An astronaut who forced Nasa's first ever medical emergency evacuation says doctors still do not know the cause as the space agency is set to launch Artemis II.
Artemis II will be Nasa's first manned mission to the moon in over 50 years, but the medical emergency highlights one of the biggest risks of deep-space travel.
Nasa astronaut Michael Fincke, who had a sudden episode while on the International Space Station (ISS) in January has said doctors have ruled out a heart attack.
Thought they have ruled out a heart attack, doctors still do not know what caused the incident, Mr Fincke told reporters at Houston's Johnson Space Centre.
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He added that he was not choking, but all other possibilities remain on the table.
Fincke, 59, said the episode lasted for 20 roughly 20 minutes and he felt fine after.
The Nasa astronaut, who is a retired Air Force colonel, said he had never experienced anything like the medical emergency before or since.
He was only five and a half months into his most recent stay on the ISS when he said the problem hit him like a "lightning bolt".
Nasa astronaut Michael Fincke helped out of the SpaceX recovery craft after his medical emergency
|NASA
Mr Fincke told the Associated Press his crewmates aboard the ISS immediately noticed there was a problem.
He said: "It was all hands on deck within just a matter of seconds."
But he said he cannot provide any more details to the press.
Nasa is keen to make sure other astronauts do not feel their medical privacy would be compromised in the case of a potential future incident.
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SpaceX Crew-11 of four landed in the Pacific Ocean after Michael Fincke's medical emergency, which he said hit him like a 'lightning bolt'
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His medical emergency cut the mission short, his 10th spacewalk but the first for Nasa astronaut and geobiologist Zena Cardman.
Artemis II, a four-man crew set to spend 10 days around the moon, will launch on April 1 at the earliest.
Three Nasa astronauts, Reid Wiseman, Victor Glover, and Christina Koch, and one Canadian astronaut, Jeremy Hansen, will take part in the mission.
The four have arrived at Nasa's Kennedy Space Center in Florida for the final preparation before the mission.
The crew of Artemis 2 has arrived at the Kennedy Space Center in Florida to prepare for the mission
|NASA
Artemis 2's mascot, designed by American student Lucas Ye, named Rise
|NASA
They have also unveiled a plush mascot as a zero-gravity indicator named "Rise".
The mascot, a cartoon Moon wearing a hat of the Earth, is used to indicate when they are in space by floating around.
Mr Hansen is set to be the first non-American astronaut to travel beyond low-Earth orbit.
If weather conditions permit, the mission will launch at 6.24pm EDT (10.24pm GMT).