SS1 propellant load

Hop David wrote:

I think there's about 3 kilograms in a gallon of gasoline. At
$2.10/gallon I'm paying about 70 cents a kilogram.

Moreover, the 'fuel' being discussed was actually fuel+oxidizer, and LOX
(which dominates the propellant mass) is very cheap.

Paul

Paul F. Dietz wrote:
Hop David wrote:

I think there's about 3 kilograms in a gallon of gasoline. At
$2.10/gallon I'm paying about 70 cents a kilogram.


Moreover, the 'fuel' being discussed was actually fuel+oxidizer, and LOX
(which dominates the propellant mass) is very cheap.

LOX works out at maybe 15c per kg.

About 60% of the weight of the propellent would be LOX, 40% hydrocarbon.
(Rockets like running very much fuel rich.)

So that gives us an overall price of 0.6*0.15 + 0.7 * 0.4 = $.37 per kg
(Using your price for fuel).

Now, using that 2% payload fraction and a 0.95 fuel fraction, that's
~$20/kg of payload. That's an order of magnitude more than was claimed
in the post I was replying to, near enough.

Paul

In article ,
Ian Woollard wrote:
LOX works out at maybe 15c per kg.

Only if you buy it from an extortionist (or a government contractor, much
the same category), or in quite small quantity. It's 2-3c/kg if you use
enough to justify your own LOX plant.

About 60% of the weight of the propellent would be LOX, 40% hydrocarbon.
(Rockets like running very much fuel rich.)

Not quite *that* fuel-rich. The maximum-Isp LOX/hydrocarbon mixture ratio
is around 2.4 (71% LOX) at sea level and maybe 2.9 (75% LOX) at high
altitude... and the optimal *stage* mixture ratio is probably a bit higher,
since LOX is denser and you save on structural mass by biasing the mixture
ratio a bit toward the lean side.

So that gives us an overall price of 0.6*0.15 + 0.7 * 0.4 = $.37 per kg
(Using your price for fuel).

That's still a somewhat high price for bulk hydrocarbons; half that is
more like it, I believe.

Figuring in all of the above, 0.75*0.02 + 0.25*0.35 = $0.10/kg. Which is
getting close to what's needed for the originally-quoted results.
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