Every week, the readers of our space newsletter, The Airlock, send in their questions for space reporter Neel V. Patel to answer. This week: how Earth's gravity changes according to the seasons and climate.
In September, scientists submitted a paper that said that it would be possible to build a space cable / elevator with current technology, which made me wonder: What do scientists think is the most promising method of building a space elevator? And have we figured out if space elevators would even be able to operate given all the space junk in low Earth orbit? –– Erin
For the uninformed, a space elevator is basically right in the name: an elevator that takes you into space (have you never read Charlie and the Great Glass Elevator??) The idea is that an elevator could bypass all the fire and noise and other expensive theatrics necessary to take a payload beyond the planet’s atmosphere and into space. With a space elevator, you basically ride up into orbit like you would if you were going up to the top floor of the Burj Khalifa.
We wrote about space elevators fairly recently. In fact, we wrote about exactly the same paper you reference in your question. I’ll let that story do the heavy lifting in explaining what the new design suggests and why this one is supposed to be the one that could work––and instead just give you a skinny version.
A space elevator has to ride up and down a cable. For one that’s going to, say, geosynchronous orbit, that’s 26,098 miles of cable. The longer the cable, the more difficult it is to ensure it’s stable enough to keep from toppling over, or breaking from stressors caused by outside elements (extreme winds, earthquakes, etc). Unfortunately, we just don’t have any materials today that are strong enough to support such a long, massive structure (and certainly nothing that wouldn’t immediately bankrupt most nations).
The researchers of this latest paper instead suggest building a “spaceline” that’s anchored to the moon and dangles toward Earth. The various forces at play in such a design are much easier to manage, insofar that the researchers think you could build this spaceline with conventional materials.
Does that mean we’re getting a spaceline soon? Nah. We don’t even need to get into the more complicated physics problems with this idea to see why not. This elevator design will only terminate slightly closer than geostationary orbit, and so we’ll still need to figure out how to get from the surface of Earth to that point. We’ve never built any sort of major structure on the moon, so it’s totally unclear how we might anchor something so massive and lengthy onto a body that has only 1/6th of Earth’s gravity. And there are questions about how much value we'd get out of such a contraption, since leaving Earth's dense atmosphere and powerful gravity is the expensive part––not arriving on the moon.
But let’s suppose those problems are solved somehow. To your second question: would orbital debris be a problem? Yes, it would. When the International Space Station is under threat from being hit by a satellite in orbit, it can fire its thrusters to get out of the way. A space elevator, whether it’s anchored to Earth or the moon, is static and immovable. It’s at the complete mercy of any object headed its way. Maybe that object is a satellite that can be moved. But maybe it’s broken or defunct. Or maybe it’s a piece of junk that we aren't even tracking. Like we talk about at the beginning of this newsletter, even a piece of debris just millimeters thick could pose serious damage.
Maybe if we ever figure out how to make a space elevator work, we’ll have also figured out how to actively clean up Earth’s orbit of all the junk zooming by at 20,000 mph. Big maybe.
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November 25, 2019 at 06:07PM
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Is it safe to build a space elevator with so much junk in orbit? - MIT Technology Review
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