Re[2]: Re: Multiple engines (was RE: Liquox)

At 12:05 AM 6/13/2004 +0200, Hans wrote:
>Brandon Fosdick wrote:
>
>BF> Hans Ulrich Ammann wrote:
> >> But personally I think his main problem at the moment is not the choice of
> >> a appropriate arrangement but the fact that whatever system he is 
> going to uses
> >> the engine, or engines have to work in a consistent and predictable way.
>
>BF> A lot of this discussion seems to be driven by the unpredictability of
>BF> the engines. Is this a characteristic of the chosen propellants? Would a
>BF> different propellant combination be inherantly more (or less) predictable?

Now that we have a single engine configuration, I am able to more 
reasonably consider going to  a real biprop, but the requirement for deep 
throttling to land a VTVL complicates the propellant decision significantly.

The most-likely direction we would look at would be 70% peroxide with a 
catalyst pack and separate kerosene injection with a spark ignition system 
and flameholder.  This would still give us deep-throttling capability, easy 
injector development, the ability to continue operating if the kerosene was 
exhausted (at a very low Isp, but probably enough to save the vehicle if we 
leave propellant margins), and it would get us a visible exhaust 
plume.  The major development would be the cooled chamber and nozzle, but 
we do already have one ready to try in the 1000lbf size range.  We would 
also have to make jet vanes out of a higher temperature material.  This 
would all, of course, be dependent on our ability to get 70% unstabilized 
peroxide.  We don't expect this to be a problem, but we haven't tested it yet.

I do think that most everyone drastically underestimates the increase in 
fabrication and operational work that a biprop will bring.  The increased 
noise might make it impossible to test our vehicles at the shop, which 
would be a huge loss of productivity.  If a fresh mixed-monoprop engine 
gives us 20 flight tests between catalyst replacement, as it did on the jet 
vane lander, it really is a good solution.

John Carmack