In June of 1956, a Convair Rocket Sled set a world’s speed record for recoverable sleds at the Experimental High Speed Track, reaching 1,560 mph. The sled, powered by 12 rocket motors, was designed to test rain erosion on aircraft components. Earlier, Col John Stapp strapped on a rocket sled and famously used himself as a lab rat to research G-force effects on pilots.
Most of the early testing was done at the Rocket Propulsion Lab (a precursor to the AFRL Rocket Lab). The early rocket test sleds were mostly liquid rocket based, using a combination of diluted alcohol and liquid oxygen. The reasons for that is because the liquid system provided for throttling and higher thrust than available with the solids of the time and because they were what the lab had on hand. These platforms were used to test missiles, supersonic ejection seats, aircraft shapes and the effects of acceleration and deceleration on humans