Would DFD itself be able to generate enough thrust to lift off from the lunar surface to orbit?
There are already fusion reactors that provide (slightly) more power than given.
Quote from: IRobot on 09/12/2013 06:14 AMThere are already fusion reactors that provide (slightly) more power than given.Really?
Quote from: QuantumG on 09/12/2013 06:55 AMQuote from: IRobot on 09/12/2013 06:14 AMThere are already fusion reactors that provide (slightly) more power than given.Really?http://en.wikipedia.org/wiki/JT-60Q = 1.25But operation times less than half minute, and Q=5 needed to be self-sustaining.
During deuterium (D–D fuel) plasma experiments in 1998 plasma conditions were achieved which would, if the D–D fuel were replaced with a 1:1 mix of deuterium and tritium (D–T fuel), have exceeded break-even—the point where the power produced by the fusion reactions equals the power supplied to operate the machine. JT-60 does not have the facilities to handle tritium; currently only the JET tokamak in the United Kingdom has such facilities.
During a full D-T experimental campaign in 1997 JET achieved a world record peak fusion power of 16 MW which equates to a measured gain Q, of approximately 0.7. (..) As of 1998, a higher Q of 1.25 is claimed for the JT-60 tokamak; however, this was not achieved under real D-T conditions but extrapolated from experiments performed with a pure deuterium (D-D) plasma.
I think the MAST experiment also achieved a Q > 1, but can't find any reference.
In any case, the fusion engine does not have to be self sufficient, it could be complemented with solar power, what matters is the overall isp and higher thrust compared to ion engines.
If you read the page you linked to, you'll see that is purely theoretical.
Quote from: QuantumG on 09/12/2013 07:37 AMIf you read the page you linked to, you'll see that is purely theoretical."Purely theoretical" is too strong a statement, and could be misleading. Rig JT-60 for tritium and you will get Q>1. The reactor can do it. It just doesn't.
Well, I was thinking that a burning plasma only needs to be sustained for <10 mins to get you to orbit. I'm talking about keeping it burning even in spite of bleeding off energy for exhaust thrust. But my point is that you don't need to strive for some perpetual indefinitely sustained fusion reaction - you just need one that lasts long enough to help you achieve escape velocity. Accordingly, you might be able to skimp on the parts you use and save launch mass, because you're not going to sustain the fusion reaction for more than 10 minutes.