Another reason to love Neil deGrasse Tyson

[Craig Murray]

worth noting the escape velocity of the moon in miles per hour is 5400 miles per hour. That's over 7 times the speed of sound.. mock 7.

It boggles my mind that people can look at all the video footage, physics data, and still come away thinking this is possible.

Blue pill is powerful voodoo.

[Amir Allam]

Alright, but only because I'm avoiding doing actual work...

The F22 engine (Pratt & Whitney F119) produces 156kn of force. Badass. The Lunar Ascent Module Engine (we'll call it LAME from now on) produces... 16kn of force. Wamp wamp wamp. As you put it, the idea that they're remotely the same is laughable; LAME is about 10% as cool as the F119. So what gives?

Because the moon has no drag (atmosphere) and the gravity is 16% of Earth, you don't need a big huge rocket; you just need an efficient one that you can sustain. The gravitational force is only (1.6m/s^2 * 4000kg) 6.4kn, or 40% of LAME. LAME is only about 1/3 the size of the descent engine! Why? It only has to carry about 1/3 of the weight back. The F119 fires for many hours; LAME only fires for minutes.

Since you like pictures, here's one of the wimpy bastard compared to the descent and maneuvering engines:
http://history.nasa.gov/SP-350/i4-9.jpg

Again, I have no idea if Apollo 11 landed on the moon or not. I don't really care; it wouldn't be the first time the government lied to us, so it isn't an important proof-of-concept. Regardless, the idea that the landing is somehow scientifically impossible is just not correct.

[Elisha J Baker]

It's "mach" but whatever.

After touching down the lunar module and its ascent engine never reached, and never needed to reach, the moon's EV. Just needed to hit a high enough orbit to link with the command module. Equations are then completely different for the command module to move into an earth intercept trajectory (different craft, and one that never decelerated from orbital velocity). The lunar module itself was ditched in orbit around the moon. Whether or not its engines could have driven it to escape velocity is irrelevant, though obviously with no atmospheric resistance it could be done, given the right amount of fuel. In the event figuring out the fuel reserves required for all phases *was* dicey. Lunar module didn't carry enough for much of a failsafe if things went badly on the ascent, although there was a planned contingency operation in case the lunar module didn't make it into as high an orbit as they hoped. Eleven and half miles was the cutoff — the minimum altitude to which the command module could have descended to link with the lander. Any less and NASA was prepared to leave two corpses on the moon. That was always an outside possibility. The math looked right at the outset but they were playing with close margins, and it's fully appropriate to be impressed at how difficult the whole operation was.

Jets aren't rockets (though trying to visually compare them certainly is totes adorbs). Most of the mass in a jet engine is the turbine/compressor system. Generally makes it a lot more efficient than a rocket in the long run, given an atmosphere, because you can use outside air instead of carrying an oxidative fuel source. It does mean that a jet engine by itself will be far bigger and heavier per unit of thrust produced than a rocket, though.

I used to know James Irwin (Apollo 15), before he died. I was just a kid, but he inspired me pretty profoundly. FWIW he had some permanent physiological issues from overheating in his EVA suit. (I know, I know, clearly a paid shill... immensely cool beans.)

[Ross Davidson]

Jesus Christ.

I'm never going to post anything positive again.

[Elisha J Baker]

Hahaha NDT is a boss, man.