Martian rescue for real-life Wall·E

Published on Thursday 12 November 2009 21:21

IT IS the story of a plucky little robot stranded on a deserted, dead planet, a million miles from home, years after its mission was completed and separated from its companion.

• An artist's impression of Spirit, the space exploration robot rover which Nasa scientists are desperately trying to free from red planet Mars

Memory fading and with a wonky wheel, it has doggedly kept on working, but time is now running out for it as it tries to escape the approaching winter.

No, it's not the sequel to Disney hit WallE, but the plight of Spirit, Nasa's Mars rover, which has been stuck in a sand trap for six months.

Last night, scientists and engineers set out their plans for a last-ditch attempt to free it, after months of testing different escape routes back on Earth, using prototype rovers and a sandpit.

Ashley Stroupe, a Spirit extraction testing co-ordinator at Nasa's Jet Propulsion Laboratory in Pasadena, California, last night described how Nasa intended to free Spirit. "We'll start by steering the wheels straight and driving, though we may have to steer the wheels to the right to counter any downhill slip to the left," she said.

"Straight-ahead driving is intended to get the rover's centre of gravity past a rock that lies underneath Spirit. Gaining horizontal distance without losing too much vertical clearance will be a key to success.

"The right front wheel's inability to rotate greatly increases the challenge."

Spirit and its twin, Opportunity, landed on Mars in 2004 and have long outlasted their primary three-month mission.

Spirit was the first of the surveyors to be parachuted on to the Martian surface after a journey of 105 million miles. Their task was to investigate and snap the surface, beaming the images back, giving scientists the best view of Mars since the Viking programme of the 1970s.

Having carried out its commands doggedly for years despite developing multiple malfunctions, Spirit finally foundered while crossing an impact crater on a site called Troy. The rover's wheels broke through a dark, crusty surface layer and became embedded in a powdery material that had been hidden underneath it.

According to John Callas, project manager for Spirit and Opportunity at JPL, the rescue bid has been hampered by it being virtually impossible to recreate the exact conditions of Mars.

He said: "We cannot spin the wheels or make use of momentum. All the experiences people have with getting their cars stuck in the sand don't apply. There's no real good Earth analogy; that's why it's so hard to test this down here and why it's such a challenge on Mars."

To compound the problems, Spirit has been suffering from episodic amnesia. This occurs when it fails to record its day's activities on to its flash memory, which can retain the data while the rover powers down for energy-conserving periods of sleep.

Scientists have already managed to make Spirit wiggle its wheels as a precursor to what is expected to be a painstaking three-month operation to free it, though the main operation will start on Monday.

But despite being immobilised, Spirit has been examining its Martian surroundings with tools on its robotic arm and its camera mast.

The rover's work at Troy has added to earlier discoveries it made, indicating ancient Mars had hot springs or steam vents, possible habitats for life.

Ray Arvidson, a scientist at Washington University in St Louis and deputy principal investigator for the science payloads on Spirit and Opportunity, described the location as a "geological treasure trove".

"The soft materials churned up by Spirit's wheels have the highest sulphur content measured on Mars."

However, he said that Spirit's mission had gone on for so long that many of its sensors had been seriously compromised by exposure to the Martian weather. There was also concern voiced that if it cannot be freed, then it may not survive the encroaching winter.