TS News - SAC-B/HETE Spacecraft No Longer Operational

TELE-satellit News, 9 November 1996

SAC-B/HETE Spacecraft No Longer Operational
  DALLAS, Texas, 96/11/08 (TS) -- Spacecraft managers at the Goddard Space
Flight Center, Greenbelt, MD, believe that the SAC-B (Scientific
Applications Satellite-B) spacecraft is no longer operating due to the loss
of onboard battery power.  Project officials said the spacecraft battery
lost power early on Tuesday, Nov. 5.

  None of the five SAC-B instruments have been operating since the battery
failure.  HETE (High Energy Transient Experiment) project officials at the
Massachusetts Institute of Technology confirmed that because the HETE
spacecraft was not separated from the Pegasus XL third stage, HETE was not
able to deploy its solar arrays. HETE
is designed to remain dormant until the solar arrays detect sunlight, an
event unlikely to occur since HETE remains sealed in the interior of a dual
payload support structure.

  Officials said the SAC-B solar arrays did not deploy automatically after
launch since the Pegasus XL third stage remained attached to the spacecraft.
The solar arrays were deployed by commands issued during the spacecraft's
first pass over the Wallops Operational Tracking Station, Wallops Island,
VA, on Monday, Nov. 4.  Ground tracking after launch showed the spacecraft
tumbling.  Due to the tumbling, combined with the shadowing of the Pegasus
XL third stage, the SAC- B solar arrays were not able to
generate enough power to keep the satellite's batteries charged.

  By early Nov. 5 morning during a spacecraft pass over the Wallops station,
there were no signals detected from SAC-B. The SAC-B attitude control system
had been turned on in an attempt to stabilize the spacecraft, but with the
additional mass of the Pegasus XL third stage, the batteries were discharged
before control could be established.  Although there is the possibility that
SAC-B could be reactivated if the current tumbling of the spacecraft were to
stop, that possibility is considered remote by NASA managers.

  HETE officials said that the spacecraft was powered on after launch
because of a previously programmed timer.  Signals were able to penetrate
the Pegasus canister and were detected during a pass at 7 a.m. on Nov. 5 by
a NOAA satellite receiving station at Wallops.  In a subsequent pass,
signals were present but weak.  Project officials said on the next pass, no
signals were detected.  Managers said that spacecraft batteries were
probably depleted at that time.

  The Pegasus launch occurred Nov. 4 at approximately 12:09 p.m. EST
offshore from NASA's Wallops Flight Facility, Wallops Island, VA. The
Pegasus vehicle achieved the desired orbit of 265 nautical miles by 297
nautical miles at an inclination of 38 degrees.  Analysis of the launch
shows that the Orbital Sciences Corporation's Pegasus XL third stage failed
to separate from the satellites.

  By: Gary Torrens
  Source: Satellite Journal International

(c)TELE-satellit 1996. All rights reserved.

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