Re: rotons again

Spike Jones (
Thu, 01 Jul 1999 21:43:06 -0700

> Spike Jones wrote: The rotary engine was what gave me confidence in RR,
> > not the landing system. {8-[
> Doug Jones wrote: That damn fastrac engine ain't gonna inspire anyone.

Ya that change was a shocker.

> A coupla points- I'm sure you meant, higher pressure to keep the LOX
> *above* the freezing point...

Yup. You only need a little pressure to keep the almost boiling lox from freezing the ethane. The phase overlap is only a few degrees F.

> and propane is a better choice than ethane

My good friend and mentor has been telling me the same thing, he too being a propane/lox fan. I admit having a lot of headaches trying to work out the density delta between lox and ethane. You lose a lot of the efficiency of a roton by going for the no-insulation-needed approach of lox and ethane. The bigger tanks may swamp the advantage of the slightly higher Isp of ethane vs kerosene. So, pont taken.

> As for two rotary engines- remember that low pressure engines have
> only a trivial (less than 1%) Isp hit in vacuum, with the same
> expansion area ratio. Make the upper stage pressure fed.

Again, a favorite idea of my friend and mentor here. I have resisted the pressure fed notion because rotary engines are wicked cool, but thats a poor reason to choose one I fear. {8^D

> If you put back the insulation between the tanks, you can Vapack
> both propellants (use their vapor pressures to drive the fluids),
> eliminating helium bottles, regulators, and heaters altogether. The
> RCS runs off the vapors left after the main engine burn.

Do you mind if I share your post with the guys? These are good points.

> There are a few still grinding away... I feel this would be great
> for freight, and with an escape rocket on the crew cabin, could be
> used to haul people.

Ya. What I really had in mind is a low cost 2 stage designed specifically for low-value high-density payloads, which one is willing to risk, such as food for astronauts. My notion is to leave the humanity hauling duties to the space shuttle.

Thanks for the ideas! {8-] spike