage burnout, indicating that they both successfully survived the shock and vibration of the rocket firing, he said.

Neither of the satellites could deploy their solar panels, resulting in the draining of battery power within the first two days.

A version of this article appeared in MIT Tech Talk on November 13, 1996.

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