11/6/92: REPORT DETAILS CAUSES OF TETHERED SATELLITE MALFUNCTIONS

Mark Hess
Headquarters, Washington, D.C.              November 6, 1992

Jerry Berg
Marshall Space Flight Center, Huntsville, Ala.

RELEASE:  92-196


     The report of NASA's Tethered Satellite System 
Investigative Board was released today, presenting the 
panel's findings on problems which prevented full deployment 
of the satellite during Space Shuttle mission STS-46.

     The 47-page report examined five problems that occurred 
during the deployment effort and identified causes for four 
of them.  It made recommendations for actions to be taken to 
prevent similar occurrences in the future.

     The board said the two snags during deployment and 
retrieval -- when first releasing the satellite from the 
deployer and when the satellite was at 735 feet -- were due 
to slack which developed in the tether at a point where it 
moves between one pulley and another -- somewhat similar to 
movie film misfeeding in a projector. 

      "The crew found a way to procedurally get around this 
slack problem," said Board Chairman Darrell Branscome.  "In 
both cases the jamming was overcome.  By itself, this problem 
would not have prevented us from fully deploying the 
satellite."  

     NASA previously had reported on Aug. 28 that the cause 
of the unplanned stops at 587 and 840 feet was a mechanical 
obstruction -- a protruding bolt -- which prevented part of 
the tether reel mechanism from moving across its full range 
of travel.  

     "We contacted the bolt when the satellite was out at 587 
feet," said Branscome.  "What we learned from our ground 
simulations was that in spite of the bolt obstruction, it was 
possible to pull additional tether off the reel, out to 840 
feet."

     According to the report, the bolt was part of a hardware 
change made late in the review process and should have been 
caught in the systems engineering review.

     "The board made some excellent recommendations in the 
report on how to deal with things like late changes to the 
hardware," said Pearson.  "We are going to look carefully at 
their recommendations and apply the lessons learned from this 
flight to future missions."

     No plausible scenario has been validated by post-flight 
demonstration regarding difficulty in retracting one of two 
umbilicals between the tethered satellite and deployer.

     Based on its findings, the board recommended several 
specific hardware assessments and modifications which should 
be made to other elements of the tethered system if NASA 
decides to refly it.  

     The board was formed on Aug. 12 by Jeremiah Pearson, 
NASA Associate Administrator for Space Flight.  The six-
member board included representatives from various NASA 
centers and the Italian Space Agency.  

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