Before the countdown clock reaches zero, launch day events at NASA's Kennedy Space Center begin unfolding hours before the actual liftoff.
SpaceX is scheduled to launch four astronauts as part of the Crew-3 mission to the International Space Station on Sunday at 2:21 a.m. ET.
NASA astronauts Raja Chari, Kayla Barron and Tom Marshburn, and European Space Agency astronaut Matthias Maurer arrived at KSC earlier this week ahead of their Falcon 9 rocket launch.
The Halloween liftoff kicks off a six-month stay in space for the astronauts where they'll be conducting science and research on the orbiting laboratory.
The weather for the instantaneous window is looking good as cool and dry conditions are moving in around the Space Coast. The 45th Weather Squadron's latest forecast indicates an 80% chance of favorable launch conditions.
While the launch happens Sunday, the countdown begins Saturday night. Here's a breakdown of critical moments in the Crew-3 launch. Some events may occur earlier, but the rocket launch will remain at 2:21 a.m.
Saturday, 10 p.m.
About 4 hours before liftoff, NASA and SpaceX will begin their live broadcast of the countdown. Around this time, the crew will have eaten their last Earth meal for a while and will be putting on spacesuits.
10: 16 p.m. -10:21 p.m. Weather briefing
The 45th Weather Squadron will provide a weather update, and the launch director will conduct a countdown briefing and readiness poll.
11:06 p.m. Saying goodbyes
The four astronauts will walk out of the KSC Operations and Checkout Building (O &C), where they will have a few minutes to wave goodbye and say a few words to their family and friends outside.
11:26 p.m. Drive to 39A
In pairs, the astronauts will get into two Teslas and then make the drive to KSC launchpad 39A, where the Falcon 9 and Crew Dragon spacecraft will be waiting.
The astronauts get to pick out the playlist for the 10-minute drive to the launchpad. Chari, the mission commander, shared on Twitter a list of the song choices including "Welcome to the Jungle" by Guns n Roses and "Starship" by Nicki Minaj.
After arriving at the launch site, the crew will go up the launch tower into the white room. At the top, they will have a few minutes to sign the wall like the other astronauts to launch with SpaceX have. They will also have time to use the red phone at the top of the tower to make a final call.
11:46 p.m. Strap in for launch
SpaceX teams will help the astronauts get into the Crew Dragon Endurance. They will be strapped in for launch before the hatch closes. Their custom seats will be rotated for launch position, and final suit leak checks will also be happening at this time.
Sunday, 12:26 a.m. Hatch close
SpaceX will close the spacecraft hatch and then check it's secured and no "foreign object debris" prevents a tight seal.
1:21 a.m. Final polls before fueling
Another weather update happens before rocket fueling. If the weather is "no go," this could delay the launch. The mission director will also conduct a final poll before giving the OK to load fuel into the Falcon 9.
1:43 a.m. Dragon escape system arms
The Dragon spacecraft escape system is armed. If there is a problem during the launch, the escape system will send the spacecraft away from the rocket, and the Dragon will land at sea, carrying the astronauts to safety. The system has to be armed before fueling can begin.
1:46 a.m. Falcon 9 fueling begins
At about T-minus 2 minutes, the rocket propellant load will be complete, and the vehicle will be on internal power.
2:21:06 a.m. Liftoff!
Falcon 9 lifts off from Kennedy Space Center with the Crew Dragon spacecraft carrying the four Crew-3 astronauts.
The spacecraft begins docking at the space station Monday night around 9 p.m. ET.
If Sunday's launch scrubs, another launch window opens Wednesday at 1:10 a.m.