Apollo 14 Passive Seismic Experiment
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Acronym | PSE |
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Uses | To detect vibrations and tilting of the lunar surface and measure changes in gravity |
The Apollo 14 Passive Seismic Experiment (PSE) was placed on the lunar surface on February 5, 1971, as part of the
Specification
The PSE unit was constructed principally of beryllium and had a mass of 11.5 kg, including the electronics module and thermal insulation. It was housed in a drum-shaped enclosure 23 cm in diameter and 29 cm in height. The enclosure was rounded on the bottom and rested on a leveling stool. The PSE consisted of two main subsystems, a sensor unit and an electronics module. The sensor unit contained three matched long-period (LP) seismometers aligned orthogonally in a triaxial set to measure one vertical and two horizontal components of surface motion. The horizontal component seismometers were very sensitive to tilt and were leveled to high accuracy by means of a two-axis motor-driven gimbal operated by ground command. A third motor adjusted the vertical component seismometer in the vertical direction. A fourth, short-period (SP) seismometer with a resonant period of 1 second measured vertical motion at a peak sensitivity of 8 Hz and a response range from 0.05 to 20 Hz. A thermal shroud and 6-W heater for thermal control comprised the rest of the experiment package. The thermal shroud was aluminized mylar which covered the instrument and the ground surrounding the base out to about 75 cm radially. A gnomon and level sensor were mounted on the top center of the shroud. The shroud was modified slightly from the one used on Apollo 12. Total power drain varied from 4.3 to 7.4 W.
The seismometers consisted of an inertial mass on a sensor boom suspended by springs and hinges, a capacitor plate and a damping magnet. The LP seismometers could function in a flat-response mode and in a peaked response mode. In the flat response mode, the LP seismometers had a natural period of 15 s. In the peaked-response mode, they acted as
Deployment
The seismometers were deployed on February 5, 1971, and operated at reduced gain while the astronauts were on the lunar surface and turned to maximum sensitivity for most of the time after that. The ALSEP central station was located at 3°38′38″S 17°28′39″W / 3.6440°S 17.4775°W. The passive seismic experiment was deployed 3 meters north of the central station. At deployment, the LP vertical seismometer was unstable in the flat response mode, so all three LP seismometers were operated in peaked-response mode until 17 November 1976 when the problem was rectified. The gimbal motor operating the leveling for the LP horizontal Y seismometer showed intermittent malfunction. The Apollo 14 ALSEP suffered several periods of loss of signal, in one case for over two months. All data were lost for these periods and commanding of the instruments was not possible. Seismic disturbances were noted throughout the lunar day, but particularly near sunrise and sunset, these were believed to be due to expansion and contraction of the
See also
References
This article incorporates public domain material from websites or documents of the
Further reading
- Description of Apollo Seismic Experiments R. Yamada
- Apollo 14 Seismic experiments Lunar and Planetary Institute