NASA are counting down to their most ambitious landing on Mars yet with the arrival of Curiosity next month. The probe, otherwise known as Mars Science Laboratory, is the heaviest rover ever sent to the Red Planet.
Skymania News spoke to NASA’s Steve Lee, one of the key personnel involved in putting Curiosity down in Gale Crater on August 6th. Because of the rover’s size – similar to that of a Mini Cooper – NASA is using a new technique which will lower it from a hovering Skycrane during a landing that is so daring it has been described as “seven minutes of terror”.
Steve, who is Guidance, Navigation and Control Systems Manager for the mission at the Jet Propulsion Laboratory in California, told us the rover needed to be big because of the work it has to do looking for clues to life.
He said: “Previous NASA and European missions have been seeking to find if there has been water on the surface of Mars. They have shown that at least some locations have been soaked in water. So now we are taking the next step to ask whether Mars could once have been habitable.
“Were there the right elements that could have fostered the growth of life? We’re not necesarily going to try to find life with this mission but we want to know if life could have evolved in that kind of envirnment.”
He added: “The sort of life we are expecting is a kind of microbial life. But we’re not looking for life itself with this mission. We’ll first look for the organic material that could indicate its presence.
“Curiosity is much larger than previous rovers (Spirit and Opportunity). It is in the order of four times larger in terms of volume and more in terms of weight.
“The reason it is so big is that the kind of instruments you need to detect organics are necessarly large. It was a big leap for us to have been able to miniaturise organic-sensing instruments to fit in this rover even though it is this big.”
Turning to the landing, Lee told Skymania: “We quickly realised that our previous strategy of using an airbag landing system would no longer work. It is not easy just to blindly scale up airbags as were used to land Spirit and Opportunity. We just became too large to make airbags practical any more.
“We looked at all sorts of options, carefully evaluating the pros and cons before deciding on the Skycrane technique.
“When we get to Mars we will jettison the cruise stage that has carried us there. The rover inside the entry capsule will have its wheels tucked up by the belly, its tall mast will be folded down and the arm tucked up against its chest to make everything smaller.
“On top of the rover will be attached the descent stage which essentially is a jet backpack. It has thrusters and a radar system that will be used to execute the Skycrane when we get there. The entire thing will be encapsulated in a heat shield because Mars has enough of an atmosphere to cause quite a bit of heating, then there is a back shell to create a closed capsule.”
Lee added: “After we’ve jettisoned the cruise stage, the capsule hits the atmosphere and a minute or so later we reach peak heating where the heat shield is really doing its job and we’re slowing down all the time. Then about three and a half minutes later when we’ve slowed down to about mach 2 we deploy our parachute.
“The parachute will slow the vehicle down quite a bit. When we get down to subsonic speeds, around four minutes into flight, the heat shield is released and jettisoned and falls to the ground. At that point the onboard radar is exposed and takes measurements of our height above the ground as well as our velocity relative to it.
“At this point we’re trying to determine the correct time to begin our propulsive manoeuvres to set up for the sky crane. We need to make sure we don’t come out too early because then we won’t have enough gas to go all the way down, and if we come out too late we may not have enough time to complete our manoeuvres. So we have to be at just the right spot.
“Around 8,000ft or so above the ground and about five minutes into the flight, then the descent stage with the rover attached detaches from the parachute and backshell. Eight thrusters are fired around the periphery of the descent stage back pack.
“The first thing we do is manoevre away from the parachute, and then the descent stage slowly lowers the rover down towards the ground. About 65 ft above the ground, the rover is released on a bridle, a long tether about 25 ft long. Then the descent stage lowers it onto the ground.
“The rover deploys its wheels ready to touch down. When they do, the rover senses the moment it does, the tether is cut and then the descent stage accelerates away. Curiosity is on the ground ready to begin its mission.”
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