Appendix D

Apollo 11 Experiments

Early Apollo Scientific Experiments Package (EASEP)

The Apollo 11 scientific experiments for deployment on the lunar surface near the touchdown point of the lunar module were stowed in the lander's scientific equipment bay at the left rear quadrant of the descent stage looking forward.

The early Apollo scientific experiments package was carried only on this flight; subsequent Apollo lunar landing missions carried the more comprehensive Apollo lunar surface experiments package.

EASEP consisted of two basic experiments: a passive seismic experiments package (PSEP) and a laser ranging retroreflector (LRRR). Both experiments were independent, self-contained packages that weighed a total of 77 kilograms and occupied 0.34 cubic meters of space.

PSEP used three long-period seismometers and one short-period vertical seismometer for measuring meteoroid impacts and moonquakes. Data gathered would be useful in determining the interior structure of the moon; for example, does the moon have a core and mantle like the earth? The seismic experiment package had four basic subsystems: a structure thermal subsystem for shock, vibration, and thermal protection; an electrical power subsystem generating 34 to 36 watts by solar panel array; a data subsystem to receive and decode Manned Space Flight Network uplink commands and downlink experiment data and to handle power switching tasks; and a passive seismic experiment subsystem to measure lunar seismic activity and to detect inertial mass displacement.

The LRRR experiment was a retroreflector array, made from cubes of fused silica, with a folding support structure for aiming and aligning the array toward the earth. Laser ranging beams from the earth were reflected back to their point of origin for precise measurement of earth-moon distances, motion of the moon's center of mass, lunar radius, and earth geophysical information.

Earth stations that beamed lasers to the LRRR included the McDonald Observatory, Fort Davis, Texas; Lick Observatory, Mount Hamilton, California; and the Catalina Station of the University of Arizona. Scientists in other countries also bounced laser beams off the LRRR.

Principal investigators for these experiments were Dr. Carroll C. Alley, University of Maryland (LRRR), and Dr. Gary V. Latham, Lamont Geological Observatory (PSEP).

Apollo Lunar Radioisotopic Heater (ALRH)

An isotopic heater system, built into the passive seismometer package that the Apollo 11 crew left on the moon, protected the seismic recorder during frigid lunar nights.

The heater, developed by the Atomic Energy Commission, was the first major use of nuclear energy in a manned space flight mission. Each of the two heaters was fueled with 34 grams of plutonium 238. Heat was given off as the well-shielded radioactive material decayed. During the lunar day, the seismic devices sent back to the earth data on lunar seismic activity, or moonquakes. During the 340-hour lunar night, when temperatures dropped as low as -173 degrees C, the 15-watt heaters kept the seismometer at a minimum of -54 degrees C. Exposure to lower temperatures would have damaged the instrument.

The heaters were 7.6 centimeters in diameter, 7.6 centimeters long, and weighed 57 grams each, including multiple layers of shielding and protective materials. The complete seismometer package weighed 45 kilograms. Both heaters were mounted in the seismic package before launch. During the lunar surface walk, the lunar module pilot transported the package a short distance away and set up the equipment. There was no handling risk to the crew. The plutonium fuel was encased in various materials chosen for radiation shielding and for heat and shock resistance. These materials included a tantalum-tungsten alloy, a platinum-rhodium alloy, titanium, fibrous carbon, and graphite, with an outer layer of stainless steel.

Extensive safety analyses and tests were performed by Sandia Laboratories at Albuquerque, New Mexico, to determine the effects of an abort or any conceivable accident in connection with the moon flight. The safety report by the Interagency Safety Evaluation Panel, made up of representatives of NASA, the AEC, and the Department of Defense, concluded that the heater presented no undue safety problem to the general population under any accident condition deemed possible for the Apollo mission.

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