A doctor volunteered to spend 437 days without gravity

They opened the hatch of the Soyuz TM-20 capsule on 22 March 1995, out on the Kazakh steppe, and Valeri Polyakov, who had gone 437 days and almost 18 hours without setting foot on Earth, asked not to be carried. He stood up on the steppe and walked the few metres to the lounger where they were going to examine him. Polyakov was a military doctor specialising in space medicine, and he had volunteered for exactly that: to spend fourteen and a half months without gravity and climb down from the spacecraft on his own two feet.

Those few metres were the experiment.

After a long stay, the usual thing is for the crew member to be lifted out and carried, sitting down, to the medical tent. The legs and the system that regulates blood pressure have spent more than a year not working against gravity, and the first hours back under your own weight are the worst.

Valeri Vladimirovich Polyakov, born in Tula in 1942, had spent years pressing one very specific piece of arithmetic inside the Soviet programme. The outbound leg to Mars lasts, depending on the mission profile, between six and nine months, and the full mission is measured in years. That a human body survives that long in orbit was already half proven. What nobody had measured was the state it arrives in: whether, when the hatch opens at the other end, the crew member can climb down, walk, assemble a piece of equipment, collect a sample. Measuring that needed someone who would spend longer in weightlessness than the outbound trip lasts, and then try to walk. He volunteered.

He knew what he was signing up for. Between August 1988 and April 1989 he had already spent 240 days on Mir, the Soviet station orbiting some 350 kilometres up. The second time he launched on 8 January 1994 aboard Soyuz TM-18 and stayed up fourteen and a half months while whole crews came and went around him. Six days before he left, Norman Thagard docked, the first NASA astronaut to live on Mir. Polyakov stayed put, going round the Earth some seven thousand times.

Up there he was both the subject and the doctor on call. He weighed himself, measured himself, drew his own blood, logged how he slept and how his mental arithmetic came out, and worked through the exercise protocol the station kept for bones and heart: treadmill, elastic cords and two and a half hours a day. None of that avoids the bill altogether: you lose bone mass, muscle mass and part of your blood volume.

The answer was a few paces long. Once in the lounger, according to the people who were there, he asked for a cigarette and a sip of brandy, and got both. Within weeks he was walking normally.

Since that day we have known that a human being can spend fourteen and a half months in zero gravity and climb down unaided. Other big problems remain open, and the biggest is radiation: in low Earth orbit the planet's magnetic field filters out much of what arrives, and on the way to Mars it filters nothing. But the problem of time, the one the programme's own reports took to be insurmountable, has had a measured answer since 1995.

Thirty-one years on, nobody has beaten the mark. Second on the list is another cosmonaut, Sergei Avdeyev, with 379 days and 14 hours on the same station, between 1998 and 1999; third is the American Frank Rubio, with 371 days on the International Space Station, between 2022 and 2023. Polyakov is still fifty-eight days ahead of the second and sixty-six ahead of the third.