Shortly before the crew of Apollo 15 (Commander David Scott, Alfred Worden, James Irwin) left the moon after a successful mission, they launched a "subsatellite", the Apollo 15 Particles and Fields Subsatellite (PFS-1), August 4, 1971. Its main objectives were to study the plasma, particle and magnetic field of the moon. PFS-1 transmitted data until January 1973. A series of failures resulted in the termination from the ground support. It's assumed that it crashed on the moon sometime after that.
