The four astronauts of SpaceX's Crew-4 mission to the International Space Station (ISS) will have to cool their heels here on Earth for at least one extra day.
The launch of Crew-4 had been scheduled for April 20. But it'll now lift off no earlier than April 21, and NASA and SpaceX are also considering the backup date of April 23 as an option, Kathy Lueders, the agency's human spaceflight chief, announced today (April 6).
"The additional spacing provides mission teams time to complete final prelaunch processing for Crew-4 following the launch of the Axiom Mission 1 to the space station. We’re taking each mission step-by-step to ensure we are moving forward safely," Lueders wrote on Twitter today.
Related: Next SpaceX NASA crew launch adds rookie astronaut Jessica Watkins
Axiom Mission 1, or Ax-1 for short, is another crewed SpaceX flight. Ax-1, which was organized by Houston company Axiom Space, will send three paying customers and Axiom employee Michael López-Alegría to the ISS for an eight-day stay. López-Alegría, a former NASA astronaut, is commanding the mission.
Ax-1 is scheduled to launch from NASA's Kennedy Space Center (KSC) in Florida on Friday (April 8). Like Crew-4, it will use a SpaceX Falcon 9 rocket and Dragon capsule and lift off from KSC's Pad 39A.
There are significant differences between the two flights, however. SpaceX is flying Crew-4 for NASA, and the crewmembers are all government astronauts — NASA's Kjell Lindgren, Robert Hines and Jessica Watkins and the European Space Agency's Samantha Cristoforetti. Crew-4 will also be a much longer mission than Ax-1, spending months at the orbiting lab.
KSC is a real hotbed of activity these days. In addition to the coming Ax-1 and Crew-4 launches, the facility's Pad 39B is hosting the "wet dress rehearsal" of NASA's Artemis 1 moon mission.
This crucial prelaunch test began last Friday (April 1) and was supposed to wrap up on Sunday (April 3), but the Artemis 1 team ran into a few problems that delayed and ultimately halted activities. The mission team plans to resume the rehearsal shortly after Ax-1 lifts off.
Editor's note: This story has been updated to correct the launch dates under consideration for Crew-4. Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.