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The end of a pioneering Mars probe?


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Mars Global Surveyor, the veteran space probe missing in action since last week, not only revealed Mars as an active, stormy planet with a watery past, it pioneered a risky space-flight technique - one that paved the way for probes to carry less fuel yet carry out more science.

In September 1997, two days after entering orbit around Mars, MGS did something space probes usually avoid like the plague: it dipped into the upper atmosphere of the Red Planet, risking the onslaught of friction and turbulence.

Surely some mistake? No, the spacecraft was using a revolutionary braking technique tentatively tested by NASA's Venus orbiter, Magellan, near the end of its five-year life. In 1994, Magellan dipped into the Venusian atmosphere, using drag on its solar panels to slow it down. The experiment provided a wealth of data on how to control drag, torque and reduce heat to protect a probe and its vulnerable solar panels.

NASA used this "aerobraking" technique to slow MGS down and move it into a circular orbit without using a rocket engine. "This meant we didn't need 900 kilograms of rocket fuel to slow the probe, and that in turn meant we could launch on a $80 million rocket instead of a $330 million one," says MGS project manager Tom Thorpe.

The technique worked, and until 2 November the craft surveyed the planet's gullies, minerals, topography, magnetic field and polar ice deposits. Since then, the Mars Reconnaissance Orbiter and Mars Odyssey probes have used aerobraking too.

The use of an advanced design feature to save cash contrasts with NASA's "faster, better, cheaper" (FBC) missions of the mid-1990s, which resulted in the loss of the Mars Polar Lander and Mars Climate Orbiter. Despite being a mid-1990s mission, MGS escaped their fate because it borrowed technology from an earlier fully funded (though still unsuccessful) mission called Mars Observer. "MGS used spares from Mars Observer and so inherited all the back-up and fail-safe technology that was not part of the FBC missions," says Thorpe.

Now a solar panel on the 10-year-old probe is refusing to move sunwards, killing its power source. NASA's rover Spirit will try to radio MGS from Mars next week, but hopes are not high for its recovery, says the agency.

Source: New Scientist



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