Re: What's a good "proton reflector"?
- From: mmeron@xxxxxxxxxxxxxxxxxx
- Date: Wed, 30 Nov 2005 17:45:10 GMT
In article <1133338318.682470.64460@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, mechdan@xxxxxxxxx writes:
>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?
>
No. Fission reaction givves about 180-200 MeV for a nucleus with A
around 240. That gives you less than 1 MeV/amu. Fussion does better,
still less than 4 MeV/amu
>> >--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.
<Shrug>. You could do the same with Orion. Now, calculate the length
of the line you need to keep the acceleration from destroying the
device and what it carries and consider how you're going to create it.
And you still didn't address the point that not that only a small
fraction of the energy goes into producing protons.
>
>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.
Indeed.
> 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.
Can't tell you off hand, would have to check the cross sections.
>
>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.
No, definitely not. The neutrons will just merrily zip through.
>
>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.
Yes, that much is very true. What you propose is replacing a nuclear
rocket with a nuclear multi-charge gun. My gut feeling is that the
performance will be very disappointing. But I didn't work all the
numbers yet.
Mati Meron | "When you argue with a fool,
meron@xxxxxxxxxxxxxxxxx | chances are he is doing just the same"
.
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