A total of 40 female mice flew on the CRS-19 Dragon when it launched on Thursday December 5th atop a Falcon 9 rocket. The lot is divided into five groups, each with a different goal. One group will be comprised of the mighty mice, one will be a control group composed of normal mice, a third set will be normal mice that are given the myostatin blocker, while the last two groups are just along for the ride. Their jobs begin when they return to Earth. At that point, each of the remaining mice will be given a dose of the myostatin-blocking drug to see if it will help them recover muscle mass lost while in space.