🚀 Faster, Please! — The Podcast #23

Thanks to SpaceX, it’s getting cheaper and cheaper to launch stuff into orbit. But just imagine if instead of using rockets, we could send cargo and people to space on an incredibly tall elevator. This may sound like a total sci-fi idea, but it has some grounding in real-world physics. In theory, we could build a space elevator by putting a counterweight in geostationary orbit and attaching a cable between the satellite and Earth. An elevator could then climb the cable, delivering payloads to space at a fraction of the cost of propulsive rockets. As you can imagine, it isn't quite that easy, which is why I'm joined today by Stephen Cohen.

Stephen teaches physics at Vanier College in Montreal and has been working on space elevator concepts for almost 20 years. Recently, he wrote “Space Elevators Are Less Sci-Fi Than You Think” for Scientific American. Stephen also has a new book, Getting Physics: Nature's Laws as a Guide to Life, which was released earlier this year.

In This Episode

* Space elevators 101 (1:42)

* The engineering challenges (7:14)

* The economics of space elevators (11:07)

* Space elevators in sci-fi (19:21)

Below is an edited transcript of our conversation.

Space elevators 101

James Pethokoukis: In the intro, I tried to do my best at explaining what a space elevator is. But the simple version is we have something big and heavy in orbit, a cable extends down from that thing, attaches somewhere on the Earth, and we run an elevator up and down it. That's a space elevator. Am I right?

Stephen Cohen: Sure.

Now that we have a picture in our heads, why is it something more than just an interesting engineering thought experiment? What attracts you to it, other than sort of a technical problem that would be interesting to solve on paper?

Well, it's space infrastructure, which is something we don't currently have and never have had. Right now, and for all time we've accessed space, going to space is like a one-off each time. Sometimes you have some reusable parts, but basically what a space elevator is, is a bridge instead of just a bunch of boats.

And the advantage of a bridge over boats is what?

Access. Right now, each time you want to plan a mission, to simply put something into orbit requires a lot of planning. The weather has to be right. And then you want to plan another mission, you sort of have to begin again. With a space elevator, you can just days in advance say, “Okay, we're going to send something up to a desired orbit.” And just hours later after that one would be sent, you could send something else. And you basically have a housing — that's what the climber is, effectively — that you put the payload inside and up it goes. That's the transformative part. But we haven't talked about really the cost savings, the energy savings, and that's just basic physics.

The way you get around in general is by applying forces. And that's something you do without thinking. When you walk, you push on the ground. When you fly through the air, you're basically pushing on air molecules and they push back. But in space, you have none of that. And so what rockets do is they literally are the medium. The fuel you bring is the medium you're pushing against — rather, you're throwing it out the back. It's a hugely wasteful, inefficient way to get around. It's preposterous when you think about it. But it's the only way we can get things to the speeds we need to get them to. Just as a mode of getting things into this is extremely practical. You can't compare the efficiencies. It’s orders of magnitude of difference.

It really strikes people. When they hear the general concept, they really think it's something big and it sounds like it's amazing. It's something that is science fictional, but maybe we could turn into science fact. There's something else about it, I think, that just grabs people's attention.

Yeah, for sure, because it's a physical connection to space. It's like, if you could just touch the cord at the Earth port, then you're in contact with something that's reaching out all the way into space, which is wild. But I think there's an element missing. People don't realize tethers in space are not a new thing. We've had missions since the ‘70s that are effectively two bodies orbiting earth connected by a long tether, sometimes kilometers long. Now, that's not in the ballpark of 100,000 kilometers long, which is a common number thrown out there for what the eventual space elevator might be. But a lot of the same technologies are involved. The biggest difference is of course, instead of two bodies connected by a tether, like a big spacecraft to a small spacecraft, say, this is a big structure connected all the way to Earth. The amount of tension is tremendous. That's the big difference. That's what effectively becomes the big engineering challenge about it all.

To be clear, the cable would be connected to something large in orbit, and that could be something we build, but I've also heard maybe it could be a small asteroid? Am I confusing two different things there?

It doesn't have to be something we build, but likely it won't be an asteroid. The way at least the first space elevator will likely be constructed would be you send the cable up in a spacecraft and you drop it, you sort of spool down the cable over time. And it would be a lengthy unspooling. The dynamics of that are super interesting. But the point is, at the end of it you can now connect that cable to the ground. It's good to have something functional at the other end, not ju