Re: "Concerned citizens" only hope for SPS......by Dr. Gerard K. O'Neill

In article <5YudnRxH6qHRh9nYnZ2dnUVZ_rGdnZ2d@xxxxxxx>,
Paul F. Dietz <dietz@xxxxxxx> wrote:
Excuse my ignorance... but what is a Brayton-cycle engine? :-)

Gas turbine (in this case, using an externally heated helium-xenon
mix in a closed cycle).

Doesn't *have* to be a turbine, although that's the usual approach now.

The two main heat-engine cycles, disregarding more-complicated oddities
like the Stirling engine, are Rankine and Brayton.

Rankine is the familiar steam cycle: heat source boils a liquid to vapor,
which is run through a turbine or some other kind of expansion engine,
condensed back to liquid by (loosely speaking :-)) a cold source, and then
recirculated by a pump. Typically it performs best, but it is fairly
complicated, and there are concerns about issues like the behavior of
two-phase flow without gravity. It's been proposed many times for big
space powerplants, but I don't believe it's ever been flown.

Brayton is a simpler version, in which the "working fluid" remains a gas
throughout heating, expansion, and cooling, with recirculation by a
compressor. As noted earlier, it's gotten much closer to flight.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@xxxxxxxxxxxxx
.

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