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SLS / Orion / Beyond-LEO HSF - Constellation => Missions To Mars (HSF) => Topic started by: alexterrell on 08/06/2012 03:00 pm

Title: Skycrane: Way to go or one off experiment
Post by: alexterrell 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?
Title: Re: Skycrane: Way to go or one off experiment
Post by: Jim 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. 
Title: Re: Skycrane: Way to go or one off experiment
Post by: pathfinder_01 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: ugordan 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: alexterrell 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.

Title: Re: Skycrane: Way to go or one off experiment
Post by: alexterrell 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?
Title: Re: Skycrane: Way to go or one off experiment
Post by: ugordan 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
Title: Re: Skycrane: Way to go or one off experiment
Post by: alexterrell 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?
Title: Re: Skycrane: Way to go or one off experiment
Post by: spectre9 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Jim 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
Title: Re: Skycrane: Way to go or one off experiment
Post by: Go4TLI 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Sparky 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?
Title: Re: Skycrane: Way to go or one off experiment
Post by: savuporo 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 ?
Title: Re: Skycrane: Way to go or one off experiment
Post by: Go4TLI on 08/07/2012 12:14 am
Could Skycrane deliver components of MSR to the surface

Who or what is gonna assemble them?
Title: Re: Skycrane: Way to go or one off experiment
Post by: savuporo 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
Title: Re: Skycrane: Way to go or one off experiment
Post by: Go4TLI 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: FinalFrontier 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.
Title: Re: Skycrane: Way to go or one off experiment
Post by: MarsInMyLifetime 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?
Title: Re: Skycrane: Way to go or one off experiment
Post by: LegendCJS 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
Title: Re: Skycrane: Way to go or one off experiment
Post by: kkattula 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.


Title: Re: Skycrane: Way to go or one off experiment
Post by: tj on 08/07/2012 04:51 am
Here are some JPL design trades on the use of the sky crane.

6/28/2010. The MSL SkyCrane Landing. Architecture. A GN&C Perspective. Miguel San Martin. Jet Propulsion Laboratory, California Institute of Technology .

www.planetaryprobe.eu/IPPW7/proceedings/.../Session5/pr478.pdf

6.4MB file

Source: public web
Title: Re: Skycrane: Way to go or one off experiment
Post by: kkattula on 08/07/2012 05:01 am
I can't see why this wouldn't scale up to larger payloads. AIUI, the scale issues would tend to be more about entry shield diameter, and parachute size.

Bigger engines, more fuel and stonger cables, are minor engineering issues, once you've cracked the basic problem.

For habitats, (and other cargo), for a manned mission, it would still be handy for the landing gear to have wheels.  Even if the payload isn't a self-powered rover, it could still be towed to a convenient location, in a surface rendezvous scenario.

This means everything doesn't have to be landed in one or two large payloads. Several smaller ones can be pre-deployed and gathered together. Landing 1 ton at a time might be a bit small, but 5 to 10 tons, looks reasonable.
Title: Re: Skycrane: Way to go or one off experiment
Post by: kkattula on 08/07/2012 05:05 am
Here are some JPL design trades on the use of the sky crane.

6/28/2010. The MSL SkyCrane Landing. Architecture. A GN&C Perspective. Miguel San Martin. Jet Propulsion Laboratory, California Institute of Technology .

www.planetaryprobe.eu/IPPW7/proceedings/.../Session5/pr478.pdf

6.4MB file

Source: public web


Link doesn't work, try: http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session5/pr478.pdf
Title: Re: Skycrane: Way to go or one off experiment
Post by: spectre9 on 08/07/2012 05:08 am
I do wonder if more than 1 of these parachutes can be used at once now it's been tested on Mars.

Good tech should be used again.  :)
Title: Re: Skycrane: Way to go or one off experiment
Post by: tj on 08/07/2012 05:20 am
37 Tons to Mars

High Mass Mars Entry, Descent, and Landing Architecture Assessment
http://www.ssdl.gatech.edu/papers/conferencePapers/AIAA-2009-6684.pdf

PublicWeb
Title: Re: Skycrane: Way to go or one off experiment
Post by: alexterrell on 08/09/2012 11:12 am
37 Tons to Mars

High Mass Mars Entry, Descent, and Landing Architecture Assessment
http://www.ssdl.gatech.edu/papers/conferencePapers/AIAA-2009-6684.pdf

PublicWeb
This paper shows the entry and descent requirements for a 37 ton payload, but not the best landing technique.

Would a skycrane still be the way to land this? The alternatives are:

- You land on top of your fuel tanks and use a crane to get down.
- You land underneath the fuel tanks which are supported by legs and the engines are out wide.
- You have have a descent rocket stage which you dump just prior to landing and landing is done with very small fuel tanks.

The skycrane literature suggests that if you know your surface (as landing at a base) to don't need skycrane.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Jim on 08/09/2012 11:21 am
I do wonder if more than 1 of these parachutes can be used at once now it's been tested on Mars.

Good tech should be used again.  :)

no, because they would interfere with each other.  Not the same as subsonic parachutes.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Robotbeat on 08/10/2012 03:20 pm
I do wonder if more than 1 of these parachutes can be used at once now it's been tested on Mars.

Good tech should be used again.  :)

no, because they would interfere with each other.  Not the same as subsonic parachutes.
Subsonic ones can also interfere with each other, too, of course.

One of the guys who modeled the MSL parachute (who was my professor) also did a lot of work with the interaction between multiple parachutes. I agree it's a complicated problem and is probably best solved by using a bigger monolithic parachute.

Another way to solve it is to accept a higher terminal velocity, using more delta-v with the skycrane maneuver (for larger payloads, it may make sense to use biprop, though for smaller payloads the added dry mass of a biprop system would outweigh the Isp advantage).
Title: Re: Skycrane: Way to go or one off experiment
Post by: manboy on 08/10/2012 05:27 pm
Is this a feasible technique for 10 tons.
No, its not scalable. But the Skycrane could be used for future missions.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Robotbeat on 08/10/2012 06:13 pm
Is this a feasible technique for 10 tons.
No, its not scalable. But the Skycrane could be used for future missions.
Based on what do you say that the sky crane maneuver is not scalable to 10 tons?

If you're not an established expert (and even if you are), you should provide a reason.

The heatshield may not be scalable, the parachute might not be scalable (other things being equal), but why not the skycrane maneuver? I see no reason.
Title: Re: Skycrane: Way to go or one off experiment
Post by: alexterrell on 08/11/2012 07:38 pm
Is this a feasible technique for 10 tons.
No, its not scalable. But the Skycrane could be used for future missions.
Based on what do you say that the sky crane maneuver is not scalable to 10 tons?

If you're not an established expert (and even if you are), you should provide a reason.

The heatshield may not be scalable, the parachute might not be scalable (other things being equal), but why not the skycrane maneuver? I see no reason.
I can't see any limit to the scalability of the skycrane manoeuvre (tricky word to spell!).

However, at some point you would no longer need it for stability. Legs might be preferable at that point.

In theory you could lower an Ocean liner this way. 
Title: Re: Skycrane: Way to go or one off experiment
Post by: ClaytonBirchenough on 05/24/2013 03:08 pm
I was wondering what the MSL payload to around -7km MOLA would be. MSL landed approximately 900kg to -4.4 km MOLA. So my question is what would the payload be if MSL were to land at an area that was -7km MOLA?
Title: Re: Skycrane: Way to go or one off experiment
Post by: Russel on 06/07/2013 02:02 pm
I was wondering what the MSL payload to around -7km MOLA would be. MSL landed approximately 900kg to -4.4 km MOLA. So my question is what would the payload be if MSL were to land at an area that was -7km MOLA?

Which raises the interesting question of where on Mars can you land a rover that's relatively low in altitude but still feasible to drive the rover (remotely) to somewhere interesting that people might land?

Where I'm wondering about sky cranes is in landing a rover that carries methane fuel plus oxygen plant. And could it manage a long traverse on the Carbon monoxide fuel it would generate as a byproduct.
Title: Re: Skycrane: Way to go or one off experiment
Post by: MickQ on 06/10/2013 12:23 am
Would Hellas not be an interesting place to land ???  2300 klm across, high probability of caves, ancient rivers flowed into the basin and the rock that made it in the first place.

Mick.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Russel on 06/14/2013 04:25 pm
A couple of thoughts here.

Suppose we had a Mars lander/ascent vehicle that was brought down to the bare minimum in mass. Say, 5 tonnes dry mass, with crew and life support. Such a vehicle would require in the order of 13 tonnes of methane/lox fuel for ascent.

That's roughly 3 tonnes of methane.

Suppose also that we take the attitude that we don't want to do any complex synthesis for fuel for ascent, but we'll simply produce oxygen - which is 77 percent of the mass needed.

Now, getting that 3 tonnes of methane landed on Mars is the issue. That and a simple oxygen production plant. You can see where I'm going here.

Its an ISPP on wheels with a methane tank. All up about 5 tonnes landed mass.

That, I think, is a candidate for an upscaled skycrane landing.

The other thing that arises is, what do we do with the used skycrane(s)? I've yet to think of a use for one that makes overall sense - like an ascent vehicle. But with a bit of good design they could make for good spare parts.
Title: Re: Skycrane: Way to go or one off experiment
Post by: MickQ on 06/15/2013 07:35 am
As I understand it, the Skycrane was designed to land a scientific payload on ground that was not contaminated by the rocket exhaust.  A manned lander or ISRU unit would not need this level of care and may actually benefit from a cleaner landing site.

Mick.
Title: Re: Skycrane: Way to go or one off experiment
Post by: Jim on 06/15/2013 12:51 pm
As I understand it, the Skycrane was designed to land a scientific payload on ground that was not contaminated by the rocket exhaust.  A manned lander or ISRU unit would not need this level of care and may actually benefit from a cleaner landing site.

No, that was only a benefit.  The Skycrane technique (it is not a vehicle) eliminated the need to roll off the lander. It can be used to place any package on the surface.  with that said, it is not good for a manned lander
Title: Re: Skycrane: Way to go or one off experiment
Post by: Russel on 06/15/2013 01:54 pm
As I understand it, the Skycrane was designed to land a scientific payload on ground that was not contaminated by the rocket exhaust.  A manned lander or ISRU unit would not need this level of care and may actually benefit from a cleaner landing site.

Mick.

That has me scratching my head. When Curiosity landed they still ended up with bits of gravel on top of it. If I remember correctly, one of the reasons for hanging it from a cable was also stability - the rover could find its own level, whilst the skycrane part could remain with a vertical attitude.

It would still be an advantage to use the landing engine to sweep the site. One option of course is to have the skycrane firmly attached, come in low, perform a "sweep" operation (basically rotate) and then ascend somewhat and then lower the payload.