Skycrane, Innovative landing technology Options

[erwan]

Such a conception with a long cable, whose lenght may be adjusted (radar sensor...) isn't an additional way to control the descent velocity of the rover, on the last meters before touchdown?

[Chmee]

My concern with the Sky Crane concept is that it is not as robust in landing in uncertain terrain. With the MER airbags, almost regardless of where the airbag first lands, it will roll to a more steady/level position. It can be used in a variety of terrains.

Contrast with the Skycrane where landing on the side of a crater or large rock would leave the lander/rover in a dangerous position. This nearly happened with Viking 1 with a very large rock nearby. I can see the Skycrane working well in Meridiani Planum, but would likely fail at the Mars Pathfinder site.

I understand that this new landing concept allows a much larger payload, but I think the risk is much great with such a system.

[cIclops]

Yes. The airbag system worked well and can cope with a more rocky environment. I think MSL will need some scene analysis capability to select a clear landing area or it will have to be restricted to safer and probably less interesting terrain.

Given the importance and cost of MSL, NASA will be looking to reduce risk not increase it which will mean a safer landing system as they want to explore more dangerous areas. It will be fascinating to see how they solve the problem

[Chmee]

Of course, I just thought of this. They could land in a relativley safe area and DRIVE to the rougher area . Heck, the MSL is nuclear powered so it should be able to go much farther (maybe faster?) the the MERs.

But trying to figure out what a relatively safe area to land in from orbit has proven tricky.....

[djellison]

But trying to figure out what a relatively safe area to land in from orbit has proven tricky.....

Until MRO gets there


Doug

[Guest_BruceMoomaw_*]

Well, the airbag system has turned out to have a large array of very serious problems -- which became apparent as soon as Pathfinder flew. (It was reused for the MERs only because those rovers had already been designed and, on balance, it was the cheapest way to get them down to the surface.)

(1) It's alarmingly heavy -- something that became apparent on Pathfinder when they had to use 5 bag layers rather than the two planned one, to prevent the bags from ripping on impact. (The MERs, with their higher weight, produced even bigger troubles in designing non-ripping bags.) It is, in fact, a far heavier system than the more complex full soft-landing systems -- which makes a big difference in launch vehicle costs.

(2) It's extremely vulnerable to dangerous crosswinds. Without that Rube Goldbergian DIMES system that was added literally at the last minute to partioally cancel out horizontal velocity, Spirit might very well not have survived its landing -- and even with that system, this very seriously restricts an airbag system's variety of landing sites.

(3) It does not allow anything like a pinpoint landing, simply because after touchdown the lander is likely to roll for hundreds of meters across the surface (and sometimes over a kilometer). This will make a lot more difference in the near future, when we start trying to make pinpoint precision landings to reach otherwise unattainable but scientifically valuable landing sites immediately surrounded by dangerously rugged terrain. (The fact that a guidance system will be added to Mars landers, starting with MSL, to allow them to actively identify and dodge patches of dangerously rugged terrain during landing also decreases the relative utility of an airbag system in that respect.)

So the widespread trumpeting about the supposed brilliant success and high reliability of the airbag system that we keep hearing from the press is -- as with so many space- and technology-related issues -- based on serious ignorance. (Another spectacular example is the endless blather we keep hearing about the supposed superiority of repairing Hubble as opposed to simply launching a new one -- but that's another story, which I won't get into now.) Regardless of whether Skycrane itself finally proves practical, the sooner we switch to full-fledged throttled-rocket soft landing systems and away from airbags for all but the smallest Mars landers, the better.

[centsworth_II]

...the sooner we switch to full-fledged throttled-rocket soft landing systems and away from airbags for all but the smallest Mars landers, the better.

And if manned missions are the ultimate goal, we might as well start getting experience with powered landings. Can you imagine a manned landing using air bags?

[djellison]

Can you imagine a manned landing using air bags?

Well, Hollywood can.

Doug

[erwan]

Bruce: thanks for your interesting last comments; i understand airbags are now an "out to date technology", adapted for landing of the first martian rovers generation, but not for the future missions; reading the JPL notes Cyclops linked on the first post of that thread, i think we may add to the disavantages you commented:
-Airbags add big volume/geometric constraints on the payload (the tetraed geometry, plus all the harware needed on MERs to deploy before egress)
-maybe the most important one: JPL's engineers argue they couldn't conceive airbags for heavier payload than MER+landing platform.
And obviously your comment, Centsworth II...

[djellison]

Put it this way - the roer was around 185kg. the entry-vehicle (minus cruise stage) was around 800kg

Not ideal really

Anyone got figures for Viking?

Doug

[chris]

From http://nssdc.gsfc.nasa.gov/database/Master...og?sc=1975-083C

The fully fueled orbiter-lander pair had a mass of 3530 kg. After separation and landing, the lander had a mass of about 600 kg and the orbiter 900 kg

[erwan]

Viking entry vehicle (lander + heatshield + chute) was 1193 kg for a 598 kg (fueled) lander.

[erwan]

Chris: our sources are the same; orbiter weight you reported is dry; the orbiter carry around 1400 kg fuel. Thus fueled orbiter account for ~2300 kg in the total mass of 3530kg; the remaining 1193 kg = entry vehicle...

[djellison]

The killer with the Airbag system is the 300+ Kg of lander structure that serves no purpose after deployment I guess.

Doug

[erwan]

Sure you're right, Doug; it's pleasant for me, since the beginning of that thread, to probably better understand the need for skycrane / new EDL technology.