RLV physicaly impossible ?

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 ?

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.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

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

(Paul Spielmann) wrote:
[...] let me remind you about the physical laws of thermodynamics (heat)
that makes it impossible to turn the engines on and off forever or
at least alot of times!

I turn my car engine on and off a lot. Jet engines get turned on and off a
lot. Not sure what physical law you are talking about.

Or am i wrong ?

I don't want to be the one to break the bad news to you....

James Logajan wrote in message 5...
(Paul Spielmann) wrote:
[...] let me remind you about the physical laws of thermodynamics (heat)
that makes it impossible to turn the engines on and off forever or
at least alot of times!

I turn my car engine on and off a lot. Jet engines get turned on and off a
lot. Not sure what physical law you are talking about.

Or am i wrong ?

I don't want to be the one to break the bad news to you....

here is the thing i am really not so sure by my own nolage, its just
that i have asked peoeple that i think are credible people that work
in the field of physics (not space engineering though) and accoarding
to what they have said: the energy and heat stress of going to orbit
and back are much more higher than for example what a car experience
and therefore it cuts back what is possible to do with space crafts.
Either the person i asked is right or wrong because he is no expert in
space crafts and is too "theoretical". I still wonder though how long
life spans sub/orbital rlv vehicles will have though..

In article ,
Paul Spielmann wrote:
that i have asked peoeple that i think are credible people that work
in the field of physics (not space engineering though) and accoarding
to what they have said: the energy and heat stress of going to orbit
and back are much more higher than for example what a car experience
and therefore it cuts back what is possible to do with space crafts.

The extent of these problems is much exaggerated, especially by people who
don't have direct knowledge of space engineering.

In some cases, there are real problems but they are artifacts of current
design practices, which can and should be changed. For example, rocket
engines often experience a great deal of thermal stress during startup,
due to very rapid temperature rises. But there is no fundamental reason
why their startup sequences need to be so fast. Limiting warmup to rates
normally found in jet engines is not a big problem, once designers start
caring about reliability and long life rather than absolute maximum
performance.

In other cases, these beliefs are simply misunderstandings, partly based
on authoritative statements from people with vested interests in keeping
spaceflight expensive and difficult. (Of *course* NASA will tell you that
space is terribly hard; it would be immensely embarrassing for them to
admit that they've been wasting your money all these years...)

...I still wonder though how long
life spans sub/orbital rlv vehicles will have though..

It's an open question. The first-generation ones may indeed have somewhat
limited lives. There is much speculation about this, most of which boils
down to religious arguments about basic assumptions. The only way to know
for sure is to try it and see.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Virtually all managers and most all engineers that have grown up in the
current space hardware design bureaus have been steeped in the "rockets
as artillery" school. Design constraints are fire the engine once for
testing, put it on the stand for its first flight, then through it away
after four or five minutes operation. Any effort or materials to give
it a longer life are considered a waste. This does not mean that large
rocket engines can't be built for longer service, only that the
engineers don't need it for "artillery" use. A good example of a flight
weight engine with long life is the RL-10. This engine used on several
upper stages was used (in the short bell version) for the DC-X, and has
had dozens of starts and hours of total time.
Another area that is not considered by most engineers developing RLVs is
that propellents used by most designs are about three orders of
magnitude lower in cost than flight hardware, and that adding propellent
to reduce the quantity of flight hardware will eliminate any failure
modes that were possible in the eliminated hardware. An example would
be if the Shuttle had no wings there would have been no wing leading
edge failure.
RLVs require companies and engineers willing to try new paradigm, not
just incremental improvements. The Space Shuttle was a try, however
many of its design requirements were made for political reasons not
economic or technical.

Mike

In article ,
(Henry Spencer) wrote:

In article ,
Paul Spielmann wrote:
that i have asked peoeple that i think are credible people that work
in the field of physics (not space engineering though) and accoarding
to what they have said: the energy and heat stress of going to orbit
and back are much more higher than for example what a car experience
and therefore it cuts back what is possible to do with space crafts.

...I still wonder though how long
life spans sub/orbital rlv vehicles will have though..

Mike Swift wrote in message ...

Another area that is not considered by most engineers developing RLVs
is
that propellents used by most designs are about three orders of
magnitude lower in cost than flight hardware, and that adding
propellent
to reduce the quantity of flight hardware will eliminate any failure
modes that were possible in the eliminated hardware. An example would
be if the Shuttle had no wings there would have been no wing leading
edge failure.

I suppose you mean an approach that is simple is prefered, to make
rlvs possible ? anyway i tend to like "simple" and "clean"
approaches... like thouse of scaled composites and armadillo
earospace. It seems the space shuttle as you meantioned is really
"complex"

Mike Swift wrote in message ...

Another area that is not considered by most engineers developing RLVs
is
that propellents used by most designs are about three orders of
magnitude lower in cost than flight hardware, and that adding
propellent
to reduce the quantity of flight hardware will eliminate any failure
modes that were possible in the eliminated hardware. An example would
be if the Shuttle had no wings there would have been no wing leading
edge failure.

I suppose you mean an approach that is simple is prefered, to make
rlvs possible ? anyway i tend to like "simple" and "clean"
approaches... like thouse of scaled composites and armadillo
earospace. It seems the space shuttle as you meantioned is really
"complex"

Virtually all managers and most all engineers that have grown up in the
current space hardware design bureaus have been steeped in the "rockets
as artillery" school. Design constraints are fire the engine once for
testing, put it on the stand for its first flight, then through it away
after four or five minutes operation. Any effort or materials to give
it a longer life are considered a waste. This does not mean that large
rocket engines can't be built for longer service, only that the
engineers don't need it for "artillery" use. A good example of a flight
weight engine with long life is the RL-10. This engine used on several
upper stages was used (in the short bell version) for the DC-X, and has
had dozens of starts and hours of total time.
Another area that is not considered by most engineers developing RLVs is
that propellents used by most designs are about three orders of
magnitude lower in cost than flight hardware, and that adding propellent
to reduce the quantity of flight hardware will eliminate any failure
modes that were possible in the eliminated hardware. An example would
be if the Shuttle had no wings there would have been no wing leading
edge failure.
RLVs require companies and engineers willing to try new paradigm, not
just incremental improvements. The Space Shuttle was a try, however
many of its design requirements were made for political reasons not
economic or technical.

Mike

In article ,
(Henry Spencer) wrote:

In article ,
Paul Spielmann wrote:
that i have asked peoeple that i think are credible people that work
in the field of physics (not space engineering though) and accoarding
to what they have said: the energy and heat stress of going to orbit
and back are much more higher than for example what a car experience
and therefore it cuts back what is possible to do with space crafts.

...I still wonder though how long
life spans sub/orbital rlv vehicles will have though..