Air-Launched SSTO Concepts?

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aaron38

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This is for a novel and I'd like it to be realistic, but theoretically possible is good enough. Given a carrier wing that can lift ~400mT to launch altitude, how much spaceplane can we get out of the air-launched SSTO architecture with a 400mT GTOW?

I searched and the most I found is this and similar articles discussing the advantages of the architecture: http://selenianboondocks.com/2008/01/or ... ched-ssto/

I'm really just looking for basic specs - overall craft size and payload. I'd prefer full reuseability but drop tanks are acceptable to increase payload (but not to reach orbit with passengers only). Was thinking of just sticking with rockets for simplicity, unless there's a study showing that a scramjet would provide a large benefit. There will be orbital tugs, so the SSTO really just needs to reach minimum LEO altitude.
Does anyone know of any design studies or concepts for an orbital vehicle designed from scratch to be air launched?
 
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aaron38

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There's the Russian MAKS-M architecture, baselined at 275mT gross, 38x24m with 7mT payload. The study was done in 1988, so there should be room for improvement. That's not a lot of payload to be interesting.

Push the carrier wing to 500mT. Fusilage is advanced composite lifting body, fuel is CH4/O2. A 20mT payload should be possible, 30mT with drop tanks. Thoughts?
 
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aaron38

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On second thought this is sci-fi, why am I bothering with chemical fuels? I came across the gas core NTR concept with ISPs up to 6000-7000, specifically the closed cycle "nuclear light bulb" which keeps the radiation out of the exhaust. I think I have just enough facts to be dangerous.

For my 400mT air-launched concept, the T/W ratio can be 1.25, requiring 500mT of thrust. I'll choose 3 engines @ 200mT each, to give single engine out capability. A 1996 NASA study benchmarked a gas core NTR at an ISP of 1200s, a Thrust of 75,000lbs (34mT) and an engine weight of 15,000lbs (6.8mT) giving a T/W of 5.(http://ntrs.nasa.gov/archive/nasa/casi. ... 043610.pdf)

I'll wave my sci-fi pen and say I can get double the ISP, 6x thrust and a T/W of 10 including shielding. This is fairly concervative per the theoretical limits of the design. 3 engines together should be able to share support systems, leaving more mass for rad shielding.

So the vehicle is now spec'd:
Delta-V: 9.5km/s
ISP: 2500s
Reaction Mass: 130mT
Dry Mass: 270mT
Engine Thrust: 200mT (x3)
Engine Mass: 20mT (x3)

130mT of LH2 is 30% more than the Shuttle LH2 tank which weighs ~20mT and the empty orbiter without engines is ~70mT. With the tanks integrated as structural elments and the whole thing redesigned into a lifting body with advanced materials, 90mT should go a long way.

If I choose a payload of 80mT, with engines and reaction mass there is 130mT available for structure, leaving 40mT for margin and more shielding. I could put a bigger crew compartment up front and balance out the 60mT of engines at the back.

And with the uranium floride fuel the gas core NTR uses, each spaceport can have a Liquid Floride Thorium Reactor to breed the fuel and burn up the remaining waste products. That's a good enough paper rocket for me.
 
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MeteorWayne

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It's not supposed to be sci-fi but I agree that wayyyyyy too many discussions in SB&T seem to think we have unlimited funds, resources, and technology...
 
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aaron38

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No what I meant was this is sci-fi brainstorming, and isn't anything that we can realistically build in the next 100-200 years. If you want to move this to a different forum, feel free.
 
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Astro_Robert

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I think any kind of air-launch should count as a stage, ...ie Pegasus and other air-launched rockets are not considered 'single-stage'.

Also, consider the cost of developing such a massive carrier aircraft. A C-5 Galaxy is the largest western aircraft, and cannot carry 400mT. Developing an aircraft that could, and that was suitable for any kind of air launch is not a trivial task.
 
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