MegaStructures 01: Orbital Rings & Space Elevators

Transcript
If you’ve been a subscriber to this channel for a while you probably remember my original video on megastructures, which covered everything from space stations a few hundred feet across to ones encompassing entire stars. We’ve come a fairly long way since then and like most initial products the quality on it is a lot lower than subsequent works and for me feels like it needs upgraded. Rather than just redoing the entire video from scratch though I thought we’d go into each piece in more detail instead. Since these are all about huge things you can build in space or on other worlds it seemed like the best place to start would be on those Megastructures designed for getting us off this world to build them in the first place. One of those, the Space Elevator, is already pretty heavily discussed elsewhere so we’ll touch on it only lightly. Incidentally you might want to flick on the closed captions if you’re having problems understanding me. Ironically the original megastructures video is the only one without closed captions since I didn’t use a script for it.

So, when it comes to getting off Earth and up into space you’ve really got two approaches. A self-contained ship or a structure to tow you up there like a space elevator. One of our big problems about going up to space is just how expensive it is to haul up every single pound of material using chemical rockets. It’s the bottleneck and means that even if we get stuff like smart robots and 3D printing that can build everything up there from materials lying around, or in situ as it’s called, we can never transport people in bulk. And that’s our real goal, making space as accessible as other continents. Being able to vacation on the Moon as easily as Venice. And conventional chemical fuels just aren’t energy-dense enough for that, nor is there any guarantee we’d ever get a working compact nuclear rocket, fission or fusion-powered.

So what are your alternatives? The Space Elevator is obviously one. You’re probably know at least the basics about space elevators already, one long super-strong tether running from the equator up to geosynchronous orbit, where it hovers stationary relative to the planet below. Or if your material can handle it, several tethers running from places other than the equator up to a shared orbital station, same as guy wires on radio masts. Your material needs to be a bit tougher, but you could then place one in New York, Paris, and Buenos Aires for instance all meeting at a central terminal at geosynch. Incidentally in our animation here the torus, the donut, would represent a rotating habitat providing artificial gravity, we’ll be talking about those a lot in future videos, and the sphere is simply a counterweight or anchor. Now finding a material strong enough to hold its own weight of tens of thousands of miles of length is easier said than done, every material has what’s called a ‘breaking length’, or how long something can be in Earth’s gravity before it breaks under its own weight. And for most materials like rope or steel this is on an order of a mile, or ten or twenty miles, and even stuff like Kevlar is only a little over a hundred miles. We need ten or twenty thousand miles for a space elevator. And while you can extend that a bit by tapering your cable to be wider at the top than the bottom, and gravity does get weaker as you get further away from Earth, the simple reality is we don’t really have anything strong enough to build an Earth Space Elevator yet.

It should be noted that even if we can’t do one on Earth that doesn’t rule them out for other places. Your tether length depends on the world’s day length and gravity, and how long they can be without breaking depends on the local gravity. You can do one on Mars that’s shorter and made of weaker material, or on the moon that’s actually longer but could be made of regular old steel or aluminum because gravity is so weak there.

Now, Space Elevators would definitely be handy but there’s no guarantee we’ll ever find a material strong enough and cheap enough to build them with. So are we screwed then if we never find a better basic rocket or stronger material? Well, no, we still have a few other options and one of those is called an Orbital Ring. In some ways this is actually a better option than a space elevator too. They don’t get as much press or coverage in science fiction so we’ll talk about them in more detail. An orbital ring is a giant ring around the planet, which might be only a few feet wide or dozen of miles wide, but around the entire planet. Unlike a space elevator whose tether is tens of thousands of miles long and straight up, these are tens of thousands of miles long and wrapped around the planet instead. They hover a few hundred miles off the ground and do not move relative to the ground below. In our animation they’re not really to scale, one can build one of these things, in theory, of any size but the first one up would probably be so thin you’d need a telescope to see it. Once in place you’d be able to lift matter up into space at energy costs far beneath what we spend moving objects by normal air freight, let alone the costs for getting things into orbit.

Now how does such a thing work? There’s a couple ways to do one. The simplest and original design is to take a long circular wire up into orbit giving off a magnetic field, spin it at orbital speeds, and magnetically levitate objects over the wire that don’t move relative to the ground below. The wire spins under them and they float in place. You can stick a second one up in parallel, add floating structure called a ring station, slap on solar panels to keep the power running, and drop a tether down to be used as an elevator that doesn’t require anything like the strength of a normal space elevator. You could also do this by building it as a big pipe surrounded with superconducting magnets, like a giant particle accelerator, and just run mass through it, similar to a magnetic rail gun or again a particle accelerator. We often call this active or dynamic support and we’ll see the idea a lot. But its fundamentally a lot like hooking up both ends of a garden hose to a pump, it will spring into a circle and resist pushing or pulling on it.

Once you have a small one in place you drop some tethers and haul up more construction material, and you could do another one higher too since it can be at any altitude. You can then build a sheath around the whole thing, an orbital ribbon if you prefer. You can keep adding more parallel rings or other rings at different angles. Orbital rings don’t have to be around the equator. Once one is up you can just keep adding more and more very cheaply. You supply power to the magnets by solar panels.

Can we build one of these? Yes. They are entirely inside known scientific laws. So why haven’t we? Same reason we don’t have a Moon Base. We can do it but it would be very expensive. When Nikola Tesla first suggested this idea not long after the American Civil War we obviously were in no position to even seriously contemplate building one and it got shelved for nearly entire century. Arthur C. Clarke of 2001: A Space Odyssey fame, and Paul Birch, a scientist who will get mentioned in these videos a lot, both played again with the notion in the late 1970s and 80s, but Birch calculated getting one up in space would cost several trillion dollars. This could be done for a lot less if the material could be sourced from off world, like the moon, but since the whole point is to make it cheaper to get stuff into space it has a flavor of being a Catch-22.

It isn’t quite though, because being able to ship people into space by the million isn’t the same as sending up giant robotic factories that built themselves, so one might be able to build those factories with robots then build the ring so you can ship people. We want to be able to put large quantities of people up in space who started on Earth, not just run robots or send a few people up who breed more people up there. That doesn’t mean we can’t go the robot route first to set the stage. The cost estimate was also circa 1980. I haven’t seen a more recent one and since then we’ve made some major improvements in materials, magnetics, and rocketry which would likely make it a lot cheaper, and since you can use these for hypersonic travel around the planet, not just off a planet, it comes with a more direct and near-term economic advantage. Plus, as huge as several trillion dollars to build one sounds, that is almost all launch costs for initial construction, expanding a ring and building a second one would be massively cheaper. It’s a one-time buy sort of item and isn’t off the radar, but understandably nobody wants to be looking at making something like that until we’ve spent many decades checking if other avenues might be available. It’s the sort of thing you build when you’re fully committed to doing off world industry and colonization, not just some scientific research. With one in place you can move freight into space for energy costs comparable to interstate shipping. They are very like Space Elevators in that respect but don’t require any super-strong materials we may not ever be able to mass produce.

So that’s Orbital Rings, our first look into megastructures in space. If you want to be informed of futures episodes, hit the subscribe button, and hit the like button if you enjoyed the video or try some of the other videos on Planetary Habitability or the Fermi Paradox. Thanks for watching, and have a great day!