Not A Blog™

Yesterday I was daydreaming about potential backup systems for spacecraft. I guess I got on that because I’m actually supposed to be studying sea-faring ships, but potential (yet unrealistic) space-faring ships are more interesting. Anyway, regular ships have backups of various sorts, not in the least of which is that you’re never more than a few thousand nautical miles from land. Of course when you’re out there, the ocean looks really big, and it’s still a dangerous place—but that’s just peanuts to space.

Although spacecraft and ships both have star fields with which to navigate, spacecraft have the slight disadvantage of moving really fast all the time. Course corrections aren’t like course corrections on ocean-going ships. There’s no rudder, and you can’t turn it. In fact, you can’t even fire the jets any time you feel like it because chances are that’s going to jack up your orbit so much you’d never get home. With orbital mechanics, you can’t just fly by the stick.

To make things even worse, the sorts of problems one can have aboard an ocean-going ship, while dire, are positively deadly in a spaceship. A loss of electrical power, for instance, is a big deal on a ship, but it’s life-or-death on a spaceship. Naturally there are batteries carried for this purpose, but the size of the batteries we could practically lift into space versus how much time it would take to mount a rescue means, in most cases, we’re just prolonging the inevitable, as they say. Likewise, ocean-going ships don’t run out of air.

Given the following situation: there’s a loss of electrical power, but the engines still work, and there’s a potential course correction coming up that could divert the ship into an area—say, a lagrangian point—where it could be rescued. But this new calculation requires a bit of technical computation, and the computer is down. What could we do in this case?

Obviously anyone in this situation is going to be an astrogator simply by virtue of the fact that they’re in that situation. Maybe they could do it by hand—maybe they couldn’t. Maybe they’re incapacitated. What we need is a way of computing orbits without electrical power: a mechanical computer. Charles Babbage’s analytical engine comes to mind.

Based on my understanding of orbital mechanics and the analytical engine[1], it doesn’t specifically solve Newton’s equations per se, but it could be reprogrammed to do so. Of course, the real thing is an unwieldy conglomerate of brass and steel—heck, it was to be powered by steam—and so completely impractical to fire off into space. Instead, what we need is a nice little microscopic version that doesn’t have much of a weight penalty.

Using nano- (or even micro-) scale manufacturing techniques, it would be possible to build such a device. There are a few problems to work out, such as how to step down the input and step up the output to human manipulatable proportions; and of course the manufacturing techniques haven’t been refined and are terribly expensive. But these engineering challenges (particularly the manufacturing ones) can and/or will be sorted out by the time we’re able to launch enough ships into orbit to worry about it in the first place.

It may be that the main computer is augmented by countless smaller, but still quite powerful computers. If we can make sufficiently powerful computers run off, say, body heat, that would be a good backup to the main system. If battery technology advances, you could keep an entire backup computer with its own power supply in a locker somewhere. But one can’t have too many backups, right? A stellar event could fire off an electromagnetic pulse, destroying all circuitry on the ship. No matter how advanced electronics get, it would still be a good idea to have a computer around that operates on completely different principles.

Futurist Recommendation of the Day: That long-duration space-faring vessels of the future have a mechanical computational back-up system for calculating orbits (or whatever else needs to be calculated) in the event of electrical or computer failure. The weight penalty would be small; hopefully the expense would be minimal; and if it saves a few lives, worth the effort. That Mr. Babbage’s work was pre-electronics age doesn’t make it irrelevant. He may yet ride again.

-Ted

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1.The analytical engine is the more general mechanical computer designed, but never built, by Babbage, the other more specific machine being the difference engine which was designed to calculate polynomials. Back]