S66-54935 (29 Oct. 1966) --- Astronaut Edwin E. Aldrin Jr., pilot for the Gemini-12 spaceflight, practices extravehicular work tasks during underwater zero-gravity training. He works on the docking collar of the Agena Target Docking Vehicle mock-up using hand-holds to secure himself to the vehicle. The underwater environment closely simulates the zero-gravity condition found in space. Photo credit: NASA