 And they've done a lot of studies on six-month to year-long missions to try to figure out if exercise could solve some of the problems. And though it does solve some of the problems, it really doesn't solve them all. And so it's been recognized that a trip to Mars, a year in weightlessness, is going to be difficult to achieve because when someone arrives at Mars, it's going to be difficult for them to stand on their own. When astronauts come back from a six-month mission,