The Construction of Space Shuttle Launch Complex 39-B
A very personal and technical written and photographic history, by James MacLaren.
Page 67: GOX Arm Beanie Cap Lift. (still being written)
Out on the Pad,
nobody ever called it the "GOX Vent Hood." Nor did anybody ever call it the "GOX Vent Tip Assembly."
It's was
always, without exception, referred to as the "Beanie Cap."
But I always thought they should call it the "Flying Saucer" because that exactly what it looked like.
Straight out of a sci-fi movie.
And it even had a nice handrail where the aliens could stand behind it and wave to you as they flew by.
It had it's own 79K number for Pad B, 79K26351, but I've never been able to lay hands on that set of drawings, alas. My guess is that they're pretty interesting, 'cause this thing was
complicated.
Quite the gizmo.
And if you look at that framework to the left of the white flying-saucer part of what's being lifted in our photograph, you can maybe start to get an idea of just how complicated this thing was, in between where the far-left side of the framework bolts on to the end of the GOX Arm (more
aircraft bolts, natch), and where the Flying Saucer part of it starts. That framework in there is not particularly large, but it's
well-packed with stuff, and what you're seeing in this image is the bare-bones configuration, which means there will be
more, before all is said and done, and it's completely-ready to do its job.
And of course it was the GOX
Arm, which we just got finished hanging on the tower, which swings this thing out and away from the FSS when it's in its stowed position, taking it out away from the tower, to a place directly above the External Tank, where it can do its job of trying to keep everybody from getting killed during launch or re-entry, but that Arm
all by itself is not enough.
Where the Flying Saucer fits down over the top of the Tank, is a pretty close-tolerance location, and the Space Shuttle's final location as it sits on its MLP, which itself sits on the Pad MLP Mount Mechanisms,
moves around a little bit, every time they park it up on the Pad Deck. Never quite the same place twice.
So it's never in
exactly the same place, ok?
Which is not to say that it goes
wandering around all over the goddamned Launch Pad, and they have to send somebody out with a lasso to catch it and bring it back, but it
does move around in its parked position, just a little bit.
The Tank also
lengthens and
shortens owing to significant thermal expansion and contraction depending on whether it's empty, or partially-loaded, or fully-loaded with Liquid Oxygen and Liquid Hydrogen.
And when the wind blows, the goddamned Tank
moves around because of that, too. It bends and flexes a small (but not so small you can
ignore it) amount under wind-loads.
And that white Vent Hood
must be able to accommodate every last one of those small variations in the exact location of where the tippy-top of the External Tank winds up, and of course that has to be done
mechanically, and maybe now you can start to see how this thing's gotta be located
dead-nuts right where it belongs, so as it has enough positional
margin to accommodate all of those differing locational
excursions which our unexpectedly-
mobile External Tank might perchance wind up
occupying, without running the risk of things going
metal-on-metal as it does so, while still-yet being
close enough that the goddamned seals will still
work, and not become
detached.
In-and-out.
Up-and-down.
Side-to-side.
And oh yeah, it's gotta be dead-nuts
level, too.
Lotta goddamned
shit going on with the location of that fucked-up Flying Saucer, and every last bit of it's gotta be
rock-solid, immovably in place, once it's reached its one-and-only correct location where it gets put to work each time.
And they don't want to
fuck it all up and get it wrong, so all of a sudden you find yourself grappling with a
Big Deal when it comes to
adjusting this thing each time a Shuttle is rolled out to the Pad, and you're playing for
keepsies every single time, with no fuckups allowed.
Lower that Hood down in the wrong place and you run a very real risk of
breaking the External Tank.
Raise the Hood back up and swing it away from the Tank on Launch Day, and you run
additional risks of fucking everything up
way worse.
Bang into the Tank with this thing, on
Launch Day, mere minutes before T-minus zero when you're
retracting it, with a full load of outrageously flammable and explosive
propellants in the Tank, and a fucking
Crew inside the Orbiter...
And...
Nah... we're not gonna be letting any goddamned shit like
that happen. Ever.
And all of a sudden, you can see that we're going to be designing ourselves a remarkably
robust, and remarkably
fine-tuned, and remarkably
adjustable gizmo that's gonna be hanging off the end of the GOX Arm. Structural! Mechanical! Electrical! You betcha!
And of course this thing is
only for
Oxygen, but the External Tank is loaded to the gills with Liquid
Hydrogen too, but we're going to have to use a wholly-separate Umbilical for
that, and yes, we're gonna get to that here soon enough, but not right now, ok?
Just Oxygen, for now. Nothing else.
And we haven't even started in on
what happens with the GOX (wafting by at a balmy 294 degrees
below zero Fahrenheit) as it comes out of the Vent Louvers up at the top of the ET.
Whole 'nother series of convolute and contrapted conundrums.
Which all have to be
solved, lest we...
Lose control of things.