The Construction of Space Shuttle Launch Complex 39-B
A very personal and technical written and photographic history, by James MacLaren.
Page 36: Of Planks and PGHM's, of Torque Tubes and CAP's, of LRU's and Many Wonderful Things.
| Pad B Stories - Table of Contents |
Inside the Payload Changeout Room.
You're up on Level 5, left side, standing at elevation 187'-1". This is the top PCR Interior Level, and you're located on the Fixed Platforms portion of things up there, looking out and across the set of Extensible Planks, of which there are four on each side.
The Planks butt together on the centerline of the PCR, and they do so at a bit of an angle.
Each Extensible Plank is independent of all the others, and can be extended to any given point along its full length of travel, from completely retracted, where it disappears inside the Fixed Platform it's enclosed within, to completely extended, which is where you are seeing all of them, in this photograph.
When the pad goes operational, and the Space Shuttle is sitting on the MLP, spanning the Flame Trench, the Planks will be more or less retracted, and the space you see them occupying now will instead be occupied by a Payload. A Satellite. A thing which will soon be swinging around in a great arc with the rest of the RSS, after which it will be inserted into the Shuttle's Payload Bay and secured for launch.
The Extensible Planks were surprisingly complex and robust things, but then again, providing near-touching access to Payloads as they did, providing near-touching access to things that routinely cost in the hundreds of millions of dollars, and occasionally billions of dollars, they were almost too close for comfort, and a fair amount of time and effort was spent in making damn good and sure they would not fail in an unpleasant way, with an unimaginably expensive device that might have taken six or ten years to build.
The Extensible Planks worked hand-in-glove with the PGHM, which, unfortunately, we're not ever going to be getting any proper images of, because it went in after I had departed the Pad, but the sense of things stands, and the sense of things with the PGHM and the Planks is that the PGHM held the Payload, and provided its own near-touching access to it, and the Planks more or less filled in the gaps around and in front of the PGHM, and provided further access between the Payload and the rest of the PCR Interior Fixed Platforming.
If I ever manage to latch on to a proper set of drawings for the PGHM, you can rest assured that I'll be incorporating that stuff into these photo essays somehow or other. The PGHM was A Thing Apart. The PGHM was pretty damn radical.
The tolerances for this stuff defy belief, and the PGHM was basically a six-story building, suspended from above, hanging under a very sturdy Bridge Beam, and it rolled back and forth, and pitched forward and back, to match the motion of a gigantic rocket ship which swayed in the breeze a little, and did so to absurd tolerances of precise location. And it lived inside of another, twenty-story, building, the bottom third of which was mostly open-air empty space between two cyclopean mechanized support towers which held it up off the ground on either side, which also rolled back and forth, carrying the PGHM along with it as it did so!
"Yeah, we need you to move your apartment building forward.... oh... let's give it six and thirteen sixty-fourths inches, ok?"
"Roger that, six and thirteen sixty-fourths inches it is."
"Ok. That's good. Right there."
Which is pretty ridiculous, if you ask me, but that's the kind of stuff that was going on in here, on a completely routine day-to-day basis, so the Extensible Planks needed to be correspondingly close-tolerance (even as they were supporting substantial live and static loads), so they put a little extra into it when they designed 'em.
And it's not just that I don't have any pictures of the PGHM, nobody does.
Not even NASA.
And it's not because they didn't photograph it, it's because they couldn't photograph it.
It was constructed, in-place, inside of an insanely cramped and confined space (well... as cramped and confined as you can get, while you're accommodating a rolling six-story building, anyway), and there's nowhere to go, where you can back far enough away from it to get a sensible picture of it.
Can't be done.
Here's a photograph that NASA took of things, trying to show it to you, and...
Yeah right. Sure thing.
This is an excellent photograph that we're going to be using here, and we cannot fault it in the slightest because of the horrendously-difficult subject matter it's attempting to show you, ok? It was taken in 2011 during operations for the last Space Shuttle mission, STS-135, and as such, the interior of the PCR had by then undergone numerous modifications, and is therefore different in many ways from the original PCR which you will be seeing in the photographs I took while we were originally building it.
You're standing on the PCR Floor holding a wide-angle camera that's looking directly straight overhead up at the top of the frame, and very nearly straight-across eye-level, down at the bottom of the frame, and that's nearly a full ninety-degree field of view, ok? To service the Space Shuttle, the PCR Doors have to be in their "open" position, and since they're bi-fold doors, it looks a little funny at first, and here's one of the very few drawings in the whole package showing you the Doors in their open position without also showing them in their "closed" position, which always comes as a complication when trying to understand what the hell it is that we're actually looking at, so ok. Doors open.
And since this is the best picture I've ever managed to lay hands on when it comes to showing this stuff all working in concert together, I'm going to stop my narrative here and now, and give this image the attention it so well deserves, and mark it up a few times, so you can get an improved idea of what the hell's going on in here. And then, hopefully, take that improved idea of what's going on in here with you, as you continue our walking tour of the tower, and maybe even after that, out into the wider world that lives beyond these pages, too.
So get ready to launch off into the outer wilds of things, and since it's over there on the upper left corner of the photograph and is completely incomprehensible without a little help, we're going to start things off with the Payload Changeout Room Main Doors.
The PCR Doors are highlighted in the photograph, and which, you might wish to note, also come with a smallish set of their own platforms! Gah! Is there no end to it? Must everything in here either be, or have, or be hanging off of the side of, yet another damned platform?!?
Yes indeed, that's the way the work gets done, and before we're finished with things, you're going to have a fine appreciation of platforms.
And this particular set of platforms is giving us access to the "Torque Tubes" and what in the name of all that's holy, might a Torque Tube be, hmm?
Glad you asked.
It's visible in our photograph, and you can see it right here, but that's not much help at all, so let's press on, farther and farther out into the deep weeds with this one, ok?
The Orbiter's Payload Bay Doors (along with the Radiator Panels which fit snugly along their inside surfaces and which may as well also be considered as part of the Payload Bay Doors) are an entire life's work all by themselves. Whole separate discipline. Waaay more than enough to keep idle hands busy for years and years and years.
Here's a nice 94-page Familiarization Handbook for you. Check it out sometime, it's got a lot of really cool stuff in it. But it's not anybody's definition of "light reading."
The Payload Bay Doors don't do well on their own, down here on the ground. They were designed and constructed for opening and closing only in a zero-G environment, and absent a thing like that, they're going to break if you try to operate them strictly on their own down here, and since we don't want that to happen, we fix 'em up with a nice set of Torque Tubes, to keep 'em unbroken when we open and close them out at the Pad.
Our nice Handbook deals with the Torque Tubes in passing, and you can read all about it, here.
And here's the Orbiter's Payload Bay Door with its set of Torque Tubes attached to it, just so you can kinda see how the Torque Tubes and the Door work together.
And of course the first rule of Torque Tubes is that a "Torque Tube" looks nothing whatsoever like any kind of "tube" I've ever seen, but that's what they're called, so we may as well get used to it, ok?
So now we can return to the PCR Doors with a better understanding of what's going on with those little platforms that are hanging off of them. Here's a similarly-near-vertical wide-angle view of their exterior sides showing the set of small platforms, except that this time we're looking down from a location above the Antenna Access Platform, up in the RCS Room, and the PCR Doors are closed.
And in this drawing, over on the left side, on the exterior elevation view, you can see that there's three of these little flip-up platforms on each door panel.
And I specifically draw your attention to the left side of that drawing, and specifically call things out for the exterior elevation view, because over on the right side, which is showing us the interior elevation view, there's another goddamned Torque Tube, but it's NOT the one we've been talking about.
Not. At. All.
The one on the right side, on the interior side of the PCR Doors, is for operating the set of latches that connect the PCR Doors together along the centerline of the PCR when they're closed, keeping the PCR sealed up tight for clean room activities.
And in a way, this remarkable bit of confusion is beneficial, because it alerts you to the fact that there's Torque Tubes and there's Torque Tubes, and they are by no means to ever be assumed to be the same thing, ok?
You're going to always need a little more information when dealing with torque tubes, to be damn good and sure you're dealing with the right ones.
And since we're already this far out into the deep weeds with this stuff, this might be a good time to let you know that a torque tube, any torque tube, is just fancy Engineer Guy talk for a pipe (and it does not even have to be a round pipe, it can be a square pipe too) that gets twisted in some way.
"Torque" is just another word for twist, ok? "Torque" is a little more rigorously defined, but for people like you and me, "twist" is the sense of things for the word "torque." Which means that a torque tube is just some damn stupid long thing that gets twisted in a way that the twisting force is applied somewhere down along it's length to something else down there, maybe at the far end, maybe not, and that's it, sum and total.
I understand why (it is a bit of a red flag for engineers, in similar fashion as "curtain wall" is a red flag, and stands as a warning that forces and reactions are being applied through the weirdly-named thing in question that are significantly different from the way forces and reactions are applied through all the stuff around it) they insist on calling 'em "torque tubes" but it doesn't keep me from strongly disliking the fact that a thing which is so simple that a three year old understands its basic sense and operation has been given a name that becomes deeply confusing at times.
Torque tubes are also very much worthy of their red-flag name insofar as that, as part of their job of imparting twist, or receiving twist, they very often can, and will, move. As they twist, they rotate, duh, but if it's a thing where the twisting only happens every once in a great while (which is common), then you need to be warned about it, 'cause if you come along unawares, and find one of these things on your jobsite, it just might sit there eternally giving no outward sign that it's different, acting like it's no different from a structural column, maybe, never moving ever, and if you need to hang something in the area (electrical conduit, GN2 purge lines, support brackets for... anything at all... you name it...), you will very reasonably go right ahead and tack your shit on to it, and then later, when it does suddenly wake up, come fully alive, and start moving... well, it's gonna take your tacked-on shit which was never intended to be there when the torque tube was designed, right along with it, and... SMASHBANG!
"Careful with that torque tube there, Lou, 'cause it'll want to get you if you let it."
So. Torque Tubes.
Meanwhile, back at the Payload Changeout Room Main Doors, now that we stand a fighting chance of actually understanding what the hell's going on here with all this stuff dancing around, tightly-choreographed, all over the place together, in this drawing you can see that our little flip-up platforms are giving us access to the stuff that came along after I was already gone, which was used to attach and remove the Torque Tubes from the Space Shuttle's Payload Bay Doors, when it's out on the launch pad. We will revisit the fact that this stuff, later on, but it was never the primary concern of this page, and I've digressed far far far too much already, and so we'll leave it be for now.
And yes, as we delve farther and farther into the fine details of our Launch Pad (all we ever wanted to do was to learn how it worked, and nobody ever warned is it was going to be like this), we continue to learn, more and more and more, that this stuff gets hairy sometimes, right?
It's the simplest thing in the world, and then you walk toward it, and as you get closer and closer to it, it resolves itself, more and more, into an endlessly-expanding fractal that defies your ever fully plumbing its depths, all the way to the bottom.
Space is hard, and this kind of stuff is one of the reason's why space is hard, and everybody would love nothing better than to be able to simplify the goddamned thing...
...but that's not possible.
Physical systems are harsh.
Physics is harsh.
Mother Nature is harsh.
And she will kill you if you give her so much as half a chance to do so.
And so you work your way along the chains of reasoning, along the chains of cause-and-effect, and you go slow, and you make absolutely sure that you understand the link in the chain you're presently working on, completely, before you move to the next one.
Lest Mother Nature find you, catch you out unawares, and kill you.
The Space Shuttle's Payload Bay Doors can never be left alone during opening and closing operations without additional support to keep them from twisting around under their own weight in a way that might bend them.
If they get bent, and nobody notices (shit like that happens all the time when you're dealing with stuff that has been pared down in weight to the absolute barest possible minimum, and everything that gets hurled into orbit receives this treatment), then they might not latch back together when the time comes to close them, and bring the Space Shuttle (and the people inside of it) back home.
And if the Payload Bay Doors don't latch back together, and you put the Space Shuttle through the nightmare of atmospheric re-entry with an improperly-latched, or unlatched, pair of Payload Bay Doors, then...
No.
This we do not want.
This we shall not stand for.
And so we go to extraordinary lengths, down here on the ground, to make double damn good and sure that our Payload Bay Doors are right, and will latch, and we will be able to bring our crew home safely.
Ok?
It's ALL for a reason.
Every.
Last.
Bit.
Of.
It.
And it all adds up, and after it's all added up, you find yourself with a stupendously large and complex job to do, to make sure your Space Shuttle flies right.
Every.
Time.
And now we can return to our highlighted photograph one last time, look straight up in the air over our head with new eyes, and better appreciate that which our new eyes are now showing us.
This exceedingly long-winded digression started out as an attempt to let you know what's going on with the PGHM, which itself was a digression that ricocheted off in an unexpected direction from our original subject which was the Extensible Planks (Which have not been forgotten, ok?) that we were looking at in the photograph at the top of this page, so let us now turn our attention once again back towards the PGHM, ok? And maybe, eventually, if we're lucky, we might even get to return to the Extensible Planks, and a bunch of other cool stuff in that photograph too, 'cause there's some nice stuff in there that we haven't even gotten to yet.
Keep in mind that it's impossible to photograph the PGHM, and instead, a small sliver of things is all we're every going to be able to get from any one photograph.
And one of the reasons we can only see just a sliver of the PGHM is because one of the LRU Strongbacks is blocking our view of things, except that in this (the very last one) incarnation of the Payload Changeout Room, it's not even an LRU anymore, it's a CAP, but it most very definitely still needs a strongback, and that CAP Strongback is most very definitely still blocking our view, no matter what it's called, so... ok... and here we go, yet again, ricocheting off into the far distance on yet another digression.
Sigh.
We met the Line Replaceable Unit back on Page 28, and were advised that it was removed and replaced with something called the Clean Access Platform, and it's the CAP Strongback that's in our way right now, ok?
Here's our ever-so-useful NASA Photograph once again, and this time it's been highlighted in a way that shows you the general sense of where the CAP Strongback that's blocking our view is, and you might notice that this time, instead of a precise cutout in the photograph, we're dealing with a kind of soft blurry region, and that's because I'm not going to sit here and burn the three days it would take to cut it out precisely and instead, just give you the general location. Look at the damn thing! There's a latticework of steel going every whichaway, and no, I'm just not ready for this one, thank you very much.
So.
Now can we look at the PGHM?
Pretty please?
There's other stuff in there you need to know, but I've beat this one so far beyond death that it's coming back to life on me, and it just might decide to turn on me, so maybe I oughtta quit while I'm ahead.
The PGHM. Yeah, we wish we had a better drawing. But we don't.
And we wish we had a better photograph, too. But we don't.
Can't be done.
Nowhere to go, to get one.
So you're looking at the best that can be done, by NASA themselves in fact, and there's an awful lot of it that's not showing.
We're basically looking up the set of "wing platforms" on the PGHM's left side, and at least we can sort of get a glimmer of an idea of the scale of the thing, which is pretty damn large, and considering the outrageously fine-tuned nature of the thing, it's actually gigantic.
And of course the little drawings disagree with the photograph because of endless modifications over the years, after the drawing was finished.
But at least it's something, right?
And now you can go back to our NASA photograph, one last time, and give it a look, bare, no highlights, no words, no arrows, and then stop and consider.
Consider what it really is that you're looking at here.
You are looking at some pretty goddamned radical stuff, ok?
So there you go.
The inner guts of the Payload Changeout room, complete with a Space Shuttle and a Payload to go with it.
And now we can return to the original subject.
And get a bit more information on the Extensible Planks.
As a memory refresh, here's the isometric view showing the whole PCR Interior Platforms setup on the right side (RSS Side 2 only), with the Extensible Planks in a variety of extensions and configurations, with and without removable handrails, posts, and safety chains, and the Level 1 Fixed Platforms in plan view on the left side, with the Extensible Planks all fully retracted.
You now know (or at least are expected to know) the circumstances in which the Extensible Planks operated, and the requirements they had to meet for rock-solid stability combined with exquisitely-smooth travel and precision location, so now you should be better able to envision yourself walking around on them.
And it's funny, because you can almost get a feel for this, just by looking at the photograph.
The Planks have a very solid look about them in that photograph, and no, I was in no way attempting to convey that solidity when I took the picture, but it's there, nonetheless.
And the look does not deceive.
You'd walk out on them, crossing a fifty-foot-deep chasm as you did so, and they were rock-solid. It felt exactly the same as if you were walking across a concrete driveway. No sensation of standing on something that could be rolled in and out, butted against similar, independently-sliding things with the thinnest of gaps on either side, and butting against still more independently-sliding things on its far end, with no gap at all out there, and instead, a solid-steel cover plate.
Solid.
The whole thing was solid.
And after traversing them for just a time or two, your senses would stop complaining about where you were and what you were walking on, and instead.....
...ho hum, we're crossing over the gaping cavity of the Payload Changeout Room, from one side to the other, and we may as well be walking across a parking lot somewhere.
And here's why.
These things were very well-engineered, and these things were stout.
The support framework for the Planks consisted of a set of longitudinal W10x15's which were about 14 feet long, and that sounds like pretty light iron, and it is, except that they were also only 2'-0" on-center apart from each other, and they were tied to a W10x26 on their far (away from the centerline of the PCR) ends, and then on the ends that did the real work, the ends that supported the cantilevered Planks themselves, there was a nice beefy W10x33 sitting underneath them that they were bolted down on top of, and then, 2'-4" on-center, out past that, at the extreme end of things, there was another transverse beam, this one a W10x12, and yeah, that whole thing wasn't going to be going anywhere.
The Planks themselves continued on with the whole "robust" thing, and consisted in a "body" comprising a pair of nice heavy W8x31's that were only 1'-2½" on-center apart (which means there was only 6½" between their adjacent half-inch-thick flanges!), which were then much-further beefed up by the additions of things like the half-inch thick stainless-steel track plates that were welded to their outboard flanges, top and bottom, plus a few half to three-quarter inch plates (welded all-around, natch') to tie them together and hold the great big acme-thread screw-jack and traveling-nut in place, and since we're here, we may as well toss in the extend and retract aircraft-grade roller bearings and the support assemblies that held them along with the guide roller bearings too on the W10x15's that encased them, and oh yeah, don't forget the quarter-inch steel cover plate, and the whole thing was put together with a set of drawing notes containing nuggets like "THE AISC STANDARD TOLERANCE SPECIFICATIONS ARE TOO LOOSE FOR PROPER PLANK OPERATION, HENCE W8'S & W10'S SHALL BE STRAIGHTENED BY THE FABRICATOR TO OBTAIN A MAXIMUM SWEEP AND CAMBER OF 0.06 INCHES IN OVERALL LENGTH." and "ALL PLANKS ON EACH LEVEL SHALL BE LEVELED TO 0.01 FEET OVERALL" and...
Yeeks!
None of this stuff was going to be going anywhere, ever, except for exactly where the techs who used it told it to go, and... yeah. Sturdy stuff. Very. Sturdy. Stuff.
And of course it was loads of fun to walk around on... I mean... look at that view out there! Look where you are!
To die for.
Every last bit of it.
Which, of course, you would do, if you didn't mind your step.
Always mind your step up here, ok?
Bad Things happen when you don't mind your step.
And, speaking of Bad Things happening, this is the area where just out of view, to the right, beneath the framing-steel of this topmost level of the PCR Interior Fixed Platforms, but over on the Column Line 7 side, lies the area where the problem which precipitated the life-threatening near-miss that Jack Petty and myself endured at Pad A, was located. This completely insane event (you really should read that story that I just linked to) occurred years after this photograph was taken, but this is as close as I'm going to get to anything depicting the actual scene of the crime, so we're gonna go with it, right now, and not worry about being a little out of sequence with things, ok?
A seemingly benign-enough mistake on the engineering drawings of the extensible planks, wherein the planks were incorrectly rendered as extending at a 90-degree angle with respect to the support steel that holds them up, led directly, through a highly-improbable, but utterly inevitable, chain of events, to two people coming a gnat's whisker from getting killed, and of course The Fates decreed that one of those lucky two people be me.
The planks did not extend at a 90-degree angle, but instead slanted off to the side, somewhat forward as they extended, toward the open doors of the PCR. You already know this. You've seen the drawings for yourself.
Across the way, on the set of fixed platforms out of view on the other side, there was a haunch that supported a strange-looking, long skinny platform that was mounted on a substantial rotating bearing, allowing it to be swung around from its nominal stowed position where it was out of the way, and extended, to give a technician access, forty-five feet or so above the cold hard steel of the PCR floor down at the 135' level, to the Space Shuttle's KU-band antenna, should such access become necessary while the bird was on the pad.
The mounting haunch for that thing was equally sturdy, as it needed to be, to allow that pivoting cantilevered platform to safely do its job while carrying its load of the technician who might be needed to perform this or that task on the KU-band antenna, along with her tools.
And the haunch was supported by the steel framing that made up the fixed platforms themselves, as well as providing support for the roller-bearings, screw jacks, and ancillary steel necessary to extend and retract the extensible planks, and the goddamned engineering drawing, for reasons that nobody ever seemed to be able to find out why, showed the planks, and their support steel, with a 90-degree orientation to the fixed platform framing steel, and the haunch that supported the KU-band Antenna Access Platform was fabricated and delivered per those very same incorrect engineering drawings, all nice and square, all the way around around, with nothing but 90-degree angles everywhere it came into contact with the existing steel framing, and the goddamned thing was wrong, and we had to go over to A Pad to see how the problem had been resolved over there.....
.....and the both of us damn nearly got killed in the process.
Like I just said, you really should read that story that I just linked to. And please keep in mind, as you read it, that every single word in that story, complete all the way down to the fine details of dialogue, is one-hundred percent true and accurate, and yes, it really did happen, and yes it really was scary as hell. That story is the very first thing I ever wrote with deliberate intent as a writer, and it was written not so very many years after the events that it recounts, so it's closer to all of this stuff than anything else you'll ever get out of me, and for that reason it can be expected to have been produced with a much sharper set of memories of the event (which burned itself into the folds of my brain as if done with a branding-iron), and therefore be that much more trustworthy, and... I'm belaboring all of this stuff because You. Will. Not. Believe. A. Word. Of. It. But it's true. Oh lordy gollamighty is it ever true.
And since I'm here, and since I have the pertinent documentation on hand as a resource, I'm going to link to all three pages of the "NASA MISHAP REPORT" which we received following this beyond-bizarre event.
Page 1 which is the cover sheet.
Page 2 which is the Mishap Report itself.
Page 3 which is a very terse and dryly-worded recounting of the events (go back and read that story I just linked to if you want the expanded, true-to-life version, including my own opinion of NASA's report).
Ok. Where were we? Oh yeah, inside the PCR, trying to explain what's in our photograph up at the top of this page.
Very well then.
Elsewhere in our photograph, you can see where they're working on the Side Seal Panels, and they've got one of the cover plates off, and you can see a little bit of the innards (and some of the outards too, near its top) of the Panel where the air supply for the Inflatable Seals lives.
Above the Side Seal Panel, the dark underside of the Antenna Access Platform curves around, and beneath it, out beyond the Side Seal Panel, a very little bit of the Side 2 Vehicle Access Platform at elevation 191'-0" can be seen peeking around past the limp Inflatable Seals draped down from the Antenna Access Platform and the Side Seal Panel.
This little guy was another really fun place to go, and you had to get to it by climbing down a ladder (and there was a whole descending series of them, and they were all fun places to go), and nobody, and I mean nobody would ever go down there, and yeah, when The Fates permitted it, I would certainly go down there, and just kind of stand and take it all in for a little while, or maybe snap a photograph from what constituted a quite-interesting and unusual point of view, and yeah, that whole deal was pretty damn nice too.
Back inside, deeply buried in the gloom, you're not standing very far away from the top of the Left LRU Strongback, but unless I beat the hell out of this picture, you're never going to see it. So here's the photograph, beat to hell, so you can see it. It's the thing with the vertical row of dots on it, and a couple of diagonal pipes coming off of it to the left, and behind the part with the vertical row of dots, you can just make out the rungs of the emergency egress ladder which was integrally built into it that not only provided vertical escape in time of dire need, but also stiffened it up even more than it already was, and it was already quite stiff and stout. The vertical thing with the dots is actually a fairly heavy tube steel with a pair of thick plates welded on to it, full-penetration welds, one on either side, both sticking out and away from it to the right, and the "dots" are actually holes and they would pin a matching piece on the LRU in place, in the gap between the plates, using one of these pairs of holes, and once it was pinned in there, it wasn't going to be going anywhere until somebody unpinned it. The far end of the ladder rungs was a somewhat lighter tube steel, but the whole assembly was quite robust.
Here's a drawing of it, but it's showing the one on the other side, so what you're seeing in the photograph is opposite hand from what the drawing shows.
This is the thing that eventually got ripped out and replaced, and became the CAP Strongback, and we got a good look at that incarnation of things earlier on this page, when we were talking about the PGHM.
And off in the far hazy distance across the rough country, the towers of Pad A float serenely against the sky, just above the horizon.
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