Explorer 4 was identical in size to the earlier Explorers but was over 3 kg heavier, primarily due to a larger instrument payload. The satellite was a 2.03 m long, 0.15 m diameter cylinder and nosecone that comprised the fourth stage of the Jupiter-C launch vehicle. The on-orbit mass (after fuel burnout) was 17.43 kg. The spacecraft body was made of stainless AISI-410 steel, 0.058 cm thick. The surface was sandblasted, no aluminum oxide striping was used as on earlier Explorers.
