Imagine the Universe!

Launch Problem Thwarts New Missions

14 November 1996

Image of the Pegasus XL third stage
Credit: Orbital Sciences Corporation (OSC)

The Pegasus XL booster, seen above being prepared to carry the two spacecraft, was built by Orbital Sciences Corporation.

The November 4 launch of two new high energy astrophysics missions, SAC-B and HETE, ended in disappointment when the third stage of the launch vehicle failed to separate. The two spacecraft and the rocket stage remained locked in a position which prevented HETE's solar panels from opening, and kept SAC-B's solar panels from pointing properly at the Sun. Unable to generate power to communicate with the Earth, run their instruments and recharge their batteries, the spacecraft will not be able to fulfill their scientific missions.

The HETE spacecraft was attached to the third stage of the launch vehicle at the ring shown in the right side of the picture. A cylindrical adaptor was mounted over HETE, and the conical adaptor shown in the lower foreground was placed over the cylinder. The SAC-B spacecraft mounted to the ring on the narrow end of the conical adaptor.

Image of Pegasus on L1011
Credit: Orbital Sciences Corporation (OSC)

The Pegasus with its payload was attached to the belly of a Lockheed 1011 aircraft, which took off from NASA's Wallops Flight Facility in Virginia and carried the Pegasus rocket to an altitude of about 40,000 feet before releasing it.

SAC-B (Satellite de Aplicaciones Cientificas-B) was a cooperative project between NASA and the space agency of Argentina. The 400 pound satellite carried three astronomical instruments, with five detectors in all. The Goddard X-Ray Experiment was intended to measure soft X-rays emitted from gamma-ray bursts and solar flares. The Cosmic Unresolved X-Ray Background Instrument was to study the background radiation emanating from our galaxy and from the Universe as a whole. An Italian instrument designed to detect energetic neutral atoms was also on board.

Image of Pegasus rocket
Credit: Orbital Sciences Corporation (OSC)

After release from the L1011, the rocket motors were ignited and the Pegasus proceeded to the planned orbit, which took about 10 minutes. Since the separation of the spacecraft from the launch vehicle didn't occur, the rocket stage and two spacecraft continue to orbit as one unit.

NASA and Orbital Sciences have each convened panels to investigate the problem.

HETE (High Energy Transient Experiment) was a collaboration between NASA and the Massachusetts Institute of Technology. It carried a gamma-ray burst detector along with X-ray and ultraviolet cameras. These instruments were intended to work together so that scientists could pinpoint the location of the bursts with greater precision.

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
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