Apollo Lunar Surface Experiments Package

Apollo Lunar Surface Experiments Package

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 1966. Specifically, the experiments, institutions responsible, and principal investigators and coinvestigators were:ref|EAweb

* 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 Apollo Lunar Surface Experiments Package (ALSEP) was built and tested by Bendix Aerospace in Ann Arbor, Michigan. 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. Thermal control was achieved by passive elements (insulation, reflectors, thermal coatings) as well as power dissipation resistors and heaters. 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 primarily to budgetary considerations. Also, by that time the power packs could not run both the transmitter and any other instrument, and the ALSEP control room was needed for the attempt to reactivate Skylab.


The ALSEP was stored in the LM's Scientific Equipment (SEQ) Bay in two separate subpackages. The base of the first subpackage formed the Central Station while the base of the second subpackage was part of the RTG. A subpallet was also attached to the second subpackage which usually carried one or two of the experiments and the antenna gimbal assembly. On Apollo 12, 13, and 14, the second subpackage also stored the Lunar Hand Tool Carrier (HTC). The exact deployment of experiments differed by mission. The following pictures show a typical procedure from Apollo 12.

List of Missions

Each mission had a different array of experiments.

Apollo 11 (EASEP)

As stated above, Apollo 11 did not leave a full ALSEP package, but left a simpler version called the Early Apollo Surface Experiments Package (EASEP). Since there was only one 2 hour 40 minute EVA planned, the crew would not have enough time to deploy a full ALSEP, which usually took one to two hours to deploy. Both packages were stored in the LM's SEQ bay.

The antenna gimbal assembly was stored on the first subpackage. The stool for the PSE, the ALSEP tools, carrybar, and the Lunar drill was stored on the subpallet. The HTC was stored on the second subpackage.

Apollo 14

Apollo 17


Encyclopedia Astronautica website, 14 February 1966 entry.


See also

* Lunar laser ranging experiment

External links

* [http://www.astronautix.com/craft/apoalsep.htm Astronautix Site]
* [http://www.myspacemuseum.com/alsep01.htm ALSEP Page @ myspacemuseum.com]
* [http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo.html NSSDC Apollo Page]
* [http://www.lpi.usra.edu/lunar/documents/NASA%20TM-X-58131.pdf Apollo Scientific Experiments Data Handbook]
* [http://www.lpi.usra.edu/lunar/documents/NASA%20RP-1036.pdf ALSEP Termination Report]
* [http://www.lpi.usra.edu/lunar/documents/NASA%20RP-1317.pdf Catalog of Apollo Experiment Operations]

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