Author Topic: Skycrane: Way to go or one off experiment  (Read 13027 times)

Offline alexterrell

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Skycrane: Way to go or one off experiment
« on: 08/06/2012 03:00 pm »
Sorry if this is discussed elsewhere- but I couldn't find it.

Skycrane method is now "proven" for landing 1 ton on the surface of Mars.

Is this a feasible technique for 10 tons.

What is the a mass penalty to this technique? It must mean hovering for 20 seconds or so using 6 seconds of Isp.

Why is this better than putting the thrusters on the side, and leaving them there?

Offline Jim

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Re: Skycrane: Way to go or one off experiment
« Reply #1 on: 08/06/2012 04:38 pm »
Sorry if this is discussed elsewhere- but I couldn't find it.

Skycrane method is now "proven" for landing 1 ton on the surface of Mars.

Is this a feasible technique for 10 tons.

What is the a mass penalty to this technique? It must mean hovering for 20 seconds or so using 6 seconds of Isp.

Why is this better than putting the thrusters on the side, and leaving them there?

It is useful for other rovers.  It doesn't hover for 20 seconds, only couple.

It separates the lander from the payload. 

Offline pathfinder_01

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Re: Skycrane: Way to go or one off experiment
« Reply #2 on: 08/06/2012 09:15 pm »

Why is this better than putting the thrusters on the side, and leaving them there?

 For MSL it was about not contaminating the landing area with rocket exhaust. i.e. They wanted to reduce that.

Online ugordan

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Re: Skycrane: Way to go or one off experiment
« Reply #3 on: 08/06/2012 09:17 pm »
For MSL it was about not contaminating the landing area with rocket exhaust. i.e. They wanted to reduce that.

That wasn't the primary consideration. It was how to deliver a rover of this size most effectively to the surface.

Offline alexterrell

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Re: Skycrane: Way to go or one off experiment
« Reply #4 on: 08/06/2012 09:41 pm »
For MSL it was about not contaminating the landing area with rocket exhaust. i.e. They wanted to reduce that.

That wasn't the primary consideration. It was how to deliver a rover of this size most effectively to the surface.
I can understand the contamination issue - but since the Rover is going to drive off for miles, so what?

It's not obvious why this is most efective method.


Offline alexterrell

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Re: Skycrane: Way to go or one off experiment
« Reply #5 on: 08/06/2012 09:44 pm »
Sorry if this is discussed elsewhere- but I couldn't find it.

Skycrane method is now "proven" for landing 1 ton on the surface of Mars.

Is this a feasible technique for 10 tons.

What is the a mass penalty to this technique? It must mean hovering for 20 seconds or so using 6 seconds of Isp.

Why is this better than putting the thrusters on the side, and leaving them there?

It is useful for other rovers.  It doesn't hover for 20 seconds, only couple.

It separates the lander from the payload. 
OK. An alternative is to land a crane with rigid legs and the payload then just drives off.

Then you've got the mass of the legs to consider. With curiosity you have no leg mass, but you have some extra fuel for hovering.

From the pictures it looks like curiosity was lowered 10m or so - I'd have guessed at 1m/s, then some time to check and break the cables?

I'm sure there are some advanced simulation trade-offs that show this was the best method for curiosity.

Would it be the best method for a 10 ton manned rover? Would it be the best method for everything?

NASA manned spaceflight seems very conservative and go for traditional lander shapes with payload above the engines. Then you have the issue of lowering cargo down from a great height. Even the Lockheed Martin 2006 "horizontal" lander concept seems a bit risqué for NASA. Will the skycrane concept transfer to manned spaceflight?
« Last Edit: 08/06/2012 09:49 pm by alexterrell »

Online ugordan

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Re: Skycrane: Way to go or one off experiment
« Reply #6 on: 08/06/2012 09:47 pm »
It's not obvious why this is most efective method.

30:17 - 33:27 into this video: http://www.youtube.com/watch?v=SwXe_X4UKoM
« Last Edit: 08/06/2012 09:50 pm by ugordan »

Offline alexterrell

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Re: Skycrane: Way to go or one off experiment
« Reply #7 on: 08/06/2012 09:54 pm »
It's not obvious why this is most efective method.

30:17 - 33:27 into this video: http://www.youtube.com/watch?v=SwXe_X4UKoM
Thanks, looked at this:

Legs: Unstable
Airbags: Not scalable

How would be this be different for a manned hab module?

Offline spectre9

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Re: Skycrane: Way to go or one off experiment
« Reply #8 on: 08/06/2012 11:26 pm »
The main reason this doesn't scale is the ballistic coefficient of the whole entry vehicle. That is the descent aero shell after it separates from the cruise stage.

It would not slow to Mach 2 and the parachute would not work if it was any heavier, it would disreef . You would need to use supersonic retro propulsion which would blow out the mass itself causing bloat to the whole system.

Inflatable decelerators or just beefing up propulsive systems are the next step besides the obvious of scaling up the heat shield diameter but that would be very complicated and expensive.

Offline Jim

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Re: Skycrane: Way to go or one off experiment
« Reply #9 on: 08/06/2012 11:47 pm »

1.  OK. An alternative is to land a crane with rigid legs and the payload then just drives off.

2. Then you've got the mass of the legs to consider. With curiosity you have no leg mass, but you have some extra fuel for hovering.

From the pictures it looks like curiosity was lowered 10m or so - I'd have guessed at 1m/s, then some time to check and break the cables?

3.Would it be the best method for a 10 ton manned rover? Would it be the best method for everything?


1.  Extra weight and same risk

2.  No extra fuel.  The same amount would be used just to go the remaining distance to the surface

3.  No, this is not for manned systems, but unmanned rovers and some platforms

Offline Go4TLI

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Re: Skycrane: Way to go or one off experiment
« Reply #10 on: 08/06/2012 11:53 pm »
For MSL it was about not contaminating the landing area with rocket exhaust. i.e. They wanted to reduce that.

That wasn't the primary consideration. It was how to deliver a rover of this size most effectively to the surface.
I can understand the contamination issue - but since the Rover is going to drive off for miles, so what?

It's not obvious why this is most efective method.



Because now the rover is saddled with the landing equipment, which is no longer needed, and is just extra mass.  The design and operations team was very careful on reducing mass so as it not be too heavy and potentially sink or get stuck in different terrains.

Offline Sparky

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Re: Skycrane: Way to go or one off experiment
« Reply #11 on: 08/07/2012 12:06 am »
So, a slightly different question is, are there any other places on the solar system where a skycrane would also be a good EDL technique, or will Mars be the only place where we see this happen?

Offline savuporo

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Re: Skycrane: Way to go or one off experiment
« Reply #12 on: 08/07/2012 12:07 am »
OK, how about a concrete example. Could Skycrane deliver components of MSR to the surface ? Whats the smallest reasonable design for MAV so far ? Could you do it in 2 or 3 landed pieces ?
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Offline Go4TLI

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Re: Skycrane: Way to go or one off experiment
« Reply #13 on: 08/07/2012 12:14 am »
Could Skycrane deliver components of MSR to the surface

Who or what is gonna assemble them?

Offline savuporo

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Re: Skycrane: Way to go or one off experiment
« Reply #14 on: 08/07/2012 12:16 am »
Could Skycrane deliver components of MSR to the surface

Who or what is gonna assemble them?
I said nothing about assembly. IIRC the last reference 3-launch MSR mission required 2 rovers to be landed on surface, with the second one being in one payload with MAV
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Offline Go4TLI

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Re: Skycrane: Way to go or one off experiment
« Reply #15 on: 08/07/2012 12:28 am »
Could Skycrane deliver components of MSR to the surface

Who or what is gonna assemble them?
I said nothing about assembly. IIRC the last reference 3-launch MSR mission required 2 rovers to be landed on surface, with the second one being in one payload with MAV

Ok, "components" imples something else. 

So the answer is it depends.  If separate vehicles working together for some integrated mission objective can be landed in this method for the concept of operations envisioned then it can be evaluated and traded along with other methods to give the lowest risk technical solution within acceptable cost and schedule targets.

Online FinalFrontier

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Re: Skycrane: Way to go or one off experiment
« Reply #16 on: 08/07/2012 12:29 am »
Sorry if this is discussed elsewhere- but I couldn't find it.

Skycrane method is now "proven" for landing 1 ton on the surface of Mars.

Is this a feasible technique for 10 tons.

What is the a mass penalty to this technique? It must mean hovering for 20 seconds or so using 6 seconds of Isp.

Why is this better than putting the thrusters on the side, and leaving them there?



If your landing rovers or sensitive data probes that have issues with dust kicked up by rocket decent stages sky crane is the ideal method.


But for large payloads, like say, pre-built habitation modules for manned stays, rocket powered decent all the way down is the ideal method.


No need to add complexity if you don't have a need for it, but sky crane may be used in the future for things that don't like dust.
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Offline MarsInMyLifetime

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Re: Skycrane: Way to go or one off experiment
« Reply #17 on: 08/07/2012 12:32 am »
Isn't "Descent Stage" the preferred name of the traction unit itself, and "sky crane" an adjective for the manner in which it maneuvers its load? It needs a better name down the road; descent operations aren't its only role. Has anyone in the engineering community suggested just calling the conceptual thing a tractor or tug to acknowledge its wider applicability and to sidestep the trademark connotations of Sky Crane?
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Offline LegendCJS

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Re: Skycrane: Way to go or one off experiment
« Reply #18 on: 08/07/2012 12:51 am »
Sorry if this is discussed elsewhere- but I couldn't find it.

Skycrane method is now "proven" for landing 1 ton on the surface of Mars.

Is this a feasible technique for 10 tons.

What is the a mass penalty to this technique? It must mean hovering for 20 seconds or so using 6 seconds of Isp.

Why is this better than putting the thrusters on the side, and leaving them there?



If your landing rovers or sensitive data probes that have issues with dust kicked up by rocket decent stages sky crane is the ideal method.


But for large payloads, like say, pre-built habitation modules for manned stays, rocket powered decent all the way down is the ideal method.


No need to add complexity if you don't have a need for it, but sky crane may be used in the future for things that don't like dust.


I was saying this earlier, but now I disagree.  Mars has global dust storms, if dust is a problem you are screwed before you start.

The MSL landing technique is about easy egress and stability of touchdown contact.  There is a very informative lecture that cured me of the "its all about being low dust" delusion located here:

http://blip.tv/scvtv/scvtv-com-8-20-2009-nasa-jpl-von-karman-lecture-from-legs-to-wheels-mars-science-laboratory-s-bizarre-landing-system-pt-1-3253827
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Offline kkattula

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Re: Skycrane: Way to go or one off experiment
« Reply #19 on: 08/07/2012 04:42 am »

...
The MSL landing technique is about easy egress and stability of touchdown contact.  There is a very informative lecture that cured me of the "its all about being low dust" delusion located here:

http://blip.tv/scvtv/scvtv-com-8-20-2009-nasa-jpl-von-karman-lecture-from-legs-to-wheels-mars-science-laboratory-s-bizarre-landing-system-pt-1-3253827

Great lecture, and from that and the video linked earlier, it's nothing to do with the dust. It's all about:

  Stability on uncertain terrain
  Rocket control at touchdown
  Exhaust plume pressure effects due to ground reflection
  Egress of the lander

I remember Armadillo had to do some tricky things to get their VTVL vehicles to handle the instant change of dynamics when the first leg touched.

When you watch the lecture above, you reallize that Pathfinder and MER did something similar. Lowering the rover air-bag capsule on a cable below the descent stage.  They were just dropped at a small, less controlled height above the ground. Hence the need for air bags.

With MSL, they improved the fine altitude control and radar sensing on the descent stage to the point where it could gently place the suspended payload on a nice looking piece of ground.

More an evolutionary change than a revolutionary one.



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