S66-40098 (17 June 1966) --- Astronaut Michael Collins, prime crew pilot of the Gemini-10 spaceflight, undergoes zero-gravity (weightlessness) training aboard an Air Force KC-135 aircraft. He practices with micrometeorite experiment-type equipment. The KC-135 flew a parabolic curve to create the zero-gravity condition. This training is in preparation for Collins' Gemini-10 extravehicular activity. Photo credit: NASA