It was placed into lunar orbit to provide radio astronomical measurements of the planets, the Sun, and the galaxy over the frequency range of 25-kHz to 13.1-MHz.

There was also a 129 m (423 ft) boron libration damper boom system used to damp out any spacecraft oscillations about the equilibrium position.

A Very high frequency (VHF) transmitter served primarily for range and range-rate measurements and as a backup.

Initially, only the 37 m (121 ft) dipole antenna was deployed, during which the spacecraft was operated in a 4-rpm spin-stabilized mode with the spin axis in the ecliptic plane normal to the spacecraft-Sun line.

A third burst receiver was connected to the dipole antenna, but it failed 1 week into the flight and no significant data resulted.

Each burst receiver was composed of a pair of redundant IF amplifiers and detectors, which shared a common set of crystal-controlled local oscillators and mixers.

Low-pass filters at the input of the burst receiver prevented strong signals at the 21.4-MHz intermediate frequency from entering the IF strip.

The limit of the input signal level resolution that was due to telemetry quantization step size was about 0.3 dB.

This problem was most acute when intense kilometer wavelength emissions from the terrestrial magnetosphere were observed at frequencies in the 200 to 300 kHz range.

A thermistor located in the receiver measured the ambient temperature, which was telemetered every 19.7 minutes in the housekeeping data.

Of the eight coarse samples, the first was not reliable since not enough time had elapsed for the receiver to stabilize after the frequency switch was made.