[clari.news.aviation] NASA studies satellite problem

clarinews@clarinet.com (WILLIAM HARWOOD, UPI Science Writer) (02/01/90)

	SPACE CENTER, Houston (UPI) -- Concerned space engineers are running
a battery of tests to pin down what caused part of a $100 million
shuttle communications satellite to fail Jan. 15 and whether the problem
can be fixed, officials said Wednesday.
	But NASA does not believe the trouble will cause any major problems
with testing and operation of the $1.4 billion Hubble Space Telescope, a
showcase astronomy satellite scheduled for launch around April 18 that
must use the Tracking and Data Relay Satellite system to send data back
to Earth.
	``Hubble will not be a problem,'' said Ray Newman, a ``TDRS''
program official at NASA headquarters in Washington. ``We will continue
to have operational antennas as needed. We expect to have full
capability for Hubble.''
	NASA's western Tracking and Data Relay Satellite malfunctioned Jan.
15, leaving the big spacecraft with only one fully operational
high-data-rate KU-band communications channel.
	While a second KU-band system is working properly, the
``TDRS-West'' satellite no longer has a backup high-speed communications
channel and another failure could cripple NASA's space tracking and data
relay network.
	Engineers have no reason to expect any additional problems, but
even so the satellite may be unable to handle KU-band traffic from more
than one satellite at a time as it could before.
	``A fuse failure is believed to have caused the problem, that means
something probably shorted in there,'' Newman said in a telephone
interview.
	As a result, a switch on board the spacecraft is locked in a
position that forces the satellite to expect a certain type of radio
signal, one with a ``right-hand circular polarization,'' or orientation,
that is based on a satellite's movement through space.
	``We have a switch (on the TDRS satellite) to switch polarizations.
The normal support configuration for most on-orbit spacecrft is
right-hand circular polarization. The switch is in left-hand circular
polarization and we've been unable to return it to right-hand
polarization.''
	The TDRS system was designed to serve as an orbital communications
network, relaying voice and data between ground control, the space
shuttle and other military and civilian satellites, eliminating the need
for costly ground stations scattered around the world.
	With two such TDRS satellites in orbit, a space shuttle crew can
stay in direct contact with mission control for more than 80 percent of
each orbit. For payloads like the Hubble Space Telescope, a two-TDRS
system is mandatory to relay the huge volumes of data that are expected
after the telescope is launched around April 18 from the shuttle
Discovery.
	Two TDRS satellites currently are in orbital operation: TDRS-East,
launched Sept. 29, 1988, during the first post-Challenger shuttle
mission, and balky TDRS-West, launched March 13, 1989. A third TDRS,
launched in 1983, is considered an orbital spare but that satellite has
suffered a variety of problems and is not considered fully operational.
	``On the 15th of January we experienced an anomaly with TDRS-West
and basically, we've been running tests to see what exactly caused the
problem and what our options will be,'' NASA spokesman Dwayne Brown
said. ``The only impact is, we don't have redundancy on this system.
	``We don't know if its generic or if its intermittent. The worst
case scenario is if it is generic.''
	If the TDRS-West satellite cannot be fixed, NASA managers could
elect to move the original TDRS farther west to serve as a backup, but
that decision has not yet been made.
	``Once the tests prove we can't fix it, that would be an option,''
Brown said.
	As for the seriousness of the current problem, Newman said he did
not want to speculate until all the tests are completed. But, he said:
``The current system capability we have is designed to operate with two
active satellites.''
	Another TDRS satellite is scheduled for launch in 1992.