"6_2_12.TXT" (3753 bytes) was created on 10-30-88

SECOND-GENERATION SET OF ONBOARD FLIGHT COMPUTERS AT JSC
 
     The first complete ship's set of an updated version of the
Space Shuttle orbiter's five onboard flight computers, more than
twice as powerful but half the size of those now flying, is being
tested at the Johnson Space Center (JSC) and may fly in 1990.
 
     Every flight control function aboard an orbiter is initiated
by or through the five onboard general purpose computers (GPCs),
including the movement of all aerodynamic surfaces and control of
the main engines. "The computers now flying were designed in the
1960s, using 1960s' technology," explained Ned Trahan, chief of
the Data Processing Section at JSC. "The new ones have 1980s'
technology."
 
     The rapid advance of technology during that period is
evident in the appearance of the new GPCs now in the JSC Avionics
Engineering Laboratory (JAEL). The new computers are half the
size of the current orbiter GPCs, made up of a single unit as
compared to two units for the current computers.
 
     And the new GPCs operate three times as fast; have more than
twice the memory capability; and weigh half as much as those now
flying, Trahan said. "They also have an error correcting code,
you could have a failure in one of the memory chips and the code
would automatically correct the data," Trahan said.
 
     It all adds up to what will be a tremendous boost in
reliability and performance, plus an open road for innovation.
The current GPCs operate at 80 percent of their capability during
periods of highest activity. Using the same software, those same
periods will push the new GPCs to only 40 percent of their
capacity.
 
     "We want to run the old software in the new machines with a
minimum of changes. It's proven reliable," Trahan said. "But
eventually we'll modify it over a period of time to take
advantage of the extended capabilities."
 
     Development of the second-generation GPCs began in 1983, but
the race with the rapid evolution of high technology never ends.
"You can see that from development to machine takes a long time,"
Trahan said.
 
     Improved integrated circuits cut down the size of the new
GPCs, and instead of the iron core memories in the current flight
computers, the new ones have a complementary metal oxide silicon
(CMOS) memory.
 
     IBM, manufacturer of the current GPCs, also manufactures the
new GPCs and began delivery of the actual flight-types to JSC in
February. The JAEL had been working with pre-production
prototypes of the computers since 1986, refining the design and
operations.
 
     Now the JAEL has six GPCs actually designated for flight,
and they differ from the prototypes very little except in their
parts. Prototypes were built with off-the-shelf, commercial
hardware; flight GPCs are built with high-reliability, space-
qualified components.
 
     "With the actual flight units, and the first flight set of
five, we're now doing what we call burning them in," Trahan said.
"It's a process where we put as many operating hours on them as
we can, hoping that any weak components in the system will fail."
JAEL workers plan to put at least 500 hours on each GPC.
 
     While the flight computers are burning in, the prototypes
are being used in simulated flights via a link between the test
bays in the JAEL and the high-fidelity Orbiter simulator in the
Shuttle Avionics Integration Laboratory (SAIL). So far, the new
GPCs have lived up to their billing. "In preliminary testing,
they've performed as well as advertised," Trahan said.
 
     At least 19 more of the second-generation GPCs will be
delivered to the JAEL, enough to outfit four orbiters plus a
spare flight set. The lab should continue to receive about one
new GPC a month, Trahan said.
 

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