NASA’S latest Mars explorer has landed on the Red Planet – and so have I (or at least my name has). The Mars Science Laboratory, known as Curiosity, carried a microchip with the names of its mission supporters, of which I am one. This was my fourth landing on Mars, as I also landed with two rovers in 2004 and the Phoenix lander in 2008. I’m also now en route to Pluto, but won’t arrive for three years.
Since we’ve sent rovers to Mars before, why do it again? It’s because this vehicle is eight years more advanced, and we’ve learnt a lot from previous missions. We also want to search in different locations. Mars has as much land area as Earth, so half a dozen spots are not going to tell us everything about the planet.
The new site is Gale Crater. It’s 154km in diameter, covering more than six times the area within the M25. The landing site is at the foot of a mountain that rises 5.5km high. The choice of site was based on the aim to “follow the water”. Over the years we have eliminated various requirements for possible locations for life, but the one that makes life possible more than anything is water. At Gale, it may have run down into the crater’s bottom. Curiosity could also explore its way up the mountain-side, reaching elevations much greater than earlier rovers.
However, getting there isn’t easy.
Curiosity is about twice as big as previous rovers – about the size of a Mini Cooper. It is also more than five times heavier, with 80kg of instruments, compared to 6.8kg on previous landers. This has led to two major differences. Firstly, the instruments need more power than solar panels can provide, so the rover is provided by a radioisotope thermal generator (RTG). Its power won’t be reduced by dusty solar panels, but there is also a limit to how long power can be provided. The primary mission is due to last for one Martian year – 687 Earth days. Although previous landers, which were only guaranteed for 90 days, have worked for much longer, once the RTG’s output falls too low, that’s the end of the mission.
The other difference is the mass of the craft. It’s too heavy to land using airbags and, if it landed with rockets, they would have to be carried around afterwards. Instead, Curiosity used a method that had never been tried on any previous space mission, a Sky-Crane. After the heat shield and parachute slowed the craft down from 5.8 km/s to 350 kph, the rover was jettisoned, the Sky-Crane’s engine fired and it lowered the rover on four tethers. Once the rover touched the surface, the tethers were severed and the Sky-Crane flew off to crash. The signals confirming the landing didn’t reach Earth until 14 minutes later, so Mission Control was helpless if things went wrong. It’s no wonder that entry and landing was known as the “seven minutes of terror”.
Jerry Stone is a freelance presenter on space exploration.
To learn more about Mars exploration, the Mars Society UK 2012 Conference is on 25 August at the National Space Centre in Leicester. It is £10 for the day. For further details, email firstname.lastname@example.org or visit www.spaceflight-uk.com