The spacecraft consisted of a thin cylindrical midsection with a squat truncated cone frustum of 6.5 inches (17 cm) high on each side. The cylinder was 29 inches (74 cm) in diameter and the height from the top of one cone to the top of the opposite cone was 76 cm. Along the axis of the spacecraft and protruding from the end of the lower cone was an 11 kilograms (24 lb) solid propellant injection rocket and rocket case, which formed the main structural member of the spacecraft. Eight small low-thrust solid propellant velocity adjustment rockets were mounted on the end of the upper cone in a ring assembly which could be jettisoned after use. A magnetic dipole antenna also protruded from the top of the upper cone. The shell was composed of laminated plastic and was painted with a pattern of dark and light stripes to help regulate temperature.
The scientific instrument package had a mass of 11.3 kilograms (25 lb) and consisted of:
- An image scanning infrared television system of the Naval Ordnance Test Station (NOTS) design to study the Moon's surface, particularly the part normally unseen from Earth.
- A diaphragm/microphone assembly to detect micrometeorites. A micrometeorite hitting the diaphragm would generate an acoustic pulse that would travel through the diaphragm to the microphone. The microphone contained a piezoelectrical crystal that rang at 100 kc under influence of the acoustic pulse. A bandpass amplifier would amplify the signal, so it could be detected.
- A search-coil magnetometer with nonlinear amplifier to measure the Earth's, Moon's and interplanetary magnetic field. At the time it was not known whether the Moon had a magnetic field or not.
The spacecraft was powered by nickel-cadmium batteries for ignition of the rockets, silver cell batteries for the television system, and mercury batteries for the remaining circuits. Radio transmission was on 108.06 MHz, a standard frequency used by satellites in the International Geophysical Year, through an electric dipole antenna for telemetry and doppler information and a magnetic dipole antenna for the television system. Ground commands were received through the electric dipole antenna at 115 MHz. The spacecraft was to be spin-stabilized at 1.8 revolutions per second, the spin direction approximately perpendicular to the geomagnetic meridian planes of the trajectory.