RSF%SU-AI@sri-unix.UUCP (12/09/83)
From: Ross Finlayson <RSF@SU-AI>
n090 1820 08 Dec 83
BC-SHUTTLE-COMPUTER
By WILLIAM J. BROAD
c.1983 N.Y. Times News Service
NEW YORK - Balky computers have nagged the space shuttle from its
first test landing in 1977, to the countdown for its maiden flight in
1981, to its most recent mission.
But Thursday's failure of two of the shuttle Columbia's five main,
general-purpose computers, a failure that almost kept the craft in
space an extra day, was unusual because never before in the space
program had more than one computer gone awry at a time.
When one of the failed computers returned to service, officials of
the National Aeronautics and Space Administration decided there was
little danger because the four operating computers on board could
back up one another, constantly checking for errors and providing
reserves.
In fact, any single computer could guide the ship to a safe landing,
operating wing flaps and other spaceship control surfaces during
re-entry. If all the computers somehow failed, it is unlikely that
manual instructions from the crew could guide the shuttle through the
critical re-entry phase.
John W. Young, the mission commander, suggested that Thursday's two
computer failures had been caused by jet thrusters that rocked the
spacecraft. NASA officials passed up two opportunities to land the
shuttle while teams of technicians and engineers looked for the cause
of the failures. Mission control gave the crew a ''go'' for landing
after engineers decided the firings did not cause them.
An official of Rockwell International, the main builder of the
shuttle, said the failures might have been touched off by an
electrical surge. ''But there's no way to know until we analyze the
flight data,'' he added.
Computer No.2 was back on line soon after it failed, but Young said
No.1 had apparently ''hard failed.'' He tried without success several
times to restart it, and finally the control center at the Johnson
Space Center in Houston told him to declare it dead.
''When you have a problem like this you can't know at the time
whether it's the computer or something leading up to it,'' said
Justin Fishbein, a spokesman for International Business Machines
Corp., which built the main computers.
In July 1977, a hint of trouble was demonstrated to flight planners
in the shuttle's first test landing. A computer on board broke down
just as the shuttle was being released from the Boeing747 that had
carried it aloft. The remaining computers guided the shuttle down
safely.
The five identical computers on the shuttle are modified versions of
off-the-shelf machines developed by IBM in the early1970s for use in
military aircraft. Each computer consists of two55-pound boxes about
the size of small suitcases.
The use of extra equipment to enhance reliability is common in the
space program, in military aircraft and in some other applications,
such as the telephone system, where reliability is crucial.
In April 1981, a computer failure delayed the maiden flight of the
space shuttle Columbia for several days. Engineers at the Johnson
Space Center in Houston identified the problem as a timing fault in
one set of spaceship computers that disrupted communications with the
backup computer.
Two years later, on the maiden flight of the Challenger in April
1983, astronauts in space were awakened one night by alarms warning
that a computer had broken down. The problem was quickly fixed and
the computer worked perfectly through the rest of the flight.
In its September flight, one of the Challenger's main computers
began producing garbled data. Mission Control shut the computer down
and sent it some new instructions, which corrected the problem.
NASA officals say more expensive, reliable computers have sometimes
been used in past programs. In the Apollo program, the command module
relied primarily on one computer, with a less sophisticated model as
backup. The main computer was painstakingly designed, handmade and
very expensive. In contrast, the five computers in the shuttle are
not the most up-to-date and are not quite so expensive, but their
ability to back up one another allows less attention to be paid to
making each individual machine reliable.
nyt-12-08-83 2112est
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