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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 RELEASE November 13, 1989
The Galileo spacecraft, on its way to Jupiter by
way of a multi-planet gravity-assist path leading past Venus
in February, completed its first trajectory-correction
maneuver Saturday night, under the control of its flight
team at NASA's Jet Propulsion Laboratory.
The maneuver took place in three daily sessions,
November 9-11, with a total of more than 2,000 brief pulses
fired from tiny rocket engines located on the spinning part
of the spacecraft. The operation was designed to change the
direction of Galileo's motion toward Venus, the equivalent ot
accelerating sunward by about 17 meters per second (38 miles
per hour). The spacecraft's current velocity in solar orbit
is more than 60,000 miles per hour.
Galileo's 12 small engines operate in the pulse
mode, thrusting for about a second and then pausing for
several seconds. This is done because they could overheat if
operated for long periods. In addition, they must be
synchronized with the spacecraft's 3-rpm rotation to avoid
possible contamination of instruments and other despun parts
of the spacecraft, and to obtain the correct lateral course
change.
The Galileo flight team took advantage of the
three-day period of the maneuver to analyze spacecraft
dynamics and the performance of the propulsion system. The
maneuver revealed some interesting but expected
idiosyncracies in the system, such as a tendency for the spin
axis to be nudged by tiny thrust imbalances or possible
impingement on parts of the spacecraft.
"It was an excellent maneuver," said mission
director Neal Ausman, "and things went very well. However,
near the end of Friday's maneuver, we may have lost the
temperature sensor on one thruster but were able to monitor
the thruster using other temperature measurements. On
Saturday, as a precaution, we reprogrammed the maneuver and
used an alternate thruster."
On Thursday when the maneuver started, Galileo was
4.5 million miles from Earth and had travelled 31 million
miles along the path to Venus. Today the Earth distance has
increased to 5.3 million miles and the trajectory mileage to
36.9 million; the spacecraft has 148 million miles to go
before its February 9 rendezvous with Venus. Arrival at
Jupiter is scheduled for December 7, 1995, when the
spacecraft will go into orbit around the planet and its probe
will enter the atmosphere.
The Galileo Project is managed by the Jet
Propulsion Laboratory for NASA's Office of Space Science and
Applications. The mission began October 18, 1989, with
launch aboard space shuttle Atlantis.
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#1273. 11/13/89 jhw