The Apollo 15 and Apollo 16 missions carried a small subsatellite designed to be released in lunar orbit just prior to the beginning of the astronauts' return flight to earth. Powered by six solar panels in 11 silver-cadmium batteries, the so-called "Particles and Fields subsatellites" contained three instruments: a magnetometer, an S-band transponder, and charged particle detectors. Instruments were designed to measure the strength and direction of interplanetary and terrestrial magnetic field, to detect variations in the lunar gravity field, and measure proton and electric flux from the solar wind.
The artifact here is the qualification model for the Particles and Fields subsatellite. It underwent extensive tests and demonstrations prior to the launch of the actual satellites. It was transferred from NASA to the Smithsonian in 1975.