On Thu, 11 Sep 2003, Ian Woollard wrote:
> >...Nobody builds unmanned cargo aircraft, and there's a reason for that.)
>
> Yeah, aeroplanes were invented before microprocessors and GPS :-)
And the airplanes have had microprocessors and GPS for a while now, and
guess what? They're still manned.
Fact is, in most non-combat situations it makes no sense to risk valuable
cargo on an unmanned vehicle, or even just to risk a long-lived, costly
vehicle, if there is any chance that having a pilot on board could save it
in a situation where it would otherwise be lost. Vehicles and cargos are
expensive, and pilots are cheap (provided you do *not* get them from JSC).
> Maybe. My engineering spider senses are twitching with a turbojet that
> was never expected to ever see 100 km+ though. Cold soak? Hot soak?
> Injector leakage at altitude? Any rubber, plastics or anything odd in
> the engine? How's that in a vacuum? Lubricants?
Lubricants mostly are expendable, continuously replenished; those that
aren't are in sufficiently non-critical areas that standard vacuum
lubricants should be usable. Not much in the way of plastics etc. due to
the extreme environment. Leakage is a valve issue, not an injector issue.
Jets see both cold soak and hot soak to a much greater extent than you'd
get with a brief hop up to 100km.
It's outside the normal operating envelope, yes, but people who have
looked at this sort of thing say that qualifying turbofans for brief
visits to the high-altitude environment should not be a big issue.
> >After how big a development bill? Remember, there are no experienced
> >ramjet development shops left (at least in the unclassified world)...
>
> Ramjets are simple, so it may not be that bad at all.
No airbreathing engine installation is really simple. Air intakes, even
simple ones, have complex behavior.
Henry Spencer
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