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Pressurized Mating Adaptor Images and Information

This image shows a view of space station assembly flight number 6a, looking toward the port-nadir (left and down) part of the space station. It has some good detail of the Pressurized Mating Adaptor.


Along the left edge, you see the edge of a solar array. Note that the array deploys with a scissors mechanism, so it will appear to fold back and forth a little bit when it's deployed.

The solar arrays attach to a box-like trusswork which contains a very large battery box. Note the grapple fixtures and trunnion pins on the support truss. The grapple fixtures are those round things, with a prong sticking out of the middle. That's where the RMS grabs the payload.

The box-like truss connects to the Z1 truss, a rectangular chunk of space station which houses the navigation and control equipment. At the top of the Z1 truss (toward the top of the picture, that is) you see the Control Moment Gyros, or CMGs. There are four CMGs. Also note that there's more of that ubiquitous trusswork to adapt the payload to the Orbiter payload bay, and more trunnion pins with scuff plates.

The Z1 truss connects to Node 1. Ignore the bold arrows drawn on the picture; those are EVA translation paths. (Note that they generally follow a line of EVA handrails.)

There are 3 Pressurized Mating Adaptors (PMAs) in this picture. PMA1 mounts on a longitudinal port at the top of Node 1. PMA3 mounts on the starboard radial port, pointing toward the left side of the picture. PMA2 is at the bottom attached to the forward longitudinal port of the Lab Module. PMA2 is attached to the Orbiter Docking System, mounted atop the Space Shuttle's external airlock.

Those lines you see all over the PMAs are power and data cables.

The PMA has two attachment mechanisms, one at each end. The big one is the Space Station Common Berthing Mechanism (CBM). You can see a hint of a CBM in the picture where the arrow points from the words "Node 1". That round thing is the CBM. The curved things attached to the edge of the CBM are the cover that protects it for launch. Generally the cover won't be moved out of the way until we're ready to plug something into that port.

Down near the bottom, near the words "Flight 6A Emergency Return Scenario", you'll see an S-band antenna.

To get a concept of scale: That's a full Orbiter payload bay at the bottom of the picture. The payload bay measures 60 feet long and 15 feet in diameter.

In this image, you see all 3 PMAs again, but this time they're all attached to Node 1. On PMA2, you see the 3 petals which make up the APAS. APAS stands for androgynous peripheral attachment system. That's a euphemism for the Russian berthing mechanism.


Those petals are not removable. Inside the envelope of the petals is a circular hole about 30 inches in diameter for the crew to squeeze through.

If you look at the underside of PMA2, you'll see a little square cone sticking out on a short pole. That is the Mode Indicator, which provides a docking target and talkback lights to show the status of the APAS when an Orbiter is docking. The Mode Indicator is visible to the Orbiter pilot through the overhead windows. (There is a full piloting station at the Orbiter's aft crew station, over on the left-hand side as you're facing aft inside the cabin. That's where the pilot -- usually the Shuttle Commander -- stands while piloting the Orbiter for precision rendezvous and docking maneuvers.)

You can also see the edge of a Mode Indicator on PMA 3. That's the one attached to the Orbiter Docking System on the external airlock. The pilot's windows would be at the top of the Orbiter PLB Foward Bulkhead, toward the right edge of the picture.

To locate yourself on the space station: PMA2 sticks out the front. When the Lab Module comes up, PMA2 will move to the front end of the Lab. It's where an Orbiter normally will dock once the space station is fully assembled. PMA1, pointing away toward the right of the picture, attaches to the FGB control block, which in turn attaches to the Russian elements.

Those box-like structures around the rim of the APAS are rigid covers for utility lines. The power and data cables dive into the mechanism at that point, and then come out on the end cone around the petals.

On top of that stuff is the Z1 truss. The circular structure on the left-hand side of Z1 is a Common Berthing Mechanism. Nothing berths there permanently; this is where PMA2 gets temporarily stowed while the Lab is shuffled into place.

On either side of the Common Berthing Mechanism you see a pair of EVA foot restraints, with workstation stanchions rising vertically above them. Those are articulating portable foot restraints (APFRs). The workstation stanchion is a pipe with a squarish open frame at the the top. It has clips where tool boards and other equipment can be attached while the crew is working.

The trunnion pins and scuff plates on Node 1 look like they're out of place because the Node is tilted when it goes up in the Orbiter.

The big black translation-path arrow near the bottom of the Node is a keel pin. The pin goes into a hole in the Orbiter's main structural keel, at the bottom of the payload bay. That carries a lof of the load during launch.

This is PMA1 seen from the side. On left is the Common Berthing Mechanism. On the right is the APAS. This shot is from the EVA worksite analysis. The astronaut is replacing the MDM (multiplexer-demultiplexor, an eletronics box) on the zenith side of PMA1.


A few of the avionics lines are shown in this picture. They're attached to a dummy connector panel next to the astronaut at the moment this picture is illustrating.

This image gives you a good view of the Control Moment Gyros (CMGs) on the Z1 truss. The detail is missing from the PMAS on PMA1, unfortunately. The model had to be simplified so it would fit into the machine for the EVA translation path analysis.


For scale: that Node is 15 feet in diameter.

Again, the big black arrows were drawn in (by none other than Howard Slade) to show the EVA translation path. This is from Howard's study of the path the crew will follow when returning to the airlock in an emergency.

This view shows the Mode Indicator a little better. The Mode Indicator is near the tip of the arrowhead labeled "PMA 3". Note that, from the Orbiter reference frame, we're looking aftward toward the port (left) wing. So you're looking at the Orbiter 576 bulkhead from the pressurized side.

You can see how the CBM covers fold back to accommodate PMA3 on Node 1's radial port. Trunnion pins with their scuff plates are obvious on the Node and Z1 segment.

This is from assembly flight 4A. The P6 segment with its solar arrays is mounted atop Z1. Later, P6 will be moved way out to the port end of the main truss.

Orthogonal view, looking down on PMA1, toward the earth. (That's nadir; the opposite of zenith.) It's a little rough because it's a scan of a fax. The lines trailing off the edges of the picture identify the EVA handrails and sockets for foot restraints, with such thrilling names as HHD1012B. The box right in the middle is the zenith MDM on PMA1. Wiring harnesses are not shown.


Here's a perspective view of PMA1. No berthing mechanisms, but you can see that it's a big hollow funnel.


Here's a port-side orthogonal view of PMA1 without an EVA crewmember in the way.


This starboard view is probably redundant with the port side, for our purposes at least, but I just had to put in the set for completeness. At least it's a mercifully small file.


And last, but not least, an orthogonal view of PMA1 looking from underneath toward the zenith.


Incidentally, the octagonal shape you are looking at is only the outer meteroid-debris shield. Inside that is a circular funnel, with many wide circumferential flanges welded onto it. The station design team had to invent a new welding machine just to put this thing together!

The circumferential flanges along the body of the circular funnel are about 3/8" thick and 6" wide. They absorb the load when a quarter-million-pound Orbiter collides into a half-million-pound space station. As I said earlier, the PMA structure is very beefy to absorb these loads. With its clothes off, the PMA looks more like a piece of military armor than part of a delicate space ship.

We could avoid a lot of this grief by going back to berthing instead of docking, even if we have a Shuttle Orbiter arriving at our facility. The Orbiter can rendezvous and go to station-keeping while its RMS reaches out to grab a grapple fixture on our facility. The the RMS gently brings the berthing mechanisms together instead of making it a controlled crash.

If we do it right, we should be able to use berthing rather than docking for all the scenarios where we bring spacecraft together in the Artemis Project. We can assemble the moon stack that way in earth orbit, after which the stack never has to come together again. Then, when the ascent vehicle arrives back at the LTV, the pilot can fly to a grapple fixture on the LTV. Or perhaps a little RMS will be on the LTV and the ascent stage will have the grapple fixture.

Or maybe we'll just have a handrail out there, and somebody will reach out and grab the darn thing. As soon as any member of the crew tethers one vehicle to the other, they'll start flying together.

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