Vince Cate just reminded me that it's more than a bit after
mid-September, and in fact the thing I was waiting for
(FALCON selections) is over, and I didn't get one of the
awards so this isn't really immediately commercially
sensitive anymore.

In mid-August we wrote:
George William Herbert wrote:
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.

Let me start with a few observations.

1) Low chamber pressure is not your enemy; it increases the
rocket engine bulk and mass, but does not decrease Isp at
altitude significantly (other than, it being a lot harder to
get very very large expansion ratio nozzles).

2) The specific impulse loss at low altitudes is annoying but
not catastrophic, even for chamber pressures down in the under-100 PSI
range for the rocket motor.

3) There is a difference between gauge and absolute pressure.
At very low pressures, the difference between PSIG (which is,
after all, what a pressure vessel will have to resist) and PSIA
(which is what matters for a number of other factors) is going
to be a useful engineering advantage.

4) At very low pressures, even really dumb ablators like spray-on
fiberglass or oak work just fine for ablative motor chamber liners.

5) If you have low Isp, stage early and often.

6) The vapor pressure of nitrous oxide at around -50 F is around 125 PSI,
and the vapor pressure of propane at around 70 F is around 125 PSI,
and both are self-pressurizing.

7) Low weight tanks for 125 PSI are *light*.


With those observations made, let me give a brief product
description of FALCON-RASER (FALCON-Retro Aerospace Self-pressurized
Expendable Rocket), our FALCON proposal...

FALCON-RASER is a 4-stage little dumb booster, all four stages
using nitrous/propane at tank pressures of around 125 PSIA.

Each stage had a stage to stage mass ratio of 4, giving a
gross vehicle mass ratio of 256 . The total 'payload' mass,
including actual payload and the electronics/GNC package,
was 2,580 lbs including some margin, and GLOW was around
660,000 lbs. I had not finalized the structural material
and mass, but of the candidates (initial set: 6061 as-welded
and post-weld heat-treated; 6013 as-welded and post-weld heat-treated)
all came in well below my notional masses, except 6061 as-welded
which is at 103% of the notional masses (and would be at
the notional mass with a very slight margins relaxation;
i was using 1.25 Fs to yield 1.60 Fs to UTS, much higher
than typical aerospace practice).

I have an engine / injector design which I intend to keep
proprietary for the time being, but which would have cost
very little to fabricate.

I believe I was able to keep the bill of materials for the
guidance and control system below $100,000, which would
hopefully mean that the total system cost would be under
$250,000.

Without giving away all my prices, with a very healthy gross
margin and a sort of liberal guess at range costs, my total
customer cost estimate was around $5m for a vehicle I think
will deliver upwards of 2,200 lbs to 200 NM LEO. And the next
size up was expected to cost about $15m for upwards of 8,800 lbs.

I am, among other things, looking for commercial funding for
this to go forwards outside the aegis of FALCON.
Development costs are estimated to be Really Low.
Not much more than seven digits.


-george william herbert