Nasa announced that four astronauts have been delayed due to a rare medical issue. This is the second delay in SpaceX's rocket launch of four astronauts.
Monday's description by the space agency was that it was a minor medical problem and was not related to Covid-19. However, it declined to give any further details or identify the astronaut involved.
Launch was originally scheduled for Sunday, but it was postponed to Wednesday due to unsuitable weather conditions. It has been rescheduled for Saturday evening, Nasa announced.
Nasa had previously delayed a planned launch due to a medical concern involving crew members. This was in 1990 for the Space Shuttle Atlantis flight, when mission commander John Creighton became ill. According to Nasa, the countdown was stopped for three days before he was allowed to fly.
This delay was followed up by two more weather-related postponements.
Matthias Maurer and Thomas Marshburn, Raja Chari, Kayla Barron, and Raja Chari during preflight training at SpaceX Headquarters in Hawthorne (California). Photograph by SPACEX/AFP/Getty Images
SpaceX's SpaceX-built vehicle, which consists of a Crew Dragon capsule, and a Falcon 9 rocket with two stages, will take off Saturday at 11.36pm from the Nasas Kennedy space center in Cape Canaveral.
If everything goes well, the US astronauts will arrive 22 hours later with their European Space Agency (ESA), crewmate. They will dock with the space station 400km (250 mi) above the Earth and begin a six month science mission.
Nasa stated that the crew members will remain in routine quarantine at Cape while they continue launch preparations.
Three Nasa astronauts joined the mission, including flight commander Raja Chari (44), Tom Marshburn (61), and Kayla Barron (34), who are mission specialists at ESA.
Chari, a US Air Force combat jet pilot and test pilot, Barron (a US Navy submarine officer and nuclear engineer) and Maurer (a materials science engineer) are making their first spaceflights aboard Endurance, a Dragon vehicle.
Marshburn is a former Nasa flight surgeon and a doctor. He has logged four spacewalks and two spaceflights before.
If successful, Saturday's launch would be the fifth human spaceflight SpaceX achieved. This follows its September inaugural launch of a space tourism company that launched the first all-civil crew into orbit.
