NASA and SpaceX postponed the launch of the next long-duration crew to the International Space Station early on Monday, minutes before the rocket was due to lift off, citing a problem with ground systems used to monitor the flow of an engine-ignition fluid.
Members of the four-man crew - two U.S. astronauts, a Russian cosmonaut and an astronaut from the United Arab Emirates - have since exited the spacecraft and returned to their quarters to await word on when the next launch attempt will be made, the U.S. space agency said.
The countdown had seemed to be progressing smoothly until about 2-1/2 minutes before launch time, when NASA and SpaceX, the rocket company founded by billionaire Elon Musk, announced during NASA's live webcast that the flight was being scrubbed for the day.
NASA said engineers decided they needed to investigate "an issue preventing data from confirming" the proper loading of a liquid chemical called TEA-TEB used to ignite the first-stage rocket engines for launch.
Mission managers have already opted to forgo the next launch opportunity early on Tuesday, due to an unfavorable weather forecast, NASA said.
Instead, NASA and SpaceX are looking to a possible launch window at 12:34 a.m. EST (0534 GMT) on Thursday, though no decision has been made as flight teams continue working to resolve Monday's technical glitch, the space agency said.
The SpaceX launch vehicle consisting of a Falcon 9 rocket topped with its Crew Dragon capsule remains in place at Launch Complex 39A of NASA's Kennedy Space Center in Cape Canaveral, Florida, ready to fly.
The trip to the International Space Station (ISS), a laboratory orbiting about 250 miles (420 km) above Earth, was expected to take about 25 hours, and the astronauts are expected to spend six months conducting a wide range of science experiments in microgravity.
Designated Crew 6, the mission marks the sixth long-duration ISS team that NASA has contracted to flown aboard SpaceX since Musk's California-based company began sending American astronauts to orbit in May 2020.
The latest ISS crew is led by mission commander Stephen Bowen, 59, a one-time U.S. Navy submarine officer who has logged more than 40 days in orbit as a veteran of three space shuttle flights and seven spacewalks.
Fellow NASA astronaut Warren "Woody" Hoburg, 37, an engineer and commercial aviator designated as the Crew 6 pilot, will be making his first spaceflight.
The Crew 6 mission also is notable for its inclusion of UAE astronaut Sultan Alneyadi, 41, only the second person from his country to fly to space and the first to launch from U.S. soil as part of a long-duration space station team.
Rounding out the four-man Crew 6 is Russian cosmonaut Andrey Fedyaev, 41, who like Alneyadi is an engineer and spaceflight rookie designated as a mission specialist for the team.
Fedyaev is the latest cosmonaut to fly aboard an American spacecraft under a ride-sharing deal signed in July by NASA and the Russian space agency Roscosmos, despite heightened tensions between Washington and Moscow over Russia's invasion of Ukraine.
The Crew 6 team will be welcomed aboard the space station by seven current ISS occupants - three U.S. NASA crew members, including commander Nicole Aunapu Mann, the first Native American woman to fly to space, along with three Russians and a Japanese astronaut.
(Reporting by Joe Skipper in Cape Canaveral and Steve Gorman in Los Angeles; Editing by Will Dunham, John Stonestreet, Gerry Doyle and Nick Macfie)
