If contact is not restored by Saturday, NASA might try to have another Mars-orbiting spacecraft take pictures of MGS to assess its condition.

    MGS is one of four spacecraft orbiting Mars. Its companions include NASA's Mars Reconnaissance Orbiter and Mars Odyssey, and the European Space Agency's Mars Express.

    "The spacecraft has many redundant systems that should help us get it back into a stable operation, but first we need to reestablish communications," said MGS project manager Tom Thorpe of NASA's Jet Propulsion Laboratory in Pasadena.

    Thorpe's laboratory lost contact with the MGS for two days last week, then received a weak carrier signal with no data on Sunday. Since then, the probe has not confirmed receiving a command to point one of its transmitters toward the Earth, Thorpe said.

    On Nov. 2, MGS managers sent commands for the probe to adjust the position of one of its solar power arrays to better track the sun. Returning data indicated a problem with the motor that moves the array, so a backup motor and control circuitry were switched on.

    But no signal was received on Nov. 3 and 4, followed by a weak signal on Nov. 5. The signal cut out completely later that day and nothing has been heard since.

    Engineers think the spacecraft has performed a programmed maneuver in which it turns its solar arrays toward the sun to maintain its power supply. When it does this, it also reorients its entire body in the same direction, thus making communication with the Earth less effective.

    It's also possible, Thorpe said, that the spacecraft was hit by a micrometeorite, and that it's antenna was jolted out of alignment.

    NASA is still trying to contact the spacecraft, because its ability to receive commands might not be impaired. But if nothing is heard from MSG by Saturday, NASA will ask the Mars Reconnaissance Orbiter team to begin preperations late next week to take pictures of MGS in order to assess its condition. The two spacecraft pass within about 100 km of each other several times a week.

    "That would help a lot to determine where we are now and what commands we should be using," Thorpe said.

    MGS was launched on Nov. 7, 1996 to systematically map the Red Planet. It was originally tasked with examining Mars for a full Martian year, roughly two Earth years. Operations were scheduled to end in early 2001, but MGS continued to perform so admirably that its mission was repeatedly extended, most recently on Oct. 1 of this year.

    (Agencies)