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Know It All: The Space Elevator -- Elevator To Heaven

Published in Geare magazine, Issue #53, 2009

We know how to get into space. We pack a few thousand tonnes of highly flammable material into a thin steel shell. We pour pure oxyen onto it. And we light a match.

The most amazing thing about the space program so far is not how much it has achieved, but how few people it has killed. And I write that sentence fully aware of the Apollo 1 launch pad fire which killed three, and the loss of two space shuttles, one on the way up, one on the way down, which took fourteen lives. Oh, and I assume that the Soviets lost their fair share of cosmonauts over the years, given that they declined to announce missions until they had successfully achieved their goals.

But what do you expect when you place an bomb under a tin can?

It might seem hard to believe, given that the US and European and Russian and Chinese and Japanese space programs all do it in much the same way, but the future may well hold radically different ways of getting into space.

At least one of them would be a much more comfortable, and possibly safer, way of doing it: the space elevator.

Consider Jack and his Beanstalk. What if, instead of stopping at some Giant-infested cloud, it had kept on growing? Kept growing so high that it reached beyond the Earth's atmosphere. Indeed, kept on going even then, perhaps to as high as, oh, say, 35,786 kilometres over our heads?

Then suppose that Jack, rather than climbing up the silly thing, attached an electrically powered car that ran up and down the beanstalk. All the way to the end. At that other end, he could hope into a nifty interplanetary space ship -- say, something powered with a low acceleration but long lasting Ion Drive -- and make his way to pretty well anywhere he liked in the solar system.

Oh, it certainly wouldn't have the pizazz of a Space Shuttle or an Apollo launch. Indeed, it would soon become positively boring.

But it would open up the heavens to the less adventurous: to the merchants, and the non-Indiana Jones scientists. Indeed, to the masses.

Of course Jack and his Beanstalk are in the realm of the fairy tale. And space elevators are in the realm of science fiction. Sort of.

But perhaps not for very long.

The reason I mentioned 35,786 kilometres is because that is the height of a geostationary orbit. A geostationary orbit is both a good and a bad place to put a communications satellite. It is bad because nearly 36,000 kilometres is a long way: just about one eighth of the distance that light travels in a second. Going both ways, up and back, at the speed of light means a delay of nearly one quarter of a second. It is that delay (combined with other latencies in the comms system) that makes for those awkward overseas interviews you see on TV, where the reporter tries to interrupt the interviewee who plows on, briefly oblivious to the attempt.

The advantage is that something in orbit at that altitude, when it is over the equator, stays directly above that spot on the equator. You can point a satellite dish at it and it will stay focused. Or you can put the top of a beanstalk -- sorry, I meant space elevator -- there and the cable, beanstalk or whatever will stay straight.

At least, it will if it is suitably counterweighted by a cable extending even further out into space.

So imagine a giant transit terminal at that altitude. Imagine elevator cars running up and down the cable. Most of the energy to run a car up the cable is derived from the energy generated by a car running down the cable. The space vehicles are at the top of the cable. The train station is at the bottom. People ascend and descend under reasonable accelerations. At one tenth of a gravity of constant acceleration (reversing half way), the time taken would be measured as a few hours. Air resistence would be a problem only during the first few tens of kilometres.

There are two obvious problems with this concept. First: what if the cable breaks? Even without a counterweight, if the cable were broken just below the top terminus, it would be long enough to wrap nearly all the way around our planet. Second: surely there is no material strong enough to make such a cable.

The latter objection is quite correct. There is no such material ... yet. But even with boring old 20th century materials the concept was viable for our Moon (one sixth Earth's gravity) and Mars (one third). So we aren't talking about a huge leap. Current proponents of the concept tend to concentrate on carbon nanotubes as the material with which an Earth-capable space elevator cable could be constructed. A carbon nanotube is a single carbon molecule, constructed from an unimaginable number of carbon atoms, which might stretch of all those tens of thousands of kilometres.

But more on those another time.

© 2002-2009, Stephen Dawson