solid-fuel rocket motors and the third stage held three Sergeants. The booster was equipped to spin the fourth stage in increments, leading to a final rate of 750 rpm about its long axis. Instrument Charged Particle Detector The purpose of this experiment was to extend the first measurements of the trapped radiation belt discovered with Explorer 1 and Explorer 3 and to provide measurements of artificially injected electrons from the three high-altitude Argus nuclear detonations. Four separate radiation detectors were used in the experiment: a shielded directional plastic scintillation counter sensitive to electrons (E>700 keV) and protons (E>10 MeV), a shielded directional caesium iodide scintillation counter sensitive to electrons (E>20 keV) and protons (E>400 keV), an omnidirectional Anton type 302 Geiger–Müller (GM) counter sensitive to electrons (E>3 MeV) and protons (E>30 MeV), and a shielded omnidirectional Anton type 302 Geiger-Müller tube sensitive to electrons (E>5 MeV) and protons (E>40 MeV). The plastic scintillation counter and the cesium iodide (CsI) scintillation counter were each viewed by a separate Photomultiplier tube. These detectors were mounted orthogonally to the longitudinal axis of the satellite with apertures facing in opposite directions. The two GM counters were located side by side along the satellite longitudinal axis. Mission Explorer 5 launched on 24 August 1958 at 06:17:22 GMT from the Cape Canaveral Missile Test Center of the Atlantic Missile Range. The spacecraft was not oriented correctly when the second stage fired about 3 minutes after liftoff, preventing it from achieving orbit. Launch It launched atop a Juno I launch vehicle on 24 August 1958 from Launch Complex 5. Explorer 5 had been intended to be one of two satellites used to gather data for Project Argus. The Explorer 5 failure occurred immediately after separation of the first stage Redstone booster from the second stage. Under normal operations, when either the propellant or oxygen is depleted in the Redstone, about 155 seconds after liftoff, the propellant main valves to the combustion chamber are shut off. Five seconds after this a timer activates six explosive bolts holding the booster to the rest of the launch vehicle. These release the Redstone from the second stage, and coil springs push them apart in preparation for the subsequent second stage firing. In this case for some reason, the Redstone continued to exert thrust after separation, causing it to catch up to the back of the second stage and collide with it