The most incredible spacecraft ever constructed was something that no one would ever see again after its mission was over.

While the Apollo Command Module testing began to ramp up for its first manned orbital flights, Grumman’s efforts with the Lunar Module were less than stellar. Reflecting challenges in developing the Command Module by its prime contractor, North American Aviation, Grumman’s experience base with spacecraft construction, as well as their comparatively late start in 1963 (Command Module development began as early as 1960) made developing processes for testing and construction slower. Grumman’s spacecraft was particularly special. It had to be as lightweight as possible and, as it would fly only in space, its shape was defined by various needs, some still unforeseen, for a lunar lander.

Construction and testing of the first four Lunar Modules had fallen behind. NASA and Grumman realized that a centralized management of the LM development was unclear. As Grumman fell farther beyond, NASA realized that Grumman lacked a deeper understanding and planning for the development and use of ground support equipment needed to check the many LM subsystems to qualify them for use. NASA moved in help in the form of supervisors as well as spare equipment used for Gemini to assist.

As the end of 1966 approached, the first two LMs were built and in test stands, although the overall production rate for the remaining spacecraft was barely keeping up to NASA’s goal of launching a man to the moon before the end of the decade.

Before astronauts would fly in the Lunar Module, it would fly unmanned and on its own, in earth orbit. Two unmanned test flights, using LM-1 and LM-2, were scheduled to verify the functionality of the spacecraft’s descent and ascent engines, as well as staging of the ascent stage in the event of an abort while descending to the lunar surface–the “fire in the hole” test.

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LM-1, ascent stage. (NASA)

January 1967 arrived but LM-1 was still not ready to fly. Command Module work had progressed sufficiently enough on three unmanned Block I test flights on Saturn I-B rockets to verify flight systems, in particular, how well the heat shielding functioned at high-speed re-entry velocities. As Grumman hurried to complete LM-1 for its test flight on Saturn I-B AS-206, Saturn I-B AS-204 was ramping up ground tests at Launch Pad 34 with its Block I Command/Service Module, spacecraft 012: Apollo 1.

That first manned Apollo test flight in February 1967 never happened, as many of you know. A flash fire engulfed CSM-012’s interior in late January, killing its three astronauts, trapped by the fire’s pressure by a inward-opening hatch.

The fallout from the Fire reverberated not only through the Command Module redesign but forced the already-behind LM development to add in fire and safety standards developed for the Block II Command Modules.

With the loss of Apollo 1, its launch vehicle, Saturn AS-204, stood idle–perhaps a pariah for re-use as a manned launch vehicle. After a verification of its integrity, the first LM flight would move from AS-206 to AS-204. AS-206 would be mothballed for seven years while AS-204 was moved to Launch Pad 37 in preparation for LM-1.

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LM-1, assembled and in preparation for mating to its adapter. (NASA)

With the end of 1966, LM-1 was sufficiently complete for its test flight. One last change was made. One of the later spacecraft in the production line, LM-5, burst one of the crew acrylic windows during a cabin pressurization test. To guard against such a problem with LM-1 for the purposes of the flight test, its windows were replaced with aluminum plates.

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LM-1, inside its SLA, being raised up to AS-204. (NASA)

In addition, LM-1 would not fly with legs, a porch or ladders to save weight and as they were unnecessary for the mission.

Unlike any LM since, the first Lunar Module would be unadorned with mostly unpainted Mylar skin, while later LMs would mix about darker orange mixtures of kapton with Mylar. AS-204 would also fly without a Command/Service Module. The Spacecraft/LM Adapter top would be covered with a nose cone.

Even if NASA wanted to do so, the final weight of the combined Command/Service Module and Lunar Modules required a Saturn V to lift them into orbit or beyond. Despite the plan and design of the Saturn I-B S-IVB-200 stage to carry a LM, anything less than a Saturn V simply hadn’t the lift power.

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The nose cone for Apollo 5 in preparation for installation. (NASA)

After some delays, the mission known as Apollo 5 launched almost a year after the Fire, on January 22, 1968.

Looking on in Mission Control during the flight was the crew originally scheduled to fly the first LM in a dress rehearsal of the landing in lunar orbit: Frank Borman and William Anders.

Liftoff was successful and uneventful. The LM separated from the S-IV-B without problems.

Time was short to complete tests, as the Lunar Module’s battery power was finite as well as its fuel. In orbit, an incorrectly programmed computer would cut LM-1’s initial test burn of the Descent Propulsion System engine short. Reworking the flight plan, Mission Control managed to complete a useful DPS burn as well as the fire-in-the-hole ascent stage burn.

Further delays in completing the LMs for manned tests would change two crews’ destiny. Due to neck surgery, Michael Collins, originally assigned with Borman’s crew, would be bumped to a later mission, with James Lovell taking his place next to his past Gemini 7 crewmate. Frank Borman’s crew would be retasked with the first manned flight of a Saturn V and the first circumlunar adventure, Apollo 8, aboard a lone CSM.

Thankfully, LM production and testing caught up and the first manned LMs made their way to Cape Kennedy. Jim McDivitt’s crew would make history with the first CSM/LM orbital tests as Apollo 9 in early 1969, using LM-3.

LM-1’s successful mission meant that LM-2’s unmanned mission would be unnecessary. As improvements to manned LMs were more important than retro-fitting the automation or weight-savings processes to LM-2, NASA earmarked LM-2 for delivery to the Smithsonian Institution once the vehicle had completed some structural and vibration tests.

LM-1’s ascent stage fell back to earth, destroyed on re-entry only two days after liftoff, on January 24. Its descent stage would follow 19 days later.

After some international touring, LM-2 found its permanent home in the National Air and Space Museum.

On display for years, it was significantly refurbished in 2016 and moved to the central entrance. You can enjoy a high-resolution 360 view of its interior, provided by its curators.