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Disagreement and Development
Even as Mercury was testing the waters in the new ocean of space for manned spaceflight, NASA was beginning design of the lunar spaceship system. And it would be a system, new from the ground up. The launch vehicle would be new, the Ground Support Equipment (GSE) would be new, the launch pad would be new, and the spacecraft would be a new breed of spaceship.
But the spacecraft designers were in a quandary as to what type of craft to design. There was a tug of concepts being waged between the Werner von Braun team at Marshall Spaceflight Center (MSC) and other engineers as to the approach to a lunar landing. Von Braun wanted a direct ascent approach, with a giant launch vehicle that would send a large vehicle to land on the moon. Then the spacecraft’s ascent stage would send it back to Earth.
Others felt this required too large a vehicle to land on the moon, and lobbied for two craft to rendezvous and dock in earth orbit, then proceed to the moon to land. Yet, this too required a fairly large vehicle to land on the moon.
Grappling with these problems, NASA set several engineers on the task. They all came up with various solutions, but it was an engineer named William Michael who came up with the solution he termed “not just one way to get to the moon by the end of the decade, but the only way."
That way was Lunar Orbit Rendezvous (LOR). In LOR, a small lander would land on the moon, then return the astronauts to the mother craft orbiting the lunar surface. Once the astronauts had transferred to the mother ship, the ascent stage would be left in lunar orbit. This required a much smaller and lighter lander and ascent stage. It was an elegant solution.
Von Braun continued to fight for the direct ascent approach, until a meeting on June 7, 1962 at MSC, when he dropped a bombshell. Unknown to his administrators, he had changed his mind. At the end of the meeting, he announced that he now favored LOR.
The Apollo program was on its way.
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By this time, designers were well along with the design of the ‘mother ship’ that would carry the astronauts to the moon. It would seat three, with an interior volume of 10.5 cubic feet. It was about 10.6 feet long and 12.8 feet in diameter at its base. The middle couch folded away to provide access to the rear of the spacecraft. An ablative heat shield would protect it when it reentered the atmosphere at 25,000 mph. The design also returned to the escape tower of Mercury for rapid escape in the event of a catastrophe at liftoff or in the first stages of flight. The actual spacecraft was covered with a protective cover that was jettisoned with the escape rocket once a safe altitude was achieved.
This part of the spaceship was dubbed the Command Module. It carried a reaction control system (RCS) of 12 rockets for use during reentry.
But its real power would come from a big 22,000 pound thrust motor in the Service Module (SM) on which the Command Module sat. This big engine boasted a huge nozzle because it would be used only in space so the exhaust gases had to expand as much as possible. The nozzle of an engine of this thrust used in the atmosphere would be much shorter.
The Service Module contained fuel for the big engine, oxygen for the crew, and fuel cells for electric power. It also had an RCS of 16 motors for attitude adjustment during flight. The module was 24 feet high and 12 feet 10 inches in diameter.
North American Aviation was chosen to build the Apollo spaceship. Now the second part of the lunar craft had to be designed—the tiny craft that would actually land men on the moon.
Continues on page 2 with a discussion of the Lunar Lander.
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The vehicle designed to land men on the Moon for the first time was an iterative process that ultimately produced the bug-like LEM, or Lunar Excursion Module. Follow the design process of the LEM on page 2 of the article, "How the Apollo Spacecraft was Developed". Apollo Space Program, LEM
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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.
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.
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All images: NASA http://www.hq.nasa.gov/office/pao/History/SP-4205/contents.html
The Apollo Program--Developing a Way to the Moon
President John Kennedy gave this country the goal of sending a man to the moon by the end of the 1960s. The result was the Apollo program, which created a new series of spacecraft, launch vehicles, and even ground support equipment.