What’s sixty thousand miles long, made of carbon nanotubes, powered by lasers and doesn’t exist yet? In case you are still guessing, yes it’s a space elevator.
The idea was first mooted in the 1960s by engineers in the USSR as a way to escape the confines of the Earth. More than 50 years on and there are groups in the US, Germany and Japan still working on the concept.
A space elevator would run on a cable that had been sent 60,000 miles up into space. A counterweight would be fixed on to the end of the cable and centrifugal force would keep it taut.
The main reason the idea lives on is that the disadvantages of rockets remain the same as they did 50 years ago. Rockets are impractical, complex, dangerous, have very limited payload capacities and are extremely expensive.
Suchi Ohno, president of the Japanese Space Elevator Association (JSEA), says: “An elevator can carry many things into space at once. It will also be possible to send passengers. If we build a space elevator it becomes safe enough for everyone to travel on.”
The primary engineering challenge for a space elevator is materials. For it to be an event remotely feasible consideration, a material strong enough to withstand the enormous forces acting upon the cable has to be developed.
Carbon nanotubes were discovered in 1991 in Japan and almost immediately it reignited interest in space elevators. A cable made from carbon nanotubes could have enough tensile strength to make the cable.
Interest grew until in 2004 Nasa asked the Los Alamos Laboratory in the US to conduct a feasibility study. Ohno says: “It found that if we had enough carbon nanotube fibre it would be feasible. That started a kind of space elevator fever in the US, but once people realised it was so far off they calmed down. But in Japan, people really want a space elevator, to the extent it is like a sub-culture.”
The second biggest engineering challenge to building a space elevator is energy. Japanese and Nasa engineers have proposed using a solar powered satellite and so-called “power beams”. Ohno says: “It is impossible to use a battery, the total energy required is so huge. Nasa are thinking of using a power beam, an infrared laser or microwave to send energy to the climber. The infrared lasers efficiency through the air is less than 5%, but it is feasible today. The laser beam’s efficiency is 20% but it is not yet available.”
Solve materials, energy and the myriad of other engineering problems, and another major barrier is political. There is no international legal infrastructure that covers the building of a giant elevator that would wrap itself around the Earth two and a half times if it fell.
However, the Japanese Space Elevator Association is confident such legalities could be surmounted. Devin Jacobson, from the JSEA, says: “If the physics problem is solved we will get around whatever legal hurdles people put around us with a new legal structure.”
But the funds required for such a long term project would be massive. A small amount from Nasa and Jaxa currently goes into materials science and research and also covers the outreach work that Ohno and Jacobson do around the world. Nevertheless they believe that funding could come from government defence funding.
Continuing research
Despite the difficulties, research into the concept continues. The longest untested cable breaking length worked out so far is more than 1000km using the material Dyneema, a thermoplastic polyethylene. Tests have been done so far on a 1.2km high tethered balloon.
Work is also ongoing by various teams, primarily students in Japan, to design the climber. The lighter the climber is the better. Nasa has also recently funded a X Prize for the climber’s design. Last year a large Japanese construction company in Japan, also began researching materials for a space elevator.
Then, later this year a space elevator experiment will be run from the International Space Station, which will deploy a 100m cable. This will be followed by a 1km experiment in 2018 with a climber.
However, Jacobson says the main trigger for the idea will be the cost effective manufacturing of the carbon nanotubes, which he believes will prompt more investment into the idea.
“We don’t quite know how strong we can make the materials yet, because we don’t have the tools to look down at that molecular level or generate the materials at that level.”
“We know we can do better, we just don’t know how much better we can get,” he says.
“The tools are getting better all the time. If we had a molecular 3D printer like we are starting to have, we might be able to do it.”
“We will know this century if we can do it. Predicting the feasibility date is not possible. But you can look at the technology trends and project when it might become feasible if it is feasible.”