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