Surveyor 3 anomalies

[Peter B]

Over at UM, a poster by the name of Derek Willis has announced his belief in the faking of Apollo 12:

https://www.unexplained-mysteries.com/forum/topic/327357-belief-in-apollo-hoax-conspiracy-could-grow/?page=6&tab=comments#comment-6729276

His post provides links to a couple of articles he's just had published at Aulis, one of which deals with the Surveyor 3 issue. In particular, he draws attention to disagreement between the Apollo 12 astronauts and Mission Control over the cause of discolouration of Surveyor 3.

During the mission, Conrad and Bean said they thought that Surveyor 3 being down inside the crater would protect it from the spray of dust blown up by the LM engine during landing - that the dust would simply blast straight across the crater. As a result they concluded that the Surveyor's brown colour was the effect of the Sun on the paint. It wasn't until some time later that one of them brushed against part of the Surveyor and found the effect was indeed dust.

Willis doesn't buy this. He still thinks the crater should have sheltered the Surveyor.

I disagree. My view is that the LM passed close enough to the edge of the crater for most of the last part of the descent that some of the engine gases sprayed directly into the crater, thus blowing dust within the crater onto the Surveyor.

However I can't prove this as I don't know how wide the exhaust spread out from the LM Descent Engine bell.

So can someone point to evidence of how wide the cone of exhaust gas was? Or explain the process?

Thank you!

Incidentally, I've invited Derek Willis here to discuss his articles.

[ka9q]

In a vacuum, the plume begins to expand immediately after exiting the nozzle, even a long one designed to be efficient in vacuum. (However low the pressure at the mouth of the nozzle, it's still lower around it.)  But most of the gas still goes straight out the back, and in the case of the LM just before landing hit the surface at nearly right angles. This created a very thin flat sheet of dust flying horizontally outward along the surface in all directions. Conrad flew the Intrepid around the right (north) side of Surveyor crater and landed on the far rim, so he had plenty of opportunities to blow dust onto the Surveyor.

NASA released guidelines for anyone landing near an Apollo site, and much of them dealt with how far away and what trajectory should be followed to avoid blowing dust over the artifacts at the site. I hope people follow them, because one of the things I'd be most interested in seeing is how much dust has built up at the Apollo 11, 14 and 15 LRRRs. Obviously you don't want to add more just by arriving to take a look.

[smartcooky]

In a vacuum, the plume begins to expand immediately after exiting the nozzle, even a long one designed to be efficient in vacuum. (However low the pressure at the mouth of the nozzle, it's still lower around it.)  But most of the gas still goes straight out the back, and in the case of the LM just before landing hit the surface at nearly right angles. This created a very thin flat sheet of dust flying horizontally outward along the surface in all directions. Conrad flew the Intrepid around the right (north) side of Surveyor crater and landed on the far rim, so he had plenty of opportunities to blow dust onto the Surveyor.

This is perfectly demonstrated if you watch a rocket launch...



As the rocket climbs, and the atmosphere becomes thinner, so it is less able to "constrain" the exhaust plume

[Peter B]

Yes, I absolutely understand this. My understanding is that an exhaust plume in a vacuum is conical. My question is what was the angle from vertical that this cone expanded in the case of the LM Descent Engine.

When I pointed this out to Derek Willis over at UM he replied with a photo of the exhaust plume of a Space Shuttle RCS engine. So I asked him whether that was comparable to the LM Descent Engine.

Does anyone have any knowledge of this?

[JayUtah]

It's possible to compute the angle, but I don't remember how off the top of my head.  I'm confident it's in Sutton and Biblarz, which I can consult when I remember where I put the book.  The problem is that the boundary of the plume is not sharp.  So you have to pick a cutoff density and say something like, "The half-angle of plume is X degrees out to D density."  That's only one of the ways that a plume is not homogeneous, especially when underexpanded.  You're still going to get the flat-sheet dispersal ka9q mentions, from the faster-moving still-somewhat-columnar core of the plume.

[Jason Thompson]

When I pointed this out to Derek Willis over at UM he replied with a photo of the exhaust plume of a Space Shuttle RCS engine.

Probably worth pointing out that there is often a fallacious assumption that a photo shows the whole plume. Especially in the case of the shuttle RCS engine, where all you are seeing is an ignition transient rather than a steady state burn. The combustion products of that propellant/oxidiser combination are transparent. All you'll see on a picture is the part of the plume that generates or scatters enough light to be visible on the film or CDD. The stuff you can't see is still significant in terms of blowing stuff around.

As I once had to point out to someone who couldn't believe that things could be blown around by a rocket exhaust he couldn't see, you can't see the air around you but you can still be blown around by it.

Way better to use the mathematical methods as suggested by Jay rather than using pictures.

[bknight]

When I pointed this out to Derek Willis over at UM he replied with a photo of the exhaust plume of a Space Shuttle RCS engine.

Probably worth pointing out that there is often a fallacious assumption that a photo shows the whole plume. Especially in the case of the shuttle RCS engine, where all you are seeing is an ignition transient rather than a steady state burn. The combustion products of that propellant/oxidiser combination are transparent. All you'll see on a picture is the part of the plume that generates or scatters enough light to be visible on the film or CDD. The stuff you can't see is still significant in terms of blowing stuff around.

As I once had to point out to someone who couldn't believe that things could be blown around by a rocket exhaust he couldn't see, you can't see the air around you but you can still be blown around by it.

Way better to use the mathematical methods as suggested by Jay rather than using pictures.

Excellent observation, but I'm not sure the poster will agree

[Peter B]

It's possible to compute the angle, but I don't remember how off the top of my head.  I'm confident it's in Sutton and Biblarz, which I can consult when I remember where I put the book.  The problem is that the boundary of the plume is not sharp.  So you have to pick a cutoff density and say something like, "The half-angle of plume is X degrees out to D density."  That's only one of the ways that a plume is not homogeneous, especially when underexpanded.  You're still going to get the flat-sheet dispersal ka9q mentions, from the faster-moving still-somewhat-columnar core of the plume.

Excellent, thank you!

The key issue is that the Apollo 12 LM made its closest approach to Surveyor 3 at a distance of about 109 metres, when it was at an altitude of about 67 metres. But, crucially, at this point the LM passed only about 50 metres from the edge of the crater.

My suspicion is that this distance, given the LM's altitude, is close enough for at least the outer part of the exhaust plume to spray directly into the crater - and thus sufficient to blow dust onto Surveyor.

On top of this, the data suggests that for most of the rest of its path until touchdown its altitude was greater than its distance to the edge of the crater. And if you track the path of the LM as it flew past Surveyor, it traced a path nearly 150 degrees around Surveyor - which would explain why so much of the Surveyor is dust-covered.

[bknight]

After reading descriptions of the hood containing the mirror, it had the appearance of being "sand" basted.  This does indicate that the descent engine was causing the surface regolith at least as far as the lander.  Because the hood was facing the LM most if not all the "dust" was in place during the landing of S3, bouncing at least twice.  Searching through history I discovered that scientists were a bit appalled by the blurred images of S3, dust on the mirror was their conclusion.
Anyway he doesn't have much of case of proving that their was an anomaly in A12's mission.  Just hard headed willful ignorance.