[ExI] Hot Rod (was:Nuclear Space)

spike spike66 at att.net
Wed Dec 26 17:54:34 UTC 2007

> bounces at lists.extropy.org] On Behalf Of John K Clark
> The working model was called "Hot Rod" and was launched in 1959 at
> Point Loma California and is now is now in the Smithsonian Air and
> Space Museum. It used 6 explosive charges to reach an altitude of
> 105 meters, the first charge was of black powder but the other 5 were
> high explosives, PETN (Pentaerythritol Tetranitrate)...
>  John K Clark

Interesting.  John I realized after I read the site that an nuclear
atmospheric launch and a deep space nuclear thruster are two very different
things.  We were talking about two completely different concepts, both of
which use nukes as an energy source.  Reasoning: an atmospheric launch Orion
vehicle would actually use air as a momentum transfer fluid as opposed to an
ablative material from the pusher plate.  

For the moment, ignore practical issues such as the legality of nuclear
blasts in the atmosphere, the hordes of protestors, all that messy real
world stuff.  In an atmospheric Orion launch, air would be superheated from
the nuclear blast.  The air itself would then transfer momentum via a shock
wave to the pusher plate.  The air behind the pusher plate would momentarily
be rarified, but would come rushing back from atmospheric pressure.  Then
the next blast would cause the air to push the bird again.  We might want to
design the pusher plate to ablate as little as possible, letting the air do
the work.

When the air gets really thin as the bird rises, and no longer an effective
momentum transfer mechanism, then the thrust would need to result from
momentum transfer via ablation of the material on the pusher plate.  Altho
these two concepts have some similarities, from an engineering point of view
they are two different things.  The deep space version would be very low
acceleration, for instance, so that solves a bunch of the structural
headaches instantly.  The engineering of a deep space Orion is way easier to
do, waaaaaay easier, than the other.  

I still don't see how the air launched Orion could be made to work.  The
acceleration loads, guidance problems from asymmetric thrust and aerodynamic
forces on an air launch Orion would make me flee silently in the night.

On the other hand, think of how relatively simple could be collecting a pile
of nuclear fusion devices on a rocky asteroid a few hundred meters on a
side, by lifting them via conventional means, all fifty year old technology.
The center of gravity of the asteroid is located via star navigation and
rocking the asteroid, a nuclear device is placed on the opposite side of the
asteroid from your pile of bombs, a spring-loaded device pushes the bomb
away and the detonation takes place when the bomb is perhaps a radius away
from the surface, or perhaps a little less (I haven't done the calcs on that
yet.)  The surface ablates, the results is an acceleration of perhaps a half
G for a tenth of a second, which is half a meter per second delta vee.  The
entire rock goes into a slow rotation from asymmetric thrust, which needs to
be cancelled by intentional compensation from the next blast.  

It would take sixty thousand such blasts to get to the 30 km/sec we used in
an earlier example.  This process could take months to get up to a really
big sexy delta vee, but the engineering is very simple, and what's the hurry


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