If you aren't watching, astronauts are heading to the launch pad right now. https://twitter.com/NASA/status/1265679515193409541

Astronaut taking "nature break." Ha!

In Russia, they'd stop and pee on the tire of the van.

That's great that they stopped to look up at their spaceship.

I don't know if they're doing it here, but the Apollo astronauts had an elevator technician in the elevator with them just in case it broke down.

Cool! They are signing the white room wall!

They are ingressing! This is very exciting!

And then they'll have two hours of waiting. Whee!

The tabs on the harnesses are pretty cool. It's an easy way for them to grab the harness and tighten it, which also tells you something about the kind of dexterity that they have in the gloves.

Oo! Bob just added what looks like a wrist mirror over his right glove. That's a way for astronauts to check things that are on the front of their suits, since they can't look down easily.

Here's a SpaceX ISS docking simulator, if you want to see their controls. https://iss-sim.spacex.com/ 

Side note: Watching the press conference, where they've put Bridenstein, interviewer, and Musk in a triangle to get them all into frame easily.

A puppet would be able to make it look like they were looking at each many without having to turn around.

Important note about their suits: These are launch suits NOT for spacewalks or moonwalks. All these do is protect the astronaut in vacuum.

The life support is external, which is why they have an umbilical on the thigh.

Someone asked about the touchscreens, which feel more fallible since we've all experienced them not working.

There are many layers of redundancy in the touch screens, including multiple touchscreens, and all critical commands are also available by physical pushbuttons.

Even with all that, the checklists are still physical and strapped to their legs.

Good news about the weather.

The reason they mentioned Cabo is that they are looking at weather at about 50 different possible abort sites.

The weather needs to be good not just for launch, but also at possible places an abort would come down.

Com checks are unreasonably exciting.

All they are doing is confirming that mics are working and that people can hear.

But it also means we're getting closer to Go.

Correction: I'm wrong about the checklist on their leg. It's a tablet.

(I just asked an astronaut, which I should have done before tweeting.)

What Christana Koch is referring to about the difference between shuttle and ISS astronauts reflects in their training.

Shuttle astronauts were task trained -- ie to do specific jobs.
ISS astronauts are skill trained, so can tackle anything.

This also means that Shuttle astronauts could practise tasks over and over to do it quickly, since they had limited time in space.

ISS astronauts have to be able to handle surprises because they are long duration missions.

When they show views from the top of Crew Dragon, it's basically a 23 story building.

For the most part, the astronauts are waiting and working through checklists. But mostly waiting.

They've done a bajillion simulations, so on the one hand this reportedly feels anti-climactic. On the other hand... they are going to space in a new vehicle.

The astronauts just said they are Go.

Which means that they've done everything they can do prior to actual launch.

The big question is still the weather. In an earlier briefing, they said that they would make the Go/NoGo call at 45 minutes pre-launch.

The arm is away!

Oh, man that is so exciting to watch.

Fingers crossed that the weather holds.

Several people have asked how the astronauts pee when they are waiting. MAGs. Maximum Absorbency Garments.

Basically adult diapers.

And in fact, we have adult diapers because of NASA.

The fact that they are getting ready to load propellant is a good sign. They weren't going load propellent if the weather looked bad.

AND IT'S STARTED!

Traditionally astronauts have a zero gravity test, which is something that will start floating when they are in orbit.

This is the dragon hitching a ride in the Dragon. https://twitter.com/AlyshondraM/status/1265733217895591936

Potential reschedule to May 30th? Now I have two reasons to want them to launch today.

May 30th is the Nebula Awards Ceremony.

The tricky thing about lightning conditions is that the spacecraft is basically a giant lightning rod that then flies through the clouds

I have never been so tense about weather before.

It's not sounding good.

The conversation they were having about "if I can have ten minutes" was about if they could hold for ten minutes.

Launch abort.

This is not unexpected. During shuttle days, one was delayed so many times that an astronaut's child asked her, "Mommy, what time is your scrub today."

There's something called "launch fever" where people will push to launch when they shouldn't. So I'm very glad that they empower individuals to say No.

The backup launch opportunities are on Sat. May 30 at 3:22 p.m. EDT and on Sunday at 3:00 p.m. EDT

For those people attending the #Nebulas2020 conference, I'll open up the Grand Ballroom in the Vorkosigan suite for a launch viewing party during the lunch break.

(For those not attending, it's a virtual space.)

PS, since people are STILL asking about astronauts peeing. https://twitter.com/MaryRobinette/status/1152277166996017152