Nasa has again delayed the launch of the SpaceX rocket set to take a crew of four to the International Space Station.
Bad weather over the Kennedy Space Centre in Florida means the SpaceX Crew-3 mission will begin no sooner than to 9.03pm on Wednesday, or 5.03am on Thursday, UAE time.
The latest delay will allow the astronauts of the previous SpaceX mission, Crew-2, to return to Earth before their replacements take off for the orbital lab.
The SpaceX Dragon capsule carrying the Crew-2 astronauts is due to splash down in the Atlantic Ocean at 12.14am GMT on November 8.
Nasa had already delayed the Crew-3 launch, saying one of the astronauts was suffering from a “minor medical issue”.
The US space agency said the condition was not an emergency and was not related to Covid-19.
Who are the astronauts on the Crew-3 mission?
The Crew-3 mission comprises Americans Raja Chari, Tom Marshburn and Kayla Barron, and German Matthias Maurer of the European Space Agency.
The four astronauts will blast off aboard a Crew Dragon spacecraft named Endurance from the Kennedy Space Centre in Florida.
Nasa will live-stream the launch on its YouTube channel.
The astronauts are expected to dock with the space station on Monday, and will spend six months conducting research into material science, botany and health.
The mission is intended to help inform future deep space exploration and benefit life on Earth.
“Last night, we got to go see Endurance in the hangar as they got ready to roll it out to the pad, and actually put our hands on the Dragon, which is a pretty special experience,” Lt Col Chari, the US Air Force colonel who is commanding the mission, said on Wednesday.
Of the four, only Dr Marshburn has been to space before. The medical doctor flew aboard a Space Shuttle in 2009 and a Russian Soyuz spacecraft on a mission from 2012-13.
Ms Barron is the most recent recruit and previously served in the US Navy’s submarine fleet. She was selected for the Nasa astronaut corps in 2017, along with Lt Col Chari, and told reporters she saw many parallels between that experience and going to space.
The pair are also in the running for Nasa’s Artemis missions to return humans to the Moon later this decade.
Dr Maurer, a materials science engineer, will become the 12th German to go to space and will join fellow ESA astronaut Thomas Pesquet of France on the ISS, an overlap that is likely to last several days before the Frenchman returns to Earth with the rest of his Crew-2 colleagues.
What science experiments will the crew conduct?
Scientific highlights of the mission include an experiment to grow plants in space without soil and another to build optical fibres in microgravity, which prior research has suggested will be superior in quality to those made on Earth.
Dr Maurer will help set up the European Robotic Arm, being installed on the Russian side of the ISS, and test out Cimon – an artificial intelligence assistant developed by the German space agency DLR, Airbus and IBM.
“It’s an experiment which is really paving the way towards exploration,” he said.
The AI assistant may one day act as a geology expert that astronauts on a future mission to Mars could consult for quick answers, because the time to communicate with Earth would be 40 minutes, he said.
The Crew-3 astronauts will also conduct spacewalks to complete the upgrade of the station’s solar panels and will be present for two tourism missions, accompanying Japanese tourists aboard a Russian Soyuz spacecraft at the end of 2021 and the Space-X Axiom crew, set for launch in February 2022.
Crew-3 is part of Nasa’s multibillion-dollar partnership with SpaceX, which it signed after ending the Space Shuttle programme in 2011 to restore American capacity to carry out human space flight.
Boeing is also part of the same commercial programme, but its Starliner capsule has been beset by delays and will not fly its first crew until the end of 2022 at the earliest.