Re: What's a good "proton reflector"?

mmeron@xxxxxxxxxxxxxxxxxx wrote:
>In article <1133332508.261525.186800@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, mechdan@xxxxxxxxx writes:

> >What if the material the photons is running into is already very
> >energetic? In my first version of this concept, the protons were
> >simply heated by thermal mixing with fission fragments. In
> >the original concept, the implosion of the inner surface of the
> >liner was incidental to the fact that it was composed of heavy
> >nuclei with roughly 84MeV per particle.

> This is not 84 MeV per particle, rather 84 MeV per nucleus. Less than
> 1 MeV/amu

Is this because of all the electrons?

> >--good for maybe .4c, which is still a heck of
> >a lot better than what an Orion style rocket could offer.

> Again, no. The velocity of the protons doesn't directly translate
> into final velocity of the rocket. There is (again) mass ratio to
> consider. Nuclear explosions do not produce copious amounts of
> protons.

Yes, but I'm not proposing a rocket.

With a "runway" style of propulsion, you do NOT accelerate
your fuel supply. Instead, the pulse units are laid out along
a line, and they detonate as the magsail passes by. Because
the fuel supply is not accelerated, a poor mass ratio only has
a linear effect on the mass and cost of the mission. It doesn't
affect top speed.

Obviously, you can't get something out of nothing. If the
average r.m.s. velocity of your bomb's explosion products
is 3%c, then there's no way to magically configure the device
to accelerate half the bomb product mass to 40%c. Simply
not enough energy there. Instead, I'm looking for a configuration
which can accelerate 1/1000 of the device mass to 40%c.
With such a device, accelerating a magsail interstellar probe
to .25c is a straightforward exercise in brute force.

I've been hoping for some real nuclear physicist to try and
conceive of a suitable device to acheive this sort of goal,
but haven't been able to generate any interest. As such,
I've been trying to learn about nuclear bomb design and
nuclear reactions to come up with a mechanism myself.

I had initially looked at D-He3 reactions as the final stage
of a multi-stage bomb, because it could produce many
protons at .17c (not quite fast enough for my purposes,
but still a heck of a lot faster than an Orion style rocket
offers). However, I couldn't get an idea of how efficient
such D-He3 fusion could be, so I've been trying to stick
to more common nuclear weapons reactions. I get the
impression that even in the hot compressed confines
of a thermonuclear bomb, the yield for D-He3 reactions
is quite low.

At one point, I even considered the possibility of using
fast neutrons from D-T fusion for thrust, relying on a
mini-magnetosphere of plasma to catch the momentum
of neutrons. Maybe that's the best option.

I'm asking for help, here. I KNOW that it's possible to
design a nuclear device to spit out a significant fraction
of its particles at .17c. I have a number of ideas for
ways to acheive faster than that, but I'm not a physicist.
My feeling is that a physicist familiar with these concepts
can figure out a good idea to get puff velocities faster
than .17c.

> And, finally, Magsail is not a magical device. At most it extracts
> the momentum of whatever goes through. Which is just what an Orion
> drive does.

An Orion style rocket accelerates its own fuel supply. This means
that any overhead has an exponential effect on the overall mass
and cost to reach a particular velocity. With a "runway" style
of propulsion, any overhead only has a linear effect on the
overall mass and cost to reach a particular velocity.

Isaac Kuo

.

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