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Simulation of the Mars Science Laboratory Sky Crane
An anonymous reader points us to Gizmodo for a fascinating video of NASA's Sky Crane. "When I read that the UFO-looking Mars Science Laboratory's aeroshell would use a floating crane — called Sky Crane by NASA — to softly land the rover on Mars, I couldn't believe it. Now, watching this hyper-realistic NASA simulation, I still can't believe how the whole thing works. I don't know about you, but the whole operation mesmerizes me to no end."
Almost realistic: the simulation approaches what the same inputs would do to the real system.
Realistic: the simulation behaves the same way as the real system.
Hyper-realistic: the simulation is better at realism that they real system?
What next, über-realistic? Or is profit next?
If I have nothing to hide, don't search me
Trebuchet's don't scale very well. AFAIR, neither did the beach ball. This thing is lots bigger and heavier.
Faster! Faster! Faster would be better!
We've got to flex some of our engineering muscle in front of our Martian friends so they will less inclined to invade us. In this light, clearly this > bouncing beach ball delivery.
Maybe have an external speaker system that blasts Ride of the Valkyries during descent, too.
It has to do with mass, the MSL rover, at 900 kg, is much too heavy to land using the airbag methods that landed the 180 kg Spirit and Opportunity rovers. To give a sense of scale, the MSL rover is the size of a minivan, while Spirit and Opportunity are the size of small riding mowers. See:
http://en.wikipedia.org/wiki/Image:Mars_Science_Laboratory_empty_chassis.jpg
I think the idea is that as you get more massive that doesn't work as well anymore. The weight of the airbags becomes untenable... I haven't looked at the math in few years, so unfortunately I can't be more specific.
Mars is one of the hardest places to land because its atmosphere is so wispy; on Earth some simple parachutes and a well-shaped capsule do the trick. On Venus the atmosphere is so thick anything you drop in will happily land softly as long as it doesn't melt. The moon and other such places you really only have the landing rocket option, which can be heavy but not particularly complicated.
On Mars though, the atmosphere is too thin to allow the capsule to slow it down to subsonic speeds on its own, meaning supersonic chutes are necessary if you want to use the atmosphere to slow you down. If you want to land with a rocket, you run into issues of trying to light an engine with supersonic flow going into the nozzle; trying to light it and flip around I imagine introduces some pretty wretched dynamic and structural problems. That tends to mean a series of parachutes including custom Mach 2 or Mach 3 chutes that would never be needed on Earth, or in this case using an aeroshell as well. Even then, you're still going too fast, so you need to slow down more. As suggested before, the airbags have worked in the past but don't scale well with higher mass vehicles. Thus you really need some kind of rocket (that ignite at subsonic speed); I'm not sure why a sky crane works better than some other system with rockets, I'd imagine its the easiest method of separation and also allows you to use less fuel since the crane itself doesn't have to slow down to a safe speed (i.e. release it down and reel it back up to reduce landing speed.)
Also, they had this option out there three years ago when I worked on a Mars mission for a class, so it's been out there a while and is probably as well developed as a non-tested system can be.
I'm on the project, and I understand all the reasons why we're doing it this way, but for what it's worth, I think it's as bat-shit insane as the rest of you. One thing no one can argue, though: it's incredibly cool.