NASA is saddened to learn of the loss of former physician-astronaut, Dr. William Thornton, who died last week at his home in Boerne, Texas, at the age of 91. Thornton was selected as an astronaut in 1967, and launched twice on the space shuttle Challenger on STS-8 and STS-51B, the Spacelab 3 mission. He logged 313 hours in space. Thornton had a significant influence in the evolution of space life sciences and held patents on a shuttle flight treadmill and waste collection facility. He worked closely with NASA’s biomedical laboratory teams on topics related to space adaptation sickness, lower body negative pressure, muscle atrophy, and exercise. He retired from NASA in 1994.