On Mon, 10 Feb 2003, Pierce Nichols wrote:
> It takes more than 4 man-hours to turn around a 747! I don't think
> it's possible to get there for a launch vehicle due to the necessity to
> load inert gas and two different propellants, instead of just kerosene...
When you get to the sort of flight volume where you're worrying about tens
of man-hours, the launch stand (or whatever) will be pre-plumbed for the
fluids, with direct connections to a tank farm. Man-hours spend on fluid
loading will be *zero*: you just put the vehicle on the stand, that
connects the built-in umbilicals, and everything after that is done by a
computerized sequencer operating valves -- no need to move trucks in and
out, couple and uncouple hoses, etc.
The Russians already fuel their launchers that way. There is *nobody* on
the pad for fueling of a Proton or a Zenit. If memory serves, DC-X was
the same way. Even the operational V-2 launch system had automated
fueling, and it was mobile.
> ...IMO, since a launch
> vehicle will probably require more inspections between flights than an
> aircraft, due to the higher stresses encountered.
Note that a commercial aircraft really doesn't *get* an inspection after
each flight. At most, it gets a quick glance over for anything obviously
wrong. Its inspections are done at regular intervals (depending somewhat
on how intensively it's used) as scheduled downtime, not as part of
turnaround.
> Achieving such a
> turnaround time would also eliminate ablative TPS systems from contention,
> requiring either re-radiative TPS (metal or ceramic tiles) or the
> transpiration cooled TPS previously discussed.
Or active cooling, or low-ballistic-coefficent drag-brake reentry, or any
of several other options. But yes, ablators are probably out if you want
a turnaround of only a few man-hours.
> The inspection situation is
> *much* worse for an SSTO, because an SSTO must push the limits so much
> farther in order to achieve a profitable payload fraction.
That is an assumption, not a self-evident fact. Hassle vs. mass ratio is
not linear or even smooth -- it goes in steps. The belief that an SSTO is
massively harder than (say) a TSTO is not shared by everyone. Harder, yes.
Massively harder? "Not proven."
> I suspect that
> you could achieve excellent cost reductions by pulling turnaround time into
> the low thousands of hours (consider the competition!).
We don't want to compete in their market at all; it's full of big hungry
dinosaurs with connections in Washington. We want to be off in a totally
different region, pursuing totally different markets, from the start.
Henry Spencer
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