PI/Engineer: D. S. Burnett, California Institute of Technology
Dorothy S. Woolum, C. A. Bauman; California Institute of Technology
Apollo Flight Nos.: 17
Apollo Exp't No.: S 229
Discipline: lunar dust, radiation attenuation, radiation, attenuation by regolith
Weight: 2.27 kg, total (1.86 kg probe and 0.4 kg container returned)
Dimensions: 2.35 m long, deployed; 1.23 m long, stowed
(2 cm dia. nom., 4.5 cm dia. at top.)
Manufacturer: Calif. Inst. of Tech.
Time integrated fluxes of thermal neutrons as a function of depth in the regolith were measured using targets of boron-10 and uranium-235 placed at intervals along a 2 m rod that was inserted into the hole left by the deep drill core. Cellulose triacetate plastic detectors were used in conjunction with the B-10 targets, and mica detectors were used in conjunction with the U-235 targets. Some information on the energy distribution of the equilibrium flux was also obtained by including 2 cadmium absorbers and 3 KBr capsules at different depths on the probe. Temperature indicators were included at 4 point along the length of the probe to record its thermal history. This information has geological relevance to the speed of regolith turnover. It is also important for the understanding of radiation protection required for longer human occupancy of the Moon. For stowage, the probe was fabricated in two 1-m long sections.
Unloading from the LM: Nominal, from LM MESA. It was stored inside its thermal bag.
Transporting by foot or MET: NA
Loading/unloading tools/exp'ts on LRV:
At beginning of EVA 1. To prevent over-heating, the two sections of the LNPE were kept in a thermal bag during the EVA before actual deployment.
The deep drill core stem sample was acquired at a site ~38 m north of the ALSEP central station and the RTG. The site was in a shallow depression and behind a meter-sized rock, which should have provided additional shielding from the RTG neutrons.
Deployed during EVA 1 on A-17. The probe was inserted into the hole left behind after obtaining the deep drill core, and recovered at the very end of EVA 3, after 49 hours of exposure. After deployment of ALSEP and recovery of the deep core, the 2 LNPE sections were removed from the thermal bags, activated, coupled, and emplaced in the hole. Nominal insertion by hand was made after 1st passing the probe through the hole in the treadle used for recovering the deep core because, in retrieving the core, the top of the hole had been widened; thus, the possibility existed that the probe would drop too far into the hole to be retrieved. Back-up procedures for emplacing the probe by hammering or with the ALSD existed. To prevent overheating, the top of the probe protruding above the surface was covered with the thermal bag during exposure.
Before insertion into the hole, the probe was activated by twisting the unit, thus aligning the neutron targets with their particle track detectors. Deactivation was accomplished by again twisting the unit to move the particle track detectors away from the neutron capture targets.
Each segment of the probe could be activated separately. The upper section was activated by depressing a bar on the large handle at the upper end and rotating 180°ree;. The lower section was activated by removing the dust cap at its upper end and using it as a tool to rotate the central rod, which was spring loaded to snap into 1 of 2 configurations 180°ree; apart. The two sections could then be coupled for deployment by simply screwing them together.
This activation/deactivation sequence was necessary to prevent the accumulation of background events from neutrons produced by cosmic ray interactions in the spacecraft and by the plutonium-238 power source for the ALSEP package.
Check-out of experiment:
Correct activation was verified after return to Earth by inspection of alpha particle tracks from the U-238 sources.
Operation of experiment:
Activated, inserted, retrieved, and deactivated probe without difficulty. Otherwise passive. It had a total activated exposure period of 49 hours.
Repairs to experiment: NA
Recovery/take-down of experiment:
Recovered probe on EVA 3. The core jacking mechanism (treadle) was used to remove it from the hole. The 2 probe segments were separated by unscrewing for storage and then deactivated by twisting within a minute or two after withdrawal from the hole. The experiment was placed in the shade of the LM within ~ 3 minutes.
Stowing experiment for return:
The probe was placed in a return container on top of a core stem return container in storage area A5 of the LM.
Loading/unloading samples on LRV: NA
Loading of exp't/samples into the LM: No comments by crew.
Stowing of package once in the LM: No comments by crew.
Sampling operations - soil, rocks: NA
Drilling the hole for the deep core presented some problems during the extraction, but all sections of the core were obtained, and the hole did not collapse , therefore allowing the insertion of the probe. The treadle was left in place to support the probe and not allow it to fall too far into the hole. Without this treadle to mark the location, the hole would have been very hard to find again after walking away to get the probe due to the shadows from random bumps on the ground.
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 was uranium 235 as a neutron absorber target which would fission and release more neutrons, which was what was actually detected by the mica. There were also uranium 238 point sources which verified correct activation and deactivation.
Was lighting a problem? No.
Were the results visible to the crew? No.
Would you recommend any design changes? None made by crew.
Were any special tools required?
ALSD required to provide hole. The dust cap of the lower segment served as a tool for its activation.
Was the orientation of the experiment (i.e. horizontal/vertical) important? Difficult?
Needed to be subsurface. Hole should be vertical so that depth of regolith is known.
Was the experiment successful? Yes.
Were there related experiments on other flights?
Thermal neutrons were to be measured as part of the cosmic ray/regolith interaction on the CRD (S 152) on A-16. Analysis of the returned lunar samples from all the flights used thermal neutron capture to explain certain isotopic abundances.
Where was it stored during flight? LM MESA in Quad IV.
Were there any problems photographing the experiment? No
What pre-launch and cruise req'ts were there?
power, thermal, late access, early recovery?
Did not want the probes to get above 333 K.
What was different between training and actual EVA? No comments by crew.
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? No comments by crew.
A-17 Preliminary Science Report
Apollo Scientific Experiments Data Handbook, JSC-09166, NASA TM X-58131, August, 1974, In JSC History Office.
Apollo Program Summary Report, section 3.2.18 Lunar Neutron Probe Experiment, JCS-09423, April, 1975.
Apollo 17 Final Lunar Surface Procedures, Vol. 1: Nominal Plans, MSC, 11/6/72
Apollo Stowage List - Apollo 17, MSC, 12 December 1972.