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)
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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.
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