A rocket sled is a test platform that slides along a track (e.g. set of rails), propelled by rockets.
A rocket sled differs from a rocket car in not using wheels; at high speeds wheels would spin to pieces due to the extreme centrifugal forces. Apart from rare examples running on snow or ice (such as Max Valier's RAK BOBs of the late 1920s[1] and Harry Bull's BR-1 in 1931[2]), most rocket sleds run on a track. Although some rocket sleds ride on single beams or rails, most use a pair of rails. Standard gauge (1.435 m / 56.5 in) is common but sled tracks of narrower or wider gauge also exist. The rail cross-section profile is usually that of a Vignoles rail, commonly used for railroads. Sliding pads, called "slippers", are curved around the head of the rails to prevent the sled from flying off the track. Air cushions and magnetic levitation have also been used as alternatives, with potential benefits including reduced sled vibration.
A rocket sled holds the land-based speed record for a vehicle, at Mach 8.5.[3]