Monday, July 27, 2009

Pie in the sky

Wishful thinking is not confined to those who think they can change human nature and make a perfect world. Wishful thinking is also engaged in by those who think that getting to the moon will be easy anytime soon.

The other week I was blindsided by Sam (I think it was Sam) mentioning that a new form of rocket had been invented which would make getting to the moon faster and easier. I didn't have my ducks in a row for a ready reply beyond expressing skepticism, since I hadn't read anything along those lines and something that would make getting to the moon much faster would be big news.

Anyway, today I came across this article in NewScientist about a new kind of ion engine that's being researched. I suspect it was an article about this engine research that started the meme that Sam saw about getting to the moon faster than the Apollo astronauts did.

It's an interesting article; and it actually is about a pretty large potential improvement in a type of space mission engine that is actually being used today for a scientific probe that's going to the asteroids. But, but, but. . . the ion engine being used today generates a tiny amount of thrust that is accelerating a very small space probe to a very fast velocity by pushing it for a very long time using solar power.

If you skim through the comments to the article you will find much trash but also some very well reasoned responses that point up the considerable problems associated with using this sort of engine for a Mars mission. And the article is talking about a Mars mission, which needs an engine that provides relatively low thrust for a relatively long time - an engine much like the ion engine described. A mission to the moon needs a very different kind of engine, one that provides a lot of thrust for a relatively short time.

Trying to use an ion engine needed to push a manned space mission to the moon faster than the Apollo mission would require a very large inon engine indeed, or a very large assembly of small engines. And it would not be possible to power those engines with solar power. Such a mission would need a heavy nuclear reactor for power, plus a lot of heavy shielding to protect the astronauts from the reactor's radiation.

It's child's play to shield nuclear reactors here on earth because it's no big deal to surround them with thick shields of cheap concrete or plain dirt (

The problem with putting a heavy nuclear reactor (even the little 25 megawatt Hyperion reactor weighs 20 tons) plus a long of heavy radiation shielding into a spacecraft is that it costs a lot (a very lot) to put payload into space in the first place. The space shuttle takes about 25 tons to low earth orbit at a cost of about $1.5 Billion per launch, so putting each ton of payload into orbit costs about $60 Million.

Sending men to the moon was an exciting stunt in the 1960's. And sending men to the moon, or to Mars, would still be a mere exciting stunt today. We can do the stunt at very great expense if we want to; but it's a lot more cost effective to send relatively lightweight expendable automated space probes to learn about the moon and the planets until our children or our grandchildren develop technology a lot more powerful than we have today.

As a start we need a truly cheap way to get lots of mass into orbit. Since it's very likely there will some environmental concerns expressed (hah, probably a revolution!) if anyone tries to build Ted Taylor's very potentially workable but very certainly insane Project Orion type booster, that probably means we need Arthur C. Clarke's space elevator.

Orion booster:

Space elevator:

Manned space flight beyond low Earth orbit will be nothing but a clever stunt until there is a space elevator or some other practical way of getting lots of mass into low Earth orbit. I suspect that if a space elevator is impossible that mass will be brought to Earth orbit from an asteroid by relatively cheap robots. Or else the robots will move a small asteroid to Earth orbit.

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