[2] Explorer 5 was a 2.05 m (6 ft 9 in) long, 16.5 cm (6.5 in) diameter cylinder and nosecone that comprised the fourth stage of the Jupiter-C launch vehicle.

Below these was the low power (10 mW, 108.00 MHz) transmitter for the carrier and sub-carrier signals, which used the stainless steel nose cone as an antenna.

[2] Below the nose cone was the detector deck, holding the instrumentation for the radiation experiments, the command receiver, for interrogations, high power playback transmitter (25-30 mW, 108.03 MHz) for interrogation response, cosmic ray experiment electronics, and Mallory mercury batteries for the high power transmitter.

[2] The launch vehicle was a Juno I, a variant of the three-stage Jupiter-C with an added fourth propulsive stage, which in this case was the Explorer 4.

The booster was equipped to spin the fourth stage in increments, leading to a final rate of 750 rpm about its long axis.

The spacecraft was not oriented correctly when the second stage fired about 3 minutes after liftoff, preventing it from achieving orbit.

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.