Active Seismic Experiment (ASE) was carried on

Apollo 14 Apollo 14 (January 31February 9, 1971) was the eighth crewed mission in the United States Apollo program, the third to Moon landing, land on the Moon, and the first to land in the Geology of the Moon#Highlands, lunar highlands. It was the las ...

and

Apollo 16 Apollo 16 (April 1627, 1972) was the tenth human spaceflight, crewed mission in the United States Apollo program, Apollo space program, administered by NASA, and the fifth and penultimate to Moon landing, land on the Moon. It was the second o ...

as part of the

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 program, Apollo missions to land on the Moon following Apollo 11 (Apollos Apol ...

(ALSEP). ASE used a thumper device and a mortar with

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...

charges to explore subsurface lunar structure and

elastic properties Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rubber used to hold objects togethe ...

. The experiment's principal investigator was Robert Kovach of

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

. The experiment was succeeded on

Apollo 17 Apollo 17 (December 7–19, 1972) was the eleventh and final mission of NASA's Apollo program, the sixth and most recent time humans have set foot on the Moon. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, ...

by the Lunar Seismic Profiling experiment.

Experiment

The ASE consisted of three major components. A set of three geophones was laid out in a line by an

astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a List of human spaceflight programs, human spaceflight program to serve as a commander or crew member of a spa ...

from the Central Station to detect the explosions.Brzostowski and Brzostowski, pp 414-416 A mortar package was designed to lob a set of four

grenade A grenade is a small explosive weapon typically thrown by hand (also called hand grenade), but can also refer to a Shell (projectile), shell (explosive projectile) shot from the muzzle of a rifle (as a rifle grenade) or a grenade launcher. A mod ...

s varying distances away from the ALSEP. Ranging of the grenade was achieved through the assumption of ideal ballistic trajectories. Finally, an astronaut-activated "Thumper" was used to

detonate Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves wit ...

one of 22 charges to create a small shock. The components weighed , drew 9.75 watts of power and recorded data at an average rate of 10,000 bits/sec.

Hexanitrostilbene Hexanitrostilbene (HNS), also called JD-X, is an organic compound with the formula O2N)3C6H2CHsub>2. It is a yellow-orange solid.Jacques Boileau, Claude Fauquignon, Bernard Hueber and Hans H. Meyer "Explosives" in ''Ullmann's Encyclopedia of In ...

was the main explosive fill in the

seismic source A seismic source is a device that generates controlled seismic energy used to perform both reflection seismology, reflection and seismic refraction, refraction seismic surveys. A seismic source can be simple, such as dynamite, or it can use more ...

generating mortar ammunition canisters used as part of the Apollo Lunar Active Experiments Package. Grenades containing of hexanitrostilbene were used with the mortar. This explosive was chosen due to its insensitivity but high explosive properties. NASA reference publication
/ref>

Missions

Apollo 14

The mortar, geophones, and thumper were stored on the first subpackage. Thirteen of the twenty-two thumper charges were fired successfully.Brzostowski and Brzostowski, pp 414-416 The thumper misfired 5 of 18 times. The problem was attributed to dirt on the firing switch actuator bearing surface. Because of concerns about the deployment of the mortar, none of the four explosives were fired. There was an attempt to fire them at the end of the ALSEP's operational lifetime, but the charges failed to work after being dormant for so long. Due to loss of uplink capability with Apollo 14 central station on March 5, 1975, the experiment could no longer be commanded and the grenades remain unfired.

Apollo 16

The new mortar base used to improve the experiment after problems were encountered with Apollo 14's. The mortar, geophones, and thumper were stored on the first subpackage. The base of the mortar box was stored on the second subpackage. Three grenades were fired, up to a distance of 900 m. After three of the explosives were fired successfully, the pitch sensor went off scale. A range wire for one grenade has been suggested as the cause of the failure, producing a downward force after grenade launch. Normal real-time event data were not received during flight. It was then decided not to fire the fourth explosive. Nineteen of the Thumper charges were successfully fired.Brzostowski and Brzostowski, pp 414-416

Results

The Active Seismic Experiments along with the Lunar Seismic Profiling experiment enabled researchers to derive a compressional velocity profile of the lunar subsurface at the landing sites of Apollo 14, Apollo 16 and Apollo 17. Whilst the

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

of the lunar surface varies in depth, the characteristics revealed were similar at the three landing sites. Seismic velocities of 108 m/s and 114 m/s were inferred for the lunar subsurface at the Apollo 14

Fra Mauro Fra Mauro, O.S.B. Cam., (c.1400–1464) was an Italian ( Venetian) cartographer who lived in the Republic of Venice. He created the most detailed and accurate map of the world up until that time, the Fra Mauro map. Mauro was a monk of the Ca ...

site and the Apollo 16 Descartes site respectively. These velocities suggested brecciated and highly

porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...

material, likely the result of fragmentation and

comminution Comminution is the reduction of solid materials from one average particle size to a smaller average particle size, by crushing, grinding, cutting, vibrating, or other processes. Comminution is related to pulverization and grinding. All use m ...

caused by meteorite impacts.

References

Bibliography

* Brzostowski, M.A., and Brzostowski, A.C., ''Archiving the Apollo active seismic data'', The Leading Edge, Society of Exploration Geophysicists, April, 2009. {{Apollo program hardware Apollo 14 Apollo 16 Apollo program hardware Geophysical survey