Lunar Excursion Module (LEM) – Explorer of the unknown

The Lunar Excursion Module (LEM), also known as the Apollo Lunar Module (LM), was a crucial component of the Apollo program. The design and construction of the LEM was carried out under the direction of the Grumman aerospace company between 1962 and 1969, to land astronauts on the Moon. The LEM was designed to transport two crew members from the Command and Service Module (CSM) in lunar orbit to the surface of the Moon and back.

A challenge to the unknown

The design of the LEM was a significant engineering challenge, as it had to be able to resist the critical environment of space and the Moon’s surface while also being light enough to be launched from Earth. Moreover, because the engineers didn’t have any data on the lunar surface, they had to be ready for anything.

On November 7, 1962, Grumman Aircraft Engineering Corporation was awarded the project, and construction began. The final design of the LEM consisted of two parts: the descent stage and the ascent stage.

Fall like a feather!

The descent stage was the lower section of the LEM and was responsible for landing the spacecraft on the Moon’s surface. The module, which had a total mass of 10,000 – 11,000 kg (22,046 pounds), contained the engines, fuel, and other equipment needed for landing and surface operations. The entire stage was covered with a thin gold-colored film called Kapton, a special thermal insulating material capable of remaining stable in a wide range of temperatures, from -269 °C to +400 °C. It also covered the body of the descent stage and the 4 legs. 

To land on lunar soil, the descent stage had a landing gear consisting of a trellis structure to which 4 telescopic legs were fixed. Fun fact, the LEM traveled with the “landing gear” folded; upon landing, the pilot deployed them using the explosion of small charges placed on the fuselage. The descent stage also provided a stable platform for the ascent stage to launch from when the mission was complete.

Fly like an eagle!

The ascent stage was the upper section of the LEM and was used to return the astronauts to the CSM in lunar orbit. It weighs about 4.5 tons (9.920 pounds). Its complex shape is asymmetrical for reasons of optimization of the interior space. It contained the crew compartment, and life support systems, called Environmental Control Subsystem (ECS), that provided liveable conditions for the two astronauts when the LEM was separated from the CSM and the ascent engine. 

During lift-off, the engine thrust was constant. Since the engine nozzle was fixed, the trajectory could not be adjusted, and the corrections were made by the maneuvering motors of the Reaction control system (RCS). They were located at each corner of the module, and their combined actions allowed the module to be maneuvered very precisely. The ascent stage also had a docking port, which allowed it to connect to the CSM for the journey back to Earth.

The incredible flying power

One of the key features of the LEM was its ability to be piloted manually by the astronauts, giving them greater control and flexibility during the landing process. The navigation system was a true engineering jewel, based on an inertial guidance system, and it allowed to carry out all the maneuvers even when communications with the Earth were cut off, as expected when the spacecraft was behind the Moon. This was particularly important as the LEM had to navigate over rough terrain and avoid obstacles such as large boulders and craters.

From theory to practice, new car smell

Finally, on January 22, 1968, 9 months late on the scheduled date, the LEM was tested for the first time during the Apollo 5 mission. The LEM made its first manned flight during the Apollo 9 mission in March 1969, when all mission maneuvers were tested in Earth orbit.

The first successful manned lunar landing was achieved during the Apollo 11 mission in July 1969, when astronauts Neil Armstrong and Edwin “Buzz” Aldrin became the first humans to set foot on the Moon. The LEM was used in a total of six manned lunar landings between 1969 and 1972.

How to accomplish a task you are not designed for

The LEM was also the protagonist of one of the scariest accidents in the history of the Apollo missions. On the journey to the Moon of Apollo 13, a fuel cell exploded in the CMS service module, destroying part of it. To save themselves, since the CMS was now unusable, the crew took refuge in the lunar module, activating it and using it as a lifeboat. The LEM’s descent motor was fired several times to correct the course.

In the iconic episode of the adaptation of the CO2 filters, when carbon dioxide levels were getting critical, air filters had to be changed. The astronauts were forced to place the CMS filters (square-shaped) on the circular slots of the LEM ones; everything worked beautifully.

Face the challenges

The design and development of the LEM represented a significant achievement in engineering and technology, and it remains an iconic symbol of the Apollo program and the space race. The success of the LEM and the Apollo program demonstrated the power of human ingenuity and innovation. Also, to develop something to challenge the unknown of which, scientists and engineers had very little data available.

Today, the legacy of the LEM lives on in the ongoing efforts to explore the Moon and other celestial bodies. The development of new technologies and spacecraft, such as the Orion capsule for NASA’s Artemis program, is building on the achievements of the Apollo program and paving the way for future manned missions to the Moon and beyond.