This Week In Rocket History: Apollo 17
Still crunching through my backlog, 2022 stories soon! More I wrote for Cosmoquest.
This week in Rocket History is the final Apollo lunar landing: Apollo 17. Despite being the last crewed mission to the Moon, it set a few firsts. It was the first and only lunar landing to have a scientist-astronaut instead of a pilot-astronaut with some geological training. It was also the only night launch of a Saturn V.
The Apollo 17 crew was chosen in 1969 and was originally supposed to be Eugene Cernan, Ron Evans, and Joe Engle, all test pilot astronauts. They were selected as the backup crew for Apollo 14 and would then be the prime crew for Apollo 17, per the pattern at the time.
However, in mid-1970, Apollo 18 through 20 were canceled because of budget cuts and the lack of a landing on Apollo 13. Scientists really wanted a trained geologist on an Apollo flight. In order for this to happen, NASA changed the crew assignment for Apollo 17 so that scientist-astronaut Jack Schmitt could fly to the Moon instead of Joe Engle, who later flew on two early Shuttle missions. The new backup crew consisted of lunar veterans John Young, Charles Duke, and Stuart Roosa.
With the crew sorted, NASA then focused on choosing the landing site. There were many constraints on what would make an acceptable landing site, including illumination at landing, the distance from the lunar equator, and scientific merit. Remember, this wasn’t just a trip to the Moon to bring back science — the geologists were looking for evidence of recent volcanism and wanted to see it first-hand.
Taurus-Littrow, a lunar valley, was eventually chosen. The relatively flat area met the landing site criteria. As for science, lunar landslides had also collected rocks from different parts of the Moon in one area. The valley floor was cratered from impacts, but the crater density was lower compared to other parts of the Moon. The lower crater density is evidence of volcanism where flowing lava would have covered up the missing craters before it cooled.
There was just one problem with Taurus-Littrow: the site of interest was smaller than the lunar module’s landing accuracy. At the time, landing guidance only guaranteed a landing in an oval three kilometers wide and two kilometers long. In order to land at Taurus-Littrow, the landing guidance was adjusted to allow a 1-kilometer circle landing area.
The assembly of Apollo 17’s Saturn V stack started in February 1971, and by August 1971, the rocket was complete and rolled out to the pad. The launch was set for December 6 but got delayed to very early on the 7th due to an abort at T-30 seconds.
The launch was flawless, as were checkouts in Earth orbit and the Trans-Lunar Injection burn. On the way to the Moon, the astronauts (probably Harrison Schmidt) took the famous Blue Marble photograph showing the entire Earth’s disc illuminated, including the South Pole which no other Apollo had seen. The photo essentially kickstarted a generation of environmentalists.
Another activity during the coast phase was realigning the mission clock to the flight plan since they had launched two hours and forty minutes later than planned. This was accomplished by doing some activities earlier than planned and then setting the clock forward the required time in one big jump, such that mission hour 65 was immediately followed by mission hour 67 and 40 minutes. Yes, NASA did something like daylight saving time but in space!
The rest of the coast to the Moon was accomplished without issue. Lunar orbit insertion was completed 88 hours into the mission.
Powered descent was initiated 112 hours 49 minutes and 56 seconds into the mission. Just over twelve minutes later, at 19:55 UTC on December 11, they were safely on the surface.
Only four hours after they had landed on the surface, they began an arduous series of scientific tasks. Ultimately, the crew would spend three days on the surface and do three EVA’s totaling 22 hours. Their very first task was setting up some experiments on the surface and using the rover to drive around and pick up samples, as directed by geologist Schmitt.
The Surface Electrical Properties experiment was designed to measure the electrical conductivity of the subsurface rocks. The experiment consisted of a transmitter placed on the ground and receiver antennas on both the Lunar Excursion Module (LEM) and the rover. The transmitter sent signals into the surface at several different frequencies to determine what was underground, especially if there was water. (The presence of water could be determined by a change in the received signal.) Astronauts drove from place to place and took data, noting where they were in relation to the LEM and the transmitter at each point. At the conclusion of the mission, the data recorder was removed and brought back to Earth. Unfortunately, not much data was actually collected by the experiment because its cloth cover was knocked off, and it overheated.
The two astronauts also placed explosive charges at various points which were later detonated after they were in orbit. The vibrations from the explosions bounced around the inside of the Moon and were picked up by special microphones placed by the astronauts.
The astronauts’ EVA time was unremarkable except for the discovery of “orange soil”, which turned out to be volcanic glass from previous volcanic eruptions. Impacts flip rock layers, which is what brought the volcanic glass closer to the surface. The geologists were able to determine that the impact was significant because a lot of that “orange soil” was present. The orange color was produced by two different glasses cooling at different rates.
Overall, Apollo 17 taught science that the lunar mare were formed by episodic welling of lava from under the surface, not from surface volcanic eruptions. Geologists also ruled out any evidence of young volcanic activity on the Moon from the sites surveyed. In the end, all the Apollo missions did was scratch the surface of how the Moon formed. It’s impressive that they were able to accomplish this using the limited hardware the Apollo program’s engineers made to accomplish President Kennedy’s goal of landing on the Moon before 1970.
A Running Start — Apollo 17 up to Powered Descent Initiation (NASA via Internet Archive)
The blue marble (NIH)
The End of the Beginning (NASA)