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STS-73 Columbia postponement
10/7/95
10:30 a.m.


NASA Launch Director Jim Harrington announced at 10 a.m. today that
the STS-73 launch would be postponed today.  The delay will be at
least 48 hours.  Officials will meet this morning to discuss repairs
and schedules.  Launch controllers identified a problem with one of
the two master events controllers before 9 a.m. today. This unit
sends the signals to fire pyrotechnic devices that fire the solid
rocket booster hold down bolts at launch, and jettison the solid
rocket boosters and the external tank during ascent.  This unit is
located in the aft compartment and may have to be replaced and
retested.  The external tank will be drained of liquid oxygen and
liquid hydrogen propellants and access to the aft compartment will be
established.

NASA Test Director John Guidi told the flight crew, "We did our best
today and we sure hope to see you back here very soon and try all
the way down to T-zero and a safe launch."

In 1984, on Mission STS 41-D, launch was delayed 24 hours because of
an incompatibility between the master events controller and the
flight software relating to solid rocket booster fire commands. 
During the 24 hour delay, a software patch was verified and
implemented to assure all three booster fire commands were issued in
the proper time interval.