The Lunar Module: How NASA Learned to Land on the Moon

On July 20, 1969, the world watched in awe as astronaut Neil Armstrong stepped onto the surface of the Moon and spoke the immortal words: "That's one small step for man, one giant leap for mankind." This historic moment was the culmination of an 8-year effort to realize President John F. Kennedy's goal of landing a man on the Moon and returning him safely to Earth by the end of the decade.

But the road from Earth to the Moon was far from smooth. NASA faced numerous hurdles and setbacks, including the tragic deaths of the Apollo 1 crew in a launchpad fire and ongoing problems with the Saturn V rocket's F-1 engines. Perhaps the greatest challenge, however, was deciding how to actually land on the Moon.

Early Concepts: Direct Ascent and Earth Orbit Rendezvous

When President Kennedy announced Project Apollo in May 1961, NASA engineers had already been studying methods for manned lunar flights for several years. Initially, two main approaches were considered:

Direct Ascent

This was the simplest approach, involving launching one big spacecraft directly to the Moon, landing the whole thing on the surface, lifting off again, and returning to Earth. This was the approach seen in most science fiction media up to that point.

However, direct ascent had major drawbacks:

• It required an extremely heavy spacecraft (estimated at 90 metric tons)
• This in turn necessitated an enormous "Nova" rocket, even larger than the Saturn V
• The Nova rocket was deemed unfeasible to develop by the end of the 1960s
• There were concerns about the stability of the lunar surface for launching such a large vehicle

Earth Orbit Rendezvous (EOR)

Proposed by Wernher von Braun, this approach involved:

• Launching the lunar spacecraft in pieces using multiple smaller Saturn rockets
• Assembling the spacecraft in Earth orbit before departing for the Moon

While eliminating the need for the Nova rocket, EOR had its own issues:

• It required perfecting orbital rendezvous and docking techniques
• Multiple launches increased overall mission risk
• Cryogenic propellants could potentially boil away during assembly
• It still faced the challenge of landing a massive spacecraft on the Moon

The Third Option: Lunar Orbit Rendezvous

As the debate raged between direct ascent and EOR, a third possibility began quietly circulating among NASA engineers: Lunar Orbit Rendezvous (LOR).

First proposed by the Chance Vought company in 1960, LOR challenged the primary assumption that the entire spacecraft had to land on and take off from the lunar surface. Instead, it proposed:

• Constructing a lightweight landing vehicle
• Using this vehicle to descend to the lunar surface
• Leaving the main spacecraft in lunar orbit
• After the mission, lifting off in the lander to rendezvous with the orbiting spacecraft
• Discarding the lander before returning home

This approach had several advantages:

• The lander could be much lighter, not needing to withstand launch and reentry
• This reduced the overall mass of the spacecraft
• A smaller rocket could be used to launch the entire mission

John Houbolt: Champion of LOR

The hero of the LOR story was NASA Langley engineer John C. Houbolt. Born in Altoona, Iowa, Houbolt joined NASA's predecessor NACA in 1942, eventually becoming chief of the Theoretical Mechanics Division in 1962.

Houbolt and his research group quickly latched onto the LOR concept, calculating it would be the most efficient approach and the only one capable of meeting Kennedy's end-of-decade deadline. However, they faced stiff resistance from the entrenched direct ascent and EOR camps.

Undeterred, Houbolt took the extraordinary step of writing directly to NASA Associate Administrator Robert Seamans in November 1961, violating protocol and risking his career. In his now-legendary letter, Houbolt passionately argued for LOR, challenging NASA's "arbitrarily set up ground rules" and demonstrating its inherent advantages.

Despite initial skepticism, Seamans was swayed by Houbolt's arguments. Resistance to the plan began to crumble as further analyses revealed the risks of lunar orbit rendezvous to be much lower than previously assumed. In July 1962, NASA officially announced LOR as the chosen mission profile for Project Apollo.

Designing the Lunar Module

On July 25, 1962, NASA invited aerospace contractors to bid on the contract for the Lunar Excursion Module (LEM). Grumman Aerospace Corporation of Bethpage, New York was selected as the prime contractor.

Designing the LEM (later renamed simply Lunar Module or LM) posed numerous challenges:

• No spacecraft had yet landed on the Moon or even taken high-resolution pictures of its surface
• The lunar surface conditions were unknown
• The vehicle had to be extremely lightweight yet capable of landing two astronauts and returning them to orbit
• All this had to be accomplished using a vehicle light enough to be launched to the Moon by a single Saturn V rocket

The Grumman engineers settled on a strange, insect-shaped vehicle comprising two main sections:

• A lower descent module with legs and a rocket engine for landing
• An upper ascent stage containing the pressurized crew cabin

Numerous clever design decisions were made to reduce weight:

• The astronauts would land standing up, secured by cables, eliminating the need for heavy seats
• This allowed for smaller, lighter windows while preserving visibility
• A new lightweight metal-coated Mylar plastic film was used for thermal protection
• The vehicle was constructed from flat panels closely faired around internal components, rather than smooth rounded surfaces
• Each body panel was only as thick as absolutely necessary, some being only a few layers of tin foil thick

Other unique features included:

• Four landing legs with crushable honeycomb shock absorbers
• A square hatch to accommodate the astronauts' backpacks
• Hypergolic propellants (igniting on contact) eliminating the need for an ignition system
• A one-shot ascent engine that could only be fired once before needing rebuilding

Testing and Refining the Lunar Module

To train astronauts in flying the LM, NASA contracted Bell Aerospace to construct the Lunar Landing Training Vehicle (LLTV). This strange, spider-like aircraft used a downward-facing jet engine and hydrogen peroxide thrusters to replicate the LM's handling on Earth.

The first unmanned test of the LM took place on January 22, 1968, during the Apollo 5 mission. Despite some issues, the mission successfully demonstrated the LM's key systems.

The first manned test came with Apollo 9 in March 1969. Crewed by James McDivitt, David Scott, and Russell Schweickart, the mission proved out the LM design and achieved several spaceflight firsts, including:

• The first docking and extraction of an LM from its adapter
• The first independent flight of a spacecraft designed only for use in space
• The first test of the astronauts' Portable Life Support System (PLSS) backpacks
• The first manned "fire-in-the-hole" test of the LM ascent stage

Apollo 10, flown in May 1969, served as the final dress rehearsal, with astronauts Thomas Stafford and Eugene Cernan bringing the LM within 15.6 km of the lunar surface before returning to orbit.

The Eagle Has Landed

Finally, on July 20, 1969, Apollo 11 astronauts Neil Armstrong and Edwin "Buzz" Aldrin piloted the LM "Eagle" to the first manned landing on the Moon. Despite some tense moments, including computer alarms and the need to manually fly over a boulder field, Armstrong and Aldrin touched down safely with only seconds of fuel remaining.

The strange-looking Grumman Lunar Module had proven itself a solid and reliable flying machine. It would go on to land five more times on the Moon, suffering only a handful of relatively minor issues throughout its career.

Perhaps its finest hour came during the ill-fated Apollo 13 mission in April 1970. When an oxygen tank explosion crippled the Command and Service Module, the LM "Aquarius" served as a lifeboat, keeping astronauts Jim Lovell, Fred Haise, and Jack Swigert alive for their harrowing four-day journey around the Moon and back to Earth.

Legacy of the Lunar Module

In total, 15 Lunar Modules were manufactured, with 10 flown operationally. The LM's success paved the way for more ambitious plans, including long-duration lunar stays and even small moon bases. While most of these advanced concepts were cancelled due to budget cuts, elements of LM technology found their way into later projects like the Skylab space station.

Today, three original production LMs are on display in museums, serving as enduring reminders of one of humanity's greatest technological achievements. The Lunar Module stands as a testament to human ingenuity, perseverance, and the power of unconventional thinking in solving seemingly insurmountable challenges.

As we look to return to the Moon and push on to Mars, the lessons learned from the development of the Lunar Module continue to inform and inspire new generations of spacecraft designers and engineers. The LM's legacy lives on in every vehicle designed to land humans on other worlds, a bridge between our first tentative steps beyond Earth and our future as a spacefaring civilization.

Article created from: https://www.youtube.com/watch?v=G2-S5ExqaSA