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NASA's Own Sky Crane

12/03/2006 1:26 PM

"Like its namesake, the Sikorsky S-64 Skycrane heavy-lift helicopter, NASA's Sky Crane carrier platform will hover above its drop site—albeit with retrorockets rather than rotor blades—and lower its payload, the compact car-sized MSL rover, to the surface using a winch and tether. As soon as the rover is ready to roll, the tether connection will be severed and the Sky Crane will fly off and crash land a short distance away." (Report by Space.com).

The main reasons for this new Mars landing concept are:

i) the "car-sized" MSL rover is too heavy for the airbag method used for the present Mars Rovers;

ii) the direct soft landing approach is considered too risky, as shown by the Mars Polar Lander failure;

iii) the difficulty in getting a rover with all wheels on soil from a lander with landing feet.

Read more here. What do you think - good idea, or not?

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#1

Re: NASA's Own Sky Crane

12/03/2006 11:05 PM

This would weigh more than the earlier bouncer, but at 1600 pounds would have a large weight penalty if they made it bounce land. The rocket concept also has a high weight penalty, but it might be a reasonable tradeoff for the higher degree of confidence.

They will need to survey the site with great precision. Possibly a millimeter radar would work, it would penentrate the mars air OK.

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#2

Re: NASA's Own Sky Crane

12/04/2006 3:06 AM

This seems unpractical to me. Why would you suffer the payload penalty to ship a one shot 'sky crane' and a Lander? You have to be thinking totally separate operating systems, fuel load, chassis construction, lifting gear etc, all for a piece of kit that has one use. Keep it simple! This sounds like someone's Baby, and their not prepared to look at a more sensible solution. Surely the talent NASA has got could come up with a way to safely land the Rover? If not, maybe their the wrong guys to go………………….?

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#3
In reply to #2

Re: NASA's Own Sky Crane

12/04/2006 5:54 AM

I would tend to agree. To me trying to get something to hover while it lowered a rover to the ground would use more fuel that something that landed then lowered the rover to the ground.

Something that comes to mind is to build the rover so it's the spacecraft, lander and rover all one then attach a propulsion package to it. Once the thing is safely on the ground you can then ditch the propulsion part, reprogram the computer from earth for exploration and go exploring.

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#7
In reply to #3

Re: NASA's Own Sky Crane

12/05/2006 2:07 AM

Right! And what about the winds?

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#4
In reply to #2

Re: NASA's Own Sky Crane

12/04/2006 10:45 AM

It's not really that different from a conventional lander. It doesn't really sit there "hovering" likie a helicopter, but uses rockets to slow it's decent. The only difference between this and landing a lander/rover combo is the way the rover is released from the lander.

From the article: (http://www.space.com/businesstechnology/061129_msl_skycrane.html)

Like NASA's two stationary Viking landers of the 1970s, the MSL will rely on parachutes to slow its fall before the eight Viking-class thrusters on the Sky Crane landing system ignite at 1,000 meters above the surface, providing a controlled descent. At 35 meters, the Sky Crane will begin lowering the rover on a tether—similar to the way the Sikorsky S-64 delivers underslung payloads—as it continues its descent. When the rover's wheels touchdown, the tether is severed and the Sky Crane platform flies off to land 500 meters to 1000 meters away, Steltzner said.

and, regarding the more conventional approach:

Steltzner said landing on a set of legs is a tricky proposition even if everything goes right. For starters, he said, there are stability issues galore as a top-heavy lander approaches touchdown, its propulsion system on notice to shut down a second or so before the legs make contact with the ground.

Failure of any of the thrusters to cease firing at just the right time could send the lander hopping across the surface, as happened with NASA's Surveyor robotic lunar lander in 1967.

Getting a rover off a legged lander after touchdown poses additional challenges, Steltzner said. Ramps are customarily used, but there is no guarantee that the martian terrain and an imprecise landing will not conspire to deny the rover a safe path to the surface. On the 1996 Mars Pathfinder mission, for example, only one of the landing platform's two ramps opened onto a clear path for the tiny Sojourner rover. NASA could have just as well found both paths blocked.

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#8
In reply to #4

Re: NASA's Own Sky Crane

12/05/2006 2:10 AM

Okay. Then why not just drop it and let it bounce...from a lower-altitude drop point?

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#9
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Re: NASA's Own Sky Crane

12/05/2006 10:13 AM

That doesn't address the issue of not being able to get the ramps down to let the rover loose. But it seems like a reasonable approach otherwise. But now you've got three items to fly to Mars, the lander, the rover, and the rover's bouncer.

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#5

Re: NASA's Own Sky Crane

12/04/2006 6:08 PM

I would think that for all that weight, they could come up with an airbag-like approach, but make the airbag a helium balloon - get it past any entry slow-down challenges, then deploy a blimp to act as the sky crane and drop the empty helium tank (ballast)?

That way NASA has 'all day' to pick a place to float over to and set down, and when the tether is released, the blimp floats off to land elsewhere...or goes back up high to use as a radio/signal transceiver platform.

Could NASA contract to develop the top surface with a flexible, thin-film solar cell using something like XsunX process, and keep a long-term satellite-like signal relay powered and going for a long service life?

Just a thought...

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#6
In reply to #5

Re: NASA's Own Sky Crane

12/04/2006 6:13 PM

Mars has such a low density atmosphere that a balloon would need to be huge to carry much payload.

Even parachures are problematical and give a far higher rate of fall than on earth, which is why they went to the bouncing method.

I suspect this is why they went to the rocket based floater so they could have a 500 foot cable that would keep the exhaust plume away from the dusty ground.

With enough tests and reliability assessments, these sky cranes may well prove to be a good method

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#10
In reply to #6

Re: NASA's Own Sky Crane

12/05/2006 10:18 AM

As the article says, this is a technology that has potential for other places, especially the moon, where low gravity makes it easier to accomplish, and where the issues with electrostatic moon dust make avoiding a dust cloud even more important. This will be important when the lunar polar moon base is established and you have supplies coming in every month - you need a way to land them close, accurately, and without coating everything with dust.

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Guru
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#11
In reply to #10

Re: NASA's Own Sky Crane

12/05/2006 1:24 PM

Hi bhankiii, yep, I tend to agree with your assessment. It is much easier to lower a rover from underneath a hovering 'helicopter' than from the same helicopter on the tarmac!

With good radio altimeters and SARs (Synthetic Aperture Radars), a fairly safe landing ground should not be too difficult to detect. And after all, you need only one direction to be 'unblocked' to make a rover drive off and explore...

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