RLV physicaly impossible ?

Paul Spielmann wrote:

I am really amazed by all these optimistic people trying to do rlvs
and i belive in these peoples cause! however it strikes me that these
people all seem a bit to optimistic for ex almoast all the groups i
have investigated are into 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! for me it seems almoast impossible to make a liquid rocket
engine reuseble. Or am i wrong ? will these people beat the heat laws
of rocket engines somehow ?

Have you heard of jet engines? The Space Shuttle Main Engine?

Are you aware that most reusable rocket engine designs (apart from
thrusters) employ active cooling?

You design them to not operate close to the physical margins (not
even as close as the SSME does). This is why the engine in your car
needs less repair and maintenance than engines used in various forms of
racing, where they're typically pushed to the limit and kept there,
sometimes for hours.

And in all the above examples, materials science doesn't stand still.

What's not to understand?

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