For Idoru:
pulled from a source after Googling (a lot of good info from Google
)
Bad: In the pictures taken of the lunar lander by the astronauts, the TV show continues, there is no blast crater. A rocket capable of landing on the Moon should have burned out a huge crater on the surface, yet there is nothing there.
Good: When someone driving a car pulls into a parking spot, do they do it at 100 kilometers per hour? Of course not. They slow down first, easing off the accelerator. The astronauts did the same thing. Sure, the rocket on the lander was capable of 10,000 pounds of thrust, but they had a throttle. They fired the rocket hard to deorbit and slow enough to land on the Moon, but they didn't need to thrust that hard as they approached the lunar surface; they throttled down to about 3000 pounds of thrust.
Now here comes a little bit of math: the engine nozzle was about 54 inches across (from the Encyclopaedia Astronautica), which means it had an area of 2300 square inches. That in turn means that the thrust generated a pressure of only about 1.5 pounds per square inch! That's not a lot of pressure. Moreover, in a vacuum, the exhaust from a rocket spreads out very rapidly. On Earth, the air in our atmosphere constrains the thrust of a rocket into a narrow column, which is why you get long flames and columns of smoke from the back of a rocket. In a vacuum, no air means the exhaust spreads out even more, lowering the pressure. That's why there's no blast crater! Three thousand pounds of thrust sounds like a lot, but it was so spread out it was actually rather gentle.
[Note added December 6, 2001: Originally in this section I said that the engines also cut off early, before the moment of touchdown, to prevent dust from getting blown around and disturbing the astronauts' view of the surface. This was an incorrect assertion; it was known that dust would blow around before the missions were launched, and steps were taken to make sure the astronauts knew their height above the surface. Anyway, the incorrect section has been removed.]
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Bad: The next argument presented on the show deals with the lunar dust. As the lander descended, we clearly see dust getting blown away by the rocket. The exhaust should have blown all the dust away, yet we can clearly see the astronauts' footprints in the dust mere meters from the lander. Obviously, when NASA faked this they messed it up.
Good: Once again, the weird alien environment of the Moon comes to play. Imagine taking a bag of flour and dumping it onto your kitchen floor (kids: ask your folks first!). Now bend over the pile, take a deep breath, and blow into it as hard as you can. Poof! Flour goes everywhere. Why? Because the momentum of your breath goes into the flour, which makes it move. But note that the flour goes up, and sideways, and aloft into the air. If you blow hard enough, you might see little curlicues of air lifting the flour farther than your breath alone could have, and doing so to dust well outside of where your breath actually blew.
That's the heart of this problem. We are used to air helping us blow things around. The air itself is displaced by your breath, which pushed on more air, and so on. On the Earth, your breath might blow flour that was dozens of centimeters away, even though your actual breath didn't reach that far. On the Moon, there is no air. The only dust that gets blown around by the exhaust of the rocket (which, remember, isn't nearly as strong as the HBs claim) is the dust physically touched by the exhaust, or dust hit by other bits of flying dust. In the end, only the dust directly under or a bit around the rocket was blown out by the exhaust. The rest was left where it was. Ironically, the dust around the landing site was probably a bit thicker than before, since the dust blown out would have piled up there.
