[extropy-chat] "Hyperdrive Engine Could Let Us Reach Mars in 3Hours"

[John K Clark]

I don't know about 3 hours but five years ago I wrote a post to this list
about a way to get to Mars in 2 weeks. Unlike most such proposals this would
require no new physics, just dangerous expensive and heroic engineering.
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The efficiency of a rocket depends on its exhaust velocity, the faster the
better. The space shuttle's oxygen hydrogen engine has a exhaust velocity of
about 4500 meters per second and that's pretty good for a chemical rocket,
the nuclear heated rocket called NERVA tested in the 1960's had a exhaust
velocity of 8000 meters per second, and ion engines are about 80,000. Is
there any way to do better, much better, say around 200,000,000 meters per
second? Perhaps.

The primary products of a fission reaction are about that fast, but if you
use Uranium 235 or Plutonium 239 the large bulk of the material will absorb
the primary fission products and just heat up the material, that slows
things way down. However the critical mass for the little used element
Americium-242 (half life about a century) is less than 1% that of Plutonium.
This would be great stuff to make a nuclear bomb you could put in your
pocket, but it may have other uses.

In the January 2001 issue of Nuclear Instruments and Methods Physics
Research A Yigal Ronen and Eugene Shwagerous calculate that a metallic film
of Americium 242 less than a thousandth of a millimeter thick would undergo
fission. This is so thin that rather than heat the bulk material the energy
of the process would go almost entirely into the speed of the primary
fission products, they would go free. They figure a Americium-242 rocket
could get to Mars in two weeks not two years as with a chemical rocket.

There are problems of course, engineering the rocket would be tricky and I'm
not sure I'd want to be on the same continent as a Americium 242 production
facility, but it's an interesting idea.

John K Clark   jonkc at att.net