The commander of the International Space Station will break the record for the longest single flight by a US astronaut on Thursday by clocking up 216 days in orbit.
Scott Kelly, who performed his debut spacewalk on Wednesday, will surpass the previous record of 215 days set by the Spanish-American astronaut Michael López-Alegría in 2007.
The former US navy captain has already amassed more cumulative time in space than any other US astronaut, having spent a combined total of 396 days falling around the planet.
Kelly’s latest stint on the station is scheduled to last 342 days. During that time, he and the Russian cosmonaut Mikhail Kornienko will endure a battery of medical investigations as part of the One-Year Mission. The results will help space agencies understand the varied effects that long-duration space travel can have on humans.
But Kelly is taking part in another study made possible by the unique genetic relationship he has with a former US astronaut: his identical twin, Mark, who retired to look after his wife, Gabrielle Giffords, the Democratic congresswoman who was shot in the head in January 2011. Scott and Mark have signed up for the Nasa Twins Study, which will examine how Scott’s brain and body change in space, compared with Mark’s on the ground.