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Mar Observer: the sounds of silence.

Acknowledging that the first U.S. mission to Mars in 17 years is almost certainly a failure, NASA has appointed a task force to find out what went wrong. Engineers lost contact with the Mars Observer spacecraft on Aug. 21, just three days before it was to begin orbiting the Red Planet. NASA scientists say they now have little hope of regaining communication with the craft.

"I think it's lost," says Glenn E. Cunningham, project director for the Mars Observer at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Because of the craft's silence, no one knows whether Mars Observer fired its thrusters on Aug. 24 as planned and entered an orbit around Mars or if it simply flew past the planet. The $980 million space vehicle might also have been blown to bits shortly after ground controllers commanded it to pressurize its fuel tanks. That normally routine procedure, which requires the craft to detonate a gas valve, may be fatally jarred electronic equipment or caused an explosive leak in the fuel system.

NASA scientists now theorize that a master clock, the timekeeper for most of the craft's computers, may have contained a faulty pair of transistors, each of which controls a duplicate timer. If both failed after the tanks were pressurized, the craft's computers could not function and the Observer would remain lost in space.

That explanation, researchers note, is only one of many under investigation by the NASA task force, headed by Timothy Coffey, director of the Naval Research Laboratory in Washington, D.C. The theory came to the fore because of problems discovered in a similar master clock before the launch of the NOA-A-13 weather satellite. During testing last June, researchers found that the satellite's master clock failed to operate. They traced the problem to a faulty weld in a transistor and replaced the defective parts before the Aug. 9 launch of the weather satellite, which has since failed for other reasons (SN: 8/28/93, p.134).

The finding came too late for the Mars Observer, launched in September 1992 with a master clock containing transistors from the same troublesome lot. However, Charles Thienel at NASA's Goddard Space Flight Center in Greenbelt, Md., says it's unlikely that two transistors failed on the Observer, because testing revealed only a few defective transistors in the manufacturing lot.

Thienel said that an earlier weather satellite, NOAA-8, had a problem with its master clock in 1984. But only one of its two timing devices was affected. After about eight months, an interval during which the satellite remained silent for weeks at a time, NOAA-8 finally switched to tis backup timekeeper. It remains unclear whether the experience with NOAA-8 warrants a glimmer of hope that Mars Observer might eventually resume useful communication with Earth.

This week, NASA began considering several strategies for carrying out some of the studies that would have been conducted by Mars Observer. NASA manager Wesley T. Huntress says that spare parts from the Observer might be assembled into another craft, possibly as early as 1994. However, a limited supply of the costly rockets needed to launch the craft and transfer it into a Martian orbit could hamper such efforts, notes John Logsdon, a space policy analyst at George Washington University.

Scientists are also considering using small satellites originally intended for defense research to study Mars. One such craft, known as Clementine, is scheduled for launch in January to explore the moon. But at least one researcher expressed concern that NASA may be grasping at straws in an effort to salvage some of the scientific treasures the agency had hoped Mars Observer would radio home.
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Title Annotation:contact with space probe lost
Author:Cowen, Ron
Publication:Science News
Date:Sep 4, 1993
Words:606
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