The Galileo spacecraft, on its way to Jupiter by way of 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 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 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 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 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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