Apollo 17 Mission Overview
Left: The night launch of Apollo 17. Right: The Taurus Littrow valley as seen from the Lunar Module a few hours before landing. The landing site in the center of the valley is indicated by a diamond. SM indicates the South Massif, studied on EVA 2, and NM and SH indicate the North Massif and Sculptured Hills, studied on EVA 3. The flat region at the top of the image is Mare Serenitatis west of the landing side.
Apollo 17 was the sixth and final Apollo mission to land on the Moon. Following a 2-hour 40-minute delay, it launched at 11:33 p.m. CST on December 6, 1972, the only night launch of the Apollo program. Prior missions had explored the Moon’s early volcanic history and the role of large impact basins such as Imbrium. Accordingly, Apollo 17 was planned to collect ancient highlands crustal material far from the Imbrium basin and to search for possible young lunar volcanic activity, which would help to constrain our knowledge of the Moon’s thermal evolution. Three sites were considered in the final phase of the landing site selection. As on Apollo 16, a landing in Alphonsus Crater was considered to collect highland crust samples from the crater rim and possible volcanic material from a dark halo crater, which was interpreted as a pyroclastic (explosive) volcanic eruption. However, there was concern that the ancient lunar crust was covered by younger deposits, making it inaccessible to the astronauts, so the site was rejected. At Gassendi Crater, the lunar highland crust would have been sampled in the crater’s central peak, but the terrain near the landing site is quite rough and there was no known young volcanic activity near the landing site. Taurus-Littrow is a narrow valley on the eastern rim of the Serenitatis impact basin. Samples of the massifs on the north and south sides of the valley would provide access to highland crustal rocks and observations by Apollo 15 astronaut Al Worden were interpreted as indicating the possible presence of young volcanic cinder cones in the center of the valley. Apollo 15 orbital photography also demonstrated that Taurus-Littrow would be a safe landing site, leading to its selection as the Apollo 17 landing site.
Commander Eugene Cernan and Lunar Module Pilot Harrison “Jack” Schmitt landed the lunar module Challenger on December 11, about 240 meters from the pre-planned landing site, while Command Module Pilot Ron Evans remained in orbit in the command module America. Schmitt had a Ph.D. in geology from Harvard and was the first geologist to walk on the Moon. Cernan and Schmitt spent a total of 75 hours on the Moon and performed three extra-vehicular activities (EVAs, or “moonwalks”), totaling 22 hours and 4 minutes. Both the total EVA time and the total time on the lunar surface were the longest of the Apollo program. The first EVA began just 4 hours after landing and lasted for 7 hours and 12 minutes. The crew began by deploying the Lunar Rover and then set up the Apollo Lunar Surface Experiment Package (ALSEP) 180 meters west of the lunar module. The Heat Flow Experiment was repeated from several previous missions, but most of the experiments were flown for the first time on Apollo 17, including a mass spectrometer to measure the composition of the tenuous lunar atmosphere, an experiment to measure the size and velocity of micrometeorites striking the Moon, and an attempt to measure gravity waves predicted by the General Theory of Relativity. They then made a short 3.3 km round trip drive to Station 1 near Steno crater, south of the landing site, to sample basalts in the central part of the Taurus-Littrow valley. On all three EVAs, the crew measured how the strength of the Moon’s gravity varied with location and deployed eight small explosive charges as part of the Lunar Seismic Profiling Experiment. The explosives were activated after the crew left the Moon, and both experiments provided data on the structure of the crust across the valley floor.
Left: Orange volcanic soil collected at Shorty crater. Right: The rough ejecta blanket at Camelot crater.
The second EVA was the longest of the Apollo program both by duration, 7 hours and 37 minutes, and by traverse distance, 20.4 km roundtrip, reaching a maximum distance of 7.6 km from the Lunar Module at Station 2. It was likely also the most complex EVA of Apollo based on the diversity of the geologic targets. Cernan and Schmitt began by repairing the right rear fender of the rover using laminated maps and small clamps. The fender had been damaged when snagged by a rock hammer during EVA 1. The repair substantially reduced the amount of dust that the rover kicked up while driving. Stations 2 and 3 were on a landslide at the base of the South Massif. The mountains surrounding the landing site were uplifted by the impact that formed the Serenitatis impact basin, and the boulders on the landslide gave the crew to access to material that had originally been located far up the South Massif slope. Stations 4 and 5 were on the valley floor while returning to the Lunar Module. Shorty Crater (Station 4) was suspected prior to the mission to be a possible volcanic vent due to the dark halo surrounding the crater. Schmitt discovered orange soil, which turned out to be 3.6 billion-year-old pyroclastic glass from an ancient volcanic eruption. Camelot Crater (Station 5) is 600 meters in diameter with a very rocky rim. The ejecta at the edge of the crater provided samples of basalt that was originally more than 100 meters below the valley floor.
Left: Jack Schmitt collecting samples at the large Station 6 boulder. Right: Schmitt collecting small rock fragments using the lunar rake.
On the third EVA, lasting 7 hours and 15 minutes, Cernan and Schmitt made a 12.0 km roundtrip drive, making three stops along the North Massif and the Sculptured Hills, northeast of the landing site. At the first stop, Station 6, they reached an elevation of about 80 meters above the plains where they landed. Although the rover handled the climb easily, the crew found it difficult to work on the steep 20° slope on the flank of the North Massif. The large boulder at Station 6 was split into several pieces totaling 25 meters across. It had a track that showed it had originated about one-third of the way up the North Massif and rolled 500 meters down slope, allowing the crew to sample material from high above the valley floor that they could not have otherwise reached. The boulder is a complex, vesicular breccia, varying in composition from one end of the boulder to the other. Additional boulder samples were obtained at Station 7 further east along the base of the North Massif and at Station 8, at the base of the Sculptured Hills. Finally, Station 9 was at Van Serg Crater on the valley floor. Pre-mission, Van Serg was thought to be a possible volcanic vent, but it turned out to be an impact crater with a very rocky rim. During the three EVAs combined, Cernan and Schmitt collected 110.5 kilograms of lunar samples. They drove the lunar rover for a total distance of 35.7 km.
During the Moon landing, Evans remained in lunar orbit in the command module. He operated a set of orbital experiments that were carried in the service module. As on Apollos 15 and 16, these included high-resolution mapping cameras and a laser altimeter, but there were also several new experiments. The Lunar Sounder Experiment was a subsurface sounding radar that imaged structures in the lunar crust more than a kilometer below the lunar surface. The Ultraviolet Spectrometer Experiment measured the composition of the lunar atmosphere and the Infrared Radiometer Experiment measured how the temperature of the lunar surface changed during the lunar day and night. Evans also made visual observations of the lunar surface, guided by detailed cue cards created prior to launch. Apollo 17 spent a total of 6 days and 3 hours in lunar orbit, circling the Moon 75 times. While on the return voyage to Earth, Evans made a 1 hour and 6-minute spacewalk to collect the film cassettes from the mapping cameras and the sounding radar, which were located in the Scientific Instrument Module, which was part of the spacecraft’s Service Module. The crew landed in the Pacific Ocean on December 19 after a flight of 12 days and 13 hours.