The Lunar Lander
Grumman Aircraft was given the contract to build the lunar lander, now called the Lunar Excursion Module, or LEM. Grumman went through several designs, most of which were too heavy or unsatisfactory from the standpoint of astronaut’s ability to see the lunar surface during descent. Here are a few of the design iterations.
All had one concept in common. The LEM would consist of a descent stage with a big, throttleable engine that would land on the moon, and a smaller ascent stage that would return the two astronauts to the Apollo craft orbiting the moon.
The descent stage was always considered as a circular craft with storage bays for equipment and tools as well as the descent engine and its fuel. It would act as the launch pad for the ascent stage as well.
The final configuration of the ascent stage was dictated by several constraints. One was placement of the fuel and oxidizer tanks in the ascent stage. The LEM of course would use hypergolic fuels. There could be no chance of the fuel not igniting while on the moon, but the oxidizer was heavier than the fuel. To maintain the center of gravity, the fuel tank was placed further outboard than the oxidizer tank. This gave the ascent stage a ‘chipmunk’ like look.
Another design factor was the windows. The astronauts had to have a clear view of the lunar surface as they descended. The early designs, as the photo shows, had large windows, but these brought with them problems. They would have had to be extremely thick, and therefore very heavy. They also would have made it difficult to maintain a stable environment in the cabin.
Grumman and NASA engineers solved the vision problem with triangular windows slanted downward, which gave the astronauts a clear view of the surface as they descended. The final exterior LEM design was set.
The cabin was not. Seats were originally planned to be installed, but a couple of Grumman engineers had a bright idea. The seats added weight. The LEM would fly only in weightlessness, or subject the astronauts to one g acceleration during flight and five gs on touchdown. The astronauts could easily handle that standing up.
So that’s the way they would fly the lander.
The flight plan for the trip to the moon required that the Apollo mate with the LEM once the two were put into a trajectory that would take them to the moon.That was called Translunar Injection, or TLI. At that point, the Apollo would separate from the booster stage, turn around, and dock with the LEM, which remained in its ‘hanger’ in the booster. Once docked, the Apollo would back away with the LEM and the two would continue on to the moon.
Now it was time to test the concept in Earth orbit.