In the last post we brought 100 million people a day to orbit. They still need to get to the planet. At this point conventional rockets are not that terribly feasible anymore. You would be looking at space traffic that is the same as our current level of air traffic and it take a lot of energy to decelerate from orbital speeds and then also a good amount to get in and out of Earth’s gravity well. So, we need better solutions.
The Space Elevator
The space elevator has been a staple of science fiction since first popularized by Arthur C. Clarke in the novel The Fountains of Paradise. I had always thought that is were the idea came from, but it dates to 1895 when Konstantin Tsiolkovsky was inspired by the Eiffel Tower, looking at it as a building a tower to space. It was Clarke who popularized it in the novel.
The concept is that you put a space station in geosynchronous orbit, 35,786 kilomters (22,236 miles) above the equator. Any object in this orbit is moving in the same speed as the Earth’s rotation. This means it would appear stationary in the sky. This is why for geosynchronous Direct TV satellites you point your dish toward the southern sky if you live in the northern hemisphere, northern sky in the southern hemisphere, and straight up at the equator. From the space station you drop a tether to the surface of the Earth and extend a counterweight above your station. The centrifugal force then keeps tension on the cable. You now have a cable to support an elevator to orbit.
There are two problems with this. First, we have no material strong enough for the cable to support its own weight, and second, it is a long elevator ride to orbit. Great if you are the infancy of your space infrastructure, but probably not to effective if you must move 100 million people daily.
In terms of the materials that it is being worked out. I recall a comment from Arthur C. Clarke as to when people would build a space elevator. “Fifty years after people stop laughing.” In about 2006 is about the time the concept of carbon nanotubes came out. This was considered the first material that might be strong enough for a cable. So this is about the time people stopped laughing, and there is a Japanese company planning to build one by 2050. Pretty good prediction.
Orbital Rings
An orbital ring is just as it sounds. It is a ring around the planet at a given height, typically low Earth orbit (LEO); which is 300 to 2000 km from the surface. In your orbit you are effectively falling around the Earth so at each height there needs to be a speed that keeps you falling and missing the Earth. In low Earth orbit (LEO) this is about 28,000 km/h (17,000 mph). At this speed you are orbiting the Earth every 90 minutes and there would be no way to have any tether to the surface.
The solution to this problem is to have a ring of material orbiting the Earth at orbital speeds. This can be some metal or even electrons. This is then encased in a tube. This will house the electromagnetic accelerators to keep the material up to speed and support the tube. The accelerated material provides the outward force against gravity and the tube can be stationary. You now have a structure to build space stations, hypersonic orbital maglev trains, etc. These are stationary to the planet and are not in free-fall so have almost the full gravity of Earth. Now you can drop cables to the surface that will support space elevators only 400 km in height and even trains to orbit. And we have the material science experience to make the cables today. For more details a great video to check out is Isaac Arthur’s YouTube video below.
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