Text 4483, 46 rader
Skriven 2006-07-21 16:42:00 av Robert E Starr JR (4980.babylon5)
Ärende: Re: Congratulations NASA
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Chris Adams wrote:
> Once upon a time, Andrew Swallow  <am.swallow@btopenworld.com> said:
> 
>>There is a major bug in the Space Shuttle Main Engine - it does
>>not work in space.
> 
> 
> Wrong.
> 
> 
>>The Space Shuttle Main Engine like cheap gas cookers needs an
>>external lighter.  NASA built a lighter into the launch pad but
>>not into the shuttles; pity matches do not work in the vacuum of
>>space.
> 
> 
> Nope, the engines are "lit" from within.
> 
> The design of the SSME does not allow for starting the engine, shutting
> it down, and restarting the engine (without inspection).
> 
> The SSME has only ever been started sitting still at one standard
> atmosphere.  For a second stage engine, it would have to be started in
> flight, in the upper atmosphere.  While it was believed to be possible,
> it was decided that the J-2X (based on the J-2 used on the Saturn V
> second and third stages) would be quicker and easier to use.  Also, the
> SSME is an expensive engine, especially if you don't recover and reuse
> it (since it is designed with reuse in mind).

The SSME is a much more complex design than those used on standard 
multi-stage rockets anyway, just because of its design criteria - it had 
to be a lot smaller yet far more powerful than existing designs of the 
time, and doing that usually means giving up longevity and/or 
reliability - think of an Indycar engine vs. your standard small car: 
same displacement, 5-10 times the horsepower... and it needs to be 
stripped down and completely rebuilt after every race, maximum lifespan 
is maybe a thousand miles and when they do die, they do so spectacularly.
                                                                  
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