This is a 10-part series on emerging technologies from the book “Soonish”, and how nanotechnology can be applied to improve the problem.
Cheap Travel to Space
Space travel itself isn’t an issue. We’ve been able to do that for more than 50 years. Affordable space travel, however, is a whole different story. Currently, it’s estimated that it costs 10,000 dollars to send a single pound to space. The reason why space travel hasn’t advanced relatively much in the last few decades, compared to say, computers, isn’t a knowledge limitation so much as it is a cost limitation.
Space travel is expensive for very few, but very important, reasons. A rocket is essentially a huge chamber that holds 1. Stuff you want to send into space, like humans or cargo, and 2. Stuff that gets you into space, like propellant. Both of these things have mass. So let’s say you have a box of cargo that you want to send into space that’s relatively light. Sending the box of cargo, which has a fixed mass, off into space requires energy, and that’s where the propellant comes in. So to send the cargo into space, you have to attach a tank full of propellant to the rocket. But now you have another problem. You now have to send the mass of the cargo, and the propellant, at the same time. So now you have to attach even more propellant. Eventually, you have to keep adding propellant until the total sum of propellant has enough energy to carry the sum of the mass of propellant, and the cargo. This comes out to be a lot. While propellant is relatively cheap, building rockets to handle that scale is not. Not only do the rockets have to be extremely large and require a lot of raw materials, but they must be build extremely precisely, as you’d want heavy fault-tolerance when you’re trying to explode something into the sky.
(A much better explanation for why rockets are heavy, with actual equations, can be found here: https://therocketscienceblog.wordpress.com/2016/10/19/why-are-rockets-so-heavy/)
The main innovation of SpaceX is that they’re attempting to make rockets easily reusable. Currently, rockets that are blasted off into space are no longer re-used, because the journey to space and back batters them enough that they can’t be re-used. Since making rockets tend to be really expensive, being able to re-use them lower the costs dramatically. The foibles of Elon Musk aside, I’m excited to see what SpaceX has in store for the future.
SpaceX aside, there are (theoretically) other ways to reach space without having to explode things into the sky. The concept of a space elevator has been around for decades, and recently, technology has advanced enough to make it seem actually possible. Imagine taking a jump rope, and tying one end to a medium-weight. Then, hold on to the other end, and spin around as fast as you can. As you spin, the weight will be suspended in the air, circling around you, and the rope will be held very tautly. This is essentially the concept of a space elevator. Substitute your spinning body with a spinning earth, the jump rope with a larger cable, and the weight with some counterweight like an asteroid. If a cable is kept taut, then humans can scale the rope without needing propellant to keep themselves from free-falling.
Previously, the limiting factor for this concept was that there wasn’t a material strong enough to support the space elevator. Titanium (300,000 Yuris) and kevlar (2.5 million Yuris), some of the stronger materials in the world, would only fulfill 8% of the required specific strength. However, the specific strength of carbon nanotubes (55 million Yuris) would do the job. A cable made of carbon nanotubes would be strong enough to create a space elevator, assuming there are no deformities in the nanotubes.
However, there are other challenges to creating a carbon nanotube space elevator. Lightning storms can lower the integrity of nanotubes, and while the tensile strength of nanotubes are astounding, their much lower shear strength means that cables can still be cut. Moreover, while a space elevator would make space travel really cheap, it would still take a lot of money to create one upfront, not to mention the fact that the manufacture of carbon nanotubes is still in its infancy, and therefore still quite expensive.
That being said, I still think the best long-term bet for making space travel cheaper is the creation of a space elevator, and look forward to the decreased cost of both the synthesis of nanotubes, and the creation of such an elevator.