Apollo Landing Sites

Historic Milestone: First human landing on another world. During the final descent, the lunar module’s guidance computer triggered a series of 1202 and 1201 program alarms caused by an overloaded data stream, requiring Mission Control to quickly determine the alarms were non-critical and approve the landing to continue. With the autopilot steering toward a boulder-strewn crater, Armstrong took semi-manual control and flew Eagle further downrange to a clearer patch of Mare Tranquillitatis, touching down with roughly 25 seconds of descent fuel remaining. Armstrong collected the “contingency sample” of lunar soil within minutes of stepping onto the surface, a safeguard in case the mission had to be cut short. The crew deployed the Early Apollo Scientific Experiments Package (EASEP), including a Passive Seismic Experiment and the Laser Ranging Retroreflector, which is still used by observatories on Earth today, and planted a specially rigged flag with a horizontal support rod to make it appear to “fly” in the airless environment. Aldrin and Armstrong spent 2 hours and 31 minutes outside before lifting off to rejoin Michael Collins in Columbia; the crew later spent 21 days in a Mobile Quarantine Facility as a precaution against unknown lunar contaminants.

Precision Landing: The Saturn V was struck by lightning twice within the first minute of launch, briefly knocking out telemetry and fuel cell power before engineer John Aaron’s quick call to switch a little-used instrumentation setting restored the data stream. Once in lunar orbit, Pete Conrad guided Intrepid to a pinpoint touchdown within about 160 meters of the unmanned Surveyor 3 probe, which had soft-landed on the Moon two and a half years earlier. Conrad and Bean walked over during their second EVA and cut pieces from Surveyor 3, including its TV camera, to bring home for engineers to study the long-term effects of space radiation and micrometeorite exposure on hardware. The mission also carried the first Apollo Lunar Surface Experiments Package (ALSEP), a suite of nuclear-powered instruments left behind to monitor seismic activity, solar wind, and the Moon’s thin atmosphere long after the crew departed. A mishap early in the first EVA, when Bean accidentally pointed the color television camera at the Sun and burned out its sensor, cut off the live broadcast for the rest of the surface stay.

Geology Focus: Alan Shepard, the first American in space back in 1961, became the fifth and oldest person to walk on the Moon at age 47 after a decade grounded by an inner-ear disorder. The mission nearly aborted in transit when the command and lunar modules struggled to dock, requiring five attempts before the probe finally latched, and a false “abort” signal from a faulty switch inside the lunar module forced ground controllers to devise an improvised software patch that Mitchell keyed in manually before descent. On the surface, Shepard and Mitchell targeted the Fra Mauro highlands, a region of rubble ejected by the ancient impact that formed the Imbrium Basin, hauling their tools on the Modular Equipment Transporter (MET), a two-wheeled cart nicknamed the “lunar rickshaw.” Among the 42 kg of samples was “Big Bertha,” a 9 kg breccia later proposed to contain a fragment that some researchers believe may have originated on Earth after an ancient impact. Before liftoff, Shepard used a modified sample-return tool to strike two golf balls one-handed in his pressurized suit, while Stuart Roosa, orbiting above in Kitty Hawk, carried several hundred tree seeds that were later germinated on Earth as the “Moon Trees.”

First J-Mission: Apollo 15 inaugurated the more ambitious “J-missions,” featuring longer stays on the lunar surface, expanded scientific objectives, upgraded spacesuits with improved mobility and life support for EVAs of up to seven hours, and the debut of the battery-powered Lunar Roving Vehicle, which let Scott and Irwin range far beyond walking distance from the lander. The crew set down on a relatively flat plain at the base of the Apennine mountain front, alongside Hadley Rille, a sinuous, roughly 1,200-meter-deep lunar valley thought to be a collapsed lava tube or ancient channel. During their second EVA, the astronauts collected a whitish, crystalline sample later dubbed the “Genesis Rock,” an anorthosite believed to be part of the Moon’s original crust and dated to about 4.1 billion years old, offering evidence for how the Moon differentiated into crust and mantle shortly after its formation. Near the end of the final EVA, Scott famously dropped a geologic hammer and a falcon feather simultaneously to demonstrate, live on camera, that in the Moon’s airless environment both fall at the same rate, confirming a thought experiment attributed to Galileo. The mission was later overshadowed by the “postal covers” controversy, after the crew carried unauthorized stamped envelopes to the surface, some of which were sold commercially, prompting a NASA investigation and reprimand.

Highland Mystery: Apollo 16 targeted the Descartes Highlands specifically because scientists expected to find evidence of ancient lunar volcanism there, a hypothesis that the mission’s rock samples ultimately overturned by showing the terrain was instead built from impact breccias, debris fused together by asteroid strikes rather than lava flows. The landing itself was nearly scrubbed in lunar orbit after a backup steering system on the command module’s main engine began oscillating, forcing NASA to delay the descent by about six hours while engineers on the ground worked out that it was safe to proceed. On the surface, Young and Duke drove the lunar rover up the slopes of Stone Mountain and Smoky Mountain, at one point setting an unofficial lunar land-speed record of approximately 18 km/h (11 mph) during a rover “grand prix” test filmed for engineers back on Earth. Among their haul was “Big Muley,” a 11.7 kg breccia and the largest single rock ever returned from the Moon, named after mission geologist William Muehlberger. Young, the mission commander, would go on to command the first Space Shuttle flight nine years later.

The Scientist: Apollo 17 closed out the program with the only nighttime launch of a Saturn V, lighting up the Florida coast before dawn on December 7, 1972. Harrison Schmitt, a trained field geologist who had originally been slated for a later canceled mission, became the only professional geologist to walk on the Moon after being reassigned to the crew in place of a test pilot, over objections from some at NASA who favored an all-astronaut lineup. During the second EVA at Shorty Crater, Schmitt spotted strikingly orange soil, which analysis later confirmed to be tiny beads of volcanic glass, the frozen remnants of a fire-fountain eruption roughly 3.5 billion years ago, giving scientists a rare direct sample of the Moon’s early volcanic activity. Commander Eugene Cernan endured a minor scare during one EVA when a torn fender on the lunar rover kicked up dust before being repaired with lunar maps and clamps improvised on the spot. Across three EVAs, Cernan and Schmitt covered more ground, spent more time on the surface, and returned more lunar material than any prior mission, and Cernan’s final steps off the ladder made him, to date, the last person to walk on the Moon.