The Lockheed X -17 was a three-stage solid-fuel rocket to the study of re-entry at high Mach numbers, which was used from 1956. The first stage rocket carried the X -17 to an altitude of 27 km, before it burned down, after which the X -17 continued its flight to 400 km altitude. On reaching the maximum height, the X -17 turned her nose down and lit the second stage, and just before re-entry to the third stage. The speed limit on the way to earth was Mach 14.5.
As part of Operation Argus three modified X -17 missiles were launched from the USS Norton Sound in the South Atlantic Seeflugzeugtender to ignite an atomic bomb in each of 1.7 kilotons of TNT equivalent explosive force outside the atmosphere in August and September 1958. The explosions took place at altitudes of 160-750 km away and led to the temporary formation of an artificial radiation belt. In contrast to the original X -17, all three stages were consecutively ignited directly in the rise in these versions.
More modified X -17 missiles were used for technology development of submarine -based Polaris missile. Lockheed planned after completion of the X -17 missions to provide the rocket under the name Pegasus as a sounding rocket.
The X -17 had a Sergeant rocket motor as the first stage. The second stage consisted of a triple block from Recruit rocket motors. A single Recruit rocket eventually formed the third stage. The X -17 had no steering and was kept by spin stabilization on their trajectory. The rotational movement of the missile about its longitudinal axis has been initialized by two small releasable rocket motors after leaving the launching pad.