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What does it make sense to bring back?
Here's something that's bothered me a bit about the current shuttle design.
You have a fixed size payload bay. And doors. Etc. Ok, that's fine if you're a launch vehicle, but are you always one? And how much of what you carry up is really valuable enough that it is cost effective to bring it back?? It seems that once you're in orbit, all you really want to return is the crew and the SSMEs. Most of the rest of the stuff, well, either leave it at the space station for future use, or let it burn up. I.e. have a modular launch stack composed of: 1. Engine and control module 2. external tank or similar cheap, non-reusable drop tanks. 3. boosters, as necessary 4. Cargo containers of various size Crew, in this design, is essentially cargo: they can be sitting in their return capsule inside a cargo container, or on top of the stack, or something. Crew is ready for a return at any point in flight, more or less. Returning the engine module with the crew module or separately is an interesting question. Putting the crew module right next to the engine module seems like a bad idea for a number of reasons; returning them together would require some orbital dancing but it doesn't seem to horribly hard. Basically, once you decide not to go 100% reusable, you have the ability to decide certain components (tanks, structure, etc) just aren't cost effective to reuse. Right? |
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What does it make sense to bring back?
On Tue, 29 Jun 2004 20:28:51 -0700, Hephaestus wrote: [...]
Basically, once you decide not to go 100% reusable, you have the ability to decide certain components (tanks, structure, etc) just aren't cost effective to reuse. Right? I worked out once shortly after Columbia broke up that for the same cost as a single shuttle mission, you could launch the same amount of cargo, personnel and habitat space on multiple Russian launches for about half the cost. I was figuring on a Soyuz capsule for the crew, and two heavylifter launches for the cargo; one for the habitat module, and one for the cargo. I believe I opted for a Proton, although it could have been an Energia. Once safely aloft, the Soyuz would dock with the habitat module, which would then rendezvous with the cargo, whatever it was. The only part of the whole assembly that would return to Earth would be the crew. Everything else would be discarded. (Unfortunately, I can't find any of my reasoning --- it's lost somewhere on the web and Google's being uncooperative.) Of course, this was a very simplistic analysis. The major cost I didn't include was the design and construction cost of the habitat module; you'd need one of these every time you wanted a mission aloft. However, given that it doesn't have to be man-rated on launch, only on orbit, and that once the decision has been made to make it disposable it's possible to simplify construction considerably --- fuel cells rather than solar panels, thrusters rather than gyros, etc --- I would expect the long-term cost per unit to be quite small. I opted not to reuse *anything* mostly because it made the calculations simpler. (All the off-the-shelf components I was using were disposable.) It might be worthwhile to reuse some components. The habitat module is a prime example; if its consumables allow, leave it in orbit and use it again. Think of it as being a short-lifetime space station. (Reusability does not necessarily mean that you have to bring it back to Earth.) Also, you may not want to deorbit them once you've finished with them --- even as dead mass in orbit, they're valuable. If your orbit allows, add them to a station-keeping platform; an orbital scrapyard. As and when technology allows, it may be cost-effective to reuse them, or at least mine them for components. -- +- David Given --McQ-+ "I smell a rat; I see him forming in the air & | | darkening the sky; but I'll nip him in the bud." | ) | --- Sir Boyle Roche +- www.cowlark.com --+ |
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