What was supposed to be an 8-day space mission turned into an 8-month ordeal for NASA astronauts Butch Wilmore and Suni Williams. Due to unexpected technical issues, their return to Earth was repeatedly delayed. Now, they are finally set to come back this Wednesday aboard a SpaceX capsule—but their challenges won’t end there. According to experts, they might have trouble walking due to weakened muscles and even painful calluses on their feet. What happens when astronauts spend too long in space? Here’s what you need to know!