Landing Craft

Apollo 11’s Lunar Module “Eagle” as it prepares to land on the moon.

Paper-thin walls that would crumple if the craft were flown in Earth’s atmosphere. Standing room only. Two tiny windows that bulge outward from the air pressure inside. Two humans, flying across a heavenly body not their own. A flying machine unlike any other Grumman Corporation has built. Called the Lunar Module, it’s what got men like Neil Armstrong, Buzz Aldrin, Alan Shepard, Pete Conrad and eight other men from their spacecraft to the surface of the moon.

May 22, 1969 marked the maiden flight for the Lunar Module in space. Tom Stafford and Gene Cernan stood inside, their feet velcroed to the floor, and flew this unusual “air”craft down into lunar orbit. They didn’t land; their mission profile called for them to only orbit the moon within 8 miles of its surface. In fact, knowing how competitive their astronauts could be, NASA only loaded enough fuel for this mission. Had Stafford and Cernan jumped the gun and landed on the moon on Apollo 10, they would have been stranded on the lunar surface.

The Lunar Module, or LM, had been developed in parallel with the command and service modules. In fact, the first iteration of the LM looked like the Command Module with legs. However, as the design progressed and as weight became a driving factor for its design, the LM transformed into the 14-foot “diameter” octoganal craft that we recognize today.

Covered in gold Mylar, which protected the structure from the temperature extremes of space and micrometeors, were the fuel tanks and several stowage spaces. Accessible from the surface, the stowage spaces carried flags, cameras, scientific experiments, and the lunar rover.

Surrounded by the tanks and stowage spaces was the main engine. The main descent engine was the first throttle-able rocket engine designed purely for space flight. It gave the LM driver very good control over thrust so that he could land safely on the moon’s surface. It gimbaled, was well, to allow it to automatically compensate for the changing center of gravity of the LM as fuel burned off. Two companies were requested to design prototypes for Grumman. Rocketdyne used helium injection to throttle the rocket, while Space Technology Laboratories used a mechanical throttle to vary the amount of fuel reaching the rocket motor. STL’s design was chosen.

The hypergolic fuels were so corrosive that an engine would degrade in just 40 days after being exposed to the fuel and oxidizer. Grumman engineers, who were more used to designing aircraft than spacecraft, had trouble fathoming the idea that the actual flight engines could not be tested before flight. Even though similar engines were tested on rocket test stands at Stennis, the first time the engines on the LM would light was 240,000 miles from home. They had to be robust.

The reaction control system consisted of 16 small rocket motors that would fire in response to the commands from the pilot. As he manipulated the controls, a small rocket on the opposite direction of where he wanted to go would fire, pushing the spacecraft in the direction the pilot desired.

When it was time to leave the moon, the ascent engine would fire and the Ascent Stage of the LM would separate from the legs, descent tanks, and stowage compartments. The ascent engine, like the descent engine, had no backup. Bell Aerosystems designed a rocket engine with only 4 moving parts. There were no igniters – the fuel self-ignited in the vacuum of space – and no pumps – compressed helium forced the fuel into the rocket motor. However, the engine proved to be susceptible to certain types of combustion instability. For 2 years, Bell and NASA engineers tried everything they could to dampen the instability to no avail. Finally, in 1967, with only months to go before the LM’s first spaceflight, Rocketdyne was asked to develop an ascent motor. Their design featured a different injector system that eliminated the combustion instability issue, but other aspects of the new motor were deemed subpar compared to the Bell design. As a last minute fix, the Rocketdyne injectors were fitted to the Bell motor and an extremely simple and reliable rocket was born.

The Lunar Module, with two computers and two humans, proved to be extremely reliable. We never stranded a man on the moon.

[Image Credit: NASA]

  • skitter

    Amazing article. I'm too used to thinking of everything NASA does as being tested down to infinitesimal detail, with triple redundancy. I remain convinced that no amount of calculation and no number of eyes on the process can replace testing and iteration.

  • OA5599

    I was searching through some old emails for a discussion I had with someone regarding a person world-famous for his involvement in the Apollo program. In searching his name, I was astonished to learn that one of the matches was not because of the body of the email, but because this historical figure's name and mine were both on the To: line of the same message.

    While I at first felt a bit honored that, at least to the email's sender, I was on equal footing with this decorated hero, I do admit to feeling a bit disappointed that an aerospace genius was using an address.

    • chrystlubitshi

      I spent a lot of time trying to come up with a "cool/smooth" vanishing point reference…. no luck… continue on