“Unlocking the Secrets of the Moon: The Ingenious Strategies That Made NASA’s Historic Landing Possible”
Other design decisions concerned the unique challenges of landing on the moon. For example, more landing legs ensured greater stability – especially if one of those legs broke on impact – but increased the vehicle’s overall weight. Extensive drop tests conducted with models revealed that four legs were an adequate compromise, and this was integrated into the final design. To avoid having to use hydraulic shock absorbers in the vacuum of space, the legs were fitted with blocks of rigid plastic foam that would crush on impact, absorbing most of the shock of landing. Originally, the astronauts were to enter and exit the LEM cabin by climbing up and down a simple rope – the assumption being that this would be easy in lunar gravity. However, tests using a full-scale mockup and a counterweight system to simulate reduced gravity proved this assumption wrong, and instead the descent stage was rotated to place one of the four landing legs in line with the ascent stage hatch and its “porch”, and ladder rungs added to the leg strut. The hatch itself was originally round, but was eventually redesigned to be square to fit the astronauts Portable Life Support System or PLSS backpacks.
The finalized Lunar Module, whose design was frozen in April 1963, measured 7 metres tall and 9 metres across with the landing legs extended and, despite Grumman’s best efforts, weighed in at 15 tons – fully half again as much as the original design goal. Thankfully, however, the Saturn V design team led by Wernher von Braun succeeded in squeezing 20% more payload capacity out of the rocket, allowing this weight increase to be accommodated. The descent stage of the LM was powered by a 45,000 Newton thrust, fully throttleable rocket engine manufactured by TRW Inc., which burned a combination of Aerozine 50 and nitrogen tetroxide. These propellants are hypergolic, igniting on contact with one another, meaning no separate igniter was needed and the astronauts only had to open a pair of propellant valves to light the engine – and for more on how these nasty substances contributed to a now-forgotten nuclear disaster, please check out our previous video When Dropping a Wrench Almost Caused Armageddon. In addition to the descent engine and propellant tanks, the descent stage also contained wedge-shaped Scientific Equipment or SEQ Bays for storing tools, scientific instruments like the Apollo Lunar Surface Experiments Package or ALSEP and – on Apollos 15-17, the Lunar Roving Vehicle or LRV – AKA the “Moon Buggy” – and for an exhaustive breakdown of the ALSEP system, please check out the video on Our Own Devices, the personal YouTube channel of this video’s author. The descent stage also housed a continuous wave doppler radar to provide the astronauts with their altitude and rate of descent above the lunar surface.
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