Wednesday, March 10, 2004

Big and slow or small and fast

Yesterday I mentioned that I thought "development of the Moon should proceed... with most of the equipment and supplies being taken to the Moon in big, slow containers, while crew exchange happens in lightweight, fast spacecraft." What did I mean?

The ESA have a current project named SMART-1, a very small lunar orbiter mission. It was launched on the back of a big commercial satellite, into an orbit much closer in than that of the Moon. What's interesting is that it is currently using an ion drive to climb out of the Earth's gravity well to the moon, while hardly using any propellant at all (ion drives have a very high specific impulse). The downside is, of course, that it takes a very long time: SMART-1 will take eighteen months to move from the orbit it was inserted into at launch to its final lunar orbit.

I find this very interesting, because it suggests an interesting scheme for getting kit to the Moon. Big containers of non-perishable equipment and supplies could be thrown into a relatively low orbit, and then could engage ion drives to move themselves into lunar orbit (probably taking a couple of years or so), before using conventional methods for landing on the Moon. That would make most efficient use of the launcher's lifting capacity by minimizing the amount of propellant needed in the cargo. On the downside, it means two different types of engine and two different sets of propellant tanks are needed, as well some way of producing quite a lot of power.

Fortunately, power isn't too much of a problem: solar panels couild be designed to first be used to power an ion drive, and then detached as part of the unloading process and used at a lunar base.

Unfortunately, perishable goods (like astronauts) couldn't use that transit method, so an Apollo-style spacecraft would be needed to transfer personnel from Earth to Moon and back again. Ideally, the L/AV would be left at the Moon and refueled by visiting astronauts, to save on Earth launch mass. My slight worry is that we currently do not have a suitable launcher for this type of mission, unless the Russian Energia launcher is available or the Saturn V could be resurrected.

This scheme is an example of Lunar Surface Rendezvous (LSR) for freight, and Lunar Orbit Rendezvous (LOR) for personnel/perishable goods.

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