For the third time, astronauts are set to hitch a ride on a private rocket to space.
Early on Friday, SpaceX, the rocket company started and run by Elon Musk, is scheduled to launch its latest mission for NASA, carrying two American, one Japanese and one French astronaut to the International Space Station. That will be a continuation of a successful effort by the space agency to turn over to the private sector the business of taking people to low-Earth orbit.
SpaceX conducted a demonstration mission with two NASA astronauts, Bob Behnken and Doug Hurley, a year ago. The two men then splashed down in the Atlantic Ocean in August. They traveled in the same capsule, named Endeavour, that will fly on Friday.
Months later, SpaceX conducted what NASA called the first routine operational missions for the Crew Dragon spacecraft with four astronauts onboard. That mission, Crew-1, launched in November, and the astronauts are still aboard the station.
Now comes the second operational mission, known as Crew-2.
When is the launch and how can I watch it?
The launch is scheduled for Friday at 5:49 a.m. Eastern time from the Kennedy Space Center in Florida. Both NASA and SpaceX will be offering marathon coverage of the mission beginning at 1:30 a.m., from the astronauts’ suiting up to the moment they launch.
Why was the launch delayed one day?
The Crew-2 launch had been set for Thursday morning, and weather at the launchpad was favorable. But mission managers had to also take into account conditions in the Atlantic Ocean where the Crew Dragon capsule would splash down if something went wrong during launch. There, NASA and SpaceX decided, the winds and waves were too high.
The weather report for Friday morning foresees a 90 percent chance of favorable conditions at the Kennedy Space Center. Conditions in the Atlantic are predicted to be better than on Thursday.
What will happen during the trip?
Hours before the launch, the astronauts start to get into their trademark SpaceX spacesuits with the help of technicians. They then bid farewell to their families and head out to the launchpad in Tesla Model X S.U.V.s. (A bit of cross-marketing between SpaceX and Tesla, both run by Mr. Musk.)
After they arrive at the launchpad, the astronauts board the capsule and spend hours working with mission control to confirm that its systems are ready for flight.
The launch is timed to when the space station’s orbit passes over Florida. When the capsule reaches orbit, it will be directly behind the space station but traveling faster in a lower orbit. That allows the Crew Dragon to catch up for docking at 5:10 a.m. on Saturday.
During their 23-some hours in flight, the astronauts will change out of their spacesuits, eat a meal or two, rest and provide updates to mission control.
Once the capsule docks with the station — an automated process — it then takes a couple of hours of checking to make sure there are no air leaks before the hatches open and the Crew-2 astronauts disembark.
Who are the astronauts?
The Crew-2 astronauts are to spend six months at the International Space Station.
Akihiko Hoshide of JAXA, the Japanese space agency. Mr. Hoshide, 52, has made two previous trips to space. He was a member of the crew of the space shuttle Discovery in 2008, and in 2012 he spent four months on the space station.
Shane Kimbrough of NASA. Mr. Kimbrough, 53, is the commander of Crew-2. He has made two previous trips to space, once on the space shuttle Endeavour in 2008 and then spending more than six months on the space station from October 2016 to April 2017.
K. Megan McArthur of NASA. Dr. McArthur, 49, flew on the space shuttle Atlantis in May 2009 on the last mission to refurbish and upgrade the Hubble Space Telescope. During that mission, Dr. McArthur, an oceanographer by training, operated the shuttle’s robotic arm to grab the telescope and place it in the cargo bay.
Dr. McArthur is married to Bob Behnken, one of the astronauts who traveled on the first astronaut flight of the same SpaceX capsule last year. She will sit in the seat he occupied during that flight.
Thomas Pesquet of the European Space Agency. Mr. Pesquet, 43, previously spent six months on the space station from November 2016 to June 2017, overlapping with Mr. Kimbrough for most of his stay. He is from France.