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1993-05-03
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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
FOR IMMEDIATE RELEASEApril 12, 1991
Flight controllers at NASA's Jet Propulsion Laboratory
are working to analyze a problem that occurred during the
unfurling of the Galileo spacecraft's main communications antenna
Thursday, April 11.
Commands to unfurl the 16-foot-diameter umbrella-like
antenna were issued by Galileo's computers on schedule at about
12:50 p.m. Pacific Daylight Time on Thursday. The action was to
be completed in less than 10 minutes.
Normally microswitches would open when the unfurling
was completed, signaling that the operation was successful. Data
received from Galileo, however, indicate that the switches did
not open.
Data suggest that the antenna partially deployed, but
did not open fully.
Members of the flight team will continue detailed
analysis of data sent by Galileo during the deployment attempt
before taking any further action on the spacecraft.
Project officials emphasized that the deployment
problem poses no immediate problems for the spacecraft, which
otherwise is functioning properly.
The antenna -- a modified version of the design used in
NASA's Earth-orbiting Tracking & Data Relay Satellites -- has a
surface made of gold-plated molybdenum wire woven into a mesh.
The mesh is stretched across 18 graphite-epoxy ribs and connected
with elastic epoxy bands.
The high-gain antenna, made of metal mesh, has been
stowed behind a sun shield since Galileo's launch in October
1989, to avoid heat damage while the spacecraft flew closer to
the sun than the orbit of Earth.
The antenna unfurling is driven by a set of redundant
motors which turn a worm gear. This gear pushes levers which
spread the antenna's ribs, much as an umbrella is opened.
The unfurling was expected to slow Galileo's spin rate,
much as the spinning of an ice skater slows when the skater's
arms are extended. Data showed that Galileo's spin rate in fact
slowed, but not as much as expected for full deployment.
Unfurling of the antenna is necessary for Galileo to
send scientific data to Earth at much higher rates over greater
distances than it can with the low-gain antennas it has used
since launch.
The Galileo Project is managed by the Jet Propulsion
Laboratory for NASA's Office of Space Science and Applications.
#####
4-12-91 FOD