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How much heating would accelerating to orbital velocity at the “edge” of the atmosphere create? I’d expect that if there’s enough atmosphere to create lift the
by mr_toad 3y ago
How much heating would accelerating to orbital velocity at the “edge” of the atmosphere create? I’d expect that if there’s enough atmosphere to create lift there’s probably enough to cause the craft to burn up.
- JumpCrisscross 3y ago> if there’s enough atmosphere to create lift there’s probably enough to cause the craft to burn up There is generally a window between these speeds. Lifting bodies are good at staying in that window. (As your speed increases, lift increases, which pushes your aircraft up and into thinner air.) This element of the problem--transitioning from aerodynamic lift to orbital speeds--is shared with SSTO. There are a lot of tough things about SSTO. But not burning up as you accelerate isn't one of them.
- gpm 3y agoSSTO doesn't rely on aerodynamic lift, it can fly higher than a lift-based vehicle can to avoid air resistance/heating. I suspect you can fly high enough that burning up isn't a problem, but I don't see how you reach that as a conclusion by analogy to single stage to orbit rockets.
- JumpCrisscross 3y ago> SSTO doesn't rely on aerodynamic lift, it can fly higher than a lift-based vehicle can to avoid air resistance/heating The only reason to do SSTO is so you can use an air-breathing engine. That's why practically every recent SSTO draft looks like an airplane. This team appears to be using a reaction engine for thrust, so I'm not sure how they're planning on dividing the work between buoyancy, lift and reaction. But the whole point of using an airship and making it massive is so it can generate lift in air too thin to keep a metal tube flying. > don't see how you reach that as a conclusion by analogy to single stage to orbit rockets Because SSTO has been extensively studied, this is a problem SSTO would have to deal with, and in no case was it a dealbreaker.
- datadrivenangel 3y agoSingle Stage To Orbit doesn't have to be an atmosphere breathing multi-engine lifting body craft, it can be a conventional rocket that just doesn't care about being efficient. Burning up as you accelerate is also an engineering problem that is not 100% solved for hypersonics. Almost solved, but not risk free.
- JumpCrisscross 3y ago> Burning up as you accelerate is also an engineering problem that is not 100% solved for hypersonics. Almost solved, but not risk free. Totally agree it's a difficult engineering concern. But it's being thrown around like a physics limit when it simply is not.
- dotnet00 3y agoAs an example, Starship can theoretically SSTO on Earth, just with no payload and no means of returning. Totally inefficient and actually useless, but technically SSTO.
- rbanffy 3y agoIt’d still lift a lot of building materials.
- dotnet00 3y agoYeah, but this is Earth we're talking about, those building materials can be sent up in a much more usable state via the proper two-stage stack.
- rbanffy 3y agoOnly when that 2-stage stack is properly validated. TBH, Superheavy+Starship, right now, is probably cheaper than the fully expendable SLS. Also, if all the materials will be cannibalized in orbit (or never land on Earth again, like the Lunar Starship), it makes no sense to send the mass in a reusable vehicle.