Washington, Oct 29 (IANS): Scott Kelly, the commander of the International Space Station, on Thursday clocked 216 days in orbit to surpass the previous record for the longest single flight by a US astronaut.

Kelly surpassed the previous record of 215 days set by the Spanish-American astronaut Michael Lopez-Alegria in 2007, media reported.

Kelly’s stint on the station is scheduled to last 342 days. During that time, he and the Russian cosmonaut Mikhail Kornienko will go through a series 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.

Kelly, a 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 out there.

Astronauts in orbit experience immediate changes to their physiology. Without gravity to push against, their bones and muscles waste away, body fluids move up to their chests and heads.

The shift is thought to raise the pressure in astronauts’ brains, squeezing their eyeballs from behind and making them long-sighted.

The world record for the longest space flight during one trip is held by Russian cosmonaut Valeri Polyakov for staying aboard the Mir space station for 437 days.