Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!elroy!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: sci.space.shuttle
Subject: Re: holds in countdown
Message-ID: <4648@jpl-devvax.JPL.NASA.GOV>
Date: 24 Mar 89 02:07:12 GMT
References: <8.UUL1.3#5131@mvac.UUCP>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Lines: 35

In article <8.UUL1.3#5131@mvac.UUCP> mvac!space@udel.edu writes:
: This may be a nieve question, but I'll post it anyway:  Countdowns for
: launches begin much earlier than the time alloted in the countdown
: timer (ie a launch is set for 72 hours away, but clock says T-50 hours,
: or whatever).  I know that 'built in holds' are the reason why the two
: clocks do not agree, but my question is why are they there?  If you
: *know* that you are going to stop the clock for 1 hour and 20 minutes
: when the countdown clock says T-xxx, than why not just add one hour and
: 20 minutes to the countdown clock and just say that from T-4:20 to
: T-3:00, there is no planned activity.

Like Henry, I doubt there's any logical answer, but I think I can guess
why they decided to do it that way.

Psychologically speaking, it's more acceptable to stretch out an already
existing hold than to stop the clock when it is running.  When the clock
is running, the default is for it to keep running.  When it's stopped, you
have to take some positive action to restart it.  For safety reasons, it's
probably better to vacillate on the question "Shall we proceed?" than on
the question "Shall we stop?", even though the launch will proceed only
if there's nothing to stop you.

It's a psychological gimmick, but if I were a launch controller, I'd rather
the clock weren't moving while I had to decide.  A moving clock gives an
unwanted (I almost said "false") sense of urgency.

But it'd be nice if they'd show the public two clocks, the current one, plus
another that gave the minimum time to launch, labeled as such, that
stops at the end of the built-in hold if they extend it.  After T-9 minutes
you would presumably have to show only one of them.  (Unless, of course,
the countdown halts at T-31 sec, in which case the minimum time to launch
should pop back up on the screen, saying something like "2 days".   :-)

Larry Wall
lwall@jpl-devvax.jpl.nasa.gov