Sunday, 16 February 2014

The Fusion Drive

The fusion drive has long been a mainstay of science-fiction propelling spacecraft to other planets and even other stars. In the real world fusion power has always a dream that has never quite made it to reality. This has led some people to say that fusion is the power of the future and always will be.

The reason why the idea of the fusion drive has hung around for so long is that our current chemical based rockets are just so inefficient. You may think that a payload that is twice the mass would simply require twice as much fuel. This extra fuel also adds mass to the rocket, which means even more fuel. The amount of fuel needed grows exponentially as the size of the payload increases. This is one of the reasons why Mars One will be a one-way trip. Carrying rockets and fuel for the return journey is just too difficult.

But all this is about change. A new way of thinking about the fusion drive has breathed new life into this old idea. It is a new way of using fusion for propulsion, while not worrying about having a sustainable reaction or providing power to the spacecraft.

Scientists and engineers have discovered that they can initiate fusion using an intense magnetic field to compress circular bands of lithium around a deuterium-tritium pellet. This creates a small fusion reaction that vaporises and ionizes the metal bands which then become propellant. This cloud of gas can then be pushed out the back of the spacecraft using magnetic fields as a “nozzle”. (A similar system is already used with ion propulsion.) They have named it the Fusion Driven Rocket, or FDR.

The result is a huge increase in efficiency. The amount of propellant needed can be cut dramatically. This fusion drive does not provide enough thrust to boost payloads into orbit, but is used for interplanetary distances.

Getting large spacecraft to the outer solar system is very difficult at the moment. Cassini spent years in the inner solar system getting repeated gravity assists to build up enough speed for it to begin its journey to Saturn. This fusion drive could cut a nine month journey to Mars down to 30 days. It easily makes it feasible for humans to get to Mars without having to die there.

It’s all very exciting, but ironically this potential breakthrough has not been widely reported in the media. It’s a bit like the silence that greeted the invention of the jet engine. Hopefully, FDR will be to spacecraft what the jet engine was to aircraft.

I found a PDF file with an absolute ton of info about this thing. It has equations and all sorts of graphs - enough to cause a nerdgasm. (I suspect you need to be a physicist to seriously understand this stuff.)

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