Space Elevators: Crazy Enough to Work?

The biggest problem with rockets is that they have to carry their own fuel. How much fuel they need to, for example, lift off from Earth is modeled using the ideal rocket equation. Thanks in part to a pesky logarithm embedded in that equation, rockets departing from Earth need to be 80-95% fuel by mass. And thus, spaceflight is absurdly expensive.

It’s not surprising, then, that engineers all across the globe have tried to think up an alternative means to reach space. What is surprising is that many of these engineers, often working independently of each other, have all come up with basically the same wacky idea: space elevators.

How to build a space elevator

First off, don’t picture a traditional elevator. Many early proposals for space elevators were essentially really tall towers with really long elevator shafts up the middle. At this point, it’s pretty clear that won’t work.

Instead, the current scheme is to launch a spacecraft into orbit carrying a spool of sturdy but lightweight material, something like a ribbon of carbon nanotubes. Once in orbit, the ribbon would be unspooled and slowly lowered back to the ground.

After the unspooling process is complete, the ribbon would be held taught on one end by Earth’s gravity and on the other by a counterweight, which would exert an enormous amount of centrifugal force due to Earth’s rotation.

An orbital station would be positioned near the ribbon’s center of mass. Ideally, that point should be located approximately 36,000 kilometers above Earth’s surface (for perspective, Earth’s diameter is roughly 12,000 kilometers). This is the altitude required to maintain geostationary orbit.

How to use a space elevator

In a proof of concept test during the 2009 X-Prize competition, a miniature space elevator car climbed a 900-meter cable dangling from a helicopter. And it did it in less than eight minutes. All we have to do now is scale up!

Unfortunately, real space elevators will probably be much slower, mainly for safety reasons. According to an article from New Scientist, it looks like a trip all the way up a full-sized space elevator would take roughly two or three weeks. So bring something to read. You’ll also need snacks.

However, your elevator car will not need to carry its own fuel, meaning it is no longer constrained by the rocket equation! The most popular design at the moment involves high-powered lasers which transmit electricity to the car as it goes.  So fuel would constitute almost 0% of the total mass, rather than 80-95%.

Crazy enough to work?

So why haven’t we done this yet? We have the technology. Well, all but one component: the carbon nanotube ribbon. We can barely make carbon nanotubes longer than a few centimeters, so a 36,000+ kilometer ribbon is out of the question—for now.

Real life space elevators are decades or maybe centuries away. In the meantime, the construction, maintenance, and defense of these futuristic Towers of Babble could be fertile ground for new science fiction stories.

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Today’s post is part of Earth month for the 2015 Mission to the Solar System. Click here for more about this series.

Links

The Space Elevator: “Thought Experiment,” or Key to the Universe? by Arthur C. Clark.

How Space Elevators Will Work from How Stuff Works.

LaserMotive Wins $900,000 from NASA in Space Elevator Games from NASA.

Space Elevator Trips Could Be Agonizingly Slow from New Scientist.