[5] Immediately after liftoff, a short circuit of the launch vehicle's guidance system caused the Rocketdyne S-3D engines to gimbal, tilting the rocket sharply to the west before almost flipping upside down.

[3][6] In an investigation conducted after the launch failure, it was found that the short circuit occurred between two diodes in the launch vehicle's power supply inverter voltage regulator, cutting off power to the guidance system and causing a full gimbal.

[6] Circuit board designs for the Juno II, and similar launch vehicles, subsequently used conformal coating to reduce the chances for a recurrence.

[6] The launch, described by commentators as "infamous" and "one of the most spectacular failures ever seen at [Cape Canaveral]",[3][6][7] was the third of the Juno II launch vehicle, after it failed to carry Pioneer 3 into heliocentric orbit in December 1958,[8][9] but succeeded in the same objective in March 1959, carrying the United States' first interplanetary mission, Pioneer 4.

[6][12] Eventually, both the Juno II and a re-launch of the S-1 mission, designated Explorer 7 or S-1A, found success on 13 October 1959.