Economics (was Critical time)

I'm not sure what you mean by "these alternate propulsion ideas for
Earth-to-orbit". If by that term you mean SSTO or TSTO, then I would say
that the serious ideas I've seen for SSTO/TSTO do not propose LOX/LH2
because of propellant cost considerations. Rather, they propose LOX/LH2
because it is the highest specific impulse chemical propellant combination
that is non-toxic and for which engine technology is well-established.
Delta-V depends only on mass fraction and specific impulse, and LOX/LH2
produces high specific impulse.

I think your overall point is correct: propellant costs are not a major
component of space launch costs today.

This contrasts with the commercial airline situation for which the
fluctuating cost of jet fuel can ideed have significant economic impact.
But any particular fleet of commercial airliner (e.g., 777) sustains more
flights in a month than all the rocket flights in history combined, so the
initial capital outlay ($6 billion for the 777, I think) get amortized over
a large number of planes and operations, allowing the cost of propellant to
become more important economically than it is in the space launch industry.

The Space Shuttle fleet has flown to orbit less than 110 times. Take any
four or five 777 airliners, and they will fly more than 110 times in a
month.

Ron Menich

"John

04/09/01
11:33 AM
Please
respond to
ssi_list

...

By the same token, most of these alternate propulsion ideas for
Earth-to-orbit are tackling the wrong problem. The cost of hydrogen
and oxygen is basically just the cost of electrolysis and
liquification. I've read conflicting analyses of what that cost is,
but I think in every case, the cost of LH/LOx fuel was less than
$10/kg payload to LEO. The rest of the tremendous Shuttle launch
costs are for employing a veritable army of technicians and for
amortizing the large capital costs. (I forget the exact figure, but
I've read that if the airlines were run the way NASA runs the shuttle,
the cost of a trip from New York to Los Angeles would be something
like $100,000 to $1 million.)

++JohnWheeler