Posted September 10, 2015

A 20 km high space tower? Seriously?

Thoth Technology of Canada has patented a partially inflatable tower 20 km high, from the top of which you could launch rockets into space., They say a 1.5 km high prototype could be built within 5 years. That's pretty wild but not crazy, since there are plans around the world for buildings around 1 km high.

The advantage of having a high launch point is clear: your rocket can be leaner and meaner. One problematic thing about rockets is this: the fuel that you need to carry your rocket from km 1 to km 2, has to be carried to an altitude of 1 km first. Of course that takes extra fuel. The fuel you require to go from km 2 to km 3 has to be lifted to 2 km before use, and even more extra fuel is needed for that. And so on. If you can skip the first 20 kms, you save a huge amount of rocket fuel, so your rocket can be smaller and lighter. On top of that, the lower layers of the atmosphere are denser and cause way more drag than the higher ones. It really makes a lot of difference.

When Thoth was awarded this patent, lots and lots of blogs and news media wrote about it without asking too many questions. But why hasn't the space business been launching from super high towers all along? Because such structures themselves are difficult and expensive to build, of course. If they can be built at all. Also, once the tower is there, you can't put your rocket on top for free. It has to be brought there, probably in parts, by plane or by elevator. People and tools need to go up and down. All of this takes energy and money too. It does not go without saying that the tower will be a cheaper option. The patent  (search for number 9085897) presents no calculations to show that it will.

Also the patent is very broad, als patents go nowadays. It's not als if Thoth has finally invented a surefire way to build such a high tower. They present various possibilities, all of which are fairly obvious. It's more like they patented an idea rather than a particular solution.

One of their original ideas is they want to stabilize the tower by having it lean into the winds, which may be different at different altitudes. And they intend to do so using pressurized cells, which could be pressurized more on one side of the tower than the other, bending or reinforcing it a little, and doing so differently at different times and on different levels. The tower could be wriggling like a snake.

What gas will they use to pressurize the cells? On this the patent is vague too. Maybe hydrogen. Maybe helium. Maybe air. The first two are interesting because they make the structure lighter. But they are notoriously hard to contain (and Helium is rare and expensive) and it is hard to believe they can be used without problems on this scale.

But hey, that being said, it is a VERY good idea to try this. Just do it. That's how progress is made. The only thing is, Thoth estimates the cost of the project to be 5 to 10 billion dollars. Somehow I don't think they're going to take this risk all by themselves. And unfortunately the patent ensures that anybody else who tries this, will have to pay Thoth for their vague patent. And so the probability that anyone will try, is significantly lowered.

About Herbert Blankesteijn

Herbert Blankesteijn is a technology journalist from the Netherlands who has written for many prominent Dutch newspapers. He presented and directed television and radio programmes and has 10 books to his name. Herbert is interested in nascent fields such as 3D printing, drones, robotics and the private space business.