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.

Suni Williams and Butch Wilmore are one more step closer to returning to Earth after an initially short mission became an extended, monthslong stay aboard the International Space Station.