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PSE Stool

Last revised 1 July 2013.


PSE Schematic

Figure 3-1 from the Apollo 12 Preliminary Science Report is a schematic drawing of the Portable Seismometer Experiment, with the round-bottomed, cylindrical canister containing the seismometers and electronics sitting on a supporting stool.

The following description can be found on page 2-82 in the 1969 ALSEP Familiarization Manual:

2-61. PSE Leveling Stool. The leveling stool is a short tripod with three thermal insulators on its upper end. These insulators, together with the rounded bottom of the sensor assembly, form a ball and socket joint which permits manual leveling of the sensor assembly to be accomplished by a single astronaut to within five degrees of the vertical. The insulators also provide the required degree of thermal and electrical isolation of the sensor assembly from the lunar surface, while transmitting surface motion up to 26.5 Hz, or more, to the sensors with negligible attenuation.

PSE with thermal shroud

Figure 2-43 from the 1969 ALSEP Familiarization Manual, showing the canister - without the thermal shroud in place - on the stool.  The electronics assembly in the foreground was installed in the Central Station pre-flight.

PSE at Air and Space

PSE unit in the collection of the National Air and Space Museum.  This unit was stored by Bendix Aerospace until NASA transferred the object to the Smithsonian in 1982.  The two connectors were connected to the ALSEP Central Station before stowage in the Lunar Module.  The purpose of the small grey box with a mail electrical plug and a black, top-mounted control knob is unknown.  Medium: Beryllium. Description: Cylindrical metallic container with removable top containing mechanical and electronic components of a working seismometer. Dimensions: Cylinder: 11 7/16 (h) x 9 1/16in (dia.), 25.4lb. (metric values: 29 x 23cm, 11.5kg).  Image courtesy Allan Needell, National Air and Space Museum.

Frame from training
          film showing stoll on SIDE Pallet

Detail from a training film showing Al examining the SIDE pallet during an ALSEP deployment familiarization session. Frame capture by Thomas Schwagmeier at 26 min 30 seconds in the 'training' section of Disk 1 in the Spacecraft Films 3-disk, 2005 Apollo 12 DVD set.  See, also, an alternate view from 27 min 04 sec in the training film. Used with permission from Mark Gray, Spacecraft Films. (Click on the image for the full frame).

The primary purpose of the PSE stool was to prevent thermal contact between the canister and the ground; and, thereby, reduce motions induced by temperature differences. The stool was mounted on the side of the SIDE pallet.  The gold colored stool was supported by three legs, which can be seen pointing to the left in the image above. The top of the stool was  an opening ring to accomodate the rounded bottom of the PSE canister.  On the Moon, Al Bean dug a small pit under the spot where he wanted to place the stool, to further decrease the chance of thermal contact between the canister and the ground.

Using the UHT to
              position the stool

Detail from a frame capture at 26 min 51 sec in the training film.  Al has the end of the UHT (Universal Handling Tool) fitted into the UHT socket built into the stool.  This allows him to move and position the stool from a standing position.  (Click on the image for the full frame.)

Detail from the
            training fil at 27:10

Detail from a frame captured at 27 min 10 seconds in the training film.  Pete is fitting a UHT in the socket.  We are looking at the upper surface of the stool.  The white dot on the upper surface at the upper left may be one of the three 'insulating standoffs'. (Click on the image for the full frame.)

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