page_title: Apollo 15
section_title: Particles and Fields Subsatellite
hierarchical_section_title: Apollo 15 / Hardware / Particles and Fields Subsatellite
caption_attribution_description: English: An artist's concept showing TRW's small lunar subsatellite being ejected into lunar orbit from the SIM bay of the Apollo 15 Service Module. The 80-pound satellite will remain in orbit a year or more, carrying scientific experiments to study space in the vicinity of the moon. The satellite carries three experiments: S-Band Transponder; Particle Shadows/Boundary Layer Experiment; and Subsatellite Magnetometer Experiment. The subsatellite is housed in a container resembling a rural mailbox, and when deployed is spring-ejected out-of-plane at 4 fps with a spin rate of 140 rpm. After the satellite booms are deployed, the spin rate is stabilized at about 12 rpm. The subsatellite is 31 inches long and has a 14 inch hexagonal diameter. The exact weight is 78.5 pounds. The folded booms deploy to a length of five feet. Subsatellite electrical power is supplied by a solar cell array outputting 25 watts for dayside operation and a rechargeable silver-cadmium battery for nightside passes.
context_page_description: Apollo 15 was the ninth crewed mission in the United States' Apollo program, and the fourth to land on the Moon. It was the first J mission, with a longer stay on the Moon and a greater focus on science than earlier landings. Apollo 15 saw the first use of the Lunar Roving Vehicle.
  The mission began on July 26, 1971, and ended on August 7, the lunar surface exploration taking place between July 30 and August 2. Commander David Scott and Lunar Module Pilot James Irwin landed near Hadley Rille and explored the local area using the rover, allowing them to travel further from the lunar module than had been possible on previous missions. They spent 18​¹⁄₂ hours on the Moon's surface on extravehicular activity, and collected 170 pounds of surface material.
  At the same time, Command Module Pilot Alfred Worden orbited the Moon, operating the sensors in the SIM bay of the service module. This suite of instruments collected data on the Moon and its environment using a panoramic camera, a gamma-ray spectrometer, a mapping camera, a laser altimeter, a mass spectrometer, and a lunar subsatellite deployed at the end of the moonwalks.
context_section_description: The Apollo 15 Particles and Fields Subsatellite (PFS-1) was a small satellite released into lunar orbit from the SIM bay just before the mission left orbit to return to Earth. Its main objectives were to study the plasma, particle, and magnetic field environment of the Moon and map the lunar gravity field. Specifically, it measured plasma and energetic particle intensities and vector magnetic fields, and facilitated tracking of the satellite velocity to high precision. A basic requirement was that the satellite acquire fields and particle data everywhere on the orbit around the Moon. As well as measuring magnetic fields, the satellite contained sensors to study the Moon's mass concentrations, or mascons. The satellite orbited the Moon and returned data from August 4, 1971, until January 1973, when, following multiple failures of the subsatellite's electronics, ground support was terminated. It is believed to have crashed into the Moon sometime thereafter.
caption: Artist's conception of subsatellite deployment
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