X-37C: plans for a crewed version of the X-37

[Ben the Space Brit]

FWIW, a crew-sized X-37 would need an SLS-sized LV to use this arrangement.

No, there is no fairing on a crew sized X-37

This particular LAS concept would require one.  That's all I'm saying.

[simonbp]

MSL has some attributes in common with an ISS Crew Return Vehicle, but I don't see threads about that.

Holy frak, can you imagine landing on Earth just in a pressure suit with a Skycrane strapped to your back! You'd have to attach a few speakers playing the James Bond theme...

[Garrett]

I doubt the size of the TPS surface makes a huge difference. Both the X-37 and the Dream Chaser are fairly small. Plus, they have the advantage of landing on a runway. I would have thought that capsules were safer because of their LAS.

Can't winged craft have similar LAS to capsules if they're launched on top of the LV?
For me, I always thought that capsules are meant to be safer because they can re-enter off-nominally, i.e. the center of gravity and the capsule shape naturally keeps the the heat shield pointing down even in the event of a guidance system failure. A nominal re-entry is desired for lower g-forces and for landing on target.
A winged craft, on the other hand, needs a perfect re-entry to survive.

Well, that's how I saw it anyway. Am I mistaken?

[savuporo]

I have no idea why this here is under commercial spaceflight, but thats the latest thread i found on X37.
http://spaceports.blogspot.com/2012/03/x-37b-space-plane-game-changing-mission.html


Makes you go hmmmm... its vewy vewy quiet ...

[Dappa]

I have no idea why this here is under commercial spaceflight, but thats the latest thread i found on X37.

Because the latest thread is not always the right one, you meant to post it here:http://forum.nasaspaceflight.com/index.php?topic=24323.465

[vulture4]

I doubt the size of the TPS surface makes a huge difference. Both the X-37 and the Dream Chaser are fairly small. Plus, they have the advantage of landing on a runway. I would have thought that capsules were safer because of their LAS.

Can't winged craft have similar LAS to capsules if they're launched on top of the LV?
For me, I always thought that capsules are meant to be safer because they can re-enter off-nominally, i.e. the center of gravity and the capsule shape naturally keeps the the heat shield pointing down even in the event of a guidance system failure. A nominal re-entry is desired for lower g-forces and for landing on target.
A winged craft, on the other hand, needs a perfect re-entry to survive.

Well, that's how I saw it anyway. Am I mistaken?

The X-37 could use same system as Dragon, just OMS thrusters that can get it clear of the LV and up to gliding speed. You can't watch the test of the Minuteman-sized LAS on the Orion and believe it would work without very precise computer control, so I think an automated runway landing for an X-37 abort is reasonable.

In this vein, lift to drag ratio at touchdown is critical to practical landing. The X-37 is certainly superior to the Dreamchaser in this regard. Dreamchaser has a much lower lift to drag ratio than X-37C. The L/D of the X-37 is about 4.5, the DC is at about 3.5, too low for a safe landing without powered lift.

So why are we so insistent on flying _without_ wings? Why did NASA abandon X-37 and all winged entry vehicles?

[BrightLight]

 Dreamchaser has a much lower lift to drag ratio than X-37C. The L/D of the X-37 is about 4.5, the DC is at about 3.5, too low for a safe landing without powered lift.

Do you have citations or other data showing these L/D ratios? It is my impression that the DC lands un-powered as a glider?

[Jim]

So why are we so insistent on flying _without_ wings? Why did NASA abandon X-37 and all winged entry vehicles?

Because they are not needed for BEO missions.

[BrightLight]

On this site, see dream chaser Q&A thread:
DC L/D of 4.0
HL-20 L/D I thought was also in this range as well, I will see if i can find the citation.
   
Re: Dream Chaser Q&A (including suggestions and improvements)
« Reply #571 on: 05/02/2011 09:01 PM »
   
Interesting Aviation Week story.

Quote

    The Dream Chaser is expected to have a cross-range capability of 1,700 km (1,000 mi.) and with a subsonic lift/drag ratio of 4:0, a “landing will be feasible on 7,000-foot runways,” he says.


That's a pretty good L/D! (joke)

[BrightLight]

I doubt the size of the TPS surface makes a huge difference. Both the X-37 and the Dream Chaser are fairly small. Plus, they have the advantage of landing on a runway. I would have thought that capsules were safer because of their LAS.

Can't winged craft have similar LAS to capsules if they're launched on top of the LV?
For me, I always thought that capsules are meant to be safer because they can re-enter off-nominally, i.e. the center of gravity and the capsule shape naturally keeps the the heat shield pointing down even in the event of a guidance system failure. A nominal re-entry is desired for lower g-forces and for landing on target.
A winged craft, on the other hand, needs a perfect re-entry to survive.

Well, that's how I saw it anyway. Am I mistaken?

The X-37 could use same system as Dragon, just OMS thrusters that can get it clear of the LV and up to gliding speed. You can't watch the test of the Minuteman-sized LAS on the Orion and believe it would work without very precise computer control, so I think an automated runway landing for an X-37 abort is reasonable.

In this vein, lift to drag ratio at touchdown is critical to practical landing. The X-37 is certainly superior to the Dreamchaser in this regard. Dreamchaser has a much lower lift to drag ratio than X-37C. The L/D of the X-37 is about 4.5, the DC is at about 3.5, too low for a safe landing without powered lift.

So why are we so insistent on flying _without_ wings? Why did NASA abandon X-37 and all winged entry vehicles?

Sub-sonic L/D on the HL-20 is well within the 4.0 to 4.5 L/D

http://www.ninfinger.org/models/vault2008/HL-20/HL-20%20MODEL.pdf

The increased weight of the X-37C for crew etc. will have a affect on landing speed.  With similar L/D for both vehicles, the landing speed will be scaled by weight. I suspect (arm waving) the X-37C will be very similar in weight to the DC and will have landing speeds on order of 150 to 200 knots.

[vulture4]

So why are we so insistent on flying _without_ wings? Why did NASA abandon X-37 and all winged entry vehicles?

Because they are not needed for BEO missions.

I would guess a lifting body is also unneeded BEO. It does not appear that any of the commercial vehicles is intended for anything other than LEO. While all alternatives are certainly worth considering, a capsule has greater volumetric efficiency than a lifting body.

[Jason1701]

So why are we so insistent on flying _without_ wings? Why did NASA abandon X-37 and all winged entry vehicles?

Because they are not needed for BEO missions.

I would guess a lifting body is also unneeded BEO. It does not appear that any of the commercial vehicles is intended for anything other than LEO. While all alternatives are certainly worth considering, a capsule has greater volumetric efficiency than a lifting body.

Are you trying to say that all the commercial vehicles are not capsules?

Any shape other than a perfect sphere can generate lift.

[vulture4]

The Shuttle has an L/D of 4.5 during final approach.
http://en.wikipedia.org/wiki/Lift-to-drag_ratio
The Shuttle is pretty close to the practical limit on speed and precision. It landed at just over 200mph, but it weighed about 100 tons. The X-37 appears to have had a much lower touchdown speed, though I'd be interested to know if anyone has the exact figures. 

it's certainly possible to land a vehicle with no wings in a simulation or in perfect weather, but to do so in real winds will be to take a risk that I don't think anyone who flew the Shuttle would welcome. Most of the lifting body tests were done at weights far below that of a returning spacecraft. The evolution of lifting bodies was a quest for better L/D that led from the from the rounded bottoms of the up to the X-24A to the flat-bottomed double-delta of the X-24B. This led to the conventional delta wing and fuselage of the Shuttle. Wings increase lift over a flattened body because thin lifting airfoils with higher aspect ratio produce more lift and less drag. The X-37 has so much lift it would have been difficult to drop it from a B-52:
http://www.spaceref.com/news/viewnews.html?id=823

Wings and fuselage do such different jobs it is difficult to design one shape that does both well. A fuselage with a non-circular cross-section has lower volumetric efficiency and is much more difficult to pressurize due to bending moments induced by internal pressure.

Second, the X-37 design was based on lessons learned from the shuttle. For example, one of the problems with the Shuttle was the limited pitch control authority due to the short coupling between the elevons and CG. This also made it quite sensitive to CG location. See pg 164 in the Shuttle document below:
http://klabs.org/DEI/Processor/shuttle/shuttle_tech_conf/1985008580.pdf

The X-37 retained the delta wing of the Shuttle, with its soft transition from hypersonic flight at high angle of attack to gliding flight, but put it amidships with separated tail surfaces and wing flaps to give much better control of pitch, trim, and lift.

[beancounter]

What are the feelings about X-37C vs DreamChaser?

Sounds like a new thread.

Why?  This is what confuses me so about "advocates" and/or the "space community".  What do "feelings" have to do with any of it?

First "we" are told that there IS a market.  That competition is good and the market will decide (implying we should WANT more possible vehicles).  In the next breath, there is seemingly only room for so many and no "others" are welcome and "commercial" must be a choice essentially between Boeing, SpaceX, Sierra Nevada and Blue Origin and only the designs that are known thus far which culminate in "versus" threads. 

It's odd to me personally but at the same time "I" am told by the "advocates" that "I" am supposed to take at face value that 10,000 jobs will be created, that SLS is a failure and pork, that SpaceX is the end-all and be-all (even though Falcon has launched only twice and it was not perfect), that more government money MUST be given to commercial, etc, etc, etc.

Just a little venting......

Perhaps instead of simply 'venting', you could consider doing some research into the various topics.  Then perhaps you could decide for yourself rather than basing it on what you are 'told'.  Just some friendly advice.  Take it or leave, the choice is your's.

[wolfpack]

I would guess a lifting body is also unneeded BEO.

More importantly, not possible from BEO. The reentry speeds and angles don't lend themselves to a gliding reentry. Unless you wanted to expend extra propellant needed to get yourself inserted back into a circularized LEO upon return from BEO, which is just plain silly. Better to design the spacecraft and TPS to take the heat of a ballistic reentry. And that's called a capsule.

[douglas100]

More importantly, not possible from BEO. The reentry speeds and angles don't lend themselves to a gliding reentry.

Is that actually the case? Can you cite evidence for that?

Don't get me wrong, I fully agree that for returning from BEO a capsule is  the right way to go. I just wondered what the show stopper for a winged shape would be.

[BrightLight]

More importantly, not possible from BEO. The reentry speeds and angles don't lend themselves to a gliding reentry.

Is that actually the case? Can you cite evidence for that?

Don't get me wrong, I fully agree that for returning from BEO a capsule is  the right way to go. I just wondered what the show stopper for a winged shape would be.

More arm waving - I remeber reading that the DC-XL could do BEO, that being said what does/did SNC intend for the "slipper" TPS - additional/thicker ablative coating? What does that do to the rentry flight profile?

[robert_d]

This I never quite understood. In principal, if you retain your environmental systems, would it not be possible to do an aerocapture into an Earth orbit with an orbital period that is long enough to dissipitate the initial heating and then either circularize for rendezvous or do a final reentry from there? 

More importantly, not possible from BEO. The reentry speeds and angles don't lend themselves to a gliding reentry. Unless you wanted to expend extra propellant needed to get yourself inserted back into a circularized LEO upon return from BEO, which is just plain silly. Better to design the spacecraft and TPS to take the heat of a ballistic reentry. And that's called a capsule.

[Lars_J]

It should be possible to aerocapture into a low earth orbit with one pass, but that would be A) very tricky maneuver and B) pick up a LOT of heat - how do you dissipate all of it?

[wolfpack]

Is that actually the case? Can you cite evidence for that?

Don't get me wrong, I fully agree that for returning from BEO a capsule is  the right way to go. I just wondered what the show stopper for a winged shape would be.

No, other than a conversation I had with some of the Orion engineers @ Dulles last April. They basically said wings are useless on the return trajectories that Orion would be flying.

I'm not well-versed in orbital mechanics, seeing as I'm an EE.