returning a spaceplane from the moon?

[Laie]

I've just spotted Doing it LUNEX Style! in challenges and wonder, could that ever have worked? Specifically reentry -- am I right to assume that shuttle-style tiles are totally out of the question? Would ablative material still work?

Edited May 3, 2017 by Laie

[sevenperforce]

Tiles will work just fine.

[Bill Phil]

You just need a thicker shield and a different flight profile, after all, wings provide lift. That could be an issue coming in from those speeds (lift depends on v^2, after all...).

[Nibb31]

Why would you want to carry wings, landing gear, hydraulics, control surfaces, and several tons of heat shield all the way to the moon and back? 

[passinglurker]

34 minutes ago, Nibb31 said:

Why would you want to carry wings, landing gear, hydraulics, control surfaces, and several tons of heat shield all the way to the moon and back? 

A space plane gives you more volume than a pod for a given diameter making it great for returning with surface samples, large crews, apollo era artifacts, that strange ring shaped interstellar rotary phone buried under the ice on the moons south poll etc...

[Steel]

2 hours ago, passinglurker said:

A space plane gives you more volume than a pod for a given diameter making it great for returning with surface samples, large crews, apollo era artifacts, that strange ring shaped interstellar rotary phone buried under the ice on the moons south poll etc...

I would argue a pod with a diameter the same as the wingspan of a space plane would have a much larger volume.

Edited May 3, 2017 by Steel

[Gh0stReaper]

Possibly because it would look cool?

[Bill Phil]

6 hours ago, Nibb31 said:

Why would you want to carry wings, landing gear, hydraulics, control surfaces, and several tons of heat shield all the way to the moon and back? 

Lower gees. That's about the only advantage... is it worth it? Probably not.

[passinglurker]

5 hours ago, Steel said:

I would argue a pod with a diameter the same as the wingspan of a space plane would have a much larger volume.

You can argue that but it'd be a silly argument a rocket the size of an advantageous space planes wing span would be silly big.  Good luck getting the money for the ground infrastructure you'd need. 

A space plane can down mass more while launched from a thin and practical rocket that is why some one would want to haul one to the moon and back so the question becomes either do you need a big enough crew to fill that space plane, or what on the moon is worth hauling back?

[wumpus]

I strongly suspect that the difference between lunar orbital speed and minimum orbital speed either won't be a factor or will be a factor largely because the simulator isn't quite good enough.

You should be able to do a series of aerobraking orbits that cut your orbital speed enough such that the re-entry speeds are similar (and probably lower than) the shuttle's.  This has been shown to work on Mars (although don't try the Mars Reconnaissance Orbiter's 6 month plan with people on board).  The biggest reason for not doing this is uncertainty: the difference in velocity needed for a one-day orbit and a one-week orbit is tiny.  Don't expect the simulation to be sufficiently exact.  Also, I think the one-day orbit might spend too much time in the Van Allan Belts.  You will need to hit exact orbits and that might not be possible to pre-plan.

Of course, all of this pales compared to the two elephants in the room: adding the extra wing mass to your payload and compounding the disaster with a direct ascent.  Either one makes mass spiral out of control and the penalties multiply together.

[Steel]

17 minutes ago, passinglurker said:

You can argue that but it'd be a silly argument a rocket the size of an advantageous space planes wing span would be silly big.  Good luck getting the money for the ground infrastructure you'd need. 

A space plane can down mass more while launched from a thin and practical rocket that is why some one would want to haul one to the moon and back so the question becomes either do you need a big enough crew to fill that space plane, or what on the moon is worth hauling back?

Except if you factor in that you'd need to launch your spaceplane in a fairing or on a rocket with enormous stabilising fins otherwise you end up with an aerodynamically unstable launch vehicle.

Edited May 3, 2017 by Steel

[passinglurker]

51 minutes ago, Steel said:

Except if you factor in that you'd need to launch your spaceplane in a fairing or on a rocket with enormous stabilising fins otherwise you end up with an aerodynamically unstable launch vehicle.

Not necessarily for example crewed dream chaser would launch without fairing or fins they pull it all off with atmosphere modeling and fly by wire. Unlike in the LUMEX days we have the number crunching power to pull it off. And besides bolt on stabilizer fins are a lot easier for ground infrastructure to handle than mega diameter rockets or you can always side mount your gliders shuttle style.

[Steel]

40 minutes ago, passinglurker said:

Not necessarily for example crewed dream chaser would launch without fairing or fins they pull it all off with atmosphere modeling and fly by wire. Unlike in the LUMEX days we have the number crunching power to pull it off. And besides bolt on stabilizer fins are a lot easier for ground infrastructure to handle than mega diameter rockets or you can always side mount your gliders shuttle style.

Dreamchaser is a slightly different kettle of fish to the sort of large spaceplanes you're talking about. Firstly it's a lifting body rather than relying on conventional wings, so generates less lift at small angles of attack. It's also pretty tiny, so the lift it generates is fairly insignificant when mounted on top of an Atlas V. If you get much bigger or start to use larger, more conventional wings then small errors in the guidance system (and these do happen, all guidance systems have error margins) get magnified to a point where you have significant risk of flipping the whole stack or tearing your spaceplane off of the top.

Shuttle style is also pretty difficult to pull off in the craft slung on the the side of the rocket doesn't have significant engines of it's own to counter-act the massively offset centre of mass.

EDIT: Ok I'm getting way too into this and I'm side-tracking the thread. I think we're going to have to agree to disagree on lunar spaceplanes and leave it at that!

Edited May 3, 2017 by Steel

[passinglurker]

13 minutes ago, Steel said:

Dreamchaser is a slightly different kettle of fish to the sort of large spaceplanes you're talking about. Firstly it's a lifting body rather than relying on conventional wings, so generates less lift at small angles of attack. It's also pretty tiny, so the lift it generates is fairly insignificant when mounted on top of an Atlas V. If you get much bigger or start to use larger, more conventional wings then small errors in the guidance system (and these do happen, all guidance systems have error margins) get magnified to a point where you have significant risk of flipping the whole stack or tearing your spaceplane off of the top.

Shuttle style is also pretty difficult to pull off in the craft slung on the the side of the rocket doesn't have significant engines of it's own to counter-act the massively offset centre of mass.

EDIT: Ok I'm getting way too into this and I'm side-tracking the thread. I think we're going to have to agree to disagree on lunar spaceplanes and leave it at that!

Energia had center mounted engines

Space planes have thier engineering issues sure but they are not insurmountable. This thread is about the feasibility of reentering a space plane from the moon, and naturally people ask why you would want to haul a spaceplane or lifting body to the moon and back in the first place. To that I say it all comes down to a combo of what do you want to bring back from the moon (be it crew, samples, etc) and how limited are you on rocket diameter, but at the end of the day a spaceplane gives you greater down mass flexibility than a traditional reentry capsule so that is why you would potentially want to use a spaceplane.

So with that logic exercise out of the way let's return to the topic at hand what sort of spaceplane could survive re-entry from lunar return velocities. Personally my money's on Lenticular craft (basically flying saucers with some winglets).

[tater]

Taking a spaceplane to the Moon is absurd.

[Steel]

6 minutes ago, passinglurker said:

So with that logic exercise out of the way let's return to the topic at hand what sort of spaceplane could survive re-entry from lunar return velocities. Personally my money's on Lenticular craft (basically flying saucers with some winglets).

To be honest there's not a whole lot of reasoning to say why any well-designed spaceplane shouldn't be able to survive lunar reentry. The aforementioned Dreamchaser reenters from LEO at 1.5 g, so doubling that to 3 g (or even tripling to 4.5 g) shouldn't be too much of a problem for a well designed thermal tile system.

[sevenperforce]

First of all, downmass isn't the issue; capsules are primarily volume-limited, not mass-limited. The point is to get high downvolume from the moon.

Getting high down-volume from the moon doesn't take a spaceplane; it just requires a biconic re-entry. Integrate the lander with the upper stage and have the whole thing come back and re-enter on its belly, like the ITS Spaceship.

[tater]

What's worth bringing back from the moon, anyway? Aluminum oxide, lol?

Wake me up when the tritium economy is a thing.

[tater]

Actually looking at the referenced lunex link, that craft is a lifting body, so it might not be terribly different in mass than a capsule, or a biconic. Though we all know how that mass scales at the launchpad (which is why Grumman was drilling holes in the structural Al of the LEM, since every kg mattered. A lot.

The topic's use of "spaceplane" is the real issue, then semantics, I suppose. Many define those as HTHL vehicles, though clearly by other definitions it could be VTHL. Generally I think it's not the best term, since it requires much more information to know what the person is actually talking about. X-15 and Spaceship One are HTHL and suborbital, Shuttle, Buran, and X-37 are/were VTHL. 

[sevenperforce]

44 minutes ago, tater said:

What's worth bringing back from the moon, anyway? Aluminum oxide, lol?

Wake me up when the tritium economy is a thing.

A larger crew, test systems for a surface hab, that sort of thing.

Oh, and the upper stage/lander itself. Because reuse is the only way a moon base will ever be economical.

[tater]

Unless isru produced rather a lot of propellants, a reusable lander should be a minimalist thing to reduce mass, I'd think. I have a few admittedly old studies about lunar base infrastructure, and they all seemed to think local propellant production would mostly just offset landing prop costs.

[Bill Phil]

2 hours ago, tater said:

Taking a spaceplane to the Moon is absurd.

Yeah. The original STS ideas called for the space plane staying in LEO.

[tater]

Then again, ideas like its take the whole critter for the round trip---but they return light.

[Laie]

3 hours ago, tater said:

Taking a spaceplane to the Moon is absurd.

To mis-paraphrase a historical figure (if mis-paraphrasing even is a word): the idea is fascinating not because it is reasonable, but because it is preposterous. For those who didn't follow the link in the OP, here's what I'm talking about:

 

Though maybe one should not be so harsh. The PDF is dated May 1961, after all: there's a lot they could not have known (like, that docking isn't all that hard) while things they thought they knew (like, what a proper spaceship looks like) turned out to be wrong.

For purposes of this thread, please accept the "spaceplane to the moon and back" approach as a given. I'm asking if the idea could have worked at all. To that end I'm calling on your capacities as armchair scientists, please don't act as if you had to actually foot the bill.

That said: getting it to the moon would probably have required something slightly bigger than a mere Saturn-V, but as I see it, that's not the most challenging part.

However, I have occasionally heard that heat load is non-linear, and that coping mechanisms don't scale well. Back-of-the-napkin math suggests that Vee-squared coming from the moon would be about twice as much as when returning from low earth orbit. The space shuttle had to zig-zag for what, fiften minutes? Could one just double that without ill side effects? Like shingles eventually getting too hot on the exposed side, or the time being long enough for sufficient heat to seep through, or something else that I don't know enough about to even think of it?

Edited May 3, 2017 by Laie

[Steel]

48 minutes ago, Laie said:

However, I have occasionally heard that heat load is non-linear, and that coping mechanisms don't scale well. Back-of-the-napkin math suggests that Vee-squared coming from the moon would be about twice as much as when returning from earth orbit. The space shuttle had to zig-zag for what, fiften minutes? Could one just double that without ill side effects? Like shingles eventually getting too hot on the exposed side, or the time being long enough for sufficient heat to seep through, or something else that I don't know enough about to even think of it?

It's dependent on so many factors it's difficult to give a reasonable answer, but there is nothing that fundamentally stops a space-shuttle style TPS from working, albeit one that would have to be significantly more robust.

Edited May 3, 2017 by Steel