Thread by @MaryRobinette

Want to watch a spacewalk with me?

https://twitter.com/NASA/status/1180792565278429185

Let's start with some vocabulary.

APFR - articulated portable foot restraint.
ORU bag - Orbital Replacement Unit
crewlock bag - A bag used to haul equipment around on a spacewalk

A gap spanner is basically a cloth handrail that spans the gap between two handrails.

When they say "good pull-test." They mean that literally.

Orbital Replacement Units are an interesting thing. Because they don't really have a workshop on the ISS, a "unit" is generally an entire device that needs replacing.

Like. You break a microwave, you buy a new one.

NASA sends up duplicates for saftey.

But on missions farther from Earth, the ORU will get smaller.

You won't be able to bring along enough duplicates for everything, or send back to Earth easily for a replacement.

You'll need the ability to do repairs, so "unit" being replaced will necessarily change to parts.

Here's a good view of a crew lock bag. Notice that it has a clear lid, so you can see what's inside without opening it.

All of the tools are tethered to the inside of the bag, because when you open it and pull anything out, they all want to float away.

"It's in RET-RET Series"

They've linked two Retractible Equipment Tethers in a series to extend their length.

For those watching live, you see how everything is floating out of the crewlock bag?

PLEASE INCLUDE TETHERS IN YOUR SCIENCE FICTION

This has been your PSA for today.

In this photo you can see the mirror on Christina Koch's left wrist. That's so she can see the gauges on the torso over space suit.

There's also a checklist on her wrist.

And actually, a pretty good view of the end of a tether.

"Interference with the bayonet"

Okay. That's not a sharp weapon in space. It's the end of a probe and goes into a socket. Usually into a WIF (worksite interface fixture) but can be other things.

This is a photo that I took at the NBL so you can see the crewlock bag and some tethers when they aren't floating around.

Great opportunity to watch the PGT in action. The Pistol Grip Tool is basically a drill. You'll note that it spins very slowly.

That's partly to make it easier to counter the torque.

Without gravity to hold you in place, you have to actively counter the drill's motion.

The PGT is also slow so they can count the number of turns. People on the ground have tested the entire spacewalk in a series "dev run."

If you strip a bolt or a socket on a spacewalk, it is not an easy fix.

In the dev runs, they practice a series of iterations of the spacewalk using the full-scale mock-up of the ISS in the NBL's giant pool.

That's turned into a set of instructions that are transmitted up to the astronauts who will actually do the spacewalk.

In the Apollo and Shuttle days, astronauts were "task trained" which means that they learned to do a specific task, because they would be the ones performing it and could practice repeatedly to become fast and perfect.

They didn't have a lot of time to spend in space.

The ISS astronauts are "skill trained" because their missions are longer duration. It's harder to know what they'll need to do while they are up there.

The answer is to train them to handle anything.

Sunset coming up! Watch how the light changes.

See how dark it just got? They have to use helmet lights to see now.

There's also a temperature difference. In sunlight it's 250F and in shadow its -250F

They mostly notice this in their hands. The gloves are not as well insulated as the rest of the suit, for mobility.

Also a reminder, for SF writers, that this day to night shift isn't just the ISS. If you have ships orbiting another planet, they would get the same shift.

The frequency will change, depending on the speed and distance of the orbit, but they'll still get multiple sunsets.

By the way, @planet4589 is also live-tweeting and covers different things than I do. He's an astrophysicist.

I'm an SF writer trained as a puppeteer.

Waaaaaay more science over in his feed.

@planet4589 If you are interested in more details, I highly recommend the "How to Plan a Spacewalk" episode of Houston, We Have a Podcast.

nasa.gov/johnson/HWHAP/…

@planet4589 Quiescent!

"Crew member must remain quiescent."

I have not heard this in use on a spacewalk before and am totally using it in a story at some point. Such a good word.

@planet4589 Honestly, besides being a giant space nerd, one of the reasons I watch these is to pick up speech patterns to use in my fiction.

Every occupation has its own jargon and in-group language. Like the fact that in the space industry, "nominal" means things went well.

@planet4589 The other voices, besides astronauts, that we hear on a spacewalk are the POA and the CapCom or EVA flight director.

The Public Affairs Officer today is Dan Huot.

Astronaut Stephanie Wilson is the one giving directions to the spacewalkers.

@planet4589 The astronauts aren't hearing the PAO, he's just for us.

Stephanie Wilson, on the other hand, would have been involved in the dev runs. So in addition to having a list of procedures in front of her, she's also seen a bunch of different approaches to doing this.

@planet4589 Glove and HAP check.

They're checking to make sure there aren't any punctures or tears on the gloves. Since they are in contact with the station, those are most vulnerable to damage.

(Also, sunrise coming up)

@planet4589 Jessica Meir is working the robotic arm right now.
Christina Koch is spacewalking.
Stephanie Wilson is CapCom
Drew Morgan is the only man actively involved in this spacewalk.

This isn't the first all-female spacewalk, but it is the first time women have outnumbered the men.

@planet4589 Well, shit. I literally just started crying a little.

Welcome to the 21st century, where it is still unusual for there to be more women than men involved in task, on Earth or in space.

@planet4589 MEANWHILE, to explain what's happening. There are times when the best way to reach a spot on the space station is to put an astronaut on the end of the giant robotic Canadarm and move her into place.

This allows her to use both hands to work.

@planet4589 In this case, the robotic arm is, I think, moving the entire pallet of batteries.

@planet4589 The PAO just said that the longest spacewalk was eight hours and 56 minutes, in 2009.

This is why you will see me get cranky when I'm reading SF set in the future in which someone only has an hour of air in their suit.

That's not even enough time to get out of the airlock.

@planet4589 If it's an emergency suit? Sure. But if it's designed that way... Come on. The Apollo astronauts could moonwalk longer than that and that was the 60s.

Also, of the consumables you're worried about, the oxygen is the easiest to manage.

@planet4589 The other limiters on a spacewalk, besides oxygen, are CO2 and battery life.

If your suit loses power, you lose comms, heating/cooling and the fans.

Without fans, the CO2 will build up around your face. That would be a bad day.

@planet4589 Even with a CO2 scrubber, the spacesuits still wind up with a higher concentration of CO2 by the end of a spacewalk. The astronauts can get a little loggy, not just with fatigue, by the end.

That's why they have a CapCom or IV (intra-vehicular) person to guide the spacewalk.

@planet4589 As Christina is working this PGT, you'll note that she's having to brace herself on a handrail while working.

Micro-gravity is all floaty, which sounds great, but it also means you aren't getting any assistance to hold yourself or your tools in place.

@planet4589 Sidenote: I've been talking with an astronaut friend (humblebrag) about what puppetry in space would look like. Think about a marionette, which relies on strings to hold it up and gravity to hold it down. Even a spring return needs a way to brace against the force of it.

Now think about prosthetics and other assistive devices in space. It's an interesting problem that we'll need to solve for long term survival in space.

"Black on black"

That's a reference to the lock indicator on a tether. It's two black lines that form a single solid line when the tether is locked.

I don't know if these will make sense to anyone but me, but these are my raw notes from when I visited the NBL to research the spacewalk scenes in #TheFatedSky.

docs.google.com/document/d/1nD…

I guess this is a good spot to insert a shameless plug for my Lady Astronaut novels.

If you order them from my local independent bookstore @ParnassusBooks1, I'll sign it. Put a note in the comment field if you want it personalized.

parnassusbooks.net/book/978076539…

@ParnassusBooks1 Things are weightless in space, but still have the same mass. Imparting momentum to an item requires force. So does stopping it.

In the NBL, the challenge is to get things moving through the water resistance.

In space, the challenge is stopping them.

@ParnassusBooks1 That's why they are so clear about the hand-offs with the call and response of "I have the battery" "You have the battery."

@ParnassusBooks1 That's a great note, that there are two CapComs on duty today. One for the spacewalkers and one for the astronauts in the ISS.

@ParnassusBooks1 In addition to the status checks of the suit, the astronaut inside is also taking damage.

NASA categorizes these into "contact injuries" and "strain injuries."

Most on orbit injuries are acquired during a spacewalk.

@ParnassusBooks1 The suit is pressurized to 4.3 psi, which requires them to exert force to move the suit. That means they are pushing against the inside of the suit.

This can lead to bruises, abrasions, blisters, fingernail delamination and... onycholysis.

The nails actually coming off.

Astronauts cut their nails really, really short when they are prepping for a spacewalk to reduce the likelihood of onycholysis.

Someone asked about suit punctures. There have been 2 instances in American suits, neither resulted in decompression.

The EMUs gloves have 5 layers. On STS-118, a tear went through two of the layers and they cut the spacewalk short to be on the safeside.

en.wikipedia.org/wiki/STS-118#W…

On STS-37, a stainless steel palm restraint punctured the bladder in the suit. The astronauts "comfort glove" sealed the hole and he didn't notice until afterward the spacewalk.

en.wikipedia.org/wiki/STS-37#Sp…

I heard a story about a cosmonaut who was using a tool and accidentally cut through his glove and clipped his hand. The blood sealed the hole. It's unofficial, because he didn't report it out of fear of getting grounded.

WARNING: I have no independent confirmation for this.

The spacesuit can have a 1/8" puncture and the astronaut would have about 22 minutes to get inside.

That said, there's also a fair chance their skin and interior garments would plug a small hole.

Remember: Even a pristine spacesuit is not entirely airtight.

If you are contemplating having, say, a character cut a hole in their glove for self-propulsion.

1. Not enough air in the suit
2. The hand would have swollen and self-sealed the hole.
3. Steering would suck.

This is why you have humans in space. They can improvise and while they are easy to damage, they are also versatile.

There's a problem installing this adapter plate. The "soft dock" means they placed it, but haven't attached it yet.

Think of it like this... Installing the adaptor plate on the ISS is like assembling an IKEA desk.

In a swimming pool.

With someone else reading the instructions from the lifeguard stand.

While swaddled in pool floaties.

Wearing oven mitts.

Also, you're wearing a diaper.

And a mistake could kill you or cost millions of dollars.

There's no pressure or anything, being an astronaut.

Space is very glamorous.

(PS If anyone wants to send a novelist into space, I volunteer as tribute.)

Also, a reminder that the EMU - Extra-vehicular Mobility Unit - is a 40 year old spacesuit.

There are designs for newer ones, but funding constraints and shifting goalposts mean that they have not completed testing, much less gone into production.

Hey! They finished the tasks on their list early.

A "get-ahead" is a task scheduled for the next spacewalk. This is a good illustration of why they get skill-training instead of task training. They can continue getting work done.

Here's a nice big picture view of where they are working today.

https://twitter.com/Space_Station/status/1180877262356389888

I was looking for a good picture of the MWS or mini-workstation. That's the bar strapped to their chest where they keep their tools.

This is Kjell Lindgren, and you can see the tethers, etc at the NBL.

(The blue foam is to make the suit neutrally bouyant in the pool.)

By the way, he told me that I probably wouldn't want to watch the entire dev run because I would find it boring.

He was wrong.

The conversation that they're having now about Christina's feet in the APFR* is because it's sometimes hard to feel where your feet are in the EMU.

You're floating in it, and often don't really have contact with the soles or tops.

*Articulated Portable Foot Restraint

(For those of you interested in writing process, scroll upthread to read the Raw Notes from my NBL visit, then read my short story "Articulated Restraint" while watching this spacewalk. You can see where it came from.)

tor.com/2019/02/06/art…

"leapfrog"

1. Astronaut A translates to the length of their safety tether, hauling astronaut B's tether with them.
2. They secure their local tether & B's tether.
3. B "leapfrogs" past them, carrying the far end of A's tether.

It extends their range while remaining tethered.

Christina just reported about the amount of force they are having to exert to counter the torque and that it seems to be consistent with the new batteries vs. the old ones.

The reason it's important to make that report, is that different astronauts will do the next spacewalk.

Those reports will be discussed during debrief and get worked into the procedure for the next spacewalk.

Spacewalks are seriously arduous, which is why you rarely see someone doing them back-to-back.

"Quebec, quebec, hotel 12" on paper would be "QQH12"

The other reason that I watch spacewalks, professionally, is to learn how things are said aloud when I'm doing audiobook narration.

At NASA which things are pronounced as words, which are individual letters and which get spelled out using the international phonetic alphabet is sometimes completely random.

Then you have things like PGNCS is pronounced "pings"

Ooo! A decent view of the inside of a mostly empty crewlock bag.

The reason it's so important to do an inventory before ingressing is that, if you left something outside the station, it's not a simple thing to go fetch it.

And watch everything tumbling around as she's doing the inventory.

Oh, wait. I'm wrong. It sounds like they are going to leave the crewlock bags outside for the next spacewalk. That's why the good "thermal config" is important.

The ISS goes in and out of shadow with each orbit, so minimizing that for the equipment prolongs its life.

So, in this context, the reason the inventory is important is for planning the next spacewalk. Knowing what's already out there will affect what the next astronauts need to take out with them.

The PAO is answering a question about how astronauts eat and stay hydrated during a spacewalk. They have a drink bag.

They USED to get dried fruit bar in a sleeve. To access it, they'd bite it and pull it up.

However...

The last bite of the fruit bar inevitably came out of the sleeve and then floated around in the suit with them.

It was...off-nominal.

So, now they just eat a big breakfast and have a hearty meal afterwards.

Apparently, during an NBL simulation, one of the astronauts bemoaned the lack of food and wished for pizza.

A support diver later swam up to them and with a piece of pizza in a ziplock bag.

Sounds like Drew is having trouble. You can hear him narrating what he's trying to do.

When Stephanie says "we're discussing" she means the backrooms and specialists are working the problem. As CapCom or Ground IV, her job is to parse and relay that to the astronauts.

He's translating back to the anchor hook to see if there's a snag in the line.

You'll note that he doesn't slid his hands as he translates along the handrail. Micrometeorite impacts can create sharp ridges. Sliding can slice a glove.

I, personally, wish this was happening while they were in daylight so that visibility for trouble-shooting was better.

A snag at handrail 3688, which he's cleared. Hopefully his tether will perform correctly and allow him to get back to the airlock.

Meanwhile, Christina has spotted MMOD which has caused a sharp edge on the station. They'll note it as a caution for future spacewalks.

MMOD - micrometeorite or orbital debris impact.

Here's more information about why these are a problem. tl;dr - they're sharp and can tear gloves.

universetoday.com/101567/how-mic…

Hello, airlock!

Note that even when they go into the airlock, they tether themselves and the equipment. Until they close the hatch and repress the airlock, they are still in space.

While they are on the spacewalk, the outside hatch of the airlock is covered with a thermal shield. That helps control temperature inside the airlock, while also making it easy to ingress.

This part of the spacewalk simulation in the NBL is a real pain, because the astronauts are inverted. The *suit* is neutrally buoyant, but inside it, they're still upside down.

If you're curious, here's an ISS EVA checklist from 2005.

nasa.gov/centers/johnso…

Hatch is closed and now they'll start "repress" which is repressurizing the airlock.

The hissing sound that you hear is the sound of air entering the airlock. I've been told that it is VERY LOUD.

The spacewalk is officially over. Thanks for joining me to watch it. I'll see you on Friday the 11th for the next spacewalk.