An American astronaut and engineer, he is best known for his role in the Apollo program. He served as the Lunar Module Pilot for Apollo 9 in 1969, where he tested the Portable Life Support System and conducted a spacewalk. Before his astronaut career, he earned degrees in aeronautics and astronautics from MIT. After NASA, he contributed to space safety and planetary defense efforts. His work has been influential in advancing human space exploration and safety initiatives.