The mission carried a complement of five instruments to map the lunar surface. The instruments were all designed to collect scientific data; there were no cameras. One additional experiment, the Doppler Gravity Experiment, used the spacecraft itself as an instrument. Brief descriptions of the instruments and the gravity experiment are provided below.
Gamma Ray Spectrometer
The Gamma Ray Spectrometer (GRS) was contained in a cylinder mounted by itself on one of the spacecraft booms. Its purpose was to map the elemental abundances of the lunar surface. It was designed to record the spectrum of gamma rays and neutrons emitted by the radioactive decay of elements contained in the Moon's crust.
The Neutron Spectrometer (NS) was designed to detect minute amounts of water ice that may exist on the Moon. It was also used to measure the abundance of solar-wind-implanted hydrogen. This instrument was a slender cylinder and was mounted on the same instrument boom as the Alpha Particle Spectrometer.
Alpha Particle Spectrometer
The Alpha Particle Spectrometer (APS) was designed to detect radon-outgassing events on the surface of the Moon. These events may relate to lunar tectonic activity. It recorded alpha particle signatures of radioactive decay of radon and polonium. The APS was shaped like a cube and was located, with the Neutron Spectrometer, on one of the instrument booms.
The Magnetometer (MAG) was used primarily to map weak lunar magnetic fields. Used in conjunction with the Electron Reflectometer, it helped locate and measure the strength of the weak localized magnetic fields on the lunar surface. This box-shaped instrument was attached by a short pole to the Electron Reflectometer, which in turn was attached to one of the instrument booms.
The Electron Reflectometer (ER) was designed to collect information on the lunar remanent paleomagnetic fields. In conjunction with the Magnetometer instrument, it helped locate and measure the strength of the weak localized magnetic fields on the lunar surface. The ER was connected to its companion instrument, the Magnetometer, and the two instruments were mounted together on one of the spacecraft booms.
Doppler Gravity Experiment
The purpose of the Doppler Gravity Experiment (DGE) was to learn about the distribution of mass in and under the surface of the Moon. It used Doppler tracking of S-Band radio signals to monitor changes in the spacecraft orbit as a way of measuring/mapping the lunar gravity field. These measurements also provided information on the lunar crust and lithosphere and on the internal structure of the Moon.