Skycrane, Innovative landing technology Options

[MarsEngineer]

Wouldn't it be nice if this great new EDL system could actually be used more than once...?

Phil

I completely agree Phil. To an extent that is not obvious from the EDL animations, there is a lot more commonality than you would think. But obviously we could do a lot better. While the MSL EDL architecture may not make sense for very small landers, I beleive that it is general purpose enough to be able to be used for a wide range of future landers and rovers. The historical diversity in the design of Mars landing systems is not as inexplicable as it looks. Someday one of us will have to write an engineering history. (I have been on the hook for a paper on this topic for a year or two now.)

-Rob

[Guest_Oersted_*]

Thanks for your replies everybody, with a special thanks of course going to MarsEngineer for his long, detailed and highly informative reply!

I will respond to Oersted's questions by italicizing his questions ...

[...]

It would be neat if the lander/skycrane itself could fly off and make a soft landing with its remaining fuel. There will now be to years extra for coding, so maybe a little proggie can be made for the skycrane computer that could try to effect that? Why would it be interesting to land softly? Maybe to scour some trenches that the rover could visit... Then again, a crashing lander should make a nice big hole on its own.

hmmm.... you are not the first to suggest that we try for a soft descent stage landing, Oersted. While that would not be impossible to consider, it would be a lot of work and as you know (and MSL folks know all too well) time is money. However I will be more than happy to tease my friend Jeff about it (he's one of the main developers of the code that controls the "flyaway" mode of the descent stage).

...If that descent stage should gently alight on the surface of Mars, I'll give out a whoop almost as big as that for MSL itself

2) The complexities of opening up a parachute can be avoided (deployment, squidding, shredding and other chaotic events).

Dang it. We can't seem to get away from needing a heatshield AND a parachute (or to be precise, some type of a supersonic decelerator). Until we invent something like a "supersonic tension cone" or "supersonic retro-propulsion" we are stuck with at least one parachute. I think the latter inventions are probably required in order to land really big things - like people.

Oops, ascribe that brainfart of mine to a late-night posting: of course MSL has a parachute!

When I hear about supersonic tension cones, I often think back on old quasi-sci-fi projects such as General Electric's MOOSE (Manned Orbital Operations Safety Equipment): http://boggsspace.com/strange_but_true.asp

- So what we need for future Mars EDL systems is a big properly shaped Mylar bag, inside that a deployable carbon-fibre erector set and lots of quickly-hardening ablative foam, and voilá, there's your supersized supersonic tension cone! Well, that'll be the day...

From considerations like these as well as the amazing chrysalis MER pop-out deployment, I am thinking that JPL would do well to hire some Japanese origami experts... Space exploration seems to be unfolding ever more - That is, unless we go for supersonic retro propulsion, in which case we should be looking more for some punchy German Huntsville kind-of-guys who know how to weld together a kick-*** rocket engine.

(Did you know that the Apollo landers each sent a cloud of lunar dust particles into lunar orbit during each landing? The command module flew through that fine cloud.)

No, I most certainly didn't, that's amazing! - I did know that the Surveyor 3 lander was practically sanded by moon dust from the Apollo 12 landing, but never heard about a cloud of dust reaching up to the CM.

I have a few questions regarding the maneuver though, maybe someone can clear them up.

[...]

Will only radar be used during descent, or will there also be a photographic system to determine drift (as with MER) and possible nature of the landing site? Will the skycrane be equipped to actively try to avoid rocks and unsuitable terrain and translate horizontally in an Armstrong-esque fashion, if necessary?

Not on this mission. The combination of a small landing area (made possible by the Apollo-like Earth-entry closed loop guidance), the wonderful MRO imaging and 3-D reconstruction of the landing sites plus MSLs very slow and safe landing on wheels allows us to land safely with the rover's "eyes closed" with very high probability. (MSL Rover can land on surfaces steeper and rockier than any prior Mars lander.) MSL can land on slopes as steep as 20 deg (or more) and can land on 50 cm high rocks. Even MER and MPF could not do that it's first bounce.

Just one last question: - Does this mean that the MSL rocker-bogie suspension system will be up and running at the moment of touchdown? Outstretched wheels ready to absorb the impact as best possible? Wheel position instantaneously changing to accommodate a possible big rock?

For future, heavier landers, it could, I guess, be worthwhile to beef up the rocker-bogie suspension for that one-off event. The stresses of landing and roving are so very different, it would be less than optimal to have to over-design the whole rocker-bogie for just that one single forceful bump. - Could it maybe be done with cheap and light one-time compression "sticks" under the main body or inserted into the rocker-bogie structure, to fall away after the initial jolt? Not replacing but supplementing the wheels. I am thinking of small versions of the ingenious Apollo LM legs that were designed to handle just one single compression by collapsing metal foil.

- If you say the weight is better spent on a perfecting soft-landing procedures I won't argue though!

Thanks again for all the replies, I am glad this thread got going again!

[centsworth_II]

Just one last question: - Does this mean that the MSL rocker-bogie suspension system will be up and running at the moment of touchdown?

It sounds like it from this:
"During powered descent, the vehicle uses radar and its propulsion system to control position and velocity. At approximately 20m above the surface (as measured by the radar), the rover is lowered on a tether from the propulsion system (known as the descent stage) in a 'sky crane' configuration and placed directly on the martian surface with its mobility system (i.e., wheels and suspension) fully deployed." http://marsoweb.nas.nasa.gov/landingsites/...uide_v4.5.1.pdf

[imipak]

The video of the tether / bridle / rappel tests that Doug posted earlier in the thread mentions tests of landing on a simulated rock. However now I come to watch it again, and going on the appearance of the test mass, those are tests of the bridle mechanism alone, rather than the rover wheels and suspension system. I can't see how the force of the impact on the wheels and bogies would be any greater for landing on an uneven, rocky surface, than for landing on a flat one, though?

[hendric]

If you are landing on a smooth surface, all three wheels on one side encounter the ground at essentially the same time. If one of your wheels hits a 50cm boulder on a 20 degree slope, that wheel will be moving upwards, pushing the rest of the wheels down, making them hit the ground "harder". Plus, the bogey linkages will be in a different configuration, putting stress in different places etc. Take a toy car and hold it horizontal, then tap it against a table. Now put something under one side and do it again, and you'll see that the opposite side is coming down faster than the rest of the car, and taking on more stress than before during impact.