Heat on reentry is only relevant of you dont slow down enough before hitting the denser atmosphere.Admitedly, the problem is structural integrity and heat on reentry...
Space X to build reusable launch vehicle
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GIThruster
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I would think that by weight, a parafoil would provide much more crossrange than small wings and they don't have to be deployed until after all the high-gee tumbling and breaking.
http://kjeldvandruten.3sc.nl/x38.html
http://kjeldvandruten.3sc.nl/x38.html
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis
I was always confused why the X38 would have a parafoil AND a lifting body. It seemed like a stupid concept to me.would think that by weight, a parafoil would provide much more crossrange than small wings and they don't have to be deployed until after all the high-gee tumbling and breaking.
For some reason I do not like parafoils at all. They seem so oldfashioned.
How bout a scissor wing with a KFm-5B foil? The foil would snuggle up right against the side of the cylindrical rocket body and could extend out, rotate 90 degrees and snuggle back against a special ring in the shell. It would taked only a minor amount of volume and when stowed parallel would add little to the overall drag of the rocket. Heck, with this setup, they could have a VERY large cross-range and could glide in slow, flair and land on rocket or even land on skids horizontally. Just a thought.
Parafoils give good crossrange, but if the X-38 parafoil is the biggest ever made then there is a problem. Falcon 9 first stage, even empty, is quite heavier than a X-38 CRV.
Anyhow it seems that decelerating after separation is a bigger problem. To do this they'll need about 2.6 km/s of delta-v.
To take it back to the launch complex much less, under 1 km/s.
And to do the powered landing even less.
By the way, I see another problem. The Merlin 1D has much more thrust than necessary (~63 tf), and you cannot throttle it down under 70%, so if the timing is not perfect, or the altitude well measured, or the estimation of the mass, then the stage could "bounce" instead of land.
With that kind of thrust it should be able to decelerate a 20 t stage at over 2.1 g, that means from 300 m/s to zero in only 14 seconds (or less), and total delta-v < 0.5 km/s.
edit: 70 tf is the Merlin 1D thrust in vacuum, at SL is ~10% less.
Anyhow it seems that decelerating after separation is a bigger problem. To do this they'll need about 2.6 km/s of delta-v.
To take it back to the launch complex much less, under 1 km/s.
And to do the powered landing even less.
By the way, I see another problem. The Merlin 1D has much more thrust than necessary (~63 tf), and you cannot throttle it down under 70%, so if the timing is not perfect, or the altitude well measured, or the estimation of the mass, then the stage could "bounce" instead of land.
With that kind of thrust it should be able to decelerate a 20 t stage at over 2.1 g, that means from 300 m/s to zero in only 14 seconds (or less), and total delta-v < 0.5 km/s.
edit: 70 tf is the Merlin 1D thrust in vacuum, at SL is ~10% less.
"The problem is not what we don't know, but what we do know [that] isn't so" (Mark Twain)
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kunkmiester
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I am afraid any concept with "deploying" wings will have problem with reliability and structural integrity. Forces that have to be transfered with wing-spar will be extreme, it will be hard to do this with fixed set of wings, with wings deploying almost impossible....KitemanSA wrote:How bout a scissor wing with a KFm-5B foil? The foil would snuggle up right against the side of the cylindrical rocket body and could extend out, rotate 90 degrees and snuggle back against a special ring in the shell. It would taked only a minor amount of volume and when stowed parallel would add little to the overall drag of the rocket. Heck, with this setup, they could have a VERY large cross-range and could glide in slow, flair and land on rocket or even land on skids horizontally. Just a thought.
Anyway, I believe that those fixed wings do not need to be big. A couple of meters wingspan and delta planform would do just fine. All that is needed is L/D in 3-4 range and required CL for wing is minimal..
The forces would NOT be extreme if the stage uses its engines to slow down. Then you will have to deal with only low grade forces on the wings.Forces that have to be transfered with wing-spar will be extreme, it will be hard to do this with fixed set of wings, with wings deploying almost impossible....
I also think that you would only need very small wings to get enough cross range. It seems like we only need a glide ratio of 2:1 or 3:1 at most.
When I saw their video I wondered why the second stage used four small thrusters to land when it had a big main restartable engine that, although optimized for vacuum, should work well enough at sea level.Skipjack wrote:That is interesting.The Merlin 1D has much more thrust than necessary (~63 tf), and you cannot throttle it down under 70%
If they cant deep throttle it, how are they going to use it for powered landing?
Now I see, it's too powerful.
"The problem is not what we don't know, but what we do know [that] isn't so" (Mark Twain)
The lifting body is for reentry. High L/D allows the craft to limit reentry Gs, very useful if carrying an injured astronaut. Though higher than 1:1 isn't much use for that purpose reentering from LEO.Skipjack wrote:I was always confused why the X38 would have a parafoil AND a lifting body. It seemed like a stupid concept to me.
For some reason I do not like parafoils at all. They seem so oldfashioned.
The shuttle does not use its engines for breaking though...There is a reason the shuttle drops like a manueverable brick. And I have seen inside the wing structure and roots, it is some very beefy stuff.
From what I understand also the very simillar Dreamchaser wont need a parafoil. The X37b which only has very short, stubby wings does not need one either...The lifting body is for reentry. High L/D allows the craft to limit reentry Gs, very useful if carrying an injured astronaut. Though higher than 1:1 isn't much use for that purpose reentering from LEO.
Hmmm. I thought the smaller engines were just because you cant get enough fine control out of a single engine for a pin point powered landing.When I saw their video I wondered why the second stage used four small thrusters to land when it had a big main restartable engine that, although optimized for vacuum, should work well enough at sea level.
Now I see, it's too powerful.
But you may be right there.
Well, definitely some interesting times ahead there. 2012 promises to be an interesting year for us space geeks. Not as interesting as I would have expected it would be in the 1980ies, but with a little bit of luck, better than the past 30 years...
The requirment for strong wingspar is not derived from reentry situation (after all, you can keep angle of attack at zero during reentry), but the spar has to hold all the weight of craft during any maneouvering. Any turn would put many Gs to the craft.Skipjack wrote:The shuttle does not use its engines for breaking though...There is a reason the shuttle drops like a manueverable brick. And I have seen inside the wing structure and roots, it is some very beefy stuff.