NASA delays Axiom-1's return to Earth again. Here's why.

The Ax-1 crew is targeting a splashdown off the coast of Florida this weekend. (Photo credit: Axiom Space Twitter)

NASA has delayed the undocking of the Axiom-1 Mission until Sunday, which in turn pushes back the crew's splashdown to Monday afternoon. 

The four private astronauts were initially planning to undock from the International Space Station Saturday night with a splashdown scheduled for Sunday. 

The crew will now undock from the ISS at 8:55 p.m. ET Saturday, April 24, NASA said, with an expected splashdown off the coast of Florida around 1 p.m. on Monday, April 25.

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NASA said the delay is due weather conditions at the splashdown site. Unfavorable weather conditions were also cited as the reason for the inital delay to undock from the ISS on Tuesday.

At this time, the delay is not expected to impact the April 27 launch date for Crew-4, but NASA officials are continuing to watch the weather conditions. 

Mission controllers are looking for specific weather criteria, including minimal wave height, low winds and no storms for a splashdown in one of seven locations around the Florida peninsula.

NASA wants 48 hours between the departure of the Dragon Endeavour carrying the private astronaut crew home and the new Dragon Freedom arriving at the space station with the Crew-4 astronauts.

"When Ax-1 departs, (the space station) then has room for Crew-4 to dock. We want to provide a two-day gap after return for data reviews and to prepare for launch and stage recovery assets," Lueders said in a tweet Wednesday. "We'll make decisions about a new Crew-4 launch date based on safely executing our plans."

The Crew-4 astronauts, NASA's Kjell Lindgren, Bob Hines, Jessica Watkins and European Space Agency astronaut Samantha Cristoforetti, of Italy, arrived at KSC Monday and will now wait for their new liftoff T-0.

NASA says the earliest available launch window for Crew-4 is now Tuesday at 4:15 a.m. ET. There are additional opportunities on Wednesday and Thursday.

The new launch date and time will be dependent upon the safe return of the Ax-1 crew and a review of the flight data.

Additionally, the Crew-3 astronauts have been on the ISS for six months and are awaiting their return ticket to Earth. NASA astronauts Tom Marshburn, Raja Chari, Kayla Barron and ESA astronaut Matthias Maurer arrived at the ISS in November. 

With the latest Axiom-1 return delay, the Crew-4 launch was unlikely to launch Saturday. However, looking at the launch forecast from the Space Force's 45th Weather Squadron, Saturday's weather would have presented a challenge.

A pattern of showers and occasional storms is expected to begin Friday and continue into the weekend, according to the forecast.

Weather for a human spaceflight liftoff is more complicated than a launch without a crew on board.

Forecasters are also tracking the weather along the ascent corridor of the SpaceX Falcon 9 rocket in case of an emergency abort that would cause the Dragon to land in the Atlantic Ocean. According to the 45th Weather Squadron, the risk along the ascent corridor is moderate from Saturday through Monday.