Apollo 12 Mission
Science Experiments - Suprathermal Ion Detector Experiment (SIDE)
The Suprathermal Ion Detector Experiment (SIDE) was deployed on Apollo 12, 14, and 15. It measured the energies and masses of positively charged ions near the surface of the Moon and also studied the interaction between the solar wind and the Moon as the Moon moved through the Earth's magnetic field. The range of masses studied varied somewhat on each mission, with a total range between 1 and 1000 atomic mass units (1 atomic mass unit is the mass of a proton). SIDE measured ions with energies of less than 50 electron volts, corresponding to velocities less than 69 kilometers per second. More energetic particles were studied by the Charged Particle Lunar Environment Experiment on Apollo 14 and by the Cosmic Ray Detector on Apollo 16 and 17.
The sources for ions measured by SIDE included the solar wind and gases in the lunar atmosphere that were ionized by solar ultraviolet radiation. On several occasions, meteoroid impacts recorded by the Passive Seismic Experiment were followed shortly thereafter by increased signal levels at two or more of the SIDE units. It is believed that the increased signal measured by SIDE is the result of gases released by the meteoroid impacts. In addition, the impacts of the Lunar Module ascent stages and Saturn rocket third stages on the Moon often released enough gas (from unused rocket propellant) to be detectable by the SIDE network. Based on the times at which these gas clouds were detected, the clouds expanded away from the impact sites at velocities of 1 to 1.5 kilometers per second.