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
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