X-15
1959-1968
The rocket plane that grazed the edge of space. Air-launched from a B-52, it set crewed-aircraft speed and altitude records that still stand.
Specs
199 flights, 12 pilots; top speed Mach 6.7 (7,274 km/h); max altitude 107.5 km - beyond the 100 km edge of space; 3 pilots were awarded astronaut wings (NASA, 2005).
Why it matters
It proved aircraft can operate at the edge of space - and that the boundary between 'air' and 'space' is a measurable altitude (100 km), not a conspiracy.