NASA Commercial Crew astronaut Sunita Williams smiles as she wears her space suit at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1,2019. Picture taken July 1, 2019.

NASA Commercial Crew astronaut Sunita Williams enters the water at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

NASA Commercial Crew Astronaut Josh Cassada is helped to get into his space suit at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

NASA Commercial Crew astronaut Sunita Williams enters the water at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019. Picture taken July 1, 2019.

NASA Commercial Crew astronaut Sunita Williams is helped to get into her space suit at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019. Picture taken July 1, 2019.

NASA Commercial Crew Astronaut Josh Cassada goes through a space suit fitting session at the Johnson Space Center in Houston, Texas, U.S., July 2, 2019.

The space suit pants of the NASA Commercial Crew Astronaut Josh Cassada are seen on a pool desk awaiting his arrival at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019. Picture taken July 1, 2019. REUTERS/Mike Blake - RC13C7704200

NASA Commercial Crew astronaut Sunita Williams is lowered into the water at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

NASA Commercial Crew astronauts Sunita Williams and Josh Cassada are seen lowered into the water at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

NASA Commercial Crew astronaut Sunita Williams high-fives fellow astronaut Josh Cassada before being fitted into the space suits at the start of training at NASA's Neutral Buoyancy Laboratory (NBL) facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

NASA Commercial Crew Astronaut Josh Cassada goes through a space suit fitting session at the Johnson Space Center in Houston, Texas, U.S., July 2 , 2019.

A control center looking out over the water at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

A view of the NASA's Neutral Buoyancy Laboratory (NBL) training facility is shown near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.

Image used for illustrative purpose. The gloves and helmet of NASA Commercial Crew astronaut Sunita William's space suit are shown at NASA's Neutral Buoyancy Laboratory (NBL) training facility near the Johnson Space Center in Houston, Texas, U.S., July 1, 2019.