— NASA's Mars Global Surveyor spacecraft has returned more data on Mars than all previous missions to the planet combined (Illustration: NASA/Corby Waste)
NASA has called on the European Space Agency's Mars Express spacecraft to look for the missing Mars Global Surveyor (MGS) after the Opportunity rover failed to locate it by listening for its radio beacon.
The 10-year-old MGS was last heard from on 5 November. It reported problems re-pointing one of its solar power arrays shortly before going silent (see NASA struggles to contact lost Mars probe).
NASA called on its Mars Reconnaissance Orbiter (MRO) to try to take pictures of MGS on 17 and 20 November. But the images did not reveal the spacecraft, perhaps because MGS had shifted in its orbit since last contact (see Mars probe probably lost forever).
After MRO failed to spot the spacecraft, NASA turned to its Opportunity rover to continue the search. Opportunity listened for MGS's radio beacon on 21 and 22 November, but heard nothing.
All these failed attempts do not necessarily mean MGS is dead, says the spacecraft's manager Thomas Thorpe of NASA's Jet Propulsion Laboratory in Pasadena, California, US. "The antenna that transmits the signal is on one side of MGS, and that may or may not have been pointed at Mars when we passed over" the rover, he told New Scientist.
The radio beam from MGS's antennas is about 60° wide, giving only about a 1 in 6 chance of it reaching the rover, since MGS's orientation is unknown.
Opportunity's roving twin, Spirit, will try to detect the beacon, too. But Spirit is just emerging from its winter hibernation and will not have enough power to spare for this task until a few weeks from now, Thorpe says.
Pass in the night
In the meantime, the European Space Agency (ESA) is joining the search: "We've asked the Mars Express people to take an image of MGS with their High Resolution Stereo Camera," Thorpe says, adding that the Mars Express HRSC team had agreed to make the attempt. They have not set a date for this attempt, but the earliest opportunity is on 7 December 2006, when the two spacecraft should come within 400 kilometres of each other.
Even though random drift of the spacecraft has led to uncertainty in its position, the field of view of Mars Express's HRSC is wide enough to include the entire area that the spacecraft could be in, Thorpe says.
MRO is just beginning its science observations and is too busy to continue hunting for MGS, he says. But if Mars Express can locate MGS, then a case could be made for a second imaging attempt with MRO, which has the only camera powerful enough to reveal the orientation of the spacecraft and the position of its solar panels, Thorpe says.
This information would help engineers to diagnose and perhaps solve the problem that is preventing the spacecraft from communicating with Earth.
Points of light
The MRO images taken on 17 and 20 November did show two extra points of light that did not correspond to any of the stars expected in the field of view. There had been speculation that these points of light were two pieces of MGS perhaps the main body of the spacecraft and a broken-off solar panel.
Thorpe says that scenario is unlikely, however. "If those blips were real, they were in two very different orbits, so it's pretty unlikely that both could have come from the spacecraft," he says. It remains possible that one of the points of light is MGS, but they are too dim to draw any firm conclusions, he says. One or both could just be instrument noise, perhaps the result of cosmic rays hitting the camera, he says.
While other probes search for MGS, NASA is beaming commands to it from Earth every day in the hope of reviving it. The agency has been trying various ways of commanding it to turn on its low gain antennas, and also ordering it to rotate in the hope of getting them pointed closer to Earth. But the spacecraft has remained stubbornly silent despite these efforts.
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