Re[3]: Re: Multiple engines (was RE: Liquox)

John Carmack wrote:

JC> I do think that most everyone drastically underestimates the increase in 
JC> fabrication and operational work that a biprop will bring.

 A vehicle with the capacity to hover must have the possibility of deep and fine
 throttling.
 Realising that with a classic biprop propulsion would increase complexity at least
 a order of magnitude compared to what John uses actually.

   -Nontrivial injector design, eventually with moving members (pintle injector)
   -Tank pressurization with regulation  from a separate high pressure tank.
   -Regenerative cooling of chamber and nozzle.
   -Reliable ignitor system with its valves and sequencing system and safety
    interlock.
   -Some sort of a propellant usage system, so that both propellants will run
    out at the same time independent of throttle setting.
   -Precise valve sequencing for starting and stopping the engine with
    some provision for purging.
   -Do to much higher exhaust temperatures beter thermal protection of the
    back of the vehicle.
   -Much more complicated equipment for static testing necessary.
   - ...............


JC> The increased noise might make it impossible to test our vehicles at the shop,
JC> which would be a huge loss of productivity.  If a fresh mixed-monoprop engine
JC> gives us 20 flight tests between catalyst replacement, as it did on the jet 
JC> vane lander, it really is a good solution.

 To have the possibility of testing near the shop is indeed a key feature of
 a god productivity in the development of rocket propulsion. Given the shop is
 not at some completely remote area, noise abatement is the predominant problem.
 At SPL we spent nearly 70% of our man hours and some 200k$ over the last two
 years, building a test facility with noise suppression. Now nearly ready for
 operation it represents an assembly of nearly 100 ton of steel, concrete and
 sand.
 
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 Hans Ulrich Ammann
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 http://www.spl.ch