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

[markus7]

vansig 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

Are you joking? If not, please explain how such a wonderous “nozzle” might work.

[vansig]

markus7 wrote:
Are you joking? If not, please explain how such a wonderous “nozzle” might work.

not joking, no; but neither have i thought it through, entirely.
these are all charged particles, all moving away from the focal point of the reaction.

so, some sort of magnetic field should do?

[markus7]

vansig wrote:

Are you joking? If not, please explain how such a wonderous “nozzle” might work.

not joking, no; but neither have i thought it through, entirely.
these are all charged particles, all moving away from the focal point of the reaction.

so, some sort of magnetic field should do?

When I said “joking” that was regarding any nozzle similar to a normal rocket nozzle. The alpha particle’s would not elastically bounce off material walls as gases do, but would burrow in, so their momentum would not be redirected aft as in a normal rocket nozzle.

Yes, a very strong magnetic field with a ‘pinch’ at the upstream end would be able to generate thrust, but that is a huge change to the design. Also, I assume the ‘pinch’ would have to enclose the hardware shown which would result in the eventual vaporization of that hardware.

The diagram shows all the alpha particles exiting in the thrust direction, apparently by magic, without the presence of any such field.

[vansig]

Seems to me, that the only way to make all the alphas exit in the thrust direction is to have extremely strong magnetic fields. As far as i know, only DPF does this.

[markus7]

vansig wrote: Seems to me, that the only way to make all the alphas exit in the thrust direction is to have extremely strong magnetic fields. As far as i know, only DPF does this.

The difference of course is that these potentially gigagauss fields are DPF’s astonishing, stupendous, mind blowing, game changing trick. They are not a detail.

I don’t yet understand how DPF’s clever trick is being done. It is strange to think of the plasma as being inherently self organizing in its ability to convert an almost blind input of energy into the forces needed to compress a plasma sufficiently for fusion to occur.

That is really cool.

Maybe with a lot of work I will understand it one day.

But as of now, it is so mysterious that I wonder things like “What is special about the present general layout (besides it being the one that has been historically developed)? Maybe very different configurations would even better exploit these same natural plasma instabilities.”

[TimS]

The article discusses using this engine for satellite station keeping, so it only needs a small force if it is on a significant time. At 100,000 alphas per pulse and 75MHz, I get 3.5 watts out and 0.6 micronewton (total momentum all alphas all directions times alpha generation pulse rate). This is likely not enough force for anything useful but I expect there is a lot of optimization to be done. It talks about being possibly only 50% efficient; perhaps some of the alphas going in the wrong direction are expected to be lost. Would depositing a few watts of alpha particles into the boron and metal film layers destroy them? How long would that take?

Note this is not a very efficient rocket in terms of force / power, because the high velocity of the alphas cause them to require large kinetic energy. However, the point is to optimize fuel use. I calculate boron used at 0.05 ng/sec, or 1.6 mg/year if the device is always active.

[Rezwan]

Also reported in “Geekosystem.com“

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