Re: Intermittent Fusion Rocket

On Wed, 07 Nov 2007 15:24:14 -0800, Uncle Al <UncleAl0@xxxxxxxxxxxxx>
wrote:

Eric Gisse wrote:

On Wed, 07 Nov 2007 11:58:20 -0800, Uncle Al <UncleAl0@xxxxxxxxxxxxx>
wrote:

tontoko wrote:

They say it's hard to send manned spacecraft to the planets further
than Mars with present chemical rocket.

Do you want them not to be pan fried by radiation? "Hard" is properly
spelled "impossible."

Future rocket will have low
energy consumption rate for propulsion enough to carry out such
mission successfully.

p=mv for maneuvering. E=(mv^2)/2 for propulsion. A fission reactor
won't power it. Three fission reactors have been suggested.

A fission drive has the specific impulse to take a craft to Mars in
two weeks and to a [cosmically] close star in a human lifetime.

Don't underestimate the power available.

Don't underestimate the shielding required and the reaction mass
necessary. It makes for a very massive vehicle. Free energy is
surprisingly expensive. The only up-tick is that rear reactor
shielding also shields the crew from solar flares. Yer gonna need
maybe 50 MW summed thermal and electical continuous. There will be
reactor cooling problems.

It wouldn't have to be isotropic shielding - who cares if you
irradiate space? Plus, it depends on what kind of design we're going
with.

I expect an Orion class design would need more shielding than a
hot-running reactor with Hydrogen or something else is pumping through
it.

Plus, 50MW is child's play for a decent sized reactor.

http://www.uic.com.au/nip60.htm

I'm sure one of these could be jury-rigged to work.


One then expects NASA to put the reactor(s) in front.

Since this is all about /_\momentum and energy is free we'd like the
hottest heaviest exhaust possible that efficiently stores. Hg boils
at 350 C and stores as dense liquid. We've got oodles of Hg from
decommissioning chlorine/caustic cells. Strike some big arcs. Feed Hg
through the engine bell as coolant then through the electrodes as
coolant before spraying into the plasma, then out through the engine
bell.

Ion drive mod 2!

Pump the mercury through the reactor then ionize it. Use the mercury
as coolant [though not exclusively, it'd be bad if the only way to
keep your engine from turning into a puddle is to run it] to heat the
mercury, and use the energy from the reactor to ionize it.

The fuel tank would also probably make for good shielding.

I wonder what the specific impulse of one of these reactors would
have. Say you wanted to make a reactor to run as hot as possible while
keeping containment. What would the maximum temperature be around? I'm
thinking something in the region of 2000C or so - say 2500 K for
concreteness.

It would *have* to perform better than our current chemical rockets -
an exhaust temperature of over 2000C, plus whatever velocity is
imparted by the accelerator. Though I'm not sure what kind of thrust
you would get out of one of these, but you are guranteed to outperform
an ion drive and have similar performance characteristics at the
minimum.

For example, if you can't heat up the fuel fast enough to be a high
thrust engine [I don't know if you can...] it could certainly work
/just fine/ as a [relatively] low thrust engine with /long/ period of
operation.


Radiation shielding toward the rear vs. a servicable engine...
waldoes! That should subcontract some fine political pork.

Yea, nothing says "servicable" than a borderline, hardly shielded
nuclear reactor. IMHO these reactor designs are for things that are
never coming back. Having exhaust that was in direct contact with a
reactor tends to be frowned upon - at least for atmospheric flight.
The other alternative is also frowned upon - detonation of a nuclear
weapon behind a pusher plate.

Though I imagine you could scale the design back a little, shield it
more, and provide a path through the reactor that doesn't directly
contact the nuclear fuel in order to prevent the working fuel from
picking up radioactive particles. Maybe.

Too bad people are too scared of nuclear anything to allow any of
these designs to be built anytime soon. Pity.

.

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