WASHINGTON NASA may try to shake, rattle and roll itsJupiter-bound Galileo spacecraft in an effort to free a stuck antennathat threatens the $1.3 billion mission.
But first, engineers will try once more to chill theumbrellalike antenna to shrink its metal mast in the deep freeze ofspace. Two such attempts have failed, but experts think Galileo wasgetting too much heat from the sun when it was only 190 million milesaway.
The antenna temperature in this month's try dropped only to 220degrees below zero. By December, Galileo will be 15 million milesfarther away from the sun, and the temperature will be 50 degreeslower.
"You try those things that are easiest," said Don Ketterer, newin the job as the Galileo program manager. "Next is to go a littlebit colder; we may try some mechanical shock activity."
Galileo, which won't get to Jupiter until 1995, has twoantennas. The low-gain antenna, which is working fine, dribbles datato Earth. The high-gain antenna is intended to send information fromJupiter in a flood of computer data.
Engineers may retract the low-gain antenna and swing it outagain, hoping the shock might jiggle the other antenna enough todislodge three stuck restraining pins. Fast spin may be tried
If that doesn't work, engineers may spin the spacecraft 10revolutions a second to see if the umbrella opens by centrifugalforce. Or, they may fire on board jets to shake the antenna free.
"I think there's very little holding it," Ketterer said. "It'sjust a matter of a little jog."
Some engineers think the dry lubricant on the pins may have beenknocked out in 1986 while the Galileo was being trucked from CapeCanaveral, Fla., to the National Aeronautics and SpaceAdministration's Jet Propulsion Laboratory in Pasadena, Calif.
The Galileo launch was postponed because of the Challengerexplosion.
Wesley Huntress Jr., director of NASA's Solar System ExplorationDivision, said loss of lubricant may have been a contributing factorbut not the only culprit.
"Sitting in the truck in the position it was, it was quitepossible that additional rubbing of the pins in the socket could havecaused some loss of lubricant, or it could have caused someadditional scoring," he said. Pins are the villains
Whatever the cause, engineers are sure that three of 18 "ribs"failed to release from the antenna's central column because of thepins, which are an inch long and the diameter of a pencil.
Shrinking the antenna, Huntress said, will cause the pin socketsto move down toward the base, relieving pressure holding the pins.
The freezing treatment in July and this month may not haveworked because the temperature on the antenna didn't get as cold aspredicted, Huntress said.
"We are going to try yet a third time, around mid-December," hesaid.
Heaters, which keep electronic components warm during thesix-year flight, will be turned off.
Ketterer said Galileo was tested on the ground while it awaitedits launch in October, 1989, but the antenna wasn't unfurled becauseit could introduce problems in Earth gravity. The pins are hiddenfrom view.
"Once you've closed up that antenna for shipment and launch youdon't want to release it," Ketterer said. "I'm not sure this is oneof those things you could look back on and say, `Gee, I wish we couldhave done that.' "
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