From: "Jeff Greason" <jgreason@hughes.net>
Newsgroups: sci.space.policy,sci.space.history
Subject: Re: Man Rating, Manned Vehicles, RLV Reliability, and other 
	subjects...
Date: Thu, 14 Dec 2000 10:10:36 -0800

Derek Lyons <elde@hurricane.net> wrote in message
news:3a38a59b.561365216@news.seanet.com...
> henry@spsystems.net (Henry Spencer) wrote:
> >(At the last Space Access, Jeff Greason showed a photo of
> >the X-1 engine running in a ground test... with a technician walking past
> >maybe 15ft away.  This was routine; it is a design requirement for
> >aircraft engines that they do not explode without warning. :-))
>
> Is it that, or the somewhat more casual attitude towards safety then?
> Or simply complacency from repeated operation?

Certainly standards have changed -- but no, that's not all there
is to it.  Once you start digging in to the engines, to the operation
practices, etc., there really are substantial differences between
the way the XLR-11 and (for example), the XLR-89 for the
Atlas were designed and operated.

Repeated operation only brings complacency if there aren't
incidents along the way.  Most engine developments
*do* have incidents -- but in an engine designed for manned
aircraft, those incidents have their causes found and squashed.
In expendable vehicle engines, frequently the decision is
made that a given problem isn't serious enough to fix -- it
can be lived with.  Just don't stand too close to the engine,
and if 2% of the missiles blow up,  that's still well within
spec.

This is nothing new, of course -- engineering is a trade off
process.  It's just another example of why, no matter how
much browbeating about "quality" management may do,
systems designed for manned flight from the start turn
out quite different from systems designed for unmanned
operation -- a thousand little design decisions, up and down
the chain, all made with different tradeoffs between cost,
schedule, and safety/reliability.

----------------------------------------------------------------
"Limited funds are a blessing, not         Jeff Greason
a curse.  Nothing encourages creative      President & Eng. Mgr.
thinking in quite the same way." --L. Yau  XCOR Aerospace
   <www.xcor-aerospace.com>                <jgreason@hughes.net>