Experiment Operations During Apollo EVAs

Experiment: Active Seismic Experiment

Acronym: ASE


The mortar package assembly (MPA) deployed at the Apollo 16 ALSEP site. Note the stable base which was an improvement over the Apollo 14 mortar (AS-16-113-18376).
See also:
The MPA on A-14.
The flags which mark the geophones of the ASE array.

PI/Engineer: Robert L. Kovack, Stanford Univ.
Other Contacts:
Tom Landers, Stanford
Joel S. Watkins, Univ. of NC

Apollo Flight Nos.: 14, 16
Apollo Exp't No. S 033

Discipline: Lunar Seismology

Weight: 11.2 kg
Dimensions: see ALSEP Flight System Familiarization Manual, p. 2-152 for data on all the ASE subsystems

Manufacturer: Bendix
(grenade launcher made by Space Ordnance Systems, Inc.)

Description/Purpose:
A string of 3 geophones was emplaced by A-14 & 16. This allowed profiling of the internal structure of the Moon to a depth of ~460 m. Two seismic sources were included: an astronaut-activated thumper device containing 21 small explosive initiators, and a rocket grenade launcher that was capable of launching 4 grenades at known times and distances (150, 300, 900, and 1500 m) from the seismometer. High frequency natural seismic activity was monitored with the geophones. Electronics for the exp't were within the ALSEP central station.

The astronaut-activated thumper was a short staff used to detonate small explosive charges -- single bridgewire Apollo standard initiators. Twenty-one initiators were mounted perpendicular to the base plate at the lower end of the staff. This flat base plate was driven down against the surface to provide a known energy pulse. A pressure switch in the plate detected the instant of initiation. An arm-fire switch and an initiator-selector switch were located at the upper end of the staff. A cable connected the thumper to the central station to transmit real-time event data. The thumper also stored the 3 geophones and connecting cable until deployment.

The 3 identical geophones were miniature moving coil-magnet seismometers. They were anchored into the surface by short spikes as they were unreeled from the thumper/geophone assembly. They were emplaced 46 m apart and were sensitive to signals with frequencies in the range of 3 to 250 Hz. The mortar package assembly (MPA) comprised a mortar box, a grenade-launch-tube assembly, and interconnecting cables. A 2 axis inclinometer provided pitch and roll angle data. Many safeguards existed on arming, launching, and detonating the grenades, all of which were done from Earth after departure of the crew. The A-16 MPA was modified to have a more stable base than the one on A-14.

Unloading from the LM: As part of the ALSEP

Transporting by foot or MET: As part of the ALSEP

Loading/unloading tools/exp'ts on LRV: NA

Site selection: As part of the ALSEP

Deploying experiment:
The geophones deployed very easily on A-14. They went into the soft surface readily and were then stepped on to implant them. However, the loose soil gave little resistance to hold them in place, and in moving the cable Mitchell pulled the second geophone out of the soil and it had to be replaced. On A-16, while deploying the ASE electronics package the cable became taut and pulled on the central station. The crewman had to go back and adjust the central station. Before unreeling the geophone cable, it was staked in place (with the aid of an extension handle) through a loop in the cable so that the LMP would not drag the central station behind him while laying out the geophone line. The foot pads on the mortar pack rotated out of the proper position, and the package had to be picked up and the pads rotated to a position in which they would rest properly against the surface. For A-14, there was a crater at the optimal location of the mortar package, and it was thus located closer to the central station than desired. The timeline for A-16 allotted ~18 minutes for the geophones to be deployed by the CDR and ~12 minutes of assistance by the LMP. Deploying the mortar was allotted another ~16 minutes of the CDR's time. The targeting area of the mortar was to be free of craters and ridges.

On A-16, the mortar box cable was lengthened from 3 m to 15.2 m for greater separation distance from the central station. Also, a subpallet was added for the mortar box to provide greater stability during firings and for ease of alignment when erecting the experiment. The deployment of the package was successful, although only 3 of the 4 stakes could be emplaced. The release pin for the 4th stake was bent and jammed so that it could not be pulled out. The crew reported the feeling that, with a pair of tweezers, they could have removed the pin, but with a pressure suit glove it was not possible. Although tests performed during the development of the MPA showed that 3 deployed stakes were adequate to provide stability, this may have allowed the assembly to tip over after the 3rd shot, although it is also possible that the sensor failed. Also on A-16, the LMP followed the CDR while he deployed the geophone line and staked the cable in place and implanted 2 of the 3 geophones to prevent them from shifting. The CDR implanted the 3rd.

Check-out of experiment:
On A-16, near the end of the 3rd EVA, the MPA roll sensor was observed (by telemetry) to be reading off scale. A TV panorama verified that it was properly positioned and aligned, suggesting that the roll sensor was inoperative. No repair was attempted.

Operation of experiment:
On A-14, the LMP was able to fire 13 thumper shots into the ground during EVA 1. Several of these required an extraordinary amount of force to fire them. The thumper failed to fire after several attempts at several initiator positions, and several firing positions (marked as white marks on the geophone line) were skipped to gain EVA time. Three initiators were deliberately not fired. Post-flight investigations showed that a malfunction occurred because lunar soil got into the arm/fire switch mechanism and the initiator selector switch was not properly seated in the detents. The total time spent on thumping operations was 28 minutes, within allowable EVA constraints. The LMP was instructed to stand still for 20 seconds before and 5 seconds after each shot. On A-16 this was changed to 10 seconds before and after. The A-16 timeline allotted ~25 minutes to this activity.

Several thumper shots were fired while the CDR was moving on the surface near the ALSEP central station. His movements generated seismic energy that was recorded by the geophones, and his movements had to be restricted during the remaining thumper operations. In the future, it may be possible to conduct thumper operations and allow the 2nd astronaut to move about, provided that he is sufficiently far removed from the central station and geophone line.

On A-14, the geophone/thumper anchor was used as a penetrometer (see Soil Mechanics - ASP) to obtain 3 two-stage penetrations into the lunar surface. This device (figure 4-11 in the A-14 Preliminary Science Report) had black and white stripes 2 cm long to provide a depth scale. After completion of these tests, the device was used to anchor the geophone cable when the cable was placed in position for the ASE.

The grenades were not launched after departure of the A-14 crew for fear that dust would land on the other ALSEP experiments. (The off-nominal deployment was necessitated because of a crater at the optimum mortar package deployment location. Post-flight tests showed that the central station would at least suffer thermal degradation and perhaps be damaged if the grenades were launched.) There was consideration of firing the mortars near the end of the life of this ALSEP, but up-link capability was lost and the arming capacitors would not charge after the long surface interval, so none of them were ever fired. Also, continued use of the LRRR required that no dust be kicked up on its reflectors. On A-16, the first 2 grenades were fired successfully, but after the 3rd was fired, the pitch-angle sensor on the mortar package went off-scale in a high direction. Consequently, its position was uncertain and the firing of the fourth grenade was never attempted.

On A-16, 19 thumper shots were successfully fired by the CDR (although the thumper had 21 shots). This took 14 minutes. For safety and experimental needs of quiet before firing, it needed to be armed for 5 seconds before it would fire.

Repairs to experiment:
On A-14, upon reaching position 11 (at the middle geophone) the LMP observed that this geophone had pulled out of the ground, apparently because of the effects of set or elastic memory of the cable. After repositioning the geophone, he resumed operations. Even though geophone 2 was resting on its side during the first 5 firings, usable seismic data was obtained.

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

Trenching: NA

Raking: NA

Drilling: 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?
The mortar in A-14 was to lob four explosive charges whose shocks would be recorded on the seismometer. However, it was placed so close to the central station that experimenters feared that firing it would cover the central station with dust, so the experiment was not performed. There was also a hand-held "thumper" unit that contained small explosive charges. Several safeguards existed on both these items.

On Apollo 16, three grenades were launched. Because the pitch position sensor then went off scale, the decision was made not to launch the 4th.

Was lighting a problem? No

Were the results visible to the crew? No

Would you recommend any design changes?
For A-16, the thumper was modified to improve the switch dust seals and to increase the torque required to move the selector switch from one detent to the next. Also, a longer cable to the MBA was provided to ensure adequate deployment.

Were any special tools required?
Thumper, UHT. On A-16, the LRV was used to provide a guideline for laying out the geophone line along a heading of 290.

Was the orientation of the experiment (i.e. horizontal/vertical) important? Difficult?
The geophone array was laid out in a linear fashion. There were little flags to assist in this alignment. There was a 7deg constraint on their deployment, most likely on their horizontal orientation, but it is unclear from reading the literature. The orientation of this array was set by driving the LRV along the required heading for 100 m to lay out a track in the regolith to be followed in deploying the line. The targeting area of the mortar was to be free of craters and ridges.

Was the experiment successful? Yes

Were there related experiments on other flights?
See S 203 - Lunar Seismic Profiling Experiment. See also, S 031 - Passive Seismic Experiment.

Where was it stored during flight? 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?
Cable memory allowed the very light cable to stick up in the low gravity.

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? NA

References:

Preliminary Science Report for A-14, 16

Mission Report for A-14, 16

Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TM X-58131, August, 1974, In JSC History Office.

Apollo Program Summary Report, section 3.2.10 Active Seismic Experiment, JCS-09423, April, 1975.

Apollo 16 Final Lunar Surface Procedures, March 16, 1972, MSC

ALSEP Termination Report, NASA Reference Publication 1036, April, 1979.

Apollo Lunar Surface Experiments Package (ALSEP) Flight System Familiarization Manual, Bendix Aerospace Division, Contract No. NAS9-5829, 1 August 1967, in JSC History Office.

Apollo 16 Technical Crew Debriefing, 5 May 1972, in JSC History Office.