Apollo 15 Mission
Science Experiments - Subsatellite
The Subsatellite measured regional variations in the Moon's gravitational acceleration and magnetic field and the distribution of charged particles around the Moon.
Prior to their return to Earth, the Apollo 15 and 16 crews deployed small, 38-kilogram subsatellites into lunar orbit. These subsatellites were identical on both missions and performed three experiments which continued the study of the lunar environment.
(1) S-band Transponder. Accurate tracking of the spacecraft from Earth allowed details of the Moon's gravity field to be mapped, which provided information about the distribution of mass in the Moon's interior. This was a continuation of the S-band transponder experiment during the main Apollo 15 mission.
(2) Magnetometer. The strength and orientation of the magnetic field near the Moon was measured. Because the Moon lies within the Earth's magnetic field, the magnetic field at the Moon varies as the Moon completes each month-long orbit around the Earth. In addition, some localized magnetic features were discovered on the Moon, such as at the craters Reiner Gamma on the lunar nearside and Van De Graaff on the lunar farside.
(3) Charged Particles. The density and energy of electrons and protons near the Moon were measured. These quantities vary with time as the Moon moves through the Earth's magnetic field and during eruptions such as solar flares on the Sun.