WASHINGTON, Nov. 11 (Xinhua) -- NASA engineers are striving to restore full communications with NASA's Mars Global Surveyor spacecraft, which celebrated its 10th anniversary in space on Nov.7.

    NASA's Jet Propulsion Laboratory in Pasadena, California, lost contact with the Mars orbiter on Nov. 3 and Nov. 4 after the spacecraft reported on Nov. 2 that the motor moving one of the arrays had experienced errors, NASA officials said.

    On Nov. 5, the signal from the spacecraft was received during four different orbits, but it did not carry any data from the spacecraft. The signal's frequency indicated that the spacecraft had entered safe mode, a pre-programmed state of restricted activity in which it awaits instructions from Earth.

    Since no further signal has been heard from Global Surveyor so far, NASA engineers concluded that the spacecraft had made an additional pre-programmed response, intended to help it survive when it senses that a solar array is stuck. The spacecraft turns that array toward the sun to maintain its power supply and rotates the rest of the spacecraft in the same direction, thereby making communication with Earth less effective.

    "The spacecraft has many redundant systems that should help us get it back into a stable operation, but first we need to re-establish communications," said project manager Tom Thorpe.

    Global Surveyor is the oldest of five NASA spacecraft currently active at the red planet. Its original mission was to examine Marsfor a full Martian year, roughly two Earth years. Once that periode lapsed, considering the string of discoveries, NASA extended the mission repeatedly, most recently on Oct. 1 of this year.

    The orbiter has operated longer than any other spacecraft ever sent to Mars. It has returned more information about Mars than all earlier missions combined. Among many important accomplishments so far, Mars Global Surveyor has found many young gullies apparently cut by flowing water, discovered water-related mineral deposits that became a destination for NASA's Opportunity rover, mapped the planet topographically and examined many potential landing sites on Mars.