PASADENA, Calif. - Engineers at NASA and Lockheed Martin are investigating whether a short circuit aboard Deep Space 1 in early November may have led to the spacecrafts now nearly four-week-long slumber in standby mode.
Protective software aboard Deep Space 1 put it into standby, or "safe" mode on November 11 after making several attempts to fix a glitch in the spacecrafts star tracker. The device uses a camera to image its surroundings, which it then compares to its on-board catalog of roughly 17,000 stars to determine where it is pointed in space.
The spacecraft apparently underwent what engineers call a "major arcing event," or short circuit, that may have caused the star tracker to cease working.
Marc Rayman, Deep Space 1s chief mission engineer, said the short circuit occurred on November 1 while the power on another instrument, the Plasma Experiment for Planetary Exploration (PEPE), was gradually being increased from 10,000 volts to 13,000 volts.
However, at 12,750 volts the power supply unexpectedly dropped to 5,500 volts, suggesting that a short of some kind occurred.
Rayman said the event could be un-related to problems with star tracker, which has been temperamental since the mission was launched more than a year ago.
"That could be one of the causes, but on the other hand it happened days before the star tracker stopped operating," Rayman said. "But its conceivable that it could have weakened it."
Also, the apparent short circuit did not cause any apparent damage to PEPE itself, he added.
Since November 11, Deep Space 1 has kept the star tracker and all its non-essential instruments switched off and turned itself toward the sun, the most easily recognizable target in its neighborhood in space. The spacecraft is now more than 149 million miles (240 million kilometers) from Earth.
The star tracker has failed intermittently during the yearlong mission.
However, the spacecraft has typically corrected the glitches in less than a minute. Previously, the longest malfunction -- which also occurred, coincidentally, on November 11, 1998 -- lasted just 28 minutes. When in standby mode, the rate at which data can be returned to the ground from the spacecraft slows to a trickle -- a pokey 79 bits per second -- since the high-gain antenna remains pointed toward the sun and away from Earth.
As a result, the mission team still has not received all the data recorded by the spacecraft prior to going into safe mode -- data that could explain the mishap. The mission team is now working on a way to coax the spacecraft into turning its high-gain antenna back toward Earth to increase the data return rate.
That could happen as early as the end of this week.
"We are still working on diagnosing what went on, but I think there are options for continuing the mission without the star tracker," Rayman said.
The $152-million mission has already completed its task of validating in space a dozen new technologies (the star tracker, although new, is not one of them), and is now on an extended mission. Plans call for the spacecraft to fly by two comets in 2001.
"Everything that we do now is bonus," Rayman said.
Those flybys could be jeopardized if engineers cannot work around the glitch on the Lockheed Martin-made star tracker.
Deep Space 1 is the first mission under NASAs New Millennium Program, which aims to test the validity of new technologies in space. Deep Space 2, comprised of two martian microprobes, is the programs second mission.
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