LANTR Bimodal + VASIMR = ?

wrote in message ...
The thought ran through my head that a nuclear thermal rocket is ideal
for getting out of LEO to GEO+ quickly for a manned mission, but VASIMR
isn't shabby for trips beyond if the power is available. They both use
the same propellant/coolant, liquid hydrogen. An NTR can be designed for
bimodal use, providing propulsion and power.

It begs the question then, can these two be suitably combined?

What I imagine is some sort of NTR that is on the very low end of
thrust, designed more for power than propulsion. A pebble bed reactor,
the one with the spheres of uranium encased in graphite, suitably
divided into areas cooled by the primary coolant of nitrogen, and areas
that can either transfer heat to or direct heat the hydrogen. Have the
nitrogen run a turbine for power.

Nitrogen for a coolant? We usually use helium for gas cooled reactors.
Neutron absorbsion cross section of zero and chemically nonexistant.
Why nitrogen? (Except its much cheaper)

Also, I'm not sure pebble bed is appropriate, though perhaps its fine.
Given the rather tight mass requirements, your fuel will likely be
highly enriched uranium to make the reactor quite small, as is used on
submarines.

Otherwise, it sounds like a good idea.

"Paul F. Dietz" writes:

Dez Akin wrote:

Nitrogen for a coolant? We usually use helium for gas cooled reactors.
Neutron absorbsion cross section of zero and chemically nonexistant.
Why nitrogen? (Except its much cheaper)

The speed of sound in helium is too high to conveniently expand it
in a turbine, I think.

You don't need supersonic, or even compressible, flow to run a perfectly
good turbine. The obvious example being hydraulic turbines as used in,
e.g., hydroelectric power plants.

However, if you want to use the existing gas turbine technology base
without extensive and perhaps unnecessary development work, there is an
argument to be made for using a working fluid at least roughly similar
to air, such as nitrogen...


This is why the proposed solar dynamic power system for the station (long
since shelved) would have used a He/Xe mixture (He for high thermal
conductivity, Xe to keep the average molecular weight high.)

...or a proper He/Xe mix, though that seems needlessly contrived compared
to straight N2. Argon, anyone?


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