Author Topic: SNC outline Dream Chaser's Enterprise-style landing test approach  (Read 33449 times)

Offline Lobo

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Can't take the spinup and scuffing from landing.

Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.

Thinking outside the box.

You think wings are useless in space? 

I do.

They are useful for catching orbital debris and micrometeors on the TPS.

;-)

Offline Rocket Science

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Can't take the spinup and scuffing from landing.

Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.

Thinking outside the box.

You think wings are useless in space? 

I do.

They are useful for catching orbital debris and micrometeors on the TPS.

;-)
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Offline vulture4

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The environment for the Shuttle tires (conventional aircraft tires inflated with nitrogen) was considered fairly benign. The X-37 uses smaller but otherwise similar tires with 300psi inflation pressure. It had one tire blowout on the first landing but otherwise no problems.

Regarding wings, I realize people have their preferences and aerodynamics may not generate a lot of interest. But the X-37 wings provide a much higher lift to drag ratio than the Dreamchaser's wingless lifting body shape and because it depends much less on body lift the X-37 can utilize a more efficient fuselage shape, with more internal volume, less structural mass, and less internal stress when pressurized. In fact this is why after decades of work with lifting bodies NASA decided to use wings for the Shuttle.

However I think the X-37 has a significant advantage over either the DC or Shuttle because of the long moment arm between its V-tail surfaces and the center of pressure, giving it greater tolerance for CG location (always a concern with the Shuttle) and much better pitch control when landing in variable or suboptimal winds, which often present themselves.

The question of wings vs parachute for landing is not a matter of mass, but of cost. A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes. The actual energy (i.e. fuel) to lift the wings into space costs almost nothing, and the X-37 of course had no foam fragments to damage its thermal tiles.

For a given booster lift capacity, a capsule will have more payload mass and volume than a runway lander, so as long as the booster is thrown away the capsule will have a cost or payload advantage. But if and when fully reusable boosters are available the initial booster cost will have little impact and one can simply choose a slightly larger booster. The easier reuse of the runway lander will then be a significant advantage.
« Last Edit: 07/24/2012 05:55 AM by vulture4 »

Offline baldusi

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Err... lifting bodies have more internal volume, they are "fatter". The Shuttle had wings because of cross range consideration. Read the history of the discussions.

Offline Rocket Science

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Err... lifting bodies have more internal volume, they are "fatter". The Shuttle had wings because of cross range consideration. Read the history of the discussions.
He doesn’t get it... He keeps repeating the same things over and over again on all the Dream Chaser and X-37 threads...
« Last Edit: 07/24/2012 02:49 PM by Rocket Science »
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Offline FinalFrontier

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The environment for the Shuttle tires (conventional aircraft tires inflated with nitrogen) was considered fairly benign. The X-37 uses smaller but otherwise similar tires with 300psi inflation pressure. It had one tire blowout on the first landing but otherwise no problems.

Regarding wings, I realize people have their preferences and aerodynamics may not generate a lot of interest. But the X-37 wings provide a much higher lift to drag ratio than the Dreamchaser's wingless lifting body shape and because it depends much less on body lift the X-37 can utilize a more efficient fuselage shape, with more internal volume, less structural mass, and less internal stress when pressurized. In fact this is why after decades of work with lifting bodies NASA decided to use wings for the Shuttle.

However I think the X-37 has a significant advantage over either the DC or Shuttle because of the long moment arm between its V-tail surfaces and the center of pressure, giving it greater tolerance for CG location (always a concern with the Shuttle) and much better pitch control when landing in variable or suboptimal winds, which often present themselves.

The question of wings vs parachute for landing is not a matter of mass, but of cost. A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes. The actual energy (i.e. fuel) to lift the wings into space costs almost nothing, and the X-37 of course had no foam fragments to damage its thermal tiles.

For a given booster lift capacity, a capsule will have more payload mass and volume than a runway lander, so as long as the booster is thrown away the capsule will have a cost or payload advantage. But if and when fully reusable boosters are available the initial booster cost will have little impact and one can simply choose a slightly larger booster. The easier reuse of the runway lander will then be a significant advantage.

All wrong.
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Offline daveklingler

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The environment for the Shuttle tires (conventional aircraft tires inflated with nitrogen) was considered fairly benign.

Are you sure?  I seem to remember that a fair amount of engineering was devoted to the tires.  They had to endure extra heat, vacuum, and a high-speed landing.  Ditto with the gear.  We may be saying the same thing, i.e. you might mean "relatively benign", but I seem to remember that the problem of tires for a winged space vehicle is nontrivial.

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Regarding wings, I realize people have their preferences and aerodynamics may not generate a lot of interest. But the X-37 wings provide a much higher lift to drag ratio than the Dreamchaser's wingless lifting body shape

A little higher, anyway, 4.5 versus 4. And here you'll note that DC uses a smaller fairing.  Increase the fairing size and nudge the vehicle size up a little bit and you could increase L/D by quite a bit pretty cheaply, if you thought it was necessary.

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and because it depends much less on body lift the X-37 can utilize a more efficient fuselage shape, with more internal volume, less structural mass, and less internal stress when pressurized.

Actually, it's the other way around.  Part of the advantage of a lifting body is that the flying bathtub can generate lift while providing more internal volume and less structural mass.  Internal stress is equal, or maybe I'm not understanding what you mean by internal stress.

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In fact this is why after decades of work with lifting bodies NASA decided to use wings for the Shuttle.

Dale Reed's opinion was that when push came to shove winged designs were always chosen because they had been chosen before, i.e. they were well inside the comfort zone.

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However I think the X-37 has a significant advantage over either the DC or Shuttle because of the long moment arm between its V-tail surfaces and the center of pressure, giving it greater tolerance for CG location (always a concern with the Shuttle) and much better pitch control when landing in variable or suboptimal winds, which often present themselves.

I could be wrong, but I thought about this after I read it and decided that pitch control between the two vehicles was probably about equal or maybe in DC's favor.  Yaw control was more of an issue with early lifting bodies, but that's why DC has a center fin.  DC's pitch stability is better due to the high fin dihedral.

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The question of wings vs parachute for landing is not a matter of mass, but of cost.

Wings versus parafoil is absolutely a matter of mass.  A large portion of an aircraft's mass lies in the wings, especially one that's supersonic (or hypersonic).  The main spar is quite heavy, and the control mechanisms aren't light either. The gear gets heavy when the high-speed landing is figured in, and the main spar gets heavier with the heavy gear.  If the wing is wet, not the case here, the spar gets even more massive, not to mention the weight of the tanks.  The X-38's parafoil was very much a way to achieve a lower stall with less mass.

Max Hunter's observation was that the wings were such a major portion of a spacecraft's weight that by leaving the wings off, one could carry so much extra propellant that vertical landing was possible.

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A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes.

Here again that's the opposite of what's true.  A single center of forward pressure is far simpler to protect than a collection of leading edges and a belly, along with the gear and tires.  That's why capsules really are easier.

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The actual energy (i.e. fuel) to lift the wings into space costs almost nothing, and the X-37 of course had no foam fragments to damage its thermal tiles.

IIRC Hunter told me the mass of the wings can sometimes approach close to 50%.  I've never done a weight trade on a spacecraft, so my opinion isn't informed, but I trust his.

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For a given booster lift capacity, a capsule will have more payload mass and volume than a runway lander, so as long as the booster is thrown away the capsule will have a cost or payload advantage. But if and when fully reusable boosters are available the initial booster cost will have little impact and one can simply choose a slightly larger booster. The easier reuse of the runway lander will then be a significant advantage.

And here's where you get into an argument with the VTVL folks, who will tell you just the opposite.  If cross range is desirable, it's a different story.
« Last Edit: 07/24/2012 05:00 PM by daveklingler »

Offline Lobo

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Wings versus parafoil is absolutely a matter of mass.  A large portion of an aircraft's mass lies in the wings, especially one that's supersonic (or hypersonic).  The main spar is quite heavy, and the control mechanisms aren't light either. The gear gets heavy when the high-speed landing is figured in, and the main spar gets heavier with the heavy gear.  If the wing is wet, not the case here, the spar gets even more massive, not to mention the weight of the tanks.  The X-38's parafoil was very much a way to achieve a lower stall with less mass.

Max Hunter's observation was that the wings were such a major portion of a spacecraft's weight that by leaving the wings off, one could carry so much extra propellant that vertical landing was possible.

Quote
A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes.

Here again that's the opposite of what's true.  A single center of forward pressure is far simpler to protect than a collection of leading edges and a belly, along with the gear and tires.  That's why capsules really are easier.

 

I’ve always liked the parafoil concept.  X-38 seemed to do pretty good with it.   Although, the thing is, with a parafoil, then you really don’t need the lifting body design.  Something like a Gemini capsule with deployable skids should be able to land just fine on a dry lake bed (or maybe a runway), and the capsule can be “flown” in a glide with the parafoil.  Using skids means you don’t need to mess with tires.  And then you can keep the heat shield protected while in orbit (which would have been particularly advantageous for a an Emergency Crew Return Vehicle that would be on the ISS for long periods of time until needed. 
Such a capsule landing horizontally with a parafoil could really be about as reusable as a spaceplane or lifting body.  Especially with a heat shield designed for say 10 reentries (like I think the Pica-X Dragon is?).  Even a reusable space plane needs a lot of TPS work between flights as we saw with the Shuttle, and I’m sure will be the case (although a lesser extent) with Dream Chaser. 
But it gets better efficiency without the wings and control surfaces and large TPS in mass and volume.  The landing skids could actually be such that the bottoms of them are flush with the sidewall of the capsule when retracted, so that they don’t actually need hatches/doors to open to deploy them.  And they could perhaps be spring loaded rather than electric or hydraulic so that they would be pretty reliable.   
The parafoil would need to be rechecked and maybe repaired and sometimes replaced, but I think that would be a pretty minor cost.  They aren’t landing in the ocean like the SRB, Apollo, or Orion chutes.
I think they had a good idea when they designed it for Gemini.  As I understand, the only reason it actually wasn’t implemented, is NASA had made the decision that Gemini wouldn’t continue during Apollo, which had originally been the plan.  Gemini would be a LEO taxi basically.  And would land using a parasail on a dry lake bed, and I think be reusable.  When the decision was made to cancel Gemini and not operate it during Apollo, they didn’t see the need to finish the horizontal landing development.  And in fact, since water recovery would be used for Apollo, it made more sense to keep with that, as it would be better practice for Apollo.  (hopefully I’m remembering that correctly anyway…).

Offline Rocket Science

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Gemini had a Rogallo wing parasail (parafoil) but also a high sink rate…

http://amyshirateitel.com/2011/05/22/losing-rogallo-from-gemini/
« Last Edit: 07/24/2012 08:46 PM by Rocket Science »
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