PI/Engineer: Gary V. Latham, Marine Biomedical Institute/Galveston, TX
Other Contacts: Maurice Ewing, Frank Press
Apollo Flight Nos.: 11, 12, 14, 15, 16
Apollo Exp't No. S 031
Discipline: lunar seismometry
Weight: 11.5 kg (A-12, 14-16) 47.7 kg (A-11)
23 cm dia., 29 cm high; thermal skirt extended to 1.5 m dia.
Manufacturer: Teledyne, Bendix
The instrument consisted of a seismometer designed to detect moonquakes and impacts. It was considered part of the EASEP on A-11. It contained 3 long-period seismometers with resonant periods of ~15 seconds, aligned orthogonally to measure surface motion in 3 dimensions, and a single-axis, short period seismometer sensitive to vertical motion at higher frequencies (resonant period of ~1 sec.) On later ALSEPs, the single vertical sensor frequency was 0.05 to 10 Hz and the 3 orthogonal sensors were sensitive to 0.004 to 3 Hz. It sat on a mounting stool, which raised the unit off the surface. A Mylar skirt surrounded the unit to reduce thermally induced tilts of the local surface around the apparatus. The A-11 instrument was powered by solar panels, the rest by the ALSEP RTG.
Unloading from the LM: As part of ALSEP.
Transporting by foot or MET:
Carried by hand (along with the LRRR on A-11) to deployment site. When part of the ALSEP, two pallets were connected by a mast and the whole was carried "barbell style."
Loading/unloading tools/exp'ts on LRV: NA
On A-11, PSEP was located behind a rock (relative to the LM) to shield it from the effects of liftoff. It was learned that the LM is a source of seismic signals of unexpectedly large amplitudes. Astronaut activities were also recorded by the instrument. Later missions located their ALSEP packages further from the LM. Other ALSEPS had the PSE 2.4 to 2.7 m west of the central station, limited by a 3 m cable and slack. A separation of 4.6 m from the RTG minimized heat input. On A-12 the crew tried to prepare the surface for exp't emplacement by tamping the surface with the ribbed soles of their boots. This did not seem to be effective - the total compaction achieved was reported to be small. The A-15 crew did the same.
The surface was first "packed down" to prevent it from sinking. The mounting stool did not provide sufficient protection against inadvertent contact of the bottom of the unit with the surface. To overcome this, the crewman dug a small hole with his boot - a procedure which was time consuming and imprecise. Leveling the unit on A-12 was simple using the bubble; however, the metal ball leveling device was useless because of the lack of adequate damping of ball motion. There was no difficulty on A-14, 15, or 16, although A-14 was unable to make the ribbon cable lie flat on the surface under the thermal shroud skirt. A timeline from A-15 shows ~11 min. for deploying the unit, but A-16 allotted only ~6 minutes. The Mylar skirt thermal shroud was not deployed until late in ALSEP deployment so that dust would not accumulate on it. On A-12, it would not lie flat; it was believed that it had been folded for so long that it had "elastic memory." It could also have been due to electrical effects. It was resolved by putting lunar soil and bolts along the skirt edges (which affected the skirt's function.) Before removing the girdle, the astronaut had to align the PSE within 20deg of the sunline by pointing the arrow on the girdle at the sun, Fine alignment was done after removing the girdle and spreading the thermal shroud. The astronaut read and reported, to the nearest degree, where the shadow of the gnomon fell on the compass rose. During transport, the sensitive sensors were held in place with expanded bellows, which were deflated for "uncaging" the experiment by means of a small explosive device.
Check-out of experiment:
Calibration signals were inherent in the experiment. Also, the signals produced by firing the LM RCS system and ascent engine provided a check on the compressional velocity of the local soil. Impacts of the 2 PLSS's after ejection from the LM were also observed. These sources caused signals which were smaller than those from the PSEP on A-11 by a factor of 80 due to the greater separation of the PSE and the LM.
Operation of experiment:
From JSC via the ALSEP command system. PSEP on A-11 worked for 21 days. It got hotter than expected (perhaps because of dust coverage), and no longer accepted commands after near-noon of the second lunar day. Since it was powered by solar cells it did not operate at night, but it did have an isotope heater for critical components. Leveling motors were operated from Earth to level the low frequency sensors to within 2 seconds of arc. On the ALSEP design, a set of 15 commands governed operation. These worked much longer and operated during the night, but were not without their problems. More detail is available in the scientific literature. There was no astronaut operation other than deployment. The PSE on the A-16 ALSEP got warmer than planned. This was likely due to dust that was inadvertently kicked onto the skirt after deployment.
Repairs to experiment:
Deployment of the solar panels on the A-11 PSEP was not nominal. One of the two retaining structures that should have fallen away when the package was righted failed. The LMP reached down with his finger and flicked it loose. After initial deployment on A-11, an attempt was made to level it more by pushing one side down into the soil more. This did not work. He had to slide it back and forth to scrape away the excess material. Placement of the shroud on A-12 required some weights to hold it down. Later shrouds had weights built in and the shroud was stitched to prevent layer separation.
Recovery/take-down of experiment: NA
Stowing experiment for return: NA
Loading/unloading samples on LRV: NA
Loading of exp't/samples into the LM: NA
Stowing of package once in the LM: NA
Sampling operations - soil, rocks: NA
Navigating/recognizing landmarks: NA
Were there any hazards in the experiment?
i.e. hazardous materials (explosive, radioactive, toxic), sharp objects, high voltages, massive, bulky, tripping hazards, temperatures?
There were small explosive devices on the bellows (used to lock the experiment for transport) which were activated to "uncage" the instrument.
Was lighting a problem? No.
Were the results visible to the crew?
There was a leveling bubble and a Sun gnomon on the instrument.
Would you recommend any design changes?
The thermal shroud was redesigned after A-12 to include some weights at its circumference and to spot-sew the laminations together. This resulted in better thermal control and the leveling commands required from Earth were less frequent. The metal ball in the bowl-leveling indicator rolled all over the place for A-11 PSEP and also on the A-12 PSE. The bubble level was added for the A-12 PSE and it worked very well. The "BB" was never used again.
Were any special tools required? UHT
Was the orientation of the experiment (i.e. horizontal/vertical) important? Difficult?
Level was very important, but was not difficult. It was leveled within 5deg of vertical by the astronaut using a bubble level. The automatic, fine-leveling gimbal system corrected the rest.
Was the experiment successful?
Yes, alone and as a network of 4 seismometers. However, several of the stations exhibited thermal control problems. For collection of tidal data, limiting the instrument operation temperature to a band of ~1.1deg K was desirable. This limitation was not achieved, partly because of problems with deployment of the thermal shroud. Corrective actions included the addition of weights to the outer edges of the shroud, the use of a Teflon layer as the outer shroud covering, and stitching of the shroud to prevent layer separation. Even so, an optimum shroud deployment was not achieved. Thus, the heat loss during lunar night and the solar input incurred during the lunar day was greater than desired.
Were there related experiments on other flights?
See Active Seismic (S 033) and Lunar Seismic Profiling Experiments (S203). See also Lunar Surface Gravimeter (S207.)
Where was it stored during flight? As part of ALSEP.
Were there any problems photographing the experiment? No.
What pre-launch and cruise req'ts were there?
power, thermal, late access, early recovery?
What was different between training and actual EVA? The skirt would not stay down.
What problems were due to the suit rather than the experiment? No comments by crew.
Any experiences inside the LM of interest from the experiment/operations viewpoint?
The PSE was sensitive enough to detect the activities of the astronauts, the hot-fire tests of the RCS jets, the liftoff, and the thermal "noises" of the LM after departure. There were also signals that were interpreted as the venting of propellants from the tanks on the descent stage. Several spent SIVB and LM ascent stages were crashed into the moon to provide seismic signals that the seismometers detected. Even though the A-17 ALSEP did not include a PSE, it did crash the SIVB and the LM into the Moon to participate in the experiment using those instruments.
Preliminary Science Reports for A-11, 12, 14, 15, 16, 17
Mission Reports for A-11, 12, 14, 15, 16, 17
Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TM X-58131, August, 1974, In JSC History Office.
Apollo 14 Final Lunar Surface Procedures, JSC, December 31, 1970
Apollo Program Summary Report, section 3.2.9 Passive Seismic Experiment, JCS-09423, April, 1975.
ALSEP Termination Report, NASA Reference Publication 1036, April, 1979.