Explorer 5

United States satellite launched in 1958

Explorer 5 was a United States satellite with a mass of It was the last of the original series of Explorer satellites built, designed, and operated by the Jet Propulsion Laboratory.

Explorer 5 was similar in all respects to Explorer 4 and was designed with the same basic science objectives, to make the first detailed measurements of charged particles (protons and electrons) trapped in the terrestrial radiation belts and to observe the effects of the Project Argus A bomb detonations.

Explorer 5 was a long, diameter cylinder and nosecone that comprised the fourth stage of the Jupiter C launch vehicle. The on orbit mass (after fuel burnout) was The spacecraft body was made of stainless AISI 410 steel, thick. The surface was sandblasted, no aluminum oxide striping was used as on earlier Explorer satellites.

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. 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 approximately 12 seconds after separation. This changed the orientation of the launch vehicle, resulting in the second stage firing in the wrong direction, so that an orbital trajectory was not achieved and the spacecraft reentered the atmosphere and fell back to Earth.