In 1967, the United States Geological Survey (USGS) collaborated with NASA to blast craters into the site of an ancient volcano in order to turn it into a lunar training ground for astronauts.
The location, Cinder Lake, Arizona, was adjusted to resemble the Moon as closely as possible, to help prepare astronauts for historic missions to our orbital neighbor. Here are 11 fascinating facts about Cinder Lake Crater Field.
1. Before the Apollo 11 crew set foot on the Moon, they had to train on Earth
One location where the Apollo 11 crew trained for the Moon landing was at northern Iceland's "terrestrial analog site," where the country's basaltic rock served as a close natural substitute for the lunar surface.
2. Cinder Lake was chosen as an analog site due to its similarities to Apollo 11's Moon landing site
A location that served as an analog site for Apollo 11 researchers, as well as Apollo astronauts for later missions, was Cinder Lake in Arizona. Located 12 miles from Flagstaff, Arizona, the area is covered in basaltic cinders from a volcanic explosion that took place around 1064.
These materials greatly resemble those of Mare Tranquillitatis, the site that was designated for Apollo 11's Moon landing.
3. Cinder Lake Crater Field #1 and #2 are still there today
Were it not for current events that mean most of us can't leave home, anyone would be allowed to visit Cinder Lake Crater Field. As the Smithsonian Magazine points out, though the craters on the sites have been worn down and corroded over time — due to Earth influences not felt on the Moon, including human interference — many people still flock to the sites today.
4. The USGS made the area more Moon-like by blasting craters into it with dynamite
As Northern Arizona University explains, NASA's Astrogeology Research Program, "started in 1963 when USGS and NASA scientists transformed the northern Arizona landscape into a re-creation of the Moon. They blasted hundreds of different-sized craters in the earth to form the Cinder Lake crater field, creating an ideal training ground for astronauts."
5. Test explosions were used to find the optimal combination of explosives for creating fake Moon craters
Using satellite photographs of the Mare Tranquillitatis region of the Moon, engineers, and scientists from the USGS set to work recreating lunar craters at Cinder Lake.
After experimenting with test explosions, the crews excavated holes and filled them with 312.5 lbs of dynamite and 13,492 lbs of ammonium nitrate to achieve the desired result.
6. Crater Field 1 had 142 craters blasted into it
In July of 1967, engineers blasted 47 craters in a 500-square-foot area of Cinder Lake. In October, 96 more craters were added, bringing the total in Crater Field 1, as it was called, to 143.
Field 1 was primarily designed to simulate a small area of the designated Apollo 11 landing site. As such, a simulated Lunar Module was installed on a ramp placed in the crater field — this helped researchers to contextualize and hone the design of the Lunar Module.
7. Crater Field 2's 354 craters were made to replicate the different ages of real lunar craters
Crater Field 2 had a total of 354 craters blasted into it. Unlike Field 1, the detonation of Field 2's craters was arranged so as to simulate the way impacts of newer craters would spread a layer of debris materials over older craters. "Older" craters were detonated first, followed by "intermediate" age craters, and finally, the "youngest" craters were detonated.
When the astronauts-in-training took samples from the craters at Field 2, they could use the layers of sediment to determine the age of the crater, a skill that they used when they were on the Moon.
8. The first astronauts to train at the site were the Apollo 15 crew
Despite the fact that the crater fields at Cinder Lake were created before Apollo 11's 1969 Moon landing, the first crew to actually train at the site was that of the Apollo 15 mission.
The sediment layers of Crater Field 2 were particularly useful for the training of the Apollo 15 mission, as it was the first lunar mission to be focused primarily on geology.
9. Lunar vehicles and equipment were tested on the site
Astronauts wore spacesuits at the site to simulate walking on the Moon. They practiced using tools and classifying geological formations. As researchers had tried to replicate the craters on Mare Tranquillitatis as precisely as possible, the fields were also used to help map potential paths across the lunar landscape.
Slopes were also built into the fields to allow astronauts to test lunar modules and lunar vehicles. One vehicle that was tested was Grover the Geologic Rover, a replica of the Apollo Lunar Roving Vehicle made to withstand the forces of Earth's gravity.
10. The last training simulation at the site took place in 1972
The last training simulation at Cinder Lake took place in 1972 with the crew of Apollo 17. After that, the site was used by news networks and entertainment companies, such as Disney, to re-create the Moon in film.
11. Cinder Lake Crater Field's legacy lives on today
From training at an off-road location to going off-world, Apollo's historic Moon landing missions are strongly linked to Cinder Lake's history. Though the location has been poorly preserved, it still stands as part of a bold legacy that saw six manned missions go to the Moon, the first of which landed on July 20, 1969.