Thread by @MaryRobinette

Want to watch another spacewalk?

Jeanette Epps is the ground IV, which means "intravehicular" in this context as opposed to the EVA, "extravehicular activity."

The EVA team outside the space station this morning is David Saint-Jacques and Anne McClain.

Some vocabulary:
"temp-stow" is exactly what it sounds like, "temporarily stow," which is important because you don't have gravity to hold things like cables down when you're working.

"t-handle tool" is basically a handle that you can place in a WIF in order to get a grip on something.

WIF=worksite interface fixture.

A reminder that you can #AskNASA questions, which they'll answer on the livestream.

You can also ask me questions, but sometimes my answers will be "I don't know! What a good question."

It sounds like they are saying "Zeus fastener" but it's actually "dzus fastener" also known, on Earth, as a quarter-turn fastener.

(I was wrong! I got it confused with a different tool.)

Whoops! I was wrong about the T-handle tool. It's the thing shaped like a T in this screenshot.

Ooo. This is interesting. They can't get the dzus fastener undone, so they are having to use a prybar on the fastener. They've got a garbage bag over the area to contain debris.

Besides the immediate concern about projectiles hitting the astronauts and compromising their EMUs, the long-term concern is that debris will stay in orbit with the station and can potentially hit it.

"verify that all of your safety tethers are clear of the cables"

These are the personal safety tethers, since if they went under the cable, the astronaut would be stuck in place. There are ways to recover, like undoing the cable, but best to not have it happen.

One of the things you can hear right now is more breath. The astronauts are on VOX, voice activated microphone. If they breath heavily, it can trigger the VOX.

So you can tell how hard something is by how much breath you hear.

So imagine that you need to pry something up, but the only leverage that you have is your own grip on a handrail. You're not just adding leverage with that grip, you have to keep your body in the same orientation and counter for any motion you do.

There's no gravity assist.

There's also stuff that's ONLY hard when they're training in the NBL. For instance, coming out the airlock on the nadir side, means being upside down. On Earth, all the blood is rushing to your head, even if the suit is neutrally buoyant.

Not a problem in space.

"I have a PGT setting for you"

Pistol-grip tool aka drill.

They're having to pull the handrail, because they can't get the cover into place. You'll notice that, even though this wasn't planned, NASA still has procedures ready for how to do it.

Anne McClain's suit has the red stripes, which means that she's EV1. This also means that she's in command of the EVA spacewalk.

Jeannette Epps is the ground IV, directing them.

It's not an all-woman spacewalk, but still take a moment to appreciate women in command.

I know I harp on this every time I live-tweet one of these, but pay attention to the number and types of tethers.

Everything is tethered. Constantly.

Wire ties! These are brass wires that they use to tie things down. The story goes that cosmonauts were training at JSC and saw the wire ties on bread.

They thought that was neat and created larger versions to tie things down in space.

NASA saw THOSE and created their own.

The glove and hat check that McClain just did is a reminder that EMUs are 40 years old.

The gloves aren't that old. Often they are custom made for each astronaut. McClain's left glove has an abbrasion, which they're keeping an eye on.

But the hat check...

This is checking to make sure that there's no fluid in the helmet. The PLSS, portable life support system, is one of the original 18 built 40 years ago. Among other things, they circulate water through the suit to keep the astronaut cool.

They can leak.

One astronaut almost drowned in space.

But a 40-year-old system, without funding to really develop a new one -- and there are plans -- means they have to find workarounds.

So there's basically a diaper behind their heads to catch water. They're checking to see if it's damp.

Right now they're trying to get Saint-Jacques glove heaters to work. They think it's a battery issue.

The lack of glove heaters means that his hands are going to get really cold. Storey Musgrove suffered frostbite from a spacewalk, that's when they added glove heaters.

Space itself won't be the cold part. It's a vacuum, so doesn't wick heat away.

But when you touch the station... anything in shadow is -250 degrees Fahrenheit.

The SAFER handle is related to the Simplified Aid For EVA Rescue. It's a jet pack that can get the astronaut back to the ISS if they come untethered.

The check is because an astronaut accidentally triggered it once. The immediate workaround was to put duct-tape over the switch.

Also fun random factoid for the SF writers out there...

Astronauts carefully trim their nails before a spacewalk, because if they catch on the inside of the glove you can "delaminate" your fingernail.

Yeah...

The tools they use in the NBL are weighted to be neutrally buoyant, so the PGT is this white foam thing. I keep being thrown when I see the bright metal one strapped to McClain's spacesuit.

Reportedly, the first time you're on a spacewalk, doing things that you've practiced multiple times in the NBL, it is surprising that everything isn't blue.

Because you're not underwater. You're in space.

They just asked Saint-Jacques to confirm if he had adjusted his thermal controls. They can see the telemetry of the suit and tell that something changed. If he didn't do the change, then that would be a sign of a potential malfunction.

Also, one of the differences between the NBL and space is that in the NBL, they have to ask someone else to control their temperature. On an EVA, they have direct control

The mirrors on their wrists are so they can see the controls on the chest of their space suit. All the labels are written backwards.

All of the modules have formal names which are printed on the outside of the ISS. The astronauts inside can apparently never remember the formal names because... they're printed on the OUTSIDE of the station.

"Do you hear that sound?"
"That spring sound?"

And then loss of signal.

I'm sure it's fine. BUT IF THIS WERE A NOVEL IT WOULD NOT BE.

Also, what sound are they both hearing in a vacuum?

The answer is that it's probably a thing related to the handover as they go from one set of satellite relays to the next, but again-- if this was one of my novels, I would totally be setting up something that was...

Oh.

Ha. Just solved a plot problem. BRB.

I've inquired with an astronaut and have learned that if they are both touching the structure an external sound could transmit to both of them.

Again, the fact that McClain has lost comms in one ear would be a great plot point for a novel.

She lost it while in the trunion.

David Saint-Jacque has encountered something he doesn't recognize in the trunion.

Again, IRL, everything is fine. But in a novel...

This is part of why I enjoy watching spacewalks, because the tiny things that can go wrong are so much more interesting than explosions.

Like...how many films have you seen where someone's spacesuit springs a leak and is wildly venting oxygen? In 400+ EVAs, it's never happened.

There WAS a spacesuit puncture on STS-37 but it came from inside the suit. There's a palm bar, which is a rod that goes across the palm to keep it from ballooning out. Somehow it slipped and punctured the suit.

But the astronaut's hand conformed to the breach and sealed it.

Afterwards, he had a small abrasion, but nothing else.

If the bar had come all the way out, he would have had a leak, but not enough to do more than register a higher than normal oxygen consumption.

Over on the Russian side, an Orlon also had a puncture. Reportedly, the cosmonaut was using a cutting took ad accidentally caught the suit, cutting deep enough to bleed.

The blood froze in the breach, sealing it.

Look how crowded the airlock is

They've just secured David Saint-Jacques suit to the equipment lock wall, which will make coming out of it a little easier because it'll give him some leverage.

The HUT, hard upper torso, is inflexible so requires some oomph to get in and out of.

PS I'm excited, because they often stop the live feed before the crew comes out of the space suits.

They at least have them off "hot mic" so they don't have to deal with us listening in.

Part of the reason for taking photos is to record the position of microphones and other gear post-EVA. It's good to know if things shifted, especially since McClain was having comm trouble.

The helmet design, by the way, is the same one that the Apollo astronauts used. It's two layers of glass, one that is airtight, the other is impact resistant.

It's a bubble like you see when they are boarding in Apollo 11 footage.

The plot point in SF where someone hit's their faceplate and cracks it, leaking air? The amount of force necessary to crack the inner bubble would probably be fatal on its own.

Underneath their EMU gloves, both astronauts have white gloves for comfort and warmth. This helps prevent the aforementioned delamination of fingernails.

Watch the way they are flexing their hands and wrists. They translate around the station by using their hands. They hold tools with their hands.

The gloves are pressurized and like fighting a heavy spring.

This was a 6.5 hour spacewalk.

Helmets are off! Underneath they are wearing a "Snoopy cap" which holds their communications gear. It's named after Snoopy for the cap he wore when fighting the Red Baron and has been called that since the early days.

Hm... I just heard them say that the pads inside the helmets were moist. This could be leaks, humidity, or potentially a ton of sweat.

That's it for today! Thanks for joining me.

A reminder that if you want to sign up for my newsletter, I will occasionally send you short stories as well as opportunities to beta-read my works in progress.

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