Mission Summary
PFS-1 was a small scientific satellite carried to the Moon aboard Apollo 15 and released into lunar orbit by the crew before they returned to Earth. Deployed on August 4, 1971, the 36-kilogram probe was built to keep studying the Moon’s environment long after the astronauts had gone, measuring magnetic fields, charged particles, and variations in the lunar gravity field.
From its orbit it tracked the strength and direction of interplanetary and terrestrial magnetic fields and recorded the flux of protons and electrons around the Moon. Its data confirmed an earlier finding by Explorer 35: where Earth’s magnetic field deflects the solar wind into a long tail, the Moon, with its feeble field, simply blocks the wind and carves a hole in it.
The satellite met all of its scientific objectives before an electronic failure ended the mission on February 3, 1972. Together with the near-twin released by Apollo 16 the following year, PFS-1 stretched the reach of Apollo science well beyond the brief days the crews spent at the Moon.
Sources and notes can be found on the Sources page.
