Reply To: Energy Policy in Chile – Economist Article

[markus7]

jamesr wrote: Has anyone noticed the slashdoted article in IEEE Spectrum on NASA engineer John Chapman’s laser based pB11 thuser design.

http://science.slashdot.org/story/11/06/28/2229224/Fusion-Thrusters-For-Space-Travel
http://spectrum.ieee.org/aerospace/space-flight/a-fusion-thruster-for-space-travel/0

It seems he presented it at 8th IEEE International Conference on Plasma Science (ICOPS) and 24th Symposium on Fusion Engineering (SOFE) in Chicago this week

Is anyone there?? Has anyone got any more detailed information?

Chapman’s fusion rocket design puzzlingly ignores a momentum conservation issue.

See in particular the conceptual diagram of his fusion rocket in the link.
http://spectrum.ieee.org/aerospace/space-flight/a-fusion-thruster-for-space-travel/0

I can provisionally accept the author’s assertion that his picosecond pulsed laser will produce a “roughly 163 kiloelectron volts” shower of protons that then strike boron nuclei, fuse, and then eject three 2.9 MV alpha particles.

My difficulty is the ejected alpha particles will be moving in three random directions (while conserving momentum about the moving center of mass of the proton and stationary boron nuclei). The total momentum of the three alpha particles in the desired thrust direction must be the same as, or less than, the incoming 163 KV incoming proton’s momentum. The diagram shows nothing that redirects their 2.9 MV energy and momentum to the thrust direction. Of course, LPP’s fusor accomplishes this neat trick with GG magnetic fields, but I see nothing to fulfill that function in Chapman’s design.

The text does say: “’Electromagnetic forces’ push the target and the alpha particles in the opposite directions, and the particles exit the spacecraft through a nozzle, providing the vehicle’s thrust”. However, I have not been able to find out anything about the origins of Chapman’s mysterious, and immensely strong, ‘electromagnetic forces’.

Anyone have any ideas, or has Chapman just slipped a gear in his thinking?