Skyhook

Imagine firing a cannonball that arcs upward for a bit, goes a certain distance, then comes back down to the Earth.

Suppose you wanted to make the cannonball go farther away next time. You use a great deal more power, and you get the arc just right, so the cannonball goes clean over that mountain range over yonder. It crashes back down to the Earth, but miles away this time.

The planet itself is a sphere, so the further out that arc goes, the more around the world the ball goes, in a manner of speaking.

This is what Isaac Newton was thinking about when he ultimately gave us the laws of universal gravitation, and he ultimately realized that you could shoot the cannonball with enough power so that it would just keep going, surpassing the shape of the planet and creating orbit, just like the Moon. Here’s a bit more writing about that, if you’re curious or if you missed it a couple of weeks ago:

So, that’s how orbit happens from a very intuitive sense, and it might help us to think about all that space junk and incredibly useful satellite technology we have circling our planet. Hundreds of millions of objects, mostly debris, stay up there for no other reason that they’re going around at just the right speed. They’re falling all the time toward the center, but they’ll never reach it.

Now, hold one of those satellites in your mind for a moment. It’s a really big and sturdy satellite, so you hook a cable onto the belly of the beast, so to speak, and point it downward toward Earth. Down and down you go, eventually creating a cable that is thousands of miles long.

At first, Earth’s gravity isn’t much help—the gravitational pull is tiny at the top, but the longer the cable gets, the more it starts to pull everything downward, and the more vertical it starts to get.

Meanwhile, down on the ground, you’ve already started building a tall tower, like way way WAY taller than the Burj Kalifa, the current tallest structure humans have ever built. That building is just over half a mile tall (830 meters), but we’ll need something at least ten times taller.

While the cable is coming down from space, the tower is climbing upward all the time. In order for this wild idea to work, though, we need one more important component: geosynchronous orbit.

That means that the planet goes around once, and so does the satellite. They are in one-to-one sync, and once something is in gravitational sync like that (and like our Moon), it is very hard to get this to deviate. Gravitational forces keep it locked in orbit, buffering against any little knocks or bumps.

If you could steadily add material to the cable from above, you could eventually connect the top of the tower to the bottom of the cable.

Now, if you’re wondering why on earth anyone would even think about doing something so audaciously difficult, I might ask if you’ve ever met humans. We tend to have very audacious ideas and very lofty opinions of what we ourselves are capable of. The funny thing is that we’re often right.

I might also point out that it’s really, really expensive to send things into space right now. It doesn’t take a rocket scientist to understand that exploding chemicals with enough force to send heavy rockets up into the sky already costs tens of millions of dollars each year, and burns up fossil fuels that go into the atmosphere. It’s not ideal, to say the least.

If we want to have the option to do things in space at a level beyond mere tourism, a skyhook seems like a necessary first step. Alongside the skyhook, the idea would be to then build an elevator that goes all the way up.

There are all sorts of concerns about the physics and economics of building a skyhook and a space elevator. While it’s a bit outside the scope of what I want to say today, we should nevertheless keep in mind that this is probably far off into the future, at least in terms of developments we’d need to make first.

I know there are obstacles and that this is currently something of a pipe dream, but I can’t help but feel a sense of wonder when I think about how all this is perfectly possible within the laws of physics. I’ve also started to realize that if it’s possible, we’re going to do it one day.