On July 20, 1969 Neil Armstrong and Buzz Aldrin executed a harrowing landing to the Lunar Surface. When the images were beamed back to Earth people marveled at… well a field of rocks really. 400km (250 miles) away, there was an object of interest humans wouldn’t discover until 2009: an exposed lava tube over 140 meters (459 ft.) in diameter. It might sound like a long way away, but had the course of Apollo 11 spacecraft been adjusted ever so slightly the Apollo program itself could have taken a very different course.

July 20th, 1969, Neil Armstrong’s hand twitches slightly during Lunar insertion, causing the Lunar Excursion Module (LEM) to pass over an exposed lava tube during descent. Recognizing the scientific opportunity, the Eagle touches down roughly 900 meters from the exposed crater. At approximately 100 meters wide at the surface and no clear way to safely explore the crater, the astronauts are only able to take images of the pit from the surface and during flight. These images compel NASA to change the parameters of future missions to the moon.

Apollo 15 is to be the first mission to explore what the press has dubbed “Neil’s Pit.” Harrison Schmitt is moved up from the backup crew of Apollo 15 to become the first geologist on the moon, replacing James Irwin as Lunar Model pilot. On July 30, 1971, Apollo 15 touched down north of Apollo 11’s landing site just under 5km (3.1 miles) to the rim of the pit. With the help of the Lunar Roving Vehicle (LRV), Astronauts Scott and Schmitt assembled a small wench and cage at the edge of the Pit over the course of two days. On August 2, 1971. Scott lowered Schmitt 70m into Neil’s Pit. Schmitt conducted 3 expeditions, returning with rocks and gathering data via the Lunar Surface Experiments Package. More importantly, on his final expedition, Schmitt discovered the opening of an expansive cave system. With limited supplies, the Apollo 15 crew were forced to leave the exploration of the caves for future teams.

The success of Apollo 15, both in terms of science and raising public enthusiasm for the program, gives NASA the confidence to schedule 3 more missions to the Pit with Apollos 17, 18, and 19, with the backing of Congress and the Nixon administration. All three missions reuse or expand Apollo 15’s wench and include professional geologists. In December of 1973, the crew of Apollo 19 ventures further into the lunar cave system than any prior mission using an additional buggy lowered into the Pit and assembled by the crew of Apollo 18. The Apollo 19 expedition covers 7km underground and uncovers a chamber 1.2km wide at its greatest extent. The footage from these missions and scientific data is enough for Congress to greenlight 5 more Apollo missions and the construction of a base inside Neil’s Pit.

Apollo 20 is the first mission since Apollo 13 to not attempt a crewed landing, instead landing the LM Truck and 5000kg of equipment for Apollo 21. The truck is remotely piloted to 100 meters from the Pit by Apollo 20s command and service module (CSM) where it will wait for the crew of Apollo 21 to make use of its resources.

While billed as the first steps toward a permanent human presence on the moon, Apollo 21 is really more of a housekeeping mission. Two astronauts lowered Apollo 15’s LRV to aid in towing the LM Truck deeper into the cave system in anticipation for the first component of the Lunar Surface Base (LSB). In addition, the moon buggies were used help build the first road and landing pad on the moon, hauling away regolith from the mound in the center of the pit one bucketload at a time.

Apollo 22 delivers the LSB into the Pit without a hitch. The LSB is a permanent structure designed to sleep 3 astronauts for extended duration missions. Radiation hardening is minimal, as the LSB is to be towed deeper into the lava tube which provides natural protection from radiation.

Apollo 23 marks the first extended mission to the lunar surface, and the first use of an autonomous CM, allowing 3 astronauts to land in an, albeit cramped, LM Taxi for a 28 day stay in the LSB. Apollo 23 also sees Harrison Schmitt’s return to the moon, making him the first astronaut to get two missions to the lunar surface. With his own experience, and data from successive missions, Schmitt is able to identify and secure some of the most valuable samples within the Tranquility Cave System, providing scientists with a trove of data on the composition and origins of the moon.

Apollo 23 and 24 see missions of 58 and 88 days respectively, with Apollo 24 being the last mission to the moon. The crew of Apollo 24 returns to Earth on February 8, 1975, marking the end of the Apollo program. During the final 3 missions to the moon, astronauts conducted extended studies of the lunar surface and subsurface, driving over 25 miles of ground. The Apollo missions would provide invaluable scientific data on the origins of the moon, methods for long term space missions, and spinoff technologies that would benefit people on Earth for generations. Unfortunately, the public simply didn’t see the benefits of continued exploration, especially as the Soviets abandoned their own effort for a crewed lunar landing. While the images from Neil’s Pit and its cave system were striking, and motivated the public to endorse several more missions to the moon, the novelty had worn off by the early 1970s. There were even those at NASA who opposed the building of the LSB as it came at the expense of the planned Skylab space station.

Post-Apollo proposals for a Space Shuttle and Mars mission were scrapped in favor of the Apollo Applications Program’s upgrades to the Saturn family of rockets and the Apollo spacecraft. NASA would rely on successive improvements to the Apollo CSM and Saturn IB launch vehicle, along with derivations made to the LM family of spacecraft. The most common of these was the LM Spacelab with which astronauts could conduct longer duration missions to orbit and carry out scientific experiments. Crewed launches were kept to a minimum for the rest of the 1970s and into the 1980s, as NASA was limited to more austere scientific missions. Saturn V rockets and their derivations came to be used mostly by the Air Force for delivering NRO satellites to orbit with their own corps of astronauts. It wasn’t until the election of John Glenn in 1980 that NASA got a new mandate.

The Glenn administration sought to radically expand missions to space through the construction of a permanent orbital station by 1990 using Saturn V-derived modules. The program required NASA to make several improvements to the Saturn-series of launch vehicles, including a recoverable first stage and an expanded Apollo CSM capable of carrying up to 10 astronauts. Unfortunately, the Space Station Liberty program was cancelled after multiple cost overruns, but only after NASA and Rockwell began production of recoverable and reusable spacecraft. The 1990s would see a boom in commercial space programs enabled by falling launch costs via by these new reusable launch vehicles.

No humans would step on the lunar surface until November 1998 with the launch of the International Lunar Base (ILB). Developed from technologies originally designed for Space Station Liberty, the ILB would use the LSB as its core module and expand over the next 12 years into the largest space-based research lab in history, playing host to astronauts from 42 countries. Thanks to the fairly stable conditions in the shadow of Neil’s Pit, LSB and ILB modules don’t experience thermal shock or even significant torsion as would a space station, and the base remained shelter from radiation. Unlike the Apollo era, astronauts at the ILB were not limited to how far they could walk or even drive over the lunar surface. By 2000, a Canadian-built Lunar Flying Vehicle allowed astronauts to take off from the Pit’s landing pad and land with small experiment packages further away from the ILB.

By the new millennium the Defense Department was working with NASA to foster greater technology transfer to the private sector. Bids were made for a new class of launch vehicle that could supplement the Saturn series for LEO and GEO flights. Multiple contractors emerged over the decade, fueled by investor capital from the tech sector and government contracts. These new vehicles were initially smaller than the Saturn IB, but were cheaper, had superior avionics, and like their Saturn, Soyuz, and Ariane competitors, partially reusable. By the middle of the decade the first of these new contractors produced a booster with propulsive landing, allowing for launch and recovery operations at less developed spaceports.

By 2009 a cadre of new launch providers were beginning to out compete the giant of Rockwell-Grumman for smaller launch contracts, particularly for NASA’s Commercial Lunar Flight Services (CLFS or “Cliffs”) program. Sometimes called the Lunar Railroad, these small spacecraft formed a near continuous flow of payloads to lunar orbit. Initially made up of imaging and communications satellites that greatly enhanced the international space community’s operations on the Lunar Surface, by 2014 flights included scientific packages bound for the lunar surface aboard small autonomous landers. Most of these flights were missions to Neil’s Pit and the ILB, but NASA and a growing number of universities and private contractors also commissioned flights to other areas of interest on the lunar surface. NASA’s Lunar Flyer Logistics Extension (LFLE) program, produced a lander capable of hauling fuel and oxygen that the astronauts flying the LFV could use to extend their missions away from the ILB.

By the 2020s, geopolitics has created a complication with the ILB program. The Russians made themselves a pariah state following their invasion of Belarus and its fledgling democracy. The other partners in the ILB are under increasing pressure to reduce access to the Russians, while the Russians themselves are threatening to pull out of the program and construct their own base at a site near Shackleton Crater. NASA is also under greater scrutiny as its long planned Mars Transport System (MTS) rocket is overbudget and years behind schedule, having only executed a single uncrewed test flight to Mars in 2018. The MTS program is seen by members of Congress and the general public as a Cost-Plus gift to Rockwell-Grumman, which now faces growing competition from a new generation of crewed systems capable of reaching the lunar surface.