Four astronauts will leave the International Space Station on Wednesday and return to Earth in what the agency has described as a “controlled medical evacuation.”
The four astronauts, riding in a SpaceX Crew Dragon capsule, were scheduled to return in February after a replacement crew arrived. Instead, a medical issue involving one of the crew members last week led NASA to decide to bring them back early.
Who is coming back?
The four returning astronauts are Zena Cardman and Michael Fincke of NASA; Kimiya Yui of JAXA, the Japanese space agency; and Oleg Platonov of Roscosmos, the Russian space agency. This was the first trip to space for Ms. Cardman and Mr. Platonov. This was Mr. Fincke’s fourth space mission and Mr. Yui’s second.
What time will the astronauts leave the space station?
The astronauts will close the hatches between the space station and the Crew Dragon at about 3:30 p.m. Eastern. NASA will provide video coverage beginning at 3 p.m.
The spacecraft is scheduled to undock from the space station at 5:05 p.m. NASA’s live coverage is to begin at 4:45 p.m.
Why are the astronauts leaving early?
Last week, NASA canceled a spacewalk by two of its astronauts, saying there had been a medical issue involving one of the astronauts on the I.S.S. NASA identified neither the astronaut nor the medical issue.
A day later, the agency announced that it was bringing back to Earth four astronauts who had been scheduled to return next month. NASA again declined to say which of the four had the health issue or any details, only that the astronaut was stable and did not require an immediate emergency trip to the hospital.
However the agency did say that the medical issue did not involve the spacewalk, and was not a work-related injury on the space station.
What will happen during the return?
Because the return of the astronauts is not an emergency, it is following the usual procedures and will not be much different from the earlier splashdowns of SpaceX Crew Dragon capsules.
After undocking, there will be a long wait in orbit — about eight hours — as the spacecraft’s trajectory lines up with the landing location. The capsule will then fire its thrusters to drop out of orbit and back into Earth’s atmosphere. As the spacecraft slows down, the astronauts will feel forces equal to several times that of gravity.
After it has slowed down enough, the Crew Dragon will deploy its parachutes and splash down in the Pacific Ocean off the coast of Southern California. Splashdown is expected at 3:41 a.m. Eastern time on Thursday; NASA’s coverage will begin at 2:15 a.m.
The capsule will be pulled aboard a recovery ship. Then the astronauts will disembark and be examined by doctors before being flown to shore by helicopter.
Who will still be on the space station?
After four astronauts depart from the International Space Station on Wednesday evening, three others will remain: Christopher Williams of NASA and Sergey Kud-Sverchkov and Sergey Mikaev of Russia.
Usually, there are more astronauts aboard. There were smaller crews in the early years of the space station when it was much smaller, and brief periods of reduced staffing have occurred between the departure of one crew and the arrival of the next.
Those three astronauts flew to the space station in a Russian Soyuz spacecraft in November and are scheduled to remain there until summer.
Mr. Williams is trained to maintain the NASA-led half of the space station, and the Russian astronauts can keep the Russian half operating.
The space station should be short-staffed for only a few weeks. Another Crew Dragon with four new astronauts — Jessica Meir and Jack Hathaway of NASA, Sophie Adenot of the European Space Agency and Andrey Fedyaev of Roscosmos, the Russian space agency — is scheduled to launch in mid-February. They are to spend nine months at the space station.
NASA officials have said they are looking to see if that launch could take place sooner.
Kenneth Chang, a science reporter at The Times, covers NASA and the solar system, and research closer to Earth.
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