How do you get a 900kg, $2.5 billion rover full of sensitive scientific equipment safely on the surface of another planet? Well, you don’t drop it from a height, for a start. At least, you don’t these days…
Here’s the latest image from JPL:
No, that blue is not natural. They’ve colourised it to emphasise a particular feature. It’s the scouring effects of the thrusters which lowered Curiosity to the surface. We’ve seen these gouges up close in earlier images , but this shot from orbit gives a more overall picture. Imagine the four thrusters were blue spray-paint cans and you can track the approach and descent from the lower right of the shot.
It’s the result of the final stage of EDL, known as Skycrane. If you haven’t seen the animated artists impression of the whole Entry Descent & Landing sequence, do so now, it’s amazing, and you’ll see Skycrane in action. But basically, it looks like this:
In the final phase of landing, the rover is lowered gently to the surface from a thruster-propelled platform that is gyroscopically stabilising itself against ambient winds affecting both itself and the descending weight. The result is the softest-ever landing of a man-made object on the red planet.
See, the last generation of rovers, Spirit and Opportunity, they basically got them about that low and then just dropped them, albeit protected by a profusion of airbags. Take a look at this video from about the four-minute mark:
Even the engineers described this as “the Achilles heel” of the project.
It was a pretty big one.
After precisely guiding the thing over 60 million kilometres, to have to just drop it and look away cringing seems a bit…well…un-NASA.
How un-NASA? Well, these are guys whose measurements, whose engineering tolerances go to finer decimal places than practically anyone else’s on the planet. So how many times did their computer simulations predict the last-generation rovers would bounce on the surface using this system?
“Between 15 and 30 times”
That’s some ‘rough enough’ rocket science right there…
Now the fact is, even if they’d wanted to keep the old system (after all, both of the old rovers survived), it wan’t an option for Curiosity, because it’s so much heavier. Hence the elegant Heath Robinsonesque arrangement of Skycrane.
It is a beautiful solution to a heck of a challenge. After all, the landing is what dealt to so many of the very early Mars probes, both Russian and American. Getting the machine to Mars is the easy part. As they say, it’s not the fall…
And it’s important for another reason. One thing that lurks in the background of the entire mission, of all the Mars missions, and which was reiterated during President Obama’s phonecall to the team, is that this mission is not in isolation. It’s part of a long, steady, meticulous journey towards a manned mission to Mars.
And they aren’t going to fancy bouncing around about twenty times…
Stoppress: A fascinating discussion paper on various descent and landing system architectures, including but not limited to those discussed above