Clementine's spin may cancel asteroid visit - space probe traveling too fast to image asteroid 1620 Geographos

Science News,  May 21, 1994  by Bruce Bower

• E-mail
• Print
• Link

Lost and gone forever? Not quite, but the Clementine spacecraft isn't likely to keep an August date with the near-Earth asteroid 1620 Geographos.

A computer problem 2 weeks ago set the craft spinning at 80 revolutions per minute (rpm), says mission manager Lt. Col. Pedro L. Rustan of the Defense Department's Ballistic Missile Defense Organization in Arlington, Va. Engineers can probably slow the spin to 30 rpm, but that would still be too fast to image the asteroid clearly, Rustan says.

Clementine, originally scheduled to pass within 100 kilometers of Geographos on Aug. 31, would have been the first craft to photograph a near-Earth asteroid.

Ironically, the glitch occurred just after the joint military-NASA mission got a last-minute reprieve. Acting under congressional pressure, the Pentagon came up with the $3.2 million needed for the craft to continue on to Geographos after its just-completed moon-mapping mission.

DOD didn't want to pay for the asteroid visit because the flyby deals more with astronomy than military testing, Rustan says. He notes that the department has given less attention to the astronomical parts of the mission. "I feel a lot like a neglected stepchild."

NASA has given little publicity to the low-cost project -- in part, apparently, because of the perceived taint of a project that has its origins in the Stars Wars program.

Though Clementine carries 23 new devices, the malfunction occurred in the flight-proven main computer. During a brief communication loss with the ground, the computer accidentally directed four attitude control thrusters, which help steer Clementine, to fire. This emptied the propellant from one of two fuel tanks and set the craft spinning.

Plenty of fuel remains in the other tank, which powers the main engine. But even if scientists can use this engine to slow the spinning to 30 rpm, the probe could take only blurry images of the asteroid and would have trouble even pointing at the rocky body. Clementine may not get any closer to Geographos than several thousand kilometers.

Rustan says his team will try instead to steer Clementine toward Earth's radiation belts. If they succeed, this should further test the durability of the craft's miniaturized detectors.

COPYRIGHT 1994 Science Service, Inc.
COPYRIGHT 2004 Gale Group