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SAC-B/HETE SPACECRAFT NO LONGER OPERATIONAL


SAC-B/HETE SPACECRAFT NO LONGER OPERATIONAL 

    DALLAS, Texas, 96/11/08 (SJI Newswire) -- 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. 

(c) Satellite Journal Itl. 1996
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