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Wednesday, November 12, 1997 Published at 10:54 GMT


Mars Surveyor mission back on course

New Surveyor pictures of an area called the Ganges Chasma (Nasa)

Nasa scientists say their efforts to rescue the Mars Global Surveyor mission have succeeded but delayed the mapping project by a year.

The final adjustment to the probe's position, due to be made on November 12, will bring Surveyor into its correct orbit for mapping.

The original plan was to lower the orbit without burning any fuel by using the drag of the Martian atmosphere on the solar panels.

The technique called aerobraking was tried before in 1993 on a successful mission to Venus, but on this occasion the Surveyor team discovered that one of the panels failed to lock in place properly and that the atmosphere of Mars was denser than expected.

Extra atmospheric drag was threatening to damage the spacecraft so mission controllers had to use some of the precious propellant to move it to a higher, safer orbit.

More gradual aerobraking manoeuvres have been successful and Nasa says it can carry out its original objectives but it will now take one year longer.

[ image: Artist's impression of Surveyor orbiting Mars (Nasa)]
Artist's impression of Surveyor orbiting Mars (Nasa)
"The spacecraft's unlatched solar panel performed as expected during the two drag passes we've conducted so far," said Mars Global Surveyor project manager Glenn Cunningham.

"Although we observed some slight movement during the passes, the panel has returned to its original position and its stiffness did not change. That performance gives us confidence that the mission can proceed without further delay," he said.

The probe will now make a series of close-range passes with all its instruments turned on. Mr Cunningham said that during the lowest part of the spacecraft's orbit the the lighting angles would be excellent and allow the cameras to pick up good surface resolution.

"We expect to gain some spectacular new data during this time," he said.

Global Surveyor has already returned some good quality images of the planet surface.

Newly-released pictures show layered rock and sediment in the canyon walls of an area called Valles Marineris and hint at the presence of active sand dunes and dried up ponds.

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