Re: About the "Mars in two weeks" nuclear rocket.

From: Robert Clark (rgregoryclark_at_yahoo.com)
Date: 03/01/05 

Date: 1 Mar 2005 02:57:49 -0800

Uncle Al wrote:
> Robert Clark wrote:
> >
> > There was a study announced a few years ago on a more efficient
> > nuclear fuel, Am-242m, that would allow a trip to Mars in two
weeks:
> >
> > Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two
> > Weeks.
> > Date: 2001-01-03
> > http://www.sciencedaily.com/releases/2001/01/010103073253.htm
>
> [snip erudition]
>
> > So in this case: M1/M2 = e^(4.937) = 139. If the ship itself
weighed
> > 100 tons the ship plus propellant would weigh 14,000 tons.
>
> Say there, git, how many kilos of americium were you planning to
> snuggle within? Do you have any idea how to manufacture it or how
> much it would cost to obtain? Or how to handle it at scale in your
> application? Remember how fission was going to generate electricity
> so cheap it would not be metered?
>
> Even xenon ion engines are obscenely expensive because isolating 10
> tonnes of xenon is no laughing matter - and it's in the air for free.

> Volatile metal fuels short out the works (and mercury also dissolves
> them). SF6, freons, and the like are horribly corrosive when
ionized,
> including toward ceramics. Argon does not store densely even as the
> cryogenic liquid.
>
> > This is large, but the "DESIGN-CENTERED INTRODUCTION TO AEROSPACE
> > ENGINEERING" web page gives the mass ratio to reach Earth escape
> > velocity for standard chemical rockets, as with the Apollo
missions, as
> > 18.7. So this nuclear Mars mission would be less than a factor of
10
> > higher.
> [snip]
>
> "Less than a factor of 10." Giggle. One Reagan-class aircraft
> carrier is ridiculous. Mulitply by eight.
>
> Hey Bob, remember the Enviro-whiner stink about a little Pu-238 in
the
> Cassini thermal isotope generators? They'll stink on your parade
much
> more - enriched U, Pu and Am are all fission bomb stuffings.
>

 Was your purpose in mentioning the Reagan-class carriers a reference
to their weight? They weigh much more than the number I remarked for
the mass of the Mars mission:

USS Ronald Reagan
"Displacement: 77,600 tons light, 98,235 tons full"
http://www.answers.com/topic/uss-ronald-reagan

 Or a reference to their cost and size multiplied by the number of
carriers built? In any case, they *were* built. A Mars mission would
likewise require a tremendous investment of national resources.
Actually, my guess is that it will be an international project.

 Note also that the ratio of actual liftoff weight of the Apollo
missions to payload was 60 to 1:

Saturn V Rocket.
# Stage m0 mp m1
1. S1C 300.0 4492.0 4792.0
2. S2 95.0 942.0 1037.0
3. SIVB 34.0 228.0 262.0
4. IU 4.5 0.0 4.5
5. payload - - 109.6
"Here m0 is the stage empty weight, mp is the propellant, and m1 is the
stage total, in thousands of pounds."
http://spider.ipac.caltech.edu/staff/waw/mad/mad3.html

 Adding up the numbers in the last column you get total weight over
6,200,000 lbs. to the payload of 109.6 lbs. Note also you probably
wouldn't launch from Earth but from space so you wouldn't have to worry
about the gravitational effects on this large mass.
 You probably also wouldn't get the fuel, both reaction mass and
radioactive materials, from Earth but from the Moon or near earth
asteroids.
 Also, as I said it is *very* likely that a reactor design can be
created for the Am-242m fuel that produces an Isp of 6000s since such
designs already exist for uranium and plutonium and Am-242m is 100
times more efficient. An Isp of 6000s would result in a mass ratio less
than 8.
 There are experimental methods now used that can efficiently separate
isotopes in small amounts. These methods very likely would scale up to
larger amounts. The cost of this scaling I estimate would be a small
fraction of the cost of the mission.
 I'm sure with your extensive knowledge you could ferret out some of
these methods. I would prefer not to say precisely in a public forum.

   Bob Clark

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