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Old October 16 2012, 06:37 AM   #239
Crazy Eddie
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Re: Envisioning the world of 2100

gturner wrote: View Post
I agree that we'll go VASIMIR, perhaps after ion thrusters for the Earth-Moon supply deliveries, and then eventually eliminate the chemical thrusters for lunar ascent/descent and go with electromagnetic launch and recovery, if not something even stranger like rotating orbital cables and such.
Chemical rockets actually work perfectly well for those short range surface-to-orbit runs, considering they're likely to be a lot cheaper and safer than any of the more exotic alternatives. To suggest otherwise is almost to imply that people in Chicago should stop driving cars just because the L-train was invented; that's an overly simplistic view of how commerce actually works.

But to get to that point, crewed lunar vehicles are going to have to get a lot cheaper and more frequent than the SLS can manage under any projection, and if something like the Falcon 9H with flyback boosters works, its launch cost will drop to that of the regular Falcon 9 or even much lower, and with a high ISP alternative it could probably do lunar missions with a crew of three or four to the surface as cheaply as the current ISS resupply flights, which we know current and projected budgets can support.
Maybe, but I'm actually thinking that you could start small with a group of four craft, scaled-down versions of the Nautilus-X as command modules for some of those earlier expeditions. Say, something like the ISS Node with a pair of logistics modules, a large lander, and a habitat. With a cluster of ion engines, the first one could spend, say, three months spiraling out to lunar orbit and once it gets there drop the lander onto the surface along with all the supplies they need to setup the expedition. When the first ship gets on station, the second ship in the series launches and spends three months spiraling out to the moon to replace it; second ship arrives to relieve the first, which can then take a three-month flight back to Earth; it passes cruiser #3 on the way up, which in turn relieves #2, and so on.

With those four craft, you can do a rotating schedule to the lunar outpost and back, and if you pack smartly you aren't just maintaining the outpost, but slowly growing it with every new shipment of personnel and equipment. The best thing is, the kinds of modules used in this plan are small enough to be launched on a Falcon-9 or an Ariane 5. That would make the infrastructure relatively cheap to deploy, since an entire cruiser could be assembled in orbit using just six F9 launches, each deploying modules of a configuration that is already trivially easy to modify (that's five for the hardware and one for propellant, although a Falcon Heavy might be needed for the last one).

Anticipating publiusr's inevitable objection: no, launching the whole thing on an SLS is NOT a better idea, given the probably timeframe we're talking about would be 2020s to 2030s, by which time the Falcon 9 would be cheap enough and common enough to sustain a flight rate of about once every five weeks. You could have all four cruisers in orbit and operational within six months, with two more under construction during the initial rotation. More importantly, for safety and risk management missions, the landers, the cargo and the crews are probably going to get sent up on different flights anyway, very likely from totally different countries, and forcing them all to send their equipment and money to Cape Cannaveral just to wait in line for ten months for the next SLS would be a real business killer.

One simple lunar fuel I don't think anyone has looked at is molten aluminum/LOX. If the tank and piping are pressure-fed titanium or stainless steel with heater elements and ceramic aerogel insulation, it wouldn't be a very big deal to make such a craft for lunar ascent, though it might need to run very oxygen rich to keep chamber temperatures manageable.
I kind of like that idea... but how would you keep the aluminum molten?
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