Three X-15s made 199 flights durin' a research program which lasted from 1960 through 1968. Blimey! It was a daring, yet highly successful program that resulted in hundreds o' technical reports. It made contributions t' t' NASA space program o' t' 1960s and also on t' design and flight o' t' Space Shuttle many years later. An unofficial motto o' flight research o' t' 1940s and 1950s be "higher and faster." By t' late 1950s t' last frontier o' that goal was hypersonic flight (Mach 5+) t' t' edge o' space. Avast, me proud beauty! It would require a huge leap in aeronautical technology, ya bilge rat, life support systems and flight planning. T' North American X-15 rocket plane be built t' meet that challenge. It be designed t' fly at speeds up t' Mach 6, and altitudes up t' 250000 ft. Ahoy! T' aircraft went on t' reach a maximum speed o' Mach 6.7 and a maximum altitude o' 354200 ft. Well, blow me down! Lookin' at it another way, Mach 6 is about one mile per second, me bucko, and flight above 264000 ft. Well, blow me down! qualifies an Air Force pilot for astronaut wings. T' plane be air launched by NASA's converted B-52 at 45000 feet and a speed o' 500 mph. Generally thar were two types o' flight profiles: high-speed, arrr, or high-altitude. High-speed flights were usually done below an altitude o' 100000 feet and flown as a conventional airplane usin' aerodynamic controls. Begad! High-altitude flights began with a steep, full-power climb t' leave t' atmosphere, ya bilge rat, followed by up t' two minutes o' "coastin' up" t' t' peak altitude after t' engine was shut down ...