Sampling the regolith
One of the most ubiquitous activities carried out on the lunar surface was geological sampling. Each successive mission returned more rock mass than the previous and in total, the amount of rock and soil brought to Earth by the Apollo missions was 382 kilograms well over a third of a tonne. But of greater importance than the sheer mass of material is the fact that the majority of it was carefully selected by trained human eye and brain and then painstakingly documented as it was sampled, especially during the J-missions. Those samples are now among the most highly prized pieces of material on Earth.
There are actually other sources of lunar rock available to scientists. Three Soviet spacecraft successfully gathered 0.326 kg of soil from various sites including a core
The gnomon next to a patch of orange soil discovered by Jack Schmitt at Shorty Crater. (NASA) "
sample from below the surface. In more recent years, a class of meteorite has been shown to have originated from the Moon, blasted into space by an impact event to eventually pass through Earth’s atmosphere and reach the surface. None of these secondary sources have the provenance of Apollo’s documented samples.
Once a desirable rock or maybe an interesting patch of soil had been identified, the two crewmen began a practised sequence of tasks to properly gain the sample along with as much contextual information as was possible in the brief time available. The normal procedure began with a gnomon being placed on the opposite side of the sample from the Sun – in the down-Sun position. The gnomon was a small tripod arrangement with a central staff that maintained true vertical, as explained by Jack Schmitt: “The gnomon gave you the local vertical, a 40-centimetre scale, a shadow which gave you azimuth, and also had a greyscale and three international colour references for photometric calibration.”
Next, a crewman took two photographs of the sample prior to it being moved. These were taken with Sun shining across the sample so that its shape stood out and were therefore called cross-Sun images. Because he took a step to one side between exposures, they constituted a stereo pair which would allow the sample’s topography to be determined back on Earth. At about the same time, the second crewman took a down-Sun image towards the gnomon which recorded the intrinsic colour and tone of the sample in the same frame as the calibration card. At some point in the sequence, another shot was taken with some notable feature in the background. “We would take a ‘locator’ back to something like the rover,” explained Schmitt years
A stereo pair of an Apollo 17 sample at Van Serg Crater. This pair of images has been arranged for cross-eyed viewing. (NASA)
later, "just so that there was something in the picture that could be used to work back to where the sample had been taken. We’d just turn around and take a picture of the rover or of the horizon. Originally it had to do with the LM being in the picture as a ‘locator’ because, from the geometry of the lunar module and knowing how it had landed, you could work back along a ray to where you were and, as well, get a distance based on the size of the lunar module.”
For photography, NASA’s crews came to favour the Hasselblad camera after Wally Schirra took one with him on his Mercury flight in 1962. For use on the lunar surface, NASA worked with the Hasselblad Company to produce a specialised version of their professional SLR camera. This took square images on 70-mm-wide thin-base film designed to maximise the capacity of the film magazines. A battery – powered autowinder was added and the normally black finish on these cameras was changed to a reflective silver to minimise the absorption and emission of heat as it was moved in and out of the Sun’s rays. Crews could hold the camera with a special handle or chest mount it on the front of their RCU.
Researchers were keen to extract as much scientific information as possible from the resulting images so changes were made for the purposes of photogrammetry, the measurement of objects using photographs. A 60-mm lens, mildly wide-angle for the format, was specially designed to give accurate image geometry. Flight lenses were individually calibrated so that their image geometry was well understood. And since the plastic base of photographic film is prone to thermal expansion and contraction, the cameras included a means of marking a known geometry within the image at the moment of every exposure. A glass screen called a Reseau plate, upon which were inscribed a series of crosses at 1-centimetre spacing, was added directly in front of the film. When a picture was taken, the crosses left their imprint in the image for a future researcher to use when measuring angles. These crosses now adorn some of the 20th century’s most iconic images and perhaps the greater imprint they leave is in the eyes of graphic designers who use them as a motif to represent space travel and science. To mitigate the build up of static electricity and resultant sparks that might affect the image, the Rescau plate had an extremely thin layer of gold applied, thin enough to pass light.
With initial photography out of the way, the sampling itself could begin. The crews carried a selection of tools to take samples, particularly a scoop and a pair of tongs. While one crewman lifted the sample, the other took a numbered bag from a dispenser, often attached to their camera, and held it in position to allow the rock or soil to be dropped in. ЛИ the while, there wfas a verbal description which ended with the bag number being called out so a geologist in the science baek room could crossreference it on return to Earth.
Two-man sampling w’as found to be much more productive than one crewman trying to work single-handedly but on occasion, perhaps when one crewman was occupied by another task, the second could usefully spend his time w orking alone. Schmitt often found himself in this position: "With two of us working together, bagging samples was fairly easy, but it was a lot harder solo. You had to hold the bag in one hand, and somehow or another get your scoop out over it so that you could dump something in it. And it was not easy, because you’re moving your arms against the pressure in the suit while gripping both the bag and the scoop."
After three days, Schmitt became quite adept at solo sampling, but not before he came a cropper at a small crater halfway through their second EVA. As Cernan worked to obtain a core sample. Schmitt Look samples at the crater’s edge, gathering soil and rock fragments in a scoop and. with some difficulty, pouring them into sample bags. When he finished with the scoop, he would rest it against his legs while using his two hands to manipulate the bag. Often the scoop would fall to the ground which forced him to bend one knee and lean down to retrieve it. Each sample bag went into a large sample collection bag that he sat on the ground beside him. As he turned at the end of this effort, he inadvertently knocked the bag over and spilled the smaller sample bags across the surface.
"Aaaah!” he cried, dropping to the surface on his hands and knees to gather his samples. "You don’t mind a little dirt here and there, do you, gang?’’
"No," replied Bob Parker in mission control.
Schmitt’s next problem was getting back up from his position kneeling on the outer slope of the crater. He brought his torso upright then straightened his legs. As he successfully got to his feet, the bag slipped from his grasp and impulsively, he leaned over to retrieve it. only to bring his centre of mass too far forward. Gravity took control and pulled him face-down into the dust once again as his legs Hailed uselessly off the surface. It Look him a while to return to a kneeling position from which he could regain his feet.
Mission control watched Schmitt’s pirouettes and spills with a mixture and bemusement and concern. "Hey, Gene, would you go over and help Twinkletoes, please?"
Cernan looked across. "Want some help. Jack? I’ll be there.’’
“No! I don’t need any help.” said Schmitt, annoyed at his display in front of the TV camera. “I just need belter bags.”
Schmitt checked his camera lens was clean and finished up at the crater. As they prepared to drive off. Parker had one further message for him. “Be advised that the switchboard here has been lit up by calls from the Houston Ballet Foundation requesting your services for next season."
“I should hope so,” replied Schmitt at which point he adopted a mock ballet pose, hopping on one leg with the other stretched out behind him. After two hops, he promptly fell on his face again. "How’s that?"
The little crater where Jack Schmitt fell, frolicked and performed his little dancing stunt will forever be known to researchers as Ballet Crater.