Kathryn Ryan Cordell Thornton (Ph.D.) (born August 17, 1952 in Montgomery, Alabama) is an American scientist and a former NASA astronaut with over 975 hours in space, including 21 hours of extravehicular activity. She was the associate dean for graduate programs at the University of Virginia School of Engineering and Applied Science, currently a professor of mechanical and aerospace engineering. She was also the academic dean for the fall 2013 Semester at Sea.