For 70 years after Sputnik, space launches happened slowly and infrequently. Today, something launches into space almost every single day. That acceleration raises a new question: what happens to the human body during extended space travel? The NASA Twin Study, which observed Scott Kelly in space for a year while his brother Mark remained on Earth, produced the first complete molecular map of the changes the human body undergoes in space. That data is now informing a new generation of research into the cell ...