|A network of sinuous wrinkle ridges as imaged from lunar orbit during the Apollo 15 mission. The low Sun angle causes the ridges to cast shadows so that they stand out; under high Sun they become be very difficult to see. Image credit: NASA.|
Two weeks after the fire's solemn first anniversary, M. Yates, an engineer with Bellcomm, NASA's Apollo planning contractor, completed a memorandum which demonstrated that renewed confidence. In it, he proposed a surface exploration plan for the third Apollo piloted Moon landing mission.
In keeping with the lunar mission nomenclature proposed in Bellcomm's January 1968 Lunar Exploration Program Plan (see "More Information" below), Yates designated the mission Lunar Landing Mission-3 (LLM-3). An "early Apollo" mission, LLM-3 would include a 35-hour stay on the Moon, three three-hour moonwalks by two astronauts, and surface exploration on foot no farther than one kilometer from the LM.
Critical for detailed geologic traverse planning would be the LLM-3 LM's ability to set down within a 200-meter-diameter circle centered on a preselected landing point. LLM-1 and LLM-2 would be counted as successful if they managed to touch down anywhere on a smooth mare (Latin for "sea") within an ellipse with a total area of 235 square kilometers; LLM-3's landing area would total just 0.25 square kilometers.
|Artist concept of an early Apollo landing site atop a rugged ridge. Image credit: NASA.|
Mare ridges are common features on the dark-hued lunar maria; some mare ridges are faults, where the mare's basaltic crust has shifted, cracked, and rumpled, while others might indicate magma movement just beneath the lunar surface in the past. Yates expected that the crater on the mare ridge would act as a natural drill hole, enabling the astronauts to collect geologic samples from deep inside the ridge which they could not obtain otherwise.
The first moonwalk of the LLM-3 mission would see the two astronauts, in Yates' plan designated A and B, working together to set up an Apollo Lunar Scientific Experiment Package (ALSEP) north of their LM. The LLM-3 ALSEP would include a hand-held drill for collecting subsurface core samples and heat-flow probes for installation in the resulting empty drill holes.
The astronauts would then move south past the LM to the rim of the fresh crater. During the second moonwalk, astronaut B would descend into the crater while astronaut A monitored his activities from its rim. In addition to keeping an eye on his colleague, astronaut A would relay radio signals from B's space suit backpack radio to the LM for transmission to Earth. This would be necessary, Yates wrote, because the crater rim would block astronaut B's radio signals.
In the third and final LLM-3 moonwalk, astronaut B would move westward down a short canyon to the mare floor, then would walk south along the ridge-mare contact. Astronaut A, meanwhile, would walk along the mare ridge crest to keep B in sight and again relay his radio signals to the LM. The astronauts would then meet up and return to the LM via the east rim of the crater.
No Apollo mission explored a mare ridge, and Yates' proposed radio-relay technique was never used. The second Apollo lunar landing mission, Apollo 12, amply demonstrated the pinpoint landing capability Yates rightly deemed crucial for geologic traverse planning by setting down near the derelict Surveyor III lander in November 1969. Apollo 14 (February 1971), the third successful Apollo lunar landing mission, used this capability to land near Cone Crater, a naturally occurring drill hole that permitted astronauts Alan Shepard and Edgar Mitchell to collect samples from deep within the Fra Mauro Formation.
"A Lunar Landing Mission to a Mare Ridge — Case 340," M. T. Yates, Bellcomm, 14 February 1968.
"A Continuing Aspect of Human Endeavor": Bellcomm's January 1968 Lunar Exploration Program
Robot Rendezvous at Hadley Rille (1968)
An Apollo Landing Near The Great Ray Crater Tycho (1969)