RLV physicaly impossible ?

Henry Spencer wrote:
In article ,
Paul Spielmann wrote:

...liquid propellant engines, and they seem to
think they can make these engines totaly reuseble, let me remind you
about the physical laws of thermodynamics (heat) that makes it
impossible to turn the engines on and off forever or atleast alot of
times!


How, exactly, do the laws of thermodynamics make it impossible to turn a
rocket engine on and off a lot? Be specific. The small engines used as
attitude-control thrusters in spacecraft are sometimes rated (by testing,
not theoretical calculation) for 300,000 or more firings.

I have an engine sitting on my desk at work that went for 632000
pulses - and still performed the last pulse within 5% of what it did on
the first!

Laws of thermodynamics (??) be damned!

Brett