Why is there no dust on the Lunar Lander's footpads?

[Tedward]

I seem to remember an article on the Mars rovers, Spirit and Opportunity, with regards the solar cells. This article went to say something along the lines that power was reduced due to Martian dust but then got better when the wind blew it off. The dust cometh and the dust goeth (them proper words?)

[JayUtah]

If dust 'flies away on a ballistic trajectory'

It does not.  It is entrained in the exhaust fluid flow, which, after surface impingement, is roughly coincident with and parallel to the lunar surface.  It does not "billow up" and it is not likely to be trapped in great amounts in an upward-facing cup (i.e., the footpad).  It will certainly not stick to Kapton-covered vertical struts.

...and 'go(es) a long way before landing', then how would you explain video footage of dust flying up behind the lunar rover's wheels

It's a completely different physical phenomenon.

It falls virtually straight down, albeit in slow motion.

But it falls; it is not aerosolized as it would be on Mars.   Therein lies the answer to your first question above.

I think you are confusing gravity with atmosphere.

No, you are.  You are using words that refer to aerosolization and asking why the lunar environment does not behave the same way as Mars in that respect.

Yes, gravity causes particles to fall to the surface in a vacuum at the same rate, plus initial conditions.  However in the case of fluid entrainment, the disturbed (and therefore entrained) particles largely left the vicinity of the lunar module horizontally at very high velocities.

The gold-colored covering on components of the lunar module is very similar to the material small potato chip bags are made out of.  Imagine high-velocity particles hitting it.  How many of them do you think are going to stick?  Do some experiments with a chip wrapper and a handful of dry sand and tell me what happens.

How informed are you? Not very much, it seems.

It's a little early in your tenure to accuse the regulars of being stupid.

[Rob260259]

[Glom]

If dust 'flies away on a ballistic trajectory', and 'go(es) a long way before landing', then how would you explain video footage of dust flying up behind the lunar rover's wheels, and not flying away on a ballistic trajectory or travelling a far distance before landing. It falls virtually straight down, albeit in slow motion.

Erm, it is.  What do you think ballistic dust plumes should look like?

And Glom, Grashtel speaks of dust 'landing'. Does this not indicate that it did indeed 'float down', even at a distant point? Hence dust does float down - even on the moon. Actually, Glom, you imply from your comment that 'floating', cannot take place on the moon, due to the lack of atmosphere. I said 'float down'. I think you are confusing gravity with atmosphere.  How informed are you? Not very much, it seems. If objects do not float down on the moon (although Grashtel states that they eventually do), why did the astronauts not fly away after each bouncing step on the moon?

There is no floating on the Moon, only falling.

[gillianren]

No.  No, a single YouTube clip is not an argument.  I don't know what it shows, because I'm not clicking on YouTube links blindly.  (Also, I'm already watching something, and I'm not pausing Oedipus Rex for this!)  The proper etiquette is to give a description of what's on the link and what you are intending to show by it.

[Rob260259]

No.  No, a single YouTube clip is not an argument.  I don't know what it shows, because I'm not clicking on YouTube links blindly.  (Also, I'm already watching something, and I'm not pausing Oedipus Rex for this!)  The proper etiquette is to give a description of what's on the link and what you are intending to show by it.

You're right. I should have quoted Glom and explained that this video is about the Apollo 16 rover 'grand prix' showing ballistic trajectories of the moon dust.

[Edwardwb1001]

True. I should not have used the word 'float', as of course dust would only 'fall' on the moon.  Jay, you state that it is "a little early in your tenure to accuse the regulars of being stupid." I was not saying categorically that any member is stupid.  However, Grashtel states that dust "flies away on a ballistic trajectory." You contradict this statement and state that "It does not", thereafter explaining your reason for saying so.  I'm not hereby implying that Grashtel is stupid, incidentally - only that believers seem to differ in their explanations and convictions. 

Jason Thompson refers to the 'rather large and powerful rocket engine' blowing dust away from the lander's footpads.
Yet it is often mentioned that the reason for no crater (or even indentation) having being created below the lander, was due to the exhaust not being powerful enough on descent to blow any dust away - thus not leaving even the slightest crater.  Too weak on descent to form even an indentation in the dust below the lander - yet 'large and powerful' enough to blow the dust away from the footpads. Which is it?

[cos]

Too weak on descent to form even an indentation in the dust below the lander - yet 'large and powerful' enough to blow the dust away from the footpads. Which is it?

Oh do I get a point for spotting the first false dichotomy?
 
You might want to read this thread -

http://apollohoax.proboards.com/index.cgi?board=theories&action=display&thread=3146&page=5

Is there nothing new in the hoax world?

[cjameshuff]

There's a wide, wide range between being able to blow dust over a mylar covered footpad and being able to excavate a crater. Film of the landings did show lose dust streaming away (and later photos showed a surface largely cleared of such dust under the lander, with small pockmarks dug out and a blast-scoured appearance), but only fine, loose surface particles were picked up.

http://www.lpi.usra.edu/resources/apollo/frame/?AS11-40-5921

[Trebor]

However, Grashtel states that dust "flies away on a ballistic trajectory." You contradict this statement and state that "It does not", thereafter explaining your reason for saying so.  I'm not hereby implying that Grashtel is stupid, incidentally - only that believers seem to differ in their explanations and convictions.

Perhaps the problem is that you are missing something....

Jason Thompson refers to the 'rather large and powerful rocket engine' blowing dust away from the lander's footpads.

Indeed...

Yet it is often mentioned that the reason for no crater (or even indentation) ..

Let me stop you there... there most certainly was a broad shallow crater. And this is visible in the photos taken.

Which is it?

You are mistaken in your assertion, that is what the problem is.

[Edwardwb1001]

You're such a tease, Trebor! Tell me, what am I missing? Don't be rude, now.

This is the trouble. You say there was a 'broad, shallow crater'. I have looked at photos of the area below the lander, and I do not see any type of crater - even shallow. You say tomato...

[nomuse]

If dust 'flies away on a ballistic trajectory', and 'go(es) a long way before landing', then how would you explain video footage of dust flying up behind the lunar rover's wheels, and not flying away on a ballistic trajectory or travelling a far distance before landing. It falls virtually straight down, albeit in slow motion.

You may have gone into more detail later (I don't have the memory to read a whole thread before going back through it!) but you are expressing yourself oddly above.  How is falling down NOT ballistic?  It doesn't matter what the ratio of the parabola is; what matters is that the dust behind the Rover doesn't aerosolize.  It doesn't hang, it doesn't disperse, it doesn't show turbulent patterns.

The distance-versus-height is entirely dependent on how the wheel flings it. 

And Glom, Grashtel speaks of dust 'landing'. Does this not indicate that it did indeed 'float down', even at a distant point? Hence dust does float down - even on the moon. Actually, Glom, you imply from your comment that 'floating', cannot take place on the moon, due to the lack of atmosphere. I said 'float down'. I think you are confusing gravity with atmosphere.  How informed are you? Not very much, it seems. If objects do not float down on the moon (although Grashtel states that they eventually do), why did the astronauts not fly away after each bouncing step on the moon?

What, are we in heavy boots territory now?

[gillianren]

You're right. I should have quoted Glom and explained that this video is about the Apollo 16 rover 'grand prix' showing ballistic trajectories of the moon dust.

I'm sorry for being so snippy about it, but it drives me crazy.  I am almost always watching something while I'm posting, and there's this expectation that whatever-it-is I'm watching (or even listening to!) isn't as important as someone's YouTube video.  I'm not saying you had that expectation, but it's the most common explanation as far as I'm concerned for the blind YouTube link.

[Trebor]

You're such a tease, Trebor! Tell me, what am I missing? Don't be rude, now.

What you are missing:
Jay stated "It [the dust] is entrained in the exhaust fluid flow," and indeed it is, but if you actually think you would realise that the exhaust as you get further from the source would expand very rapidly and the effect on the dust would quickly become insignificant.
After this point the dust particles would follow nicely parabolic trajectories. With a hefty initial velocity...

This is the trouble. You say there was a 'broad, shallow crater'.

Correct.

I have looked at photos of the area below the lander, and I do not see any type of crater - even shallow. You say tomato...

Interesting, because the fluid erosion marks formed by the exhaust are very apparent in them.
AS11-40-5920 is a very good example...
AS14-66-9261 onward are also excellent examples, what were you expecting to see exactly?

[JayUtah]

...only that believers seem to differ in their explanations and convictions.

Yes, that will happen in life.

Jason Thompson refers to the 'rather large and powerful rocket engine' blowing dust away from the lander's footpads.

Did he quantify "large and powerful?"  Did I?  Did you?

Too weak on descent to form even an indentation in the dust below the lander - yet 'large and powerful' enough to blow the dust away from the footpads. Which is it?

What's your justification for believing both can't be simultaneously true?

I spoke of exhaust gas velocity.  Is that the only parameter that determines whether a crater will be excavated?  How about exhaust gas density?  How about collimation?  Did you consider those factors, or are you just trying to drive meaningless wedges wherever you think you see a crack?