Vincent Cate wrote:
(Henry Spencer) wrote:
N2O, nitrous oxide, is what I meant.
Its performance is better than you would think based on its small oxygen
content, because it also has quite significant stored energy.

The combination of Nitrous-Oxide(N2O) and Propane(C3H8) seems
interesting. It seems to have a high ISP. Both self pressurize, and
are relatively safe and easy to handle. At the URL below they say "an
ISP of 230 at sea level, 290 at high elevation". I have not verified
this, but if accurate, that is rather good. Anyone else have ISP
numbers?

It's rather bad by standards of 'good' propellants; upper stage
lox/kero engines can get upwards of 330 S ISP, and hydrazine/tetroxide
can get upwards of 320 S.

I think those numbers are accurate for a higher pressure
motor; for lower pressure motors things are correspondingly worse.

http://web.wt.net/~markgoll/rse3.htm

Somewhere I found that propane has a pressure of 124 PSI at 70° F. I
think Nitrous Oxide is about 750 PSI at room temp.

Get thee to a library (or $$ and Amazon) to a copy of
Matheson's Gas Handbook. Therin are many secrets of the
thermodynamics and gas behaviour world explained clearly
for all to see.

You're not grossly off, but precision is important.
Especially with people who think 1.25 is a fine safety
margin in a pressure vessel 8-P

Seems like we use
the N20 to cool the engine (since it has extra pressure) and run the
engine with just 124 PSI feeds. Or maybe a simple pump that uses some
of the extra pressure from the N2O to increase the pressure on the
propane.

Not needing separate tanks to pressurize the Nitrous-oxide or Propane
simplifies things a little.

As a guy who thinks the rocket only need to get to about 5 km/sec and
then tethers/ion-drives can do the rest, the N2O/Propane seems like it
has a high enough ISP and would be easier/safer than most
fuels/oxidizers.

But is this ISP of 290 seconds real? Can we get that at 100 PSI?

Not at 100 PSI. (and do you mean tank pressure or chamber pressure 8-)

After mid-september I will have some more detailed discussion
in this thread, but it's a bit proprietary right now.


-george william herbert