MIT Seeks New Gamma Ray Experiment After Launch Failure


CAMBRIDGE, Mass.--The Massachusetts Institute of Technology Center for Space Research, deeply disappointed in the failure of the Pegasus XL rocket launch on Nov. 4 that doomed its high energy astrophysics probe into the mystery of gamma ray bursts, is seeking to try again.

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. The National Aeronautics and Space Administration (NASA) is mounting an investigation to establish why Orbital's release systems did not function as planned.

Ricker said he hopes to re-fly the experiment in about two years. "Our partners in Japan and France strongly support this effort," said Ricker. "If we are successful in obtaining approval and funding for a 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."

Ricker believes the scientific approach originally chosen for HETE in the early 1980's is still the most promising one for solving the gamma-ray burst mystery. "We are determined to see it implemented," he said.

The HETE project was the first of a new generation of small scientific "microsats" pioneered at the MIT Center for Space Research. Managed entirely by the Center for Space Research, the international HETE effort included participation by France and Japan. US funding was provided by NASA.

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 to carry out the first multiwavelength study of gamma ray bursts. It was carrying a gamma-ray burst detector, an X-ray camera viewing the sky through a coded aperture and ultraviolet cameras. A unique feature of the mission was its capability to localize bursts with several arcsecond (1/3600 of a degree) 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 primary and secondary 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. It was carrying three astrophysical instruments.

Ricker said that 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," Ricker said.

In particular, power was lost in the third stage immediately after separation from the second stage. The three pyrotechnics releasing SAC-B, opening the Dual Payload Attachment Fitting and finally releasing HETE, did not fire. The entire third stage SAC-B and HETE assembly is now circling the earth at an altitude of approximately 550 kilometers.

A little more than one hour after launch, Dr. Joseph Salah, Dr. Dennis Hall, and their colleagues at MIT's Millstone Radar facility quickly imaged the assembly during its first orbital pass over Massachusetts, conclusively proving that separation had not occurred.

Neither of the satellites could deploy their solar panels, resulting in the draining of battery power within the first two days. There is no chance for either satellite to be released, Ricker said.

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.

Ricker said scientists received six minutes of telemetry from HETE's VHF beacon picked up by a 26 meter National Oceanographic and Atmospheric Administration antenna in Virginia on Nov. 5, 18 hours after the launch. A shorter HETE transmission was received at Los Alamos National Laboratory in the afternoon of the same day.

"The radio signals from HETE were actually radio frequency emission leaking out of the Orbital Sciences third stage canister, but they provided unambiguous evidence that the satellite had survived the launch and had been turned on by its internal timer, just as planned," Ricker said.

He explained that since HETE was not seeing the day-night transition patterns that its sun sensors and on-board computer were expecting (it was dark inside the Orbital canister), the satellite would periodically go into a sleep mode and awaken every 72 minutes to check for daylight.

By Tuesday evening, battery power was drained, and no signals were detectable.

The spacecraft was largely constructed by AeroAstro Inc., of Herndon, VA. Spacecraft integration and environmental testing took place at the Center for Space Research and at Lincoln Laboratory.

Members of the MIT Science Team included Dr. John P. Doty (Project Scientist), Dr. Roland K. Vanderspek, Dr. Geoffrey B. Crew, Professor Saul A. Rappaport, and Dr. Jesus N. S. Villasenor. Dr. Francois Martel was HETE's Project Coordinator. Tye M. Brady was the HETE Project Engineer. In the US, there are HETE co-investigator teams at Los Alamos National Laboratory, the University of California (Berkeley and Santa Cruz), and the University of Chicago.

Participating in the Launch Operations at Wallops Flight Facility (VA) with Brady, Martel, and Ricker were Robert Dill, Frederick E. Miller, and Dr. Eric J. Gaidos. Preparing with Crew, Doty, Vanderspek, and Villasenor at the MIT Control Center and Ground Tracking Sites to receive the first orbits of HETE data were David Breslau, Arnaud G. Dupuy, Rosemary Hanlon, John E. Hanson, Greg M. Huffman, Dr. Steven E. Kissel, Dominique Martel, Scott McDermott, Kenton C. Phillips, Michael J. Pivovaroff, Gregory Y. Prigozhin, and Peter C. Tappan.


Topics: Space, astronomy and planetary science

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