Apollo Lunar Surface Experiment Package

From Wikipedia, the free encyclopedia

ALSEP of the Apollo 16 mission

The Apollo Lunar Surface Experiments Package (ALSEP) comprised a set of scientific instruments placed by the astronauts at the landing site of each of the five Apollo missions to land on the Moon following Apollo 11 (Apollos 12, 14, 15, 16, and 17). Apollo 11 left a smaller, temporary, package called the Early Apollo Scientific Experiments Package, or EASEP.

The instrumentation and experiments that would comprise ALSEP were decided in February of 1966. Specifically, the experiments, institutions responsible, and principal investigators and coinvestigators were:^[1]

Passive Lunar Seismic Experiment, Massachusetts Institute of Technology, Frank Press; Columbia University, George Sutton.
Lunar Tri-axis Magnetometer, Ames Research Center, C. P. Sonett; MSC, Jerry Modisette.
Medium-Energy Solar Wind, Jet Propulsion Laboratory (JPL), C. W. Snyder; JPL, M. M. Neugebauer.
Suprathermal Ion Detection, Rice University, J. W. Freeman, Jr.; MSC, F. C. Michel.
Lunar Heat Flow Management, Columbia University, M. Langseth; Yale University, S. Clark.
Low-Energy Solar Wind, Rice University, B. J. O'Brien.
Active Lunar Seismic Experiment, Stanford University, R. L. Kovach; U.S. Geological Survey, J. S. Watkins.

The instruments were designed to run autonomously after the astronauts left and to make long term studies of the lunar environment. They were arrayed around a central station which supplied power generated by a radioisotope thermoelectric generator (RTG) to run the instruments and communications so data collected by the experiments could be relayed to Earth. The central station was a 25 kg box with a stowed volume of 34,800 cubic cm. Thermal control was achieved by passive elements (insulation, reflectors, thermal coatings) as well as power dissipation resistors and heaters. Communications with Earth were achieved through a 58 cm long, 3.8 cm diameter modified axial-helical antenna mounted on top of the central station and pointed towards Earth by the astronauts. Transmitters, receivers, data processors and multiplexers were housed within the central station. Data collected from the instruments were converted into a telemetry format and transmitted to Earth.

The ALSEP system and instruments were controlled by commands from Earth. The stations ran from deployment until they were turned off on 30 September 1977 due to budgetary considerations.