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Date"Another excellent accomplishment in a long string of accomplishments by the Galileo mission!" said Don Ketterer, NASA's Galileo Program Manager, at the July 27 press conference held at JPL. Full-scale models of the Galileo spacecraft and its Probe could be seen in the background as viewed on the television monitors.
It was the morning after the orbiter deflection maneuver (ODM), the first major use of the 400-newton engine--so essential for performing two key maneuvers still to come, the Jupiter orbit insertion (JOI) and the perijove raise maneuver (PJR). Bill O'Neil, Project Galileo Manager, expressed his delight, "This is a joyous morning. . . . Therefore, the excellent propulsion system worked beautifully. First the probe release--and now another excellent event." After this first operational sustained burn, both vehicles were on the proper trajectories to Jupiter. The Probe had been released two weeks earlier. Marcie Smith, Galileo's Probe Manager at NASA's Ames Research Center, added, "The Probe is on target and fully configured, heading for encounter at Jupiter."
A warm welcome was given to the assembled guests from the Federal Republic of Germany; representatives of Daimler Benz Aerospace AG (DASA) (formerly Messerschmitt-Bolkow-Blohm), designers and builders of the propulsion system; Deutsche Agentur für Raumfahrtangelegen-heiten (DARA), a German space agency that manages the contract with DASA; and Deutsche Forschungsanstalt für Luft- und Raumfahrt (DLR), a German research agency that conducts the day-to-day operation of the propulsion system. Included in this recognition of success were personnel from Ames, who manage the Probe, and from Hughes Space and Communications Co., who designed and built the Probe.
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pressurization gas is helium. The ODM could have been accomplished by the 10-N thrusters usually assigned for trajectory correction maneuvers (TCMs). Why did the Galileo team opt to use their one and only 400-N engine for this trajectory change? Because, until its release, the Probe sat directly in front of the 400-N engine nozzle, precluding any inflight checkout. With the Probe on its way, the 400-N engine could finally, after almost 6 years, demonstrate its operational capability, in advance of the crucial maneuver to occur at Jupiter, the JOI.
And what a demonstration it was! From 0 to about 97 km/h in 135 seconds. The burn was 1.2 percent less than predicted but well within the permissible 6 percent. For the past 2 years, the Galileo team has been checking and preparing scenarios for every possible contingency. None of these plans had to be implemented. A joyous Bill O'Neil said, "This flawless maneuver gives us the confidence that the 400-N engine is ready to perform orbiter insertion at Jupiter and the perijove raise maneuver to follow. We have a beautiful system."
Since execution of the command to sever the umbilical cable that united the Orbiter and its Probe, there can be no communication until, during descent to Jupiter, the Probe relays its data via radio to the Orbiter, a one-way "conversation." The Probe will coast 82 million km until 6 hours prior to arrival on December 7, when a timer will activate systems and instruments in preparation for the entry and parachute descent. Entry speed will be 170,600 km/h or 47 km/s--100 times the muzzle velocity of a bullet fired from a 0.45-caliber gun. This will be the highest impact speed ever to be experienced by a manufactured object. It must then undergo extremes of deceleration, temperature, radiation, and pressure.
Today, the Galileo team continues to prepare for the final approach to Jupiter (see story, Jupiter At Last! Galileo's Longest Day: December 7, 1995) buoyed by their successes in probe release and the ODM. Again, the news has been good--the reason for all those smiling faces at Project Galileo on the morning after.
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