NASA astronauts Sunita Williams and Butch Wilmore face significant physiological and psychological challenges upon returning from microgravity. They may experience muscle atrophy, bone loss, dizziness,

The return was initially planned for no earlier than Wednesday but was moved up due to unfavorable weather expected later in the week.

The crew-swap mission will enable NASA’s Butch Wilmore and Suni Williams to return to Earth from the International Space Station.