How did apollo missions slow down in space?

06 May 2007

Apollo-16 Moon Landing

The Apollo-16 astronauts on the surface of the moon

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Question

When sending a spacecraft to the moon (230,000 miles away) - at a rough guess at about 8,000 mph, how did the command module reduce its speed in space (no friction) to land in a graceful way on the Moon?

Answer

This is all based on rockets and thrusters. The moon landing was done by going into orbit around the moon, and then a small command module detached and went down to land on the surface, using thrusters to control the speed and angle of descent.

In the rocket or thruster, it pushes gas out of the rocket, so the gas pushes the spaceship in the other direction.

Actually, there was a hair-raising moment during Neil Armstrong's moon landing. The landing is usually all computer-controlled, but he realised that they were going to land in a boulder field, which would basically cause them to crash. He took manual control away from the computer, and landed safely with only 16 seconds of fuel left.

Comments

The engine selected was the AJ10-137 which used Aerozine 50 as fuel and nitrogen tetroxide (N2O4) as the oxidizer.The ascent engine produced 3,500 pounds of force (16 kN) of thrust which produced a velocity of 2,000 meters per second from lunar launch to lunar orbit rendezvous. Vf=3.1*ln( 28.8 / (28.8 - 16.9))= 2.74 km/sec. It takes a change of 0.7 km/sec to enter lunar orbit and the same change to leave lunar orbit as far as the CSM is concerned..

It's very bothersome to physicists like me when people who know nothing about the subject post comments about physics. One of Isaac Newton's simplest laws to understand is "for every action there is an equal, and opposite reaction". First of all, rockets don't need a medium. They use gyroscopes, and multiple independently moving engines to maintain a strait trajectory. Slowing down is where Newton's law applies. Turn the vehicle around 180 degrees, and ignite the engine. Fuel flows to the engine, explodes in the combustion chamber, and pushes against the vehicle slowing it down. This is not an argument for, or against the "moon hoax". Just a basic rocketry explanation. For more information try cracking open an 8th grade science book.

I'm glad your physics is better than your English...

LOL! I can't believe I didn't catch that. Nice.

'rockets need a medium to react against' This is false.

I'm not a rocket scientist, so what confuses me is how did they slow down and land perfectly a vehicle that was carrying enough reserve fuel to blast any vehicle that was carrying two blokes and all their life support stuff and that said fuel off the surface of the moon and up to a speed to meet up, again perfectly, with the orbiter?

According to NASA the LEM was traveling at a speed of 10,000mph in moon orbit, 50000 feet up. And within minutes it comes to complete stop-not even a jerk. Here on earth the planes flying at 180mph and with the help of friction on the runway they need 6000-8000 ft to stop. The LEM did not hover like a helicopter (not possible on the moon, anyway, as it has no air/atmosphere). You can hear the astronauts talking to mission control but you cannot even hear a murmur from the 10,000lbf rocket engine.
Its a complete farce.

Yes, absolute fakery. Just watch the "official video" of the lem docking with the Control Module. And yea, i get it, it probably looked really convincing in 1969. But no, in 2019, that video makes me cringe.

There's a simple two-word answer to this whole conspiracy business, and it nails the issue completely. It is: "The Russians". Do you not think, given how invested the Russians were in this whole thing, how close they came to winning, and how disappointing is was for them to be beaten, that, were there even the thinnest shred of doubt, they would have said so? These people knew everything, right down to the President's collar size, about everything the US was doing, including the space programme. If they could have rescued their bid by calling the opposition's bluff they would have done.

Accept that it happened, that it's not a conspiracy and that you are wasting your time being a troll.

submarines need water to move. airplanes need air to move. there was no force to react against in moon orbit except the gravity of the moon. rockets need a medium to react against. you cant slow down or take off with rockets when landing on the moon. watch the original CBS footage if you can find it, it is comical, even Walter Cronkite does the classic nose pull and groan, very indicative of liars lying.

NOTE:pay attention to the altitude and velocity of the screen, it doesn't even make sense, it took 6 minutes to land from 33,000ft going 1500ft./sec.? huh?

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