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

[twik]

To Jason - yes I do concede that 'billowing' would not apply in a vacuum, but I need to study the answers given further before I can accept that no dust at all would have fallen on the footpads.

I don't think you have to assume that "no dust at all" fell, just "not enough to make a significant layer, or even to be visible in photographs".

[raven]

No dust at all verses masses is a false dichotomy. There is in fact dust visible, just not much, on the footpads. Not enough for a layer, but enough to be visible in some close up photographs that have already been linked to earlier in this topic.

[Glom]

It probably got there from being kicked up by the astronauts.

[sts60]

The astronauts kicked up a lot of dirt.  Also, some footpads shoveled dirt onto themselves as the LM drifted slightly at touchdown.  That said, I expect that some dust managed to get onto the footpads as a result of the DPS plume, but not necessarily in amounts visible without very close inspection.

[Edwardwb1001]

Thank you Ka9q, for injecting some common sense into this thread. Contrary to what a number of members suppose, I do not have a subversive 'agenda'. The only agenda I do have is a 'truth' agenda. I might be a hoax believer, but I'm a reasonable one! Jason, that is a good point that the LM's engine may have been shut down before the contact probes touched the surface...etc. Twik - good point - as you say some dust may have fallen, but not enough to be visible in photographs.

Glom, I didn't 'struggle' to grasp the concept of their being no billowing in a vacuum - you are exaggerating. My response which WAS rather unkind (perhaps even obnoxious) was however my own response to a member saying "I have a few problems" - which I found rather irritating. Perhaps it wasn't meant as an insult.

I can see that dust may well not have fallen to any appreciable level on the footpads, unlike on those of the Phoenix lander and I accept the reasons given.  I am looking at photographs of the moon's surface under the LM regarding any scouring or removal of regolith.

[gillianren]

A reasonable hoax believer would answer questions posed.  A reasonable hoax believer would start with the thing that had convinced them that the Apollo landings were faked.  A reasonable hoax believer . . . does not exist, because there is no reasonable doubt about Apollo.

[ka9q]

Edward, another explanation that I don't think has been given yet is that in a vacuum, the exhaust plume from the LM closely hugged the surface as it went out radially in all directions at very high velocity. The dust entrained in the plume would have followed the plume itself; there was simply nothing to cause it to rise off the surface, much less fall into the landing pads.

Look at the flow of water in a sink when you turn the faucet away from the drain. The water hits the sink and flows smoothly outward as a sheet in all directions; it doesn't billow above the sink, right? Water is about 1,000 times as dense as sea level air, so the air has no significant effect on it. On the moon, even the rapidly expanding engine exhaust gas is far more dense than the lunar atmosphere, which for all practical purposes doesn't exist at all. So it too flows outward as a surface-hugging sheet.

Neil Armstrong said he was surprised to see the dust flying away toward the horizon and disappearing almost instantly when he shut off the descent engine. He said that he then realized it was exactly as it should have been, but he was still surprised because he hadn't thought of all the ramifications of the lack of a lunar atmosphere in advance. So if even a guy who went there was surprised by how the lunar dust behaved, it is not at all surprising that someone like you who hasn't been there might at first also think it unusual until the physics are explained.

[smartcooky]

This is something that I think a lot of people still don't get their heads around.

In a vacuum, even a microscopic dust particle that weighs 0.000000000000000000001 of a gramme will fall at exactly the same rate as a 10lb concrete breeze-block; on the moon that is 1.63 m/s

Another thing that people don't get is that an object on a ballistic trajectory that starts at 'h' height above the ground, a with an initial motion parallel to the ground, will fall to the ground at the same rate and in the same time as an object that fall directly from 'h' height to the ground.



So in a vacuum, discounting the curvature of the moon, if a bullet leaves the muzzle a gun (the barrel of is which is parallel to the ground) at 'A' and at the same moment, a second bullet is dropped from 'A', the dropped bullet will arrive at 'B' at precisely the same moment that the fired bullet strikes the ground 400 yards away at 'C'. This holds for all muzzle velocities, and it holds for dust particles as well.

[Andromeda]

Smartcooky, did you see the Mythbusters episode where they tested that with a gun?  The air resistance was negligible for the bullet so they got a great result.  It was very well done and a great teaching tool.

[smartcooky]

Smartcooky, did you see the Mythbusters episode where they tested that with a gun?  The air resistance was negligible for the bullet so they got a great result.  It was very well done and a great teaching tool.

Yes, I did see it.

It was ka9q's remark about the dust not rising that made me think of it.

[Kiwi]

Jason, that is a good point that the LM's engine may have been shut down before the contact probes touched the surface...etc.

You have apparently studied Apollo, but how much time have you spent on JayUtah's website Clavius, where he deals with most of the well-worn hoax claims?

And you don't appear to have spent much time at the online Apollo Lunar Surface Journals and the Apollo Flight Journals, with their stunning abundance of reference materials and links.

If you had read just the first section of the Apollo 11 and Apollo 12 Lunar Surface Journals you would probably have noticed that Eagle touched down with the engine still running (which you can also see in the 16mm landing film), and Intrepid landed with enough of a thump to almost cause Pete Conrad to let out just one more of his umpzillion expletives, as he relates in the journal here:

110:32:28 Carr: 30 seconds (of fuel remaining).

110:32:29 Bean: 18 feet, coming down at 2. He's got it made! Come on in there. 24 feet.

110:32:35 Bean: Contact Light.

110:32:36 Carr: Roger. Copy Contact.

[Jones - "I gather from the tech debrief that you actually dropped the last two or three feet."]

[Conrad - "You're supposed to."]

[Jones - "And the theory on that was?"]

[Conrad - "Lunar contact light came on and the probes were six feet below the gear. We were supposed to shut the engine off right then because they did worry about the bell mouth too close to the ground."]

[Bean - "Or hitting a rock and denting the bell mouth."]

[Conrad - "And I said, always, 'I'll never do that; who wants to shut off a good engine when you're still in the air?' But we had to train to shut it off. Neil landed with his (engine still) on. And, so, I was going to do the same thing. And, whoever said 'lunar contact light', I went 'bamm' and shut it down. (Laugh) Somewhere in there, I think there's an 'Oh shit'. Or there almost was. But about that time we were on (the Moon), and I didn't have to get it (the 'oh shit') the rest of the way out. I remember that."]

You might have also seen in the Apollo 11 Lunar Surface Journal, among the plentiful details about Eagle's powered descent and landing, Eric Jones's comment about the astronaut's use of "air":

102:45:43 Armstrong (on-board): Shutdown.

102:45:44 Aldrin: Okay. Engine Stop.

[Neil had planned to shut the engine down when the contact light came on, but didn't manage to do it.]

[Armstrong, from the 1969 Technical Debrief - "I heard Buzz say something about contact, and I was spring-loaded to the stop engine position, but I really don't know...whether the engine-off signal was before (footpad) contact. In any event, the engine shutdown was not very high above the surface."]

[Armstrong - "We actually had the engine running until touchdown. Not that that was intended, necessarily. It was a very gentle touchdown. It was hard to tell when we were on."]

[Aldrin - "You wouldn't describe it as 'rock' (as in, 'dropping like a rock'). It was a sensation of settling."]

[Some of the other crews shut down 'in the air' (meaning 'prior to touchdown') and had a noticeable bump when they hit.]

[Aldrin - (Joking) "Well, they didn't want to jump so far to the ladder."]

[Readers should note that, although the Moon has no atmosphere, many of the astronauts used expression like 'in the air' to mean 'off the ground' and, after some thought, I have decided to follow their usage.]

[Armstrong, from the 1969 Technical Debrief - "The touchdown itself was relatively smooth; there was no tendency toward tipping over that I could feel. It just settled down like a helicopter on the ground, and landed."]

[On a final note about engine shutdown, Ken Glover calls attention to the following from an interview done with Neil on 19 September 2001 by historians Stephen Ambrose and Douglas Brinkley at NASA Johnson.]

[Brinkley: "Was there anything about your Moon walk and collecting of rocks and the like that surprised you at that time when you were on the Moon, like, 'I did not expect to encounter this,' or, 'I did not expect it to look like this'? Or included in that, the view of the rest of space from the Moon must have been quite an awesome thing to experience."]

[Armstrong: "I was surprised by a number of things, and I'm not sure (I can) recall them all now. I was surprised by the apparent closeness of the horizon. I was surprised by the trajectory of dust that you kicked up with your boot, and I was surprised that even though logic would have told me that there shouldn't be any, there was no dust when you kicked. You never had a cloud of dust there. That's a product of having an atmosphere, and when you don't have an atmosphere, you don't have any clouds of dust."]

["I was absolutely dumbfounded when I shut the rocket engine off and the particles that were going out radially from the bottom of the engine fell all the way out over the horizon, and when I shut the engine off, they just raced out over the horizon and instantaneously disappeared, you know, just like it had been shut off for a week. That was remarkable. I'd never seen that. I'd never seen anything like that. And logic says, yes, that's the way it ought to be there, but I hadn't thought about it and I was surprised."]

I'm pasting from the DVD-ROM version, which may differ a little from the more-up-to-date online version.

My response which WAS rather unkind (perhaps even obnoxious) was however my own response to a member saying "I have a few problems" - which I found rather irritating. Perhaps it wasn't meant as an insult.

The quote, "I have a few problems" very clearly means that the person writing it is admitting to having problems, but I cannot find such a quote in this thread.  If the quote was "You have problems" then the writer is clearly referring to the reader(s), but that quote doesn't appear here either.

By my estimation, the words "problem" or "problems" have been used in this thread the following number of times:

Trebor, post 24, 2x
JayUtah, post 41, 1x
Abbadon, post 46, 2x
Edwardwb1001, posts 47 and 64, 3x
Cos, post 49, 1x
Total, nine times.

I certainly wouldn't bother myself over words like, "You have a couple of problems" and I cannot imagine why anyone else would want to. If that were true I'd want to fix them because getting rid of problems is a very good thing. Could you have perhaps been oversensitive and overemotional and imagined slights where there are none?  It has happened here many times before.

[Kiwi]

The only agenda I do have is a 'truth' agenda.

Then please, pursue that agenda with the utmost vigour (as I and others here do), and don't spend so much time complaining about how others do exactly the same.

In other words, get on with it!

[Abaddon]

Glom, I didn't 'struggle' to grasp the concept of their being no billowing in a vacuum - you are exaggerating. My response which WAS rather unkind (perhaps even obnoxious) was however my own response to a member saying "I have a few problems" - which I found rather irritating. Perhaps it wasn't meant as an insult.

Reacting in this way to someone pointing out problems with your hypothesis is not a good sign.

I can see that dust may well not have fallen to any appreciable level on the footpads, unlike on those of the Phoenix lander and I accept the reasons given.  I am looking at photographs of the moon's surface under the LM regarding any scouring or removal of regolith.

Ok, you accept there would be no expectation for much dust to be on the pads.
Moving on to the "crater" try AS11-40-5918 or AS11-40-5921 for starters.

[Peter B]

This is something that I think a lot of people still don't get their heads around...an object on a ballistic trajectory that starts at 'h' height above the ground, a with an initial motion parallel to the ground, will fall to the ground at the same rate and in the same time as an object that fall directly from 'h' height to the ground.

I remember watching a demonstration of this in about Year 9 physics. The teacher had a simple spring-loaded device which popped one ball-bearing out sideways, while simultaneously dropping another ball bearing vertically onto the ground. The experiment worked really well in the lab with its lino-on-concrete floor, as the ball bearings hit the floor with a very audible click. And only one click, because they hit the ground simultaneously.

[ka9q]

So in a vacuum, discounting the curvature of the moon

That's actually not always a realistic thing to do. The moon is so much smaller than the earth, and has such a lower escape velocity (about 2.38 km/sec) that particles moving at high speeds will see quite a bit of surface curvature during their flight. The effective exhaust velocity of a hypergolic engine like that on the LM is about 2940 m/s, above lunar escape velocity, so a particle entrained in that exhaust has a very good chance of escaping the moon entirely, if not flying much of the way around before falling back. This would happen even if the particle's initial trajectory has it leaving the surface at a very low altitude and angle; as long as it doesn't hit a rock or hill right away, the surface will fall away faster than it itself falls, and then it'll just keep going.

This even happens with the ejecta from many large lunar impacts.