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Early on Monday Nasa will attempt its most ambitious Martian landing so far. If an extraordinarily complex series of manoeuvres come off safely, a $2.5bn car-sized rover called Curiosity will be placed gently on the surface of the red planet.
The nuclear-powered Curiosity will then spend at least two years exploring the chemistry and geology of the Gale Crater just below the Martian equator, providing evidence for scientists to decide whether microbes ever lived there.
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Project engineers at Nasa’s Jet Propulsion Lab in California call the planned descent from interplanetary space to the Martian surface “seven minutes of terror” – and it all had to be programmed in to the spacecraft in advance, because radio signals take 14 minutes to travel between Mars and Earth, making real-time communications impossible.
The probe will enter the upper Martian atmosphere at 13,200 miles per hour. It will be slowed down first by its heat shield to about 1,000 mph and then by a huge parachute to about 180 mph. For the final descent the parachute is cut away and eight engines on the descent stage, a “rocket backpack” attached to Curiosity, provide further deceleration.
Previous Nasa rovers, such as the Spirit and Opportunity twins in 2004, were safely cocooned by air bags that inflated around them for touch-down. But the engineers judged that the one-tonne Curiosity would be too heavy for such cushions.
Instead the rocket backpack will become a “sky crane”, hovering 20 metres above the surface and lowering Curiosity gently to the ground on cables at less than 2 mph. When it senses touch-down, the connecting cords are cut and the rocket backpack, now redundant, flies safely out of the way to crash at least 150 metres away.
It sounds crazily complicated, Doug McCuistion, Nasa’s Mars exploration director, conceded at a pre-landing press conference. But he added: “We’ve done everything we could. We’ve tested everything we could test. We built everything to the best of our ability. Once you understand it, it’s not a crazy concept.”
Even so, success is far from certain, because Mars has a habit of jinxing spacecraft sent from Earth to explore it. The 1976 Viking landings were spectacularly successful, as were the Spirit and Opportunity twins, but many other missions have failed.
If Nasa engineers get the message they want, that Curiosity’s complex manoeuvres have landed it successfully, they will not rush it into action. Several weeks will be spent checking its condition and upgrading its computers.
The first pictures beamed back to Earth will be in black and white, with colour images to follow after a few days. Curiosity may take a test drive a week or two after landing but serious exploration will not begin for a couple of months.
First destination is the foothills of Mount Sharp, which rises from the middle of Gale Crater. Orbiting spacecraft indicate that layers of rock there were probably laid down at a time when Mars was wet – and more likely to have harboured simple life forms than today’s desiccated planet.