Laser pB11 space thuster design presented at ICOPS2011 conference – mentioned on slashdot

[jamesr]

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?

[DerekShannon]

Eric and Murali are there, but I’ll have to check if they spotted this ;-D

[Lerner]

His and mine were almost simultaneous. John had to walk out of mine to present his. I’ll talk to him later.

[zapkitty]

Space travel… we [strike]lose[/strike] gain more fusion reactors that way…

[Breakable]

zapkitty wrote: Space travel… we [strike]lose[/strike] gain more fusion reactors that way…

To put things in perspective:
http://forums.macrumors.com/showthread.php?t=967311
Anyone wants to put fusion budget in comparison?

[zapkitty]

Breakable wrote:

Space travel… we [strike]lose[/strike] gain more fusion reactors that way…

To put things in perspective:
http://forums.macrumors.com/showthread.php?t=967311
Anyone wants to put fusion budget in comparison?

Not counting what’s eaten by ITER?

About zilch. The amount left over for non-oligarch approved fusion research is not even a rounding error in the NASA budget.

[Brian H]

I’m really puzzled and frustrated that Elon Musk (TeslaMotors/SpaceX) isn’t backing LPP to the hilt. It would provide the ultra-cheap distributed power that would make EVs super-competitive, and power his spacecraft (he wants to transport humans to Mars in 10 yrs.) and even his dream of VTOL electric planes able to fly around the globe. For >1% of what’s been spent developing his chemical boosters (which are the class of the planet, btw.) Somebody needs to buttonhole him. He’s not in my social circle, unfortunately, though I’m a bigtime Tesla fan.

:down: :coolsmile:

[Ivy Matt]

Conference is over. Will we be getting any reports on “X-Ray Diagnostics in a Mega-Amp Dense Plasma Focus Device – Focus Fusion-1” or “X-Ray Spectrum from a Mega-Amp Dense Plasma Focus Device – Focus Fusion-1 and Its Correlation to the Plasmoid Formation”? Or wait for the proceedings?

Did you hear any novel ideas apart from Chapman’s laser-beam-target thruster?

[jamesr]

So does anyone have any more details? I would think that any laser based system would be far heavier, and less efficient than a DPF based thruster.

[dennisp]

More info at NextBigFuture: http://nextbigfuture.com/2011/07/fusion-energy-without-radioactivity.html#more

It’s not just a thruster, they think they can generate net power with it.

For a practical system they need a pretty high-power laser that fires at 75MHz. It doesn’t exist yet, but according to Talk-Polywell folks there are commercially-available lasers that meet the specs, except they only fire at around 10kHz. That ought to do for “scientific feasibility,” I’d think. Lasers are advancing pretty quickly, too.

One thing that’s interesting is that according to their analysis, boron fusion isn’t much harder than DT fusion in this configuration.

[Ivy Matt]

Wow, George Miley sure gets around.

[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?

[TimS]

I see nothing about a source of magnetic force in this article, but the description starts by saying that a very strong electric force is created when the laser drives electrons off the foil, which is next to the boron film. The electric force would be in the correct direction to drive the alphas. Would this force be strong enough to reverse the path of high speed alphas heading toward it? Apparently it is strong enough to strip protons from metal nuclei… (is this really what is meant?)

Also, given the second to last paragraph of the article, it does not sound like Chapman has missed these problems:

The NASA engineer acknowledges that this collection of ideas is still a long way from being a practical device. For example, losses from the alpha particles striking the walls of the exhaust nozzle or each other lower the net power output. [em]Figuring out how to control the particles’ path is an important consideration.[/em]

[markus7]

TimS wrote: I see nothing about a source of magnetic force in this article, but the description starts by saying that a very strong electric force is created when the laser drives electrons off the foil, which is next to the boron film. The electric force would be in the correct direction to drive the alphas. Would this force be strong enough to reverse the path of high speed alphas heading toward it? Apparently it is strong enough to strip protons from metal nuclei… (is this really what is meant?)

Also, given the second to last paragraph of the article, it does not sound like Chapman has missed these problems:

The NASA engineer acknowledges that this collection of ideas is still a long way from being a practical device. For example, losses from the alpha particles striking the walls of the exhaust nozzle or each other lower the net power output. [em]Figuring out how to control the particles’ path is an important consideration.[/em]

The initial “very strong electric force .. created when the laser drives electrons off the foil” is sufficient for generating, it is claimed, 163Kev protons. The alpha particles are 2.5 to 3.8 Mev (see second figure). No, I don’t see any way that any electric field generated by the initial light pulse could be strong enough to deflect the alphas in the thrust direction.

Remember that almost half these alphas will be moving in the wrong direction. Electric fields totaling million of volts would be needed to get them to go the ‘right’ direction.

This does not look like a detail to be worked out, but as an obvious, irrecoverable fatal flaw.

[vansig]

markus7 wrote:
This does not look like a detail to be worked out, but as an obvious, irrecoverable fatal flaw.

hardly a problem, at all. that’s what nozzles are for

[Author]

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