Experiment Operations During Apollo EVAs

Experiment: Heat Flow Experiment

Acronym: HFE


The HFE during emplacement on Apollo 15. The drill rack is in the foreground and the ALSD is on the surface behind the borestem, which is emplaced in the ground. The dark, two-segment rod in the left hand of the crewman is the heat probe. The white probe emplacement tool is in his right hand (AS-15-92-12407).

PI/Engineer: Marcus G. Langseth, Columbia Univ.
Other Contacts:
Sydney P. Clark, Jr./Yale
J.L. Chute, Jr., S. J. Keihm/Lamont-Doherty Geological Observatory

Apollo Flight Nos.: 15, 16, 17
Apollo Exp't No.: S 037

Discipline: lunar geology, heat flow

Weight: 9.9 kg, total (4.6 kg, electronics box)
Dimensions: Probes - 4 x 50 cm segments (stowed 8.6 x 11.4 x 64.8 cm)
Electronics box 28 x 25 x 24 cm

Manufacturer: Columbia University, Arthur D. Little, Martin-Marietta

Description/Purpose:
This experiment was designed to make temperature and thermal-property measurements in the lunar subsurface in order to determine the rate at which heat flows out of the interior of the Moon. This heat loss is directly related to the rate of internal heat production and to the internal temperature profile; hence the measurements resulted in information about the abundances of long-lived radioisotopes within the Moon and increased the understanding of the thermal evolution of the body.

The essential measurements were made by two slender temperature-sensing probes that were placed in pre-drilled holes in the subsurface (the borestems were left in the ground, as well), spaced ~10 m apart. Each probe consisted of 2 nearly identical 50 cm long sections. Each section of each heat flow probe had two accurate (+/-0.001 K) differential thermometers that measured temperature differences between points separated by 47 and 28 cm. The probe segments also contained heaters which provided heat to measure the thermal conductivity. The electronics were contained in a separate box which rested on the lunar surface and was connected to the ALSEP central station.

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:
The electronics package was placed 7.6 to 9.1 m north of the central station, at least 3 m from all other experiments, and at least 6 m from the PSE. Two holes needed to be drilled for emplacement of the probes below the surface. These were located 4.6 - 5.8 m from the electronics package and ~7.6 m from the RTG. Also, the holes/probes needed to be at least 60 m from fresh craters with surrounding stones and at least 5 diameters from large isolated boulders > 0.7 m across exposed at the surface.

A third constraint on the placement of the probes (although it may not have ever been documented) was that they not be deployed within one crater radius of large old craters. A few weeks before the mission the P.I. worried that the official target point for the landing was too close to the crater Camelot and that the effects of the crater topography would cause the heat flow data to be skewed. Although one can correct for topography, it adds uncertainty to the data that could be avoided. A change in the landing coordinates (stored in the computer) at that late date was unheard off. The P.I. did let his concerns be known at NASA Headquarters and it eventually made its way to Gene Cernan whose reaction was... "no problem, I'll simply redesignate a little short if necessary to stay one crater radius short of the rim of Camelot." The important thing, as far as the crew was concerned, was to get the very best data possible for this experiment on the last opportunity to do so. They did, indeed, land short by the necessary distance, although it is unclear whether it was necessary to redesignate.

Deploying experiment:
The general operation involved assembling the first two bore stems, inserting them into the drill chuck, and drilling into the surface until ~1/3 of a section protruded above the surface. Using a wrench, the chuck was released and the drill was removed. A second pair of bore stems was assembled and attached to those already emplaced in the surface. The drill chuck was reset and the drill placed atop the new bore stem sections and the total bore stem assembly was drilled further until again about one third of a section remained above the surface. The procedure was repeated for a third pair of bore stems until ~15 cm remained above the surface. The drill was then removed and the HFE probe was inserted as far as possible into the bore stem using the emplacement tool. The depth of penetration was indicated by markings on the tool. The drill and rack was carried to the second probe site and the entire procedure was repeated. The timeline for A-15 planned ~61 minutes for the entire activity. A-16 allotted 64 minutes.

On A-15, drilling the holes to emplace the probes was more difficult than had been expected. The resistant nature of the subsurface or the poor borestem design prevented penetration to the planned depth of 3 m. Instead, at the probe 1 site, the borestem penetrated 1.62 m; and, at probe site 2, the borestem penetrated 1.60 m. An obstruction, probably a break in the stem at a depth of 1 m, prevented probe 2 from passing to the bottom of the borestem. This "break" may have been caused by pulling up on the borestem, causing a decoupling of the segments. Because of the very large temperature differences over the upper section, no valid temperature measurements were obtained by the upper section of this probe. Probe 1 was inserted 140 cm into the borestem. The crew had to report probe depth, stem height, and thermal shield depth during the activities.

On A-16, the first hole was drilled and the probe inserted successfully, but the cable connecting the electronics package to the central station was then inadvertently pulled loose from the connector on the central station when the CDR caught his foot in the loose cable. The cable had looped and become snagged on a boot. This rendered the experiment useless and drilling of the second hole was eliminated. The CDR did not know that the cable had broken because pressure suit mobility is restrictive and he could not normally see his lower legs or feet. The mission report pointed out that it was well known that the ALSEP package cables had memory and stood off the surface in low g. This condition required a crewman to jump clear of cables which he could not adequately see.

Both probes were successfully inserted to their full depth on A-17. Probe 1 went to 2.36 m and probe 2 went to 2.3 m. A photo shows the CDR on his knees while inserting the probe into the hole (although he needed a "prop" to kneel.)

Check-out of experiment: From Earth.

Operation of experiment:
From JSC via the ALSEP command system. Platinum resistors provided heat, and the temperature rise at known distances from these heaters was measured via thermocouples. With the heaters off, the diurnal temperature cycle was measured at known depths.

Repairs to experiment:
See drilling. After the cable broke on A-16, it could not be repaired. The incident precipitated the inclusion of strain relief in the cable connectors on the A-17 instruments. A contingency plan existed to place the probes in a trench if the drilling was difficult, but this was not performed.

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:
During the drilling, the bore stems were drilled into the surface in sections. After the 1st was drilled in part way, a wrench was used to release the chuck from the stem, the second section was screwed into the lower section, and the drill attached to this upper section. This process was repeated to attach the third section. The holes were to be within 15 degrees of vertical, as visually determined by the astronaut once the probes were inserted. The cores were left in place.

Drilling the second hole for the heat flow probe on A-15 proved difficult. Because of the high torque levels on the chuck-stem interface, the drill chuck bound to the stem; in one case it was necessary to destroy the stem to remove it from the chuck. A trick to make the operation easier involved puting the wrench onto the stem which was in the ground and holding it in place with an ankle while turning the drill handle to remove it from the borestem.

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?
During deployment on A-16, the cable was pulled loose of the central station during deployment by tripping. This was due to memory in the cable which did not allow it to lie flat, causing a tripping hazard. This was evident during training but not corrected. On A-15, Scott had also tripped over one of the wires to the probe and moved the electrical box from its position. It had to be realigned on the next EVA.

Was lighting a problem? No.

Were the results visible to the crew?
Other than the drilling effort and alignment, no.

Would you recommend any design changes?
The drill stem was redesigned based on the A-15 experience. The cable attachments were strengthened for the A-17 instruments so that even the excessive force of tripping over the cable would not pull it loose.

Were any special tools required?
The Apollo lunar surface drill. The borestems had a solid-faced bit (so that a hole would remain open, unlike the core samples where the drill stem filled with regolith) and were made of boron filament reinforced epoxy rather than titanium, for low thermal conductivity. Also, a Probe Emplacement Tool (PET, a.k.a. rammer) was packaged with the two probes in a box separate from the electronics package. It had marks to measure the depth of the probes. A type of Stillson wrench was used to decouple the borestems from the ALSD chuck.

Was the orientation of the experiment (i.e. horizontal/vertical) important? Difficult?
The electronics package was leveled to within 5 degrees of vertical with the universal handling tool. It was not difficult. Alignment was accomplished with a shadowgraph, using the shadow of the UHT on a decal as a guide.

Was the experiment successful?
On A-15, partially. On A-16, one cable was broken and the hardware became inoperative. On A-17 the experiment was successful.

Were there related experiments on other flights? No.

Where was it stored during flight? LM MESA.

Were there any problems photographing the experiment? No

What pre-launch and cruise req'ts were there?
power, thermal, late access, early recovery?
None.

What was different between training and actual EVA? Drilling effort.

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

References:

Apollo Lunar Surface Experiments Package - Apollo 17 ALSEP (Array E) Familiarization Course - Handout for class of 1 September 1972, in JSC History Office

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

Apollo 15 Final Lunar Surface Procedures, JSC, July 9, 1971

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

Apollo 17 Final Lunar Surface Procedures, Vol. 1: Nominal Plans, MSC, 11/6/72

Apollo Program Summary Report, section 3.2.14 Heat Flow Experiment, JCS-09423, April, 1975.

Apollo 15 Technical Crew Debriefing, 14 August 1971, in JSC History Office. ALSEP Termination Report, NASA Reference Publication 1036, April, 1979.

"Lunar Sourcebook - A User's Guide to the Moon" G. Heiken, D. Vaniman, and B. French, Eds., Cambridge University Press, Cambridge, 1991.

Personal communication, Jack Sevier to Thomas Sullivan, May, 1993