Fifty years of Apollo conspiracy theories

[toast]

22 minutes ago, Derek Willis said:

To me there are two likely answers to the mystery. (1) a relatively local meteorite that threw dust onto the probe. (2) Dust was thrown up during the "bouncy" landing. But without some physics and maths, neither of these suggestions can be said to have definitely caused the dust to be there.

There is no mystery and it does not need physics or math, it only needs the web:

Quote

(...) Note the imprint in the lunar soil which was caused when the Surveyor 3 bounced upon landing. (...)

NASA

Case closed.

[Derek Willis]

On 12/21/2018 at 1:02 PM, Peter B said:

You've asked a good question.

I don't know for sure, but I wonder if the dust might have been deposited on Surveyor as the LM came in to land, blown onto it by the LM's Descent Engine.

Have a look at the map here: https://www.hq.nasa.gov/alsj/a12/landpath.jpg

It shows the path the LM followed as it descended to the surface. You'll see the LM approached Surveyor from the east, passed a little over 100 metres to the north of Surveyor, and finally landed north-west of Surveyor. Therefore, the dust-coated side of Surveyor shown in the photo would be the eastern side - the side the LM initially approached from.

Now sure, the LM was a couple of hundred metres away and more than 70 metres up as it approached. Would that be close enough to the surface to kick up enough dust to coat Surveyor like the photos show? I don't know. But I don't see any particular reason why not; after all, there was no atmosphere to constrain the rocket exhaust, so the exhaust would have spread out in a conical fashion, but the lack of atmosphere would mean there was nothing to slow the exhaust down. The question would be whether the gas had spread out so much that the pressure it exerted on the dust on the surface would be strong enough to blow it away.

Initially, it was believed the Lunar Module descent engine blew surface material onto the Surveyor 3. It was then realized that fragments blown up by the descent engine "sandblasted" dust off the Surveyor 3. This meant that the dust was already there.

https://www.sciencedirect.com/science/article/abs/pii/S001910351000432X

Now, it may be that as the Lunar Module made its approach, it blew dust onto the Surveyor 3, and then as it flew past the probe, blew some of it off again. The diagram you linked to shows this to be a distinct possibility. As the Lunar Module approached it would have been blowing dust up which would then - because of the lack of an atmosphere on the Moon - have landed some distance away, including where the Surveyor 3 was. Much of this dust would have been falling from a high angle, and so would have coated pretty much all of the probe. Then as the Lunar Module flew past the Surveyor 3 and landed, it would have blown up dust that "sand blasted" away the original deposit from the areas of the probe facing the Lunar Module. 

[Derek Willis]

4 minutes ago, toast said:

There is no mystery and it does not need physics or math, it only needs the web:

Case closed.

How is the case closed?

[toast]

2 minutes ago, Derek Willis said:

How is the case closed?

Because there is no mystery about the dust on the landing gear of Surveyor 3.

[Derek Willis]

2 minutes ago, toast said:

Because there is no mystery about the dust on the landing gear of Surveyor 3.

Can you describe what you mean? 

[toast]

3 minutes ago, Derek Willis said:

Can you describe what you mean? 

You wonder about the dust on the landing gear of Surveyor 3, from post #1 on:

Quote

I know that Surveyor 3 had a difficult landing in that it bounced twice before settling on the surface. But does that explain why it was covered in dust?

Looking at the image I posted in post #34 its quite obvious that the material on the landing gear was moved there because of the bouncy landing.

[Derek Willis]

17 minutes ago, toast said:

Because there is no mystery about the dust on the landing gear of Surveyor 3.

In #4 you suggested the dust on the landing gear had been moved there by the astronaut, i.e. he kicked it there. So are you now suggesting the dust is there because the Surveyor 3 bounced?

[toast]

Just now, Derek Willis said:

In #4 you suggested the dust on the landing gear had been moved there by the astronaut, i.e. he kicked it there.

That was my first impression but I took a deeper look into the matter later on.

Quote

So are you now suggesting the dust is there because the Surveyor 3 bounced?

Yes.

[Derek Willis]

20 minutes ago, toast said:

That was my first impression but I took a deeper look into the matter later on.

Yes.

Here is a link to an interesting paper.

https://physics.ucf.edu/~yfernandez/psjc/fall14/177-nov21/20120000029.pdf

It seems the case is far from closed. The researchers took into account all the possibilities, including the dust being thrown up by the difficult landing of Surveyor 3. Chemical analysis of the dust suggests it is not from the immediate region of the Surveyor 3, but more likely to be from a region in the landing path of Apollo 12. That would suggest the dust was blown onto the probe, and then partly blown off, by the Lunar Module's descent engine.

It may be the case that the mound of lunar soil on the landing pad was put there by the final bounce, but that the dust covering the rest of the Surveyor 3 was a result of the landing of Apollo 12.

[Obviousman]

Was Surveyor 3 the one where they 'beeped' the engine after landing? I seem to recall that happening with one of the lunar probes.

[Derek Willis]

4 hours ago, Obviousman said:

Was Surveyor 3 the one where they 'beeped' the engine after landing? I seem to recall that happening with one of the lunar probes.

No, that was Surveyor 6, which landed on November 10th 1967. The three small engines were re-ignited for 2.5 seconds, lifting the probe to a height of 3 meters, and landing it again 2.4 meters to one side.

[Derek Willis]

On 12/21/2018 at 1:46 PM, flyingswan said:

The way Surveyor 3 landed with its rockets still firing and slid down the side of the crater obviously raised a lot of dust as its camera performance was degraded from the start.

However, I think the main difference from the LM comes from the different engine layout.  When the single jet from the LM hit the ground it spread out in a thin sheet moving dust outwards in every direction.  Surveyor had three jets, so under the centre of the vehicle the sheets from each of the three jets would have come together and, having nowhere else to go, would have pushed dust upwards to bounce around the rather open grid of the vehicle structure.

An analogous effect is seen with the Harrier aircraft which generates an upward jet on to its underside during vertical landings.

You make an interesting point. According to the paper below, just prior to touch-down of the Lunar Modules, dust was ejected away at an angle of only three degrees. Consequently, the vast majority of the dust was thrown away from the Lunar Modules. The three engines of Surveyor 3 were supposed to switch off at a height of 4 meters. However, they didn't, and this is why the probe "bounced" twice. So, the engines were still firing when the probe touched down for the first and second times. Each engine would have produced a "sheet" of dust just like the Lunar Modules (though of course far smaller). However, under the probe these sheets would have impinged. Perhaps, as you say, the dust somehow made its way up through the probe. But whether it could have made its way to the solar panel/antenna mast seems unlikely.

In any case, the chemical analysis of the dust on parts of the Surveyor 3 brought back to Earth seems to suggest the dust was not from the immediate vicinity of Surveyor 3, but was blown onto the craft when Apollo 12 landed (and then some was blown off again).

https://physics.ucf.edu/~yfernandez/psjc/fall14/177-nov21/20120000029.pdf

I don't think any of the research into the dust on Surveyor 3 is conclusive, which is perhaps why the paper I have linked to is called: Further Analysis on the Mystery of the Surveyor III Dust Deposits. The Apollo 12 mission planners knew if the Lunar Module landed too close to Surveyor 3 the probe may well have been coated in dust. That might explain why, after having landed a safe distance away, the astronauts were expecting the probe not to be covered in dust. After the metal parts returned to Earth were analysed, it did seem to be a surprise that they were pitted by particles thrown a distance of 180 meters by the Lunar Module. This leads to another "mystery" that ought to be solved.

The descent engine of the Apollo 11 Lunar Module was still firing when the craft landed. That means for a moment at least, a sheet of particles was still being ejected at an angle of three degrees. Some of this would have hit the back of the landing pads and the lower end of the landing leg struts. If particles thrown 180 meters by Apollo 12 were able to cause pitting on Surveyor 3, surely the larger particles hitting the back of the Apollo 11 landing pads and struts would have caused visible marks? These components were covered in mylar film, so perhaps there ought even to have been damage or tearing of this. I can't see any marks, damage, or tearing of the mylar film in the photograph of the Apollo 11 landing pads in post #1 above. Also, I can't see any mention of this in the voice transcripts on the Apollo 11 Surface Journal. It could be argued that the layer of dust beneath the Lunar Module had been blown away prior to touchdown, and so there was none left to mark or damage the mylar on the pads/legs. However, Armstrong planted his "small step" in dust just beyond the pad. Also, the photograph above shows there is still dust behind the pads. Like I say, this is a conundrum worthy of investigation.

Edit: On second thoughts, there are grey marks on the mylar. I thought that was shadowing. Perhaps it is dust? 

Edited December 23, 2018 by Derek Willis

[aztek]

20 hours ago, Derek Willis said:

In #4 you suggested the dust on the landing gear had been moved there by the astronaut, i.e. he kicked it there. So are you now suggesting the dust is there because the Surveyor 3 bounced?

it sure is very possible,  and likely, people bounced off trying to walk there.  every plane that lands here on earth bounces, unless it crashes. 

[Derek Willis]

2 hours ago, aztek said:

it sure is very possible,  and likely, people bounced off trying to walk there.  every plane that lands here on earth bounces, unless it crashes. 

With the Lunar Modules, and probes such as the Surveyors, the intention was that they dropped towards the surface at a gentle rate and then shock absorbers prevented any bouncing. As far as I know, none of the Lunar Modules bounced. One or two of them skidded slightly. Surveyor 3 "bounced" because the engines didn't switch off when they were supposed to. It could be said that rather than actually bouncing, the probe lifted off again. Undoubtedly the impact and the firing engines would have raised dust. It seems, thought, that this isn't the dust that came to rest on the probe. Instead, the dust was blown onto Surveyor 3 when Apollo 12 landed. The behavior of dust on the Moon is obviously still not fully understood. Perhaps when humans return to the Moon they will take a look at the other Surveyor probes and we will find out if they are free of dust, or not. 

[Obviousman]

On 12/24/2018 at 7:37 AM, aztek said:

it sure is very possible,  and likely, people bounced off trying to walk there.  every plane that lands here on earth bounces, unless it crashes. 

I take offense at that! Sure, I have made some 'controlled crashes' in my time but I have also pulled off some landings that were slick and smooth as the proverbials.

[aztek]

On 12/24/2018 at 7:21 PM, Obviousman said:

I take offense at that! Sure, I have made some 'controlled crashes' in my time but I have also pulled off some landings that were slick and smooth as the proverbials.

no matter how smooth i land nose wheel always bounces a bit.  does not make the landing scary or dangerous, but small bounce is always there.  every commercial plane i flew (as a passenger) bounced a bit during landing, i consider it normal.

[ChrLzs]

Maybe I've missed something (skim reading, too much other stuff to do today), but I am not seeing the/a problem.

As you already said, no dust on landing pads is because of ballistic dust movement, as there is no air to make the dust 'billow' or hang about.  Most of the dust blown by the exhaust travelled very low, and only a few particles would have bounced up or had a parabolic path that would land in the pad.  Also, we are talking about a period of just a few days, so no real time for deposition by other sources.

For Surveyor, much longer times are involved, plus by the random nature of meteor strikes there may have simply been a small or large local event.  Or electrostatic differences, either anomalies in that region, or perhaps due to the space craft design, materials, electronics... It's an extremely complex topic, and no way to easily guess at what combinations / what balance of factors was involved.

And to Derek (you devil's avocado you!), can you show me the maths for ... oh say a Harrier landing's dust deposition, or anything earthly but similar?  That is surely a much easier question .. as we could be there to measure it and then run the numbers....

And yes, if that sounds silly (and it is) that's my point.  No-one could (or more to the point, would) possibly do 'the maths' on such a complex problem with so many variables, and with so little reason to bother.

[Derek Willis]

On 12/27/2018 at 1:37 AM, ChrLzs said:

Maybe I've missed something (skim reading, too much other stuff to do today), but I am not seeing the/a problem.

As you already said, no dust on landing pads is because of ballistic dust movement, as there is no air to make the dust 'billow' or hang about.  Most of the dust blown by the exhaust travelled very low, and only a few particles would have bounced up or had a parabolic path that would land in the pad.  Also, we are talking about a period of just a few days, so no real time for deposition by other sources.

For Surveyor, much longer times are involved, plus by the random nature of meteor strikes there may have simply been a small or large local event.  Or electrostatic differences, either anomalies in that region, or perhaps due to the space craft design, materials, electronics... It's an extremely complex topic, and no way to easily guess at what combinations / what balance of factors was involved.

And to Derek (you devil's avocado you!), can you show me the maths for ... oh say a Harrier landing's dust deposition, or anything earthly but similar?  That is surely a much easier question .. as we could be there to measure it and then run the numbers....

And yes, if that sounds silly (and it is) that's my point.  No-one could (or more to the point, would) possibly do 'the maths' on such a complex problem with so many variables, and with so little reason to bother.

The point of my OP was to demonstrate how when there is something potentially inexplicable regarding an aspect of Project Apollo, that allows the Moon Landing Conspiracy Theory to fill the vacuum. So in this case, the claim was that there ought to be dust on the Lunar Module landing pads, but there isn't. Ergo, the Apollo missions were faked. Basic physics shows that it is unlikely there would be any dust on the pads, for the reasons described above. However, the dust covering Surveyor 3 could lead to the legitimate question, "If physics demonstrates why there isn't dust on the Lunar Modules, then why is there dust on Surveyor 3?" In the absence of a definitive answer, that could open up a can of worms as far as the conspiracy theorists are concerned. Of course, it is only because Apollo 12 landed on the Moon that we know Surveyor 3 is covered in dust. But that is not a problem to the conspiracy theorists because of the "Whistle-blower Hypothesis". According to this, what happened is that one or more whistle-blowers working in the studio where the Apollo missions were faked coated Surveyor 3 with dust as a "clue" that "something is not right with Project Apollo".

As for the physics and maths regarding the Harrier, as you well know that is an extremely difficult problem. Initially, conservation of momentum can explain what is happening - i.e. some or all of the momentum of the exhaust gasses is transferred to the dust/particles on the ground, and they fly off rapidly. But almost immediately, all hell breaks loose. The dust/particles impinge on the atmosphere, and what follows can only be described by fiendishly complex differential equations with god knows how many variables. I would say it is impossible to solve those equations - especially when convection currents and other dynamics are taken into account. An iterative algorithm might produce an approximation, but I doubt anyone has ever bothered to try. So, I will pass on your challenge.

Fortunately, the Surveyor probes landed on the Moon, so it is possible to make a reasonable stab at what went on with Surveyor 3. The first thing to note is that the imprints of the foot pad in the image provided by Toast in #34 were not caused by the "bouncing" during the difficult landing. They were caused by what could be called "micro-bounces" as the craft finally settled on the surface. I will return to this later.

The landing procedure of the Surveyors was supposed to be straightforward. The probes were intended to be slowed to zero velocity at an altitude of 3.4 meters. At that point the three engines were shut-down, and the probe fell to the surface and impacted at 3 m/s. The force of landing was absorbed by the shock absorbers, and so no bouncing would occur.

Unfortunately for Surveyor 3, spurious reflections from the surface confused the Doppler radar and so neither the altitude nor velocity were known. The probe continued down to the surface at about 1 m/s, but without the engines switching off. This link describes what happened next.

https://honeysucklecreek.net/other_stations/tidbinbilla/Surveyor_3_hl.html

Basically, Surveyor 3 lifted-off again and "hopped" a distance of twenty meters, landed again, and then hopped another eleven meters before finally settling on the surface. The only reason this hopping stopped was because 34 seconds after the initial touchdown a signal sent from Earth switched off the engines. 

I believe very little - if any - of the dust deposited on Surveyor 3 was put there by this unorthodox landing. Firstly, the force of the engines impacting on the surface was too low to raise much dust. At the time of the landing, each engine had been throttled down to a thrust of 30 kg (the minimum level). The exit area of an engine nozzle was about 200 cm² , so that meant the exit pressure was about 0.15kg/cm². That is pretty low. By comparison, a human can blow at a pressure of about 0.1kg/cm² . And bear in mind, in a vacuum the gasses rapidly expand as they exit a rocket nozzle, and so rapidly reducing the pressure. I estimate the pressure from the engines hitting the surface during each "landing and take-off" was about a tenth of the nozzle exit pressure, i.e. about 0.015kg/cm² . That really is very gentle, and so wouldn't have blown up hardly any dust at all.

As the landing pads impacted the surface they would have kicked up some dust. But the probe was descending at only 1 m/s so there wouldn't have been much dust. And, during its first "hop", Surveyor 3 reached a height of 10 meters and a distance of 20 meters, so I doubt any of the dust kicked up would have come to rest on the craft. The same would be the case for the second hop.

When the Surveyor 3 finally came to a rest there were three "micro-bounces", and a slight sliding. This was because the probe came down on a 12 degree slope on the inside of a crater. The extra "drop" of the pad furthest down the slope, and then the sliding, caused the probe's frame to "judder" and flex, and one of the pads bounced gently twice. The pad lowest down the slope became partially dug-in due to the slow sliding motion caused by the Moon's gravity. Any dust disturbed as the pad dug-in would have been thrown away from the probe, so it seems unlikely any would have reached the top of the solar panel/antenna mast.

Toast initially mentioned that the small clump of dust on one of the pads looked like it had been kicked there by one of the astronauts. It turns out it was! According to the Apollo 12 Surface Journal, one of the astronauts was asked to kick the soil near the pad.

The best answer to why Surveyor 3 was covered in dust is that it was blown there as Apollo 12 flew past, and then partially blown off when the Lunar Module landed. At the time the astronauts - Pete Conrad and Alan Bean - did not believe the dust could have been deposited by their Lunar Module. But a chemical analysis seems to confirm that is the case. 

Anyway, I am sure few people are interested in my analysis, but it has whiled away a couple hours before New Year. My point is that the "bald facts" - Lunar Modules aren't covered in dust, Surveyor 3 is covered in dust - could be made to fit the Moon Landing Conspiracy theory, especially when the full facts are missed out.

Now, wait until I get onto my next pet subject. Along with the famous "makeshift" fender, Gene Cernan brought part of each of the fenders from their Apollo 17 Lunar Rover back home from the Moon. Said fender parts are now in American museums. Apparently, however, Cernan's co-astronaut Jack Schmitt had no idea about that. During the 1990s the astronauts were being interviewed for the compilation of their Surface Journal, and were shown the last photograph Cernan had taken of the Rover after he'd parked it up for the famous film of the Lunar Module lift-off. Schmitt had asked: "Where are the other fenders?" Now there's a mystery. How could those fender parts have been brought all the way home without Schmitt knowing ...        

[Derek Willis]

Here is something I didn't notice earlier. According to the conclusions of the paper linked to below (which was funded by NASA), Surveyor 3 was coated in dust when the Apollo 12 Lunar Module flew past on its way to the landing site. Then, as the Lunar Module landed, the engine exhaust propelled particles horizontally and these "sandblasted" some of the dust off Surveyor 3.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120008741.pdf

This seems to make sense when you look at the diagram below (provided by NASA). As the Lunar Module came in to land, it's closest approach to Surveyor 3 was 109 meters. This would have been to point where the dust was being blown onto Surveyor 3. Then, when the Lunar module landed at a distance of 155 meters, the parts of Surveyor 3 facing the Lunar Module were "sandblasted".

The problem is, when the Lunar Module was at its closest approach to Surveyor 3, it was at an altitude of 67 meters. According to the diagram, dust only began to be seen by the astronauts when the Lunar Module was at an altitude of 30 to 35 meters. This accords with what Alan Bean said during the descent: "130 feet (39 meters). Going to get some dust before long."

So, if no dust could be seen blowing from the surface until the Lunar Module was at an altitude of 30 to 35 meters, how when the Lunar Module was at twice that altitude - i.e. 67 meters - was enough dust blown up to cover Surveyor 3? 

[flyingswan]

Simplest explanation is that the dust began moving at a higher altitude than the one at which the crew first observed it.

[toast]

1 hour ago, Derek Willis said:

So, if no dust could be seen blowing from the surface until the Lunar Module was at an altitude of 30 to 35 meters, how when the Lunar Module was at twice that altitude - i.e. 67 meters - was enough dust blown up to cover Surveyor 3? 

While approaching its landing site, the LM had to manage at least 2 speeds: the sink rate and the vertical speed. To reduce both, the LM had to tilt to point its exhaust cone at a ?-angle in flight direction, maybe in the direction of Surveyor 3 (I dont know yet). In addition, the propulsive force at various steps during approach may vary, means, a big boost at around 67 meters of altitude may whirl up more material than the trust level short before touchdown.

[Derek Willis]

38 minutes ago, toast said:

While approaching its landing site, the LM had to manage at least 2 speeds: the sink rate and the vertical speed. To reduce both, the LM had to tilt to point its exhaust cone at a ?-angle in flight direction, maybe in the direction of Surveyor 3 (I dont know yet). In addition, the propulsive force at various steps during approach may vary, means, a big boost at around 67 meters of altitude may whirl up more material than the trust level short before touchdown.

The video of the LM landing shows how dust only becomes visible after Alan Bean made his comment about "going to get some dust before long". So whatever the thrust of the engine was, or the angle of the exhaust cone, no dust was blowing about until this point. I would say the dust first becomes visible when Bean mentions the altitude is 120 feet (35 meters). Below that point the dust increases. What you have to bear in mind is that the large amount of dust created as the LM lands is what supposedly blew off some of the dust previously deposited on Surveyor 3. But there doesn't appear to have been any dust beforehand to have been deposited.

https://video.search.yahoo.com/yhs/search?fr=yhs-adk-adk_sbnt&hsimp=yhs-adk_sbnt&hspart=adk&p=apollo+12+landing+video#id=3&vid=77e290e80a59bc226051d031ab3865dd&action=click 

[Peter B]

54 minutes ago, Derek Willis said:

The video of the LM landing shows how dust only becomes visible after Alan Bean made his comment about "going to get some dust before long". So whatever the thrust of the engine was, or the angle of the exhaust cone, no dust was blowing about until this point. I would say the dust first becomes visible when Bean mentions the altitude is 120 feet (35 meters). Below that point the dust increases. What you have to bear in mind is that the large amount of dust created as the LM lands is what supposedly blew off some of the dust previously deposited on Surveyor 3. But there doesn't appear to have been any dust beforehand to have been deposited.

https://video.search.yahoo.com/yhs/search?fr=yhs-adk-adk_sbnt&hsimp=yhs-adk_sbnt&hspart=adk&p=apollo+12+landing+video#id=3&vid=77e290e80a59bc226051d031ab3865dd&action=click 

The dust on Apollo 12's landing is discussed in the Apollo Lunar Surface Journal. It quotes the post-mission briefing back in 1969 where Conrad reckons he started seeing dust around the time he stopped the LM's forward motion. In the briefing he reckoned he did that at an altitude of around 300 feet/90 metres, but the data shows forward motion stopped at around 240 feet/75 metres. Either way, if dust was visible at that altitude, it could well have been in motion at a higher altitude.

I still don't see any reason for it to be a problem for dust to be blown around at that sort of altitude - there was nothing to stop the exhaust gases hitting the ground at the speed they left the combustion chamber. The only issue would be whether they'd spread out so far they didn't have the dynamic pressure to disturb the dust, and I wouldn't know how to calculate that.

I wouldn't not pay much attention to what Bean had to say about the dust during the landing. As the Lunar Module Pilot he was responsible for monitoring data and informing Conrad. He therefore had little time to look out the window and offer useful commentary about the dust. By contrast, Conrad was pretty much looking out the window all the time, but was concentrating too much on flying the LM to describe what he could see in much detail; but based on the post-mission briefing he appears to have seen dust long before Bean warned him about it.

Here is a pretty awesome video which synchs the camera view out the window with the voices of the astronauts and Mission Control, and also adding in commentary and other data such as altitude and which computer program was running: https://www.youtube.com/watch?v=kFSa6vUix70

[Derek Willis]

1 hour ago, Peter B said:

The dust on Apollo 12's landing is discussed in the Apollo Lunar Surface Journal. It quotes the post-mission briefing back in 1969 where Conrad reckons he started seeing dust around the time he stopped the LM's forward motion. In the briefing he reckoned he did that at an altitude of around 300 feet/90 metres, but the data shows forward motion stopped at around 240 feet/75 metres. Either way, if dust was visible at that altitude, it could well have been in motion at a higher altitude.

I still don't see any reason for it to be a problem for dust to be blown around at that sort of altitude - there was nothing to stop the exhaust gases hitting the ground at the speed they left the combustion chamber. The only issue would be whether they'd spread out so far they didn't have the dynamic pressure to disturb the dust, and I wouldn't know how to calculate that.

I wouldn't not pay much attention to what Bean had to say about the dust during the landing. As the Lunar Module Pilot he was responsible for monitoring data and informing Conrad. He therefore had little time to look out the window and offer useful commentary about the dust. By contrast, Conrad was pretty much looking out the window all the time, but was concentrating too much on flying the LM to describe what he could see in much detail; but based on the post-mission briefing he appears to have seen dust long before Bean warned him about it.

Here is a pretty awesome video which synchs the camera view out the window with the voices of the astronauts and Mission Control, and also adding in commentary and other data such as altitude and which computer program was running: https://www.youtube.com/watch?v=kFSa6vUix70

Can you tell me where in the Surface Journal I can find the reference to the post-mission briefing. That would save me a lot of time.

The molecules of gas would hit the ground at essentially the same speed they left the engine nozzle. But as you indicate, it is the pressure that matters. The exhaust expands rapidly in a vacuum, so the pressure would be very low when the gasses hit the surface from an altitude of 75/90 meters.

I guess we should also not pay much attention to when Buzz Aldrin said they were "picking up some dust" at 40 feet.

The video is the same one I linked to. Perhaps the astronauts could see the dust much earlier than the video indicates.

For the record, I am not claiming anything I have said demonstrates the Moon landings were faked - far from it. I am simply curious to know where the dust on Surveyor 3 came from.

Edit: I found the reference to the dust:

Conrad, from the 1969 Technical Debrief - "As soon as I got the vehicle stopped in horizontal velocity at 300 feet (figure 4-12 (redrafted by Thomas Schwagmeier) from the Apollo 12 Mission Report indicates that he stopped almost all of his forward motion at about 220 feet), we picked up a tremendous amount of dust - much more than I had expected. It looked a lot worse than it did in the movies I saw of Neil's landing. It seemed to me that we got the dust much higher than Neil indicated. It could be because we were in a hover, higher up, coming down. I don't know. But we had dust from - I think I called it around 300 feet. I could see the boulders through the dust, but the dust went as far as I could see in any direction and completely obliterated craters and anything else. All I knew was (that) there was ground underneath that dust. I had no problem with the dust, determining horizontal (fore and aft) and lateral (left and right) velocities, but I couldn't tell what was underneath me. I knew I was in a generally good area and I was just going to have to bite the bullet and land, because I couldn't tell whether there was a crater down there or not."]

Who am I to question someone who went to the Moon! However, looking at the video, at an altitude of 300 or even 240 feet the "craters and anything else" don't appear to be "completely obliterated". But I wasn't there!

 

 

Edited January 30, 2019 by Derek Willis

[Obviousman]

I think people are possibly missing something here: there is an altitude / speed where dust is visible from the LM, and an altitude where dust is created and could affect the Surveyor.

The altitudes do not have to be the same.