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Message: <blockquote data-quote="Paracelsus" data-source="post: 959593" data-attributes="member: 8098">According to Armstrong they could and did, but since their suits weren't exactly the most robust things in the world they weren't going to screw around with it.  Neil Armstrong reported that he was able to jump to the third step of the lunar module ladder, which he estimated to be five or six feet from the lunar surface "I did some fairly high jumps," said Armstrong, "and found that there was a tendency to tip over backward on a high jump. One time I came close to falling and decided that was enough of that". Falling over backward would risk damaging the PLSS.  There are frames from the Apollo 11 EVA which are consistent with that jump.  They just didn't want to fuck up their suits.Four things:(1) Dust clouds form in an atmosphere, where the mass of the air itself creates resisting force to dust particles falling.  It's why despite Galileo's theoretical calculations, a feather and a bowling ball dropped at the same time from the top of a building don't hit the ground at the same time -- because the air and friction provide resistant force, enough to slipslide the feather around in the air.  But there isn't any atmosphere on the Moon, meaning that any dust displaced falls back to the Moon's surface at one-sixth the speed it does in Earth's gravity, but it falls nonetheless.(2) The LM is standing on solid rock.  The layer of dust on the Moon is quite thin and thus any dust blown away from the impact then resettles away from the lander.  No blast crater forms.(3) The lunar module (LM) descent stage engine had a maximum thrust of 9870 ft-lb, but this was throttleable back to a minimum of 1050 ft-lb. Sounds like a lot. But, the diameter of the nozzle was 63 inches, which is an area of about 3120 in2. Dividing this into the force (thrust) and you have a pressure range of 0.4-3.2 ft-lb/in2, otherwise known as psi. This is equivalent to the metric 2760-22,100 N/m2. But let’s stick with psi.Anyone who owns a car probably knows that this is already significantly less than your tire pressure … by a factor of 10-100. When Apollo 11 landed, the thrust was down to about 1/3 of max, so down to around 1 psi.Now let’s look at the average adult footstep: The average non-American weighs around 150 lbs. The average human footprint is around 50 in2 (don’t believe me? do the math yourself!). Divide the first into the second and you have the average human footstep exerting a simple 3 psi.This is 3x larger than Apollo’s engines.The very fact that the astronauts walking on the moon did not create “blast craters” underneath them should be explanation enough as to why the engine did not create a blast crater under it — the pressure was simply too low.(4) Saying "the lander weighs 3T on the Moon" is unintentionally misleading.  Newton's Second Law tells us that what counts is the amount of force required to bring the lander to a halt, consequent on Newton's First Law of inertia in a perfect vacuum.Force = mass x acceleration.Mass does not change (well, in the case of the LM it reduces over time as fuel mass is expended).  The LM on Earth is exerting a force that causes our scales to assess its weight as 17 tons.  On Earth, acceleration is at least 9.8 m/s squared, which is Earth's gravitational force.  Consequently the force required to escape Earth's gravity is at least mass x 9.8 m/s squared (not counting for air pressure or friction).On the Moon, however, acceleration is 9.8 m/s squared divided by 6, because the Moon's gravity is one sixth that of Earth.  Mass does not change - it's still an object that would weigh 17T on Earth - but the force required to counter the Moon's gravity, change the object's velocity, and thus bring it to the ground safely is much, much less, meaning that the fuel and intensity of the burn is also much less than would be required on Earth.  (Not that you could see the LM's engine burning anyway - the fuel mix they had was colourless and lightless.)</blockquote>

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