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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."
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!
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
That is the reason for the skycrane. If the air were as dense, a standard parachute landing would be all that is required. The problem is an inability to decelerate to a stop without the sudden stop part. I believe that gliders are also out of the question due to atmospheric conditions. This is a compromise of all known possible options. One that will land the heavier weight, and perhaps give them much greater accuracy in choosing a landing spot... With the speed of the rover hitting the right spot first try can be quite a bit of savings.
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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.
As cool as this is, we've succesfully landed rovers on mars (and the moon, though not a robotic system), as well as landing non-motile craft on other planets. All used relatively simple delivery systems, and frankly, worked pretty well. The Apollo system (at 40 years old) landed softly enough not to smash human beings, which can be a lot more sensitive than robots. Maybe this type of technology will have a use in the future (though it's not like it's a super-high-tech idea). All of that being said, GOD DAMN that's cool!
Airbags don't work on something as big as the MSL rover. It's that simple.
Not exactly. It is radioisotope power but it is not nuclear power in the sense that there is a reaction going on. The simple decay gives off heat. As I recall it's not that much, either. Something on the order of 110 watts. Still, it's much better than relying on solar panels. Here's a nice page of fact sheets for the mission.
http://www.rootstrikers.org/
The problem with soft-landing heavy objects on Mars is that there's not enough atmosphere for aerobraking and parachutes to do the job, so the approaches used for Earth re-entry won't work. There's too much gravity for landing on rockets. as with lunar landers, without most of the payload being landing fuel. The problem gets harder as the mass goes up. This was realized only about five years ago, to the embarrassment of some within NASA. So there are now various complicated hybrid schemes, like this.
The scheme with the cables does not look promising. Unlike Luna, Mars has winds and weather. This looks like one of the student lander designs from NASA's high school curriculum.
One bad feature of this design is that the actual landing forces have to be taken by the rover's suspension. Previous designs had the rover inside the landing module, not underneath it. That approach uses crushable components (air bags, crushable blocks, collapsible legs, etc.) to cushion the landing. With this "flying crane" approach, the autopilot has to do a really, really smooth landing or the rover will be broken.
The whole operation is horrendously complicated, with dozens of potential failures at each point, and no realistic means of allowing for such failures. Every step would have to function perfectly, or we've just sent another multi-billion paperweight to a dead planet.
Whatever happened to KISS?
The engineer who proposed this really needs to look into alternate fields of employment. I suggest Fecal Matter Relocation.
kartune85 : Incapable of reason, observation or learning. A kind of dim, drab, flightless parrot.
Just a little longer...
http://www.space.com/businesstechnology/081001-tw-phoenix-microphone.html
And as you tread the halls of sanity, You feel so glad to be, Unable to go beyond. I have a message, From another time..
The cables allow for some leeway in how hard you can hit the ground and still have a functioning rover. If you come in too fast with a single piece of equipment, the whole thing goes crunch. The rockets and ground acquisition sensors are good, but not perfect.
With the rover on the end of the bridle, this decouples the weight of the scientific payload from the weight of the support equipment needed to ensure a soft landing of the payload. Once the thing is on the ground, you don't need any of the support equipment anymore. You can make the rover tough enough to handle a harder-than-expected landing, even tough enough to bounce a bit. Accelerometers on the rover will send the signal back up the umbilical to give the crane the green light to cut loose and go away. I suppose that you could even have tilt sensors on the rover to tell the crane, "This is a bad place to leave me, pick me up and put me someplace else."
A lot of the weight of the (rover + sky-crane) is up in the crane. This set up will let you have a thinner engineering margin in the crane part, saving weight that can be used for more fuel. As long as the crane can fly, it can take pictures and serve as a supplementary probe.
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You can see the pedigree of the concept. The airbag system used a brutal retro-rocket on the teather milliseconds before impact to slow the airbag-lander from smush speed to bounce speed.
This is similar. The retro rocket is far more gentle and precise but basically we have a last-second retro rocket on a tether dropping the lander onto the surface.
I presume tradeoff studies were done to find the optimum balance between the amount of crane hover precision and winch control precision for a giving touchdown speed tolerance at min weight.
As noted, there are a lot of things deploying in rapid sequence, and a winch. Winch bad. Winch have many fiddly bits. I wonder if they also did a tradeoff study of reliability vs capacity of this concept and a brute-force lander.
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