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Skycrane, Innovative landing technology
cIclops
post Mar 11 2005, 08:51 AM
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In his recent long piece on spacedaily.com Bruce Moomaw reports:

... JPL's Pete Theisinger and Mike Meyer (chief engineer and scientist of the 2009 Mars Surface Lab) confirmed that the current plan is to have MSL land using a strange, Rube Goldbergian system called "Skycrane".

Skycrane is a very innovative landing system and now that MSL appears to be planning to use this approach there are lots of open questions, such as: How exactly does it work? What advantages does it have over legs, airbags or pallets? What the heck is it anyway?

Some background info:

JPL note

Space.com article


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djellison
post Mar 11 2005, 10:08 AM
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Essentially the whole things enters in an aeroshell as usual - drops the heatshield, drops the backshell and enters a viking like terminal des. phase - but comes to a hover about 5m off the ground. The paylod ( rover in this case ) is then dropped down on cables, the cables are cut, and the crane flys off.

Some people think it's stupid and will never work

10 years ago - people thought the same thing regarding the three-body chute-backshell-airbag mechanics for MPF and MER smile.gif

Doug
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remcook
post Mar 12 2005, 11:49 AM
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If you look at planetary missions, and especially landings, the scenarios always look highly unlikely to me. The margins are terribly small (for instance reentry angle, or time to burn your rocket). But somehow most things just work smile.gif
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cIclops
post Mar 12 2005, 05:07 PM
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QUOTE (remcook @ Mar 12 2005, 11:49 AM)
If you look at planetary missions, and especially landings, the scenarios always look highly unlikely to me. The margins are terribly small (for instance reentry angle, or time to burn your rocket). But somehow most things just work smile.gif

They "just work" because of the enormous amount of effort, experience and knowledge put into their design, construction and operation. The MERs cost more than $800 million and took several years to build based on the pathfinder design, which in turn was based on Viking, and in its turn based on Surveyor and Ranger technology.

Most landers haven't worked but much was learned from those failures. For example MPL, Deep Space 2 as well as several Surveyor and Ranger lander probes. And I won't mention the numerous Russian lander failures ...


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remcook
post Mar 12 2005, 07:51 PM
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obviously.

that was kind of my point: it's amazing what people can do. So although the skycrane looks very difficult, I wouldn't say it is impossible. There will be an Earth-based test at some point I suppose.
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dvandorn
post Mar 13 2005, 12:09 PM
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QUOTE (cIclops @ Mar 12 2005, 05:07 PM)
Most landers haven't worked but much was learned from those failures. For example MPL, Deep Space 2 as well as several Surveyor and Ranger lander probes. And I won't mention the numerous Russian lander failures ...

Since you don't want to get into Soviet/Russian lander failures, looking at just American attempts, there have been three loss-of-vehicle failures in thirteen attempts at lunar/planetary soft landings(*). 10-3 is a pretty decent track record.

Now, if you add in American attempts at hard landers, at which we're zip out of five(**), you're still talking seven failures out of seventeen attempts. 10-8 is still a winning record.

Finally, if you include American manned soft-lander attempts into the total -- one failure (in which the landing itself wasn't even attempted) out of seven tries(***) -- you achieve a whopping sixteen successes versus only nine failures. Winning nearly twice as often as you lose will get you thrown out of any casino in Vegas. And if you look just at American soft-landers, both manned and unmanned, the record is a phenomenal 16-4.

So, I'm thinking maybe NASA is a little better at landing probes on other planets than you suggest... *smile*... At the very least, "most landers haven't worked" is an inaccurate assessment of American lunar/planetary landing attempts.

All of that said, I agree with your main point. We learn from our failures just as much as we learn from our successes. In fact, we learn the things we want to learn from our successes, but we more often learn the things we need to learn from our failures...

* - American soft-lander failures: Surveyors II and IV, Mars Polar Lander. Successful soft-landers: Surveyors I, III, V-VII; Vikings 1 and 2; Mars Pathfinder; MERs A & B (Spirit and Opportunity).

** - American hard-lander failures: Rangers 3-5; Deep Space 2 (two hard landers). No successful hard-landers.

*** - American manned soft-lander failure: Apollo 13. Successful manned soft-landers: Apollos 11-12, 14-17.

-the other Doug


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tedstryk
post Mar 13 2005, 12:46 PM
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Of course, the Pioneer Venus Day Probe could be considered an accidental success at a hard landing.


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OWW
post Mar 13 2005, 01:35 PM
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You could say the Galileo probe was a successful 'lander' too. smile.gif And what about NEAR on Eros?

Back on topic. What I worry about with that skycrane landing is the wheels of the rover. Are they protected in some way at the moment of touchdown? It seems to me only the slightest horizontal velocity will tear a wheel off or at least bend it into an unusable piece of metal.
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djellison
post Mar 13 2005, 02:22 PM
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I think the idea is that the crane will hover stationary - although anyone who's ever flown a helecopter simulator, or been lucky enough to fly a real helecopter will know - it's damn hard to hover on the spot in a cross wind

Doug
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cIclops
post Mar 13 2005, 02:31 PM
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QUOTE (djellison @ Mar 13 2005, 02:22 PM)
I think the idea is that the crane will hover stationary - although anyone who's ever flown a helecopter simulator, or been lucky enough to fly a real helecopter will know - it's damn hard to hover on the spot in a cross wind

Doug

Yes but the Martian atmosphere is very thin and MSL/Skycrane won't have much surface area so the jets should easily be able to compensate for drift during the short hover time. The really hard part IMO will be ensuring that MSL is placed in a safe location.


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djellison
post Mar 13 2005, 04:25 PM
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The atmosphere was thing - yes - but the wind speeds can be very high - and I can imagine that Skycrane would still offer considerable X-section.

Take MER - Granted - much bigger X-Section whilst being much lighter - but some quite high speeds before using DIMES and the sideways motors before touchdown

Doug
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Guest_BruceMoomaw_*
post Mar 13 2005, 08:17 PM
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Theisinger says that winds are not a problem -- even Martian winds of 50 kph or so produce almost no horizontal effect on the rover. The real worry is slight instabilities in the attitude control and horizontal hover stability of the lander itself, and the possibility of a slightly uneven unlatching of the rover from the lander's bottom -- any of which could set the rover swinging. The ground tests this year will be absoltuely crucial on whether to switch to a pallet lander design instead.
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cIclops
post Mar 13 2005, 08:59 PM
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QUOTE (BruceMoomaw @ Mar 13 2005, 08:17 PM)
The real worry is slight instabilities in the attitude control and horizontal hover stability of the lander itself, and the possibility of a slightly uneven unlatching of the rover from the lander's bottom -- any of which could set the rover swinging.

Holding the rover tight to the frame of the Skycrane by the winch cable should damp any oscillation during unlatching.


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OWW
post Mar 13 2005, 09:34 PM
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By the way, why lower the thing from a tether in the first place? Wouldn't it be less risky to keep the rover attached to the skycrane and at the moment of touchdown fire some pyros and let the crane fly away? Lots of dust on the rover, but that's no problem since it's nuclear powered.
This way the final descent will be more precise and you keep the advantage that the rover is on the surface immediately.
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Guest_BruceMoomaw_*
post Mar 14 2005, 12:29 PM
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Ciclops may have a point, but Theisinger did tell me he was worried about instabilities during unlatching. As for ObsessedWithWorlds' idea (can I just call you OWW from now on?), I imagine the problem is that the lander -- unless it had control of its descent speed during the last few feet of its descent too fine to be feasible with any confidence -- might actually end up pounding the rover into the surface with its own weight, thereby damaging its wheels or suspension, before unlatching from the rover and flying back up off the surface.
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