In less than a week, Scott J. Kelly will once again feel weight.

On Tuesday, a day after turning over command of the International Space Station to a fellow NASA astronaut, Timothy L. Kopra, he willclimb into a Russian Soyuz capsule. A few hours later, he will land in Kazakhstan, ending 340 consecutive days in space — a record for a NASA astronaut.

The previous record was 215 days, reached by Michael Lopez-Alegria during a trip to the space station in 2006 and 2007. Counting his three previous trips to space, Mr. Kelly will have spent a total of 520 days in orbit.

“We’ll learn a lot about longer-duration spaceflight,” Mr. Kelly said during a news conference on Thursday broadcast on NASA Television. “I’d like to think this is another of many steppingstones to landing on Mars sometime in our future.”