On Mon, 2004-05-03 at 15:56, John Carmack wrote:
> Roll control is critical for a longer burn time vehicle. Multiple engines
> is something we are trying to get away from. If we have another engine, we
> want to get full redundancy out of it, not make it a necessary part of the
> control system.
If you have eight engines, you can have full redundancy against any two
engine failures and maintain roll control. The thing I like about the
Goddard vane design is that you can just use a slab of refractory backed
up with something stronger, which opens up your practical material
choices and lets you look into some mechanically weak but inexpensive
and very heat resistant ceramic materials to coat your paddles with.
> Erosion is a non-issue for our current propellant, and if we move to a
> hotter propellant later on, I would be inclined to make refractory jet
> vanes. Cutting and machining those would be a lot easier than the
> refractory chamber we made for our biprop work, and the temperatures are a
> lot cooler past the nozzle, so I expect they could run indefinitely. Good
> refractory coatings are something that was developed in the 60's, after
> launchers had already moved away from jet vanes.
Tungsten carbide is probably a good one to investigate. MP is ~2800 C,
and it can be readily EDM wire cut. I had a conversation with one of our
neighbors (and effectively, one of our sponsors), Dan Bowlin of BoJo,
Inc about it, and he told me that it wire cuts very well.
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