Low wing-loading space craft

[n72.75]

I was reading through this: http://www.thespacereview.com/article/1880/1 article this morning, particuarly the part about low wing loading reentry vehicles, which got me thinking. I did a bit of googling to no avail, does anyone know of a low wing-loading space plane concept.

Everything I've ever seen has been high density, with a very low L/D.

 

[boogabooga]

I think Skylon is supposed to have "low" wing loading. At least, lower than the shuttle.

 

[RisingFury]

There's no such thing as low wing loading spacecraft. Keep in mind that the wings are dead weight, drag and instability when going up. When coming down, however, they offer no real advantage when coming down.

High wing loading works at high speed. There's plenty of that...

 

[Fabri91]

After skimming through the article very quickly I believe that what you mentioned might be a concept planned to be used in the Skylon SSTO spaceplane: not quite "low wing loading", but rather a "low ballistic coefficient (on re-entry)", with this implying a realtively large external surface for a low vehicle mass, since by this point in the mission Skylong would basically be an empty hydrogen tank.

The net result, however, should be the same: by having a "large and light" structure the spaceplane should be able to slow down earlier, and reach the lower atmosphere at comparatively lower speeds, providing a more "extended, moderate heat pulse", to quote the article.

 

[n72.75]

There's no such thing as low wing loading spacecraft. Keep in mind that the wings are dead weight, drag and instability when going up. When coming down, however, they offer no real advantage when coming down.

High wing loading works at high speed. There's plenty of that...

Reentry is all about energy dissipation. Vehicles with lower masses will have lower kinetic energies at the same speed. If you could make a large, low mass, vehicle you could spread that energy over a

The stagnation temperature at 90km at Mach 25 is ~23000K

But the density is verrry low and most of your heat transfer will be from radiation from the compressed air on the other side of the shock.

As long as you have the hypersonic L/D ratio, I think you could glide around the earth, slowly bleeding off speed without needing a TPS.

Getting such a vehicle into orbit is another story entirely.

 

[Andy44]

Hence the concept of inflatable heat shields.

 

[RisingFury]

Reentry is all about energy dissipation. Vehicles with lower masses will have lower kinetic energies at the same speed. If you could make a large, low mass, vehicle you could spread that energy over a

Yea, nice. But the thing is, if you could make a large, low mass vehicle, you'd be able to make existing designs lighter as well, lessening the load on the heat shield.

The stagnation temperature at 90km at Mach 25 is ~23000K

But the density is verrry low and most of your heat transfer will be from radiation from the compressed air on the other side of the shock.

And the current heat shields can obviously take the heat.

As long as you have the hypersonic L/D ratio, I think you could glide around the earth, slowly bleeding off speed without needing a TPS.

Getting such a vehicle into orbit is another story entirely.

It's more than that. The shuttle had an L/D of 1 to 1 at 40° AOA. It had too much lift - hence the S turns. Yet they went for that approach anyway.

 

[Fabri91]

Yea, nice. But the thing is, if you could make a large, low mass vehicle, you'd be able to make existing designs lighter as well, lessening the load on the heat shield.

I cite again the proposed Skylon design as an example: it carries its whole propellant load internally, which means that on re-entry it is such a large, low mass vehicle. Existing designs more or less completely rely on an external booster, which means that they cannot afford to have large empty internal spaces for the heck of it.

 

[RisingFury]

I cite again the proposed Skylon design as an example: it carries its whole propellant load internally, which means that on re-entry it is such a large, low mass vehicle. Existing designs more or less completely rely on an external booster, which means that they cannot afford to have large empty internal spaces for the heck of it.

Except for living spaces, you mean. And Skylon is by no means a low wing-loading concept.

 

[Urwumpe]

Except for living spaces, you mean. And Skylon is by no means a low wing-loading concept.

... because you say so.

 

[Fabri91]

Except for living spaces, you mean. And Skylon is by no means a low wing-loading concept.

Yes, that may be true but possibly irrelevant: what I said was that the low ballistic coefficient might enable the same "soft re-entry" detailed in the original article.

 

[Urwumpe]

Yes, that may be true but possibly irrelevant: what I said was that the low ballistic coefficient might enable the same "soft re-entry" detailed in the original article.

More important: Fuselage lift is not used in wing loading calculation. So, it doesn't matter if it is empty fuel tank or living volume.

If you can cheaply use the empty fuel tank as "heat shield amplifier" by not discarding it - fine. Who cares that it is not used for payload up or down the orbit?

 

[n72.75]

Yea, nice. But the thing is, if you could make a large, low mass vehicle, you'd be able to make existing designs lighter as well, lessening the load on the heat shield.

It's more than that. The shuttle had an L/D of 1 to 1 at 40° AOA. It had too much lift - hence the S turns. Yet they went for that approach anyway.

The point is that you can build a low density high strength design; perhaps as importantly, you probably couldn't have in the 1970s, especially when, with the exception of the U-2, most research for high speed high altitude vehicles had been on things shaped like HL-10s and X-15s.

Like everything else in engineering, it's a design compromise. The shuttle's TPS does present some challenges, but on the other hand it doesn't take a week to reenter, it's relatively easy to launch, and can carry heavy payloads to and from orbit.

A reentry vehicle like this presents some colossal challenges, less so from an engineering standpoint, and more so in required paradigm shift. To suggest that this is a "better" alternative than low aspect ratio, blunt vehicles, categorically, is absurd, I know that.

I think it can be done and I think it would be interesting to see someone do it, but I don't exactly have a list of wherefores and whys here either.

I think, "low density" is a better term than low wing loading or high L/D in this context.

 

[sputnik]

It was called FIRST.

http://www.astronautix.com/craft/firlider.htm

 

[n72.75]

That is exactly what I was looking for.

 

[Andy44]

It was called FIRST.

http://www.astronautix.com/craft/firlider.htm

Yup, inflatables. I love some of those designs and wish to see that line of research continue on some day.

Although this line from the astronautix article may be a poor choice of words to use when presenting the idea to astronauts:

In an emergency the escaping crew member would enter the coffin-sized cylinder

 

[MaverickSawyer]

Y'know, gave it some thought today...

A low-density spacecraft returning would absolutely fit with a reusable SSTO. It'd be mostly fuel tanks, anyways, right? It would remove the problems on ascent by the fact that it'd be pretty heavily loaded with fuel.

 

[Linguofreak]

My understanding is that designs that decelerate more gently higher up experience lower temperatures, but on the other hand take more total heat load. In other words, fewer Watts, more Joules. So there's less risk of material failure of the heat shield or structural elements, but it's much harder not to parbroil the cargo when the spacecraft does make it home in one piece.