Hopes For Space Elevator Lifted

Something interesting has happened: a Canadian company called Thoth has filed a patent for a space elevator. Now, don’t get too excited, for the right fee I could go and file a patent for a Death Star tomorrow afternoon, it doesn’t mean it’s going to become a reality any time soon. Nevertheless, it’s encouraging to know that there are people out there taking the concept seriously as it has huge potential. But perhaps I should begin by explaining what on earth a space elevator is.

A space elevator, or at least the concept of it, is very simple. There is a structure that goes from the surface of the earth up into space which is capable of taking loads up into orbit. The reason we might be interested in doing this is that it is phenomenally expensive to loft stuff into space using rockets; in the order of $20,000 per kilogram. If we had a reusable platform that allowed us to shuttle cargo both up and down quickly and efficiently using nothing more than electrical energy then the cost of space exploration could be slashed significantly. This is a good thing.

Now, you’re probably thinking, “Hang on a minute; space is high. Like, really, really high.” And you’d be right. Currently the tallest structure we have ever built is the Burj Khalifa hotel in Abu Dhabi, it is 828m tall and if you look at pictures of it, which you should, you’ll see that it is jaw-droppingly high. Stupidly, crazily high. If you live in London, it’s more than 2.5 times the height of the Shard. If you live in New York , it’s nearly double the height of the Empire State, more than double if you take away the pointless spike on the top. Okay, so you get it; it’s tall. It, though, would be as the most inconsequential speck in comparison to the scale of the structure that would be required for a space elevator; 50,000 kilometres.

Why so high? Allow me to elaborate. Obviously you can’t just build up into space like the biblical tower of Babel; nothing is strong enough to do that and we don’t want to have any smiting going on when we’re trying to explore space. So instead there is the idea that you would have a cable that is tethered to the ground here on earth and then extends up into space like an Indian rope trick on steroids, crack and crystal meth all at once.

Space Elevator

The way the cable stays up is quite wonderfully elegant. The cable would need to extend to the height of a geosynchronous orbit, an orbital height where an object will keep the same pace as the earth rotates, i.e. if you put it right above Quito at a height of 35,800 km then that’s where it’ll stay, always right overhead. But this height is important for another reason. Below this height the cable would be pulled down towards the earth, the gravitational pull of the planet would be tugging it down; above this height, though, the centrifugal force of the spin of the planet would overcome the gravitational force and it would actually be pushed out towards space. What is required, then, is for enough of the structure to be above this critical height such that the centrifugal force acting on the mass above the GEO mark is enough to counterbalance the force of gravity pulling on the mass below the GEO mark.

It’s beautiful. It’s also impossible. There is no substance we know of that is strong enough to bear such weight, nor that we could manufacture to such a length. Periodically people get all excited about carbon nanotubes and other such developments but these are taking a frustratingly long time to develop into useful materials. No carbon nanotube has ever been grown to more than a metre in length so 50,000 km is still pie in the sky at this point. In, theory, once you do have your cable going up to space you can literally run an elevator up it and Bob’s your mother’s brother: you have a space elevator.

Thoth is taking an entirely different approach from the traditional cable method, though. They say that you can build a structure straight out of the earth to space. Details are thin, as they are on most patents, but their idea is to use a stack of pressurised chambers about 300 metres in diameter that would ‘actively guide’ themselves to remain over its base and stay upright; and they want to do this to a height of 20 km. Apparently these pressurised modules would provide huge rigidity and strength so that the structure could support itself. At the top there would be a large platform from which rockets could be launched. Yes, you would still need rockets. As high as 20 km is it’s still not space. The rockets needed to reach space from that height though would be significantly smaller and therefore cheaper than the titans we have to use today for heavy lifts. They estimate that an electrically powered elevator to the top would be about 60-70% efficient in terms of power consumption whereas a rocket to the same height is only 2% efficient. Another little trick they’d like to use is to build on a mountaintop. If you start from the peak of a 5 km mountain then that’s 25% less structure you need to build.

Also at the top would be a hotel and restaurants; in fact they plan to have a thousand people per day visiting for the purposes of tourism. There certainly would be a great view, I’ll give them that. A further potential use of the tower would be for power generation. At a height of about 14 km the wind blows with the force of a hurricane all day every day whereas here on the surface the average wind turbine is only expected to be at peak production approximately 20% of the time. Imagine if the side of the tower were covered in huge turbine blades. It’d certainly produce enough power to be self-sufficient and would likely be able to export a lot as well.

If something like this were able to be built it would be a remarkable accomplishment. We would truly have entered the Space Age. Frustratingly, it’s not going to happen. At least not in this century in my opinion. Whether you want to use ‘pressurised modules’ or the cable method we simply don’t have the technology at hand to build anything like this. The patent, let’s be honest, is little more than a publicity stunt for a company on a funding drive; but by God, wouldn’t it be marvellous if they pulled it off?

What a cable-based elevator might look like. Superb image by Glen Clovis
What a cable-based elevator might look like. Superb image by Glen Clovis

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