Although the makeup of the Moon's surface had been debated since the dawn of Mankind, the need to understand the lunar surface commanded greater attention as humans began to journey to from the Earth to the Moon.
The debate about the lunar surface raged right up until Armstrong and Aldrin landed on the Sea of Tranquility on July 20th, 1969. There were many scientists, including Thomas Gold, who claimed that the lunar module (LM) might disappear into the deep dust of the lunar regolith. Unmanned probes, such as Surveyor and Luna, landed on the Moon prior to Man's arrival to test and determine the strength of surface soil. Unmanned probes provide a limited amount of information based upon their landing location, mobility and experiments carried on their mission. There was a need to continue to gather of information on the mechanics of the lunar soil even after men had landed on the Moon.
NASA requested proposals from scientists for lunar soil experiments. One such experiment dealt with directly with the question on the weight bearing characteristics of the lunar regolith. The name of the experiment was the "Self Recording Penetrometer."
The penetrometer is the device with the cylinder on top at the far left of the LRV tool rack as shown below in the Apollo 15 photograph of the lunar rover.
As shown in the Apollo 15 EVA training photograph below, the objective of the Self-Recording Penetrometer was to provide quantitative data on soil penetration resistance as a function of depth below the lunar surface.
The Self Recording Penetrometer (SRP) consists of the reference pad assembly that rests on the surface, the upper housing assembly that contains the recording drum, and the shaft that joins them and is used for the penetration. The data was recorded on a drum on the upper end of the instrument. The moonwalkers would then disconnect the drum and return it to Earth. The principle investigator (PI) would review the data. The resulting study was published in the mission preliminary science report approximately six month after the mission's completion.
The Self-Recording Penetrometer was used on both the Apollo 15 and the Apollo 16 lunar missions. While there were no still photographs taken when the tool was in actual use on either mission, both missions LRVs camera caught Irwin and Duke using the tool during their EVAs on the lunar surface.
The video still shown here is of Charlie Duke performing the penetrometer plate experiment on test site 7 at Station 10 during EVA 2.
Art has captured a still portrait of a moonwalker using the penetrometer. In the painting below entitled "Charlie Duke, Soil Scientist-Maximum Push," Alan Bean recorded Charlie Duke using the SRP at Station 10 during the final EVA .
As shown below, the SRP take probes of various shapes and sizes and uses them to determine how deep they could penetrate into the lunar surface. One of the probes, highlighted in yellow, is the penetrometer plate probe. At one by five inches, the penetrometer plate was the largest probe used in the SRP system. While the other probes were used for penetration, the plate was used to determine soil compression. During it's use on the Moon's surface, the moonwalkers used the plate to compare compressibility between virgin and trodden areas.
Recently, I was able to procure the Self Recording Penetrometer plate that Charlie Duke used on the lunar surface during Apollo 16. The photograph below shows the plate used at Station 10 at the Descartes Highland. The scale cube accompanying the plate is one inch cubed.
The plate also appears in the "Apollo Stowage Lists" within the "Apollo 16, Mission J-2 CM-113 and LM-11" section under the title of "LM Earth Launch Stowage List." The part, highlighted in yellow on the page below, is labeled "Large Base Assy" and is shown on page 73 with the rest of the Self Recording Penetrometer equipment. The part was stored in Quad Three of the lower bay within the LM descent stage during liftoff from Earth and would not unstowed until Young and Duke were working on the surface of the Moon.
The page shown below is Page 19 of Charlie Duke's cuff checklist that he wore on his spacesuit during his EVA. The page is a map that provides a short hand menu of all the tasks that were to be performed at Station 10 during the second EVA. The sections of the map that are highlighted in yellow are where the penetrometer plate was used and the map key that described the plate symbol.
In November of 1972, NASA released the initial lunar experiment results in the "Apollo 16 Preliminary Science Report." In the two pages listed below, NASA scientists reviewed the results of the Self Recording Penetrometer tests performed by Charlie Duke at Station 10. The yellow highlighted area at the bottom of the page provides the penetration results achieved with the plate.
In both attempts with the 1 x 5 inch (2.54 x 12.7 cm) plate attached, the probe penetrated between two and four inches into the lunar surface.
In April of 2008, Charlie Duke posed with the penetrometer plate that he carried back from the lunar surface.
The plate is one of the few remaining tools used out on the lunar surface during the Apollo era as such it represents Man's continuing quest for knowledge of the worlds around us.
It is now mated with an original painting of Charlie Duke leaning onto the Self Recording Penetrometer into the lunar soil. The artist is an English painter by the name of Gavin Mundy.
I perserved the penetrometer plate in a shadow box frame with museum glass for protection.
There is a brass plaque affixed to the frame that identifies the Penetrometer Plate as part of an experiment performed on the Moon.