The Descent to Mars

This article is taken from the Winter 2011 issue of I, Science.

Joel Winston deconstructs the creative mechanism planned to help land NASA’s Mars Curiosity rover next year, and what this might mean for the evolution of space exploration.

As Mars continues to intrigue us and yield ever more ambitious missions, even greater technological advances are required to land there. As NASA’s Mars Science Laboratory hurtles towards the red planet with its precious cargo, the Curiosity rover, scientists wait in the hope of a successful landing in August 2012. However, with over half of all Mars missions having failed, it is clear that the stakes are high and the technological challenges immense.

After years of development followed by months of space travel, the biggest gamble for the Curiosity rover comes in the last few crucial minutes, when, after travelling 25 times faster than a speeding bullet, it needs to touchdown safely.

The ‘Entry, Descent and Landing’ phase begins 80 miles above the surface of the planet when the spacecraft hits the Martian atmosphere at an astonishing 12,000mph. This speed has to decrease to zero in just six minutes, requiring a carefully orchestrated sequence of events – all performed by a spacecraft running on autopilot.

Navigating the Martian atmosphere is particularly problematic. While it is thick enough to create dangerous amounts of friction and heat, it is too thin to help slow the spacecraft’s descent. The exterior temperature caused by friction during entry is nearly 6000°C, as hot as the surface of the Sun. The heat shield of the craft needs to resist this for 30 seconds and prevent the equipment inside from even reaching room temperature.

Small rockets guide the spacecraft’s entry into the lower atmosphere. Once it slows down to 1000 mph a parachute opens, triggering a powerful drop in speed to 250 mph and the beginning of a tricky landing sequence. Previous missions have used airbag-assisted landings; however, the Curiosity rover weighs in at nearly five times heavier than previous rovers at 900 kilos, making this impossible.

This is where the new ‘sky crane’ landing system comes in. A first for space exploration, it involves lowering the rover onto the Martian surface via a hovering rocket-powered sky crane, requiring some hair-raising robotic flight manoeuvres.

At around a mile above the surface, and still travelling at over 200 mph, the rover remains attached beneath the descent stage. This then detaches from the parachute, and four rocket thrusters fire-up to control their descent. Once slowed to just 2 mph Curiosity is lowered from the descent stage using bridles. The sky crane then gently lowers the rover to a soft-landing on its wheels, ready for it to begin its mission.

While it is uncertain whether such an ambitious procedure will work, creative landing solutions like these are becoming increasingly vital as Mars missions with even heavier payloads are developed. The result of August’s descent will therefore have huge implications for the possibility of future human exploration.

More > Check out NASA’s Curiosity: Destination Mars.

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