JF Mezei wrote on Wed, 22 Aug 2018
14:09:45 -0400:

On 2018-08-22 08:26, Fred J. McCall wrote:

OK, I have to ask the obvious question. Why? If it's really an
emergency, how long does it take to unbutton the capsule and get
everyone out as opposed to just firing the escape system?


Consider theye are also pad crews at some periods (the ones who tuck
crews in, close hatches etc etc). They need some means of emergency
egress as they do not have a capsule jettison system.


But when they 'tuck the crew in' there's no fuel in the rocket, so
there's not really anything that can 'go wrong' that would endanger
ground crew. Besides, would such an emergency escape system have much
utility for ground crew? They'd all have to gather where the basket
is, get in, hope the basket has sufficient room for them all, then get
away. Easier to just take cover in place.


jeff mentioned that for Dragon itself, it is more likely an automated
capsule jettison gets triggered than crews unstrapping themselves and
leaving capsiule to take the joy ride down the zip line.


Quite right, so the utility of the zip line is what, again?


However, during crew ingress when the hatch is opened and there are both
flilght cerws and pad crews in capsule, doubtful that the capsule
jettison would be armed. So egress via bridge and then down the zip line
more likely.


But there's nothing to blow up, since there's no fuel in the rocket
yet.


With fueling happening after crew are strapped in and hatches closed,
the odds of problems while crews get into capsule are much lower.


Essentially non-existent.


At the time crews will ingress, will any part of the stack be alreayd
fueled? Or does fueling "at last minute" involved fueling not only stage
1, but also stage 2 and fuel inside Dragon ?


Everything is empty but the hypergolic fuel in the capsule itself. If
THAT goes wrong (and the odds of that are virtually zero), there is no
escape. Capsule, basket, zip line, and all go up.

So I'm still puzzled at the actual utility of such a system.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden