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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 19, 1991
Intensive analysis of the problem that prevented
deployment of the Galileo spacecraft's high-gain antenna is
continuing at NASA's Jet Propulsion Laboratory.
A "tiger team" of specialists from a variety of
engineering disciplines -- including consultants from contractor
companies -- has been assembled to study the problem and how to
correct it.
Galileo Project officials say they expect to carry out
considerably more analysis and ground tests before determining a
date to make another deployment effort. The deployment
difficulty poses no immediate problems for the spacecraft, which
otherwise is functioning properly.
The problem arose Thursday, April 11, when the
spacecraft's umbrella-like main communications antenna was
commanded to deploy.
Commands to unfurl the antenna were issued by Galileo's
computers on schedule April 11. The deployment action -- very
similar to opening a conventional umbrella -- was expected to be
concluded in less than three minutes.
Data from Galileo, however, indicate that the antenna
unfurled partially but did not completely unfold. One side of
the antenna appears to be deployed more fully than the other
side, suggesting that some restriction may be affecting a portion
of the antenna.
Data that the JPL team has been studying include
readings from a spacecraft sun sensor and from its spin
detectors, which offer engineers information on the current state
of the antenna. In addition, data from Galileo's power system
provide details on how the deployment attempt proceeded and
possible clues on the nature of the restriction.
Engineers say that continued analysis of the data --
and tests of identical antenna equipment on the ground -- are
important to avoid any action that could damage onboard
equipment.
The 16-foot-diameter high-gain 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 quartz cords.
The antenna 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 deployment is driven by a set of redundant
motors which turn a worm gear. This gear pushes a nut connected
to levers which spread the antenna's ribs, much as an umbrella is
opened.
Unfurling of the antenna is necessary for Galileo tosend scientific data to Earth at much higher rates over greater
distances than it can with the two low-gain antennas it has used
since launch.
Project officials say Galileo will still conduct its
planned flyby of the asteroid Gaspra on October 29 even if the
antenna is not open. In that event, pictures and other data
would be stored on the spacecraft's onboard tape recorder and
relayed to the ground when Galileo approaches for its flyby of
Earth in December 1992.
JPL manages the Galileo Project for NASA's Office of
Space Science and Applications.
#####
4-19-91 FOD