It was the third of six identical Explorer satellites launched to study air density and composition, and the second to reach orbit.

Uniformly distributed over the aluminum surface were 5.1 cm (2.0 in) diameter dots of white paint for thermal control.

The two hemispheres of aluminum foil were separated with a gap of Mylar at the spacecraft's equator and served as the antenna.

[3] This experiment was designed to determine nonsystematic changes of upper atmospheric density by conducting studies of the drag on a 3.6 m (12 ft) diameter, low-density sphere caused by short-term variations in solar activity.

Density values near perigee were deduced from sequential observations of the spacecraft position using optical (Baker-Nunn camera network) and radio/radar tracking techniques.