Robert Aitken “Bob” Rushworth (October 9, 1924 – March 18, 1993[1]) was an American United States Air Force major general, World War II, Korean War and Vietnam War pilot, mechanical and aeronautical engineer, test pilot and Astronaut. He was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the Air Force and NASA. He flew 34 of the program’s 199 flights, more than any other pilot.
On June 27, 1963, he flew the X-15 to an altitude above 50 miles, thereby qualifying as an astronaut according to the United States’ definition of the boundary of space. However, this altitude did not surpass the Kármán line, the internationally accepted boundary of 100 kilometers (62 miles).
Source: Wikipedia