[4] Instrumentation included:[4] These were designed to operate simultaneously to fulfill the objectives of locating observation points (geodetic control stations) in a three-dimensional Earth center of mass coordinate system within 10 m (33 ft) of accuracy, of defining the structure of the Earth's irregular gravitational field and refining the locations and magnitudes of the large gravity anomalies, and of comparing results of the various systems on board the spacecraft to determine the most accurate and reliable system.

[4] Laser corner reflectors, composed of fused quartz cubes with silvered reflecting surfaces, were used for determining the spacecraft's range and angle.

The 322 cubes were mounted on fiberglass panels on the bottom rim of the spacecraft and provided a total reflecting area of 0.18-m2.

The reflectors conserved the narrow beamwidth of incoming light and reflected a maximum signal to the Earth, almost exactly to where it originated.

Fifty percent of the light which struck the prism area at a 90° angle was reflected within a beam of 20 arc-seconds.

Reflected light received by ground telescopes was amplified by a photomultiplier tube that converted the optical impulse to an electrical signal.

[6] The optical beacon system, used for geometric geodesy, consisted of four xenon 670-watt (1580 candle-second/flash) flash tubes housed in reflectors.

[7] The Doppler technique of timing and measuring the frequency shift of radio transmissions from a moving spacecraft was used to help establish the structure of the Earth's gravitational field to an accuracy of approximately five parts in 100 million.

The transponder provided valuable ranging data for four U.S. SECOR stations to make possible inter-comparison tests from 29 December 1965 to 1 May 1966.

Inter-datum and inter-island ties were completed from Tokyo to Hawaii using data from SECOR tracking stations and other geodetic observations made between 24 May 1966 and 8 February 1967.