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@blank000blank

Oh really? Yet you don’t think that Jarrah’s “facts” are made up? Jarrah doesn’t even have a college education, yet you readily believe his “facts.”

@Aurinkohirvi

That makes sense to me as well.

@GoneToPlaid

Yeah, I would agree with that: the bowl shape ejects the soil slightly upwards. More so when the lander gets lower.

In the beginning though the flow would be more level with the ground. If one looks at the Apollo 11 footage, you can see the flow of soil (or exhaust gas?) against the rocks quite far from the LEM.

Also at the later phase with bowl there, I would think there is all the time exhaust gas preassure from upwards to downwards, as well from the center to outwards.

Just the same pointless excuses and made up ‘facts’ from philwebb and gonetoplaid – why do you two even bother?

Those shallow yet slightly upward sloping crater walls now force the dust and engine gasses to deflect slightly upwards as the dust and gasses radially expand. This shields the surrounding lunar terrain beyond the crater from further erosion. Yet the dust ejected from the crater will follow ballistic trajectories and get deposited onto the surrounding terrain. Really, its a very similar phenomenon as the visible impact craters on the moon. Why should you expect any different of a result?

Aurinkohirvi, look at it this way. Ideally the LM should descend at 2 feet per second. Thus the engine bell is only really close to the surface during the last 10 seconds or so. During the last few seconds before landing the engine does scour out a very shallow crater which roughly the width of the LM body and up to about a half foot deep. This crater would deepen and grow wider if the engine remained running long after landing. Now think about this crater’s very shallow sloped walls. More…

Ever since I encountered the issue of deep footprints right next to LEM, I found that very peculiar indeed.

I do not buy there should be any loose soil left there so near the LEM, unless the powdery soil goes REALLY deep (and no deep hole under LEM). The fast flowing soil should brush clean the loose soil in near vicinity of LEM.

What I would buy is that there being pebbles broken from a harder surface with the last breaths when the engine is shut down.

No, but that is what you implied by saying that loose pebbles should have been long gone — even though there still is scoured topsoil (and pebbles) under the descent engine.

Better yet, do a leaf blower experiment with dry talc in which small pebbles have been thoroughly mixed. Even dry sand into which small pebbles are thoroughly mixed will produce fairly similar results.

GoneToPlaid wrote: “Loose pebbles are easier to move compared to the fine dust which they were buried in?”

What? I said nothing of the sort. Read again.

Oh really? Loose pebbles are easier to move compared to the fine dust which they were buried in? The dust blows away first, exposing the pebbles until enough dust is blown away to allow the pebbles to be blown away if the engine continued to run. That is a continuous process until either then engine cuts off or until the top foot or so of lunar topsoil has been blown away to expose either bedrock or the extremely tightly compacted subsoil underneath. Think it though.

@GoneToPlaid

You’re right on the nozzle shape. But there is also difference with the engine power, as Jarrah explains.

Draws the atmosphere along the sides of the plume? It does? What does that do? I thought the exhaust plume pushes the atmosphere away. Anyways the atmosphere reduces the power of the exhaust plume.

@GoneToPlaid

It’s really a no-brainer there should be no loose soil left at all under the lander. If it’s pebbles kicked out the nedrock by the dying exhaust, that might be a different thing. But loose soil pebbles should have been long gone under the LEM.

And of course Jarrah doesn’t even take into account that the engine bell on the test rig is extremely narrowly tapered, strongly concentrating its thrust to push against earth’s atmosphere and draw in earth’s atmosphere along the sides of its high velocity plume.

The LM engine bell on the other hand is a giant paraboloid which is designed to work in zero atmosphere. The fat paraboloid shape make a huge difference in its ability to scour a surface.

8:32 “Yet we see loose pebbles and grains directly where the plum would have struck.”

Jarrah, when the engine cuts off it doesn’t instantly cut off since a small amount of propellant in the fuel lines flushes into the engine bell and reacts. Thus the engine dies down over a second or so. The result is that the engine’s dying thrust will still blow away some dust under the engine yet leave freshly uncovered pebbles undisturbed. It really is a no-brainer.

Wooo 7:15,
Wow you have 2 references, you are comparing the exhaust diameter at the ground to the nozzle diameter of the lunar nodule?

assuming that the lunar module has the same exhaust shape as this small lander

1.31 lbs sq inch / 173 = 0.0075 lbs per /inch!!!

(Sorry not used to none metric system)

“And why is there a prestine (totally unscortched) white bolder under the LEM at 8:25?” –SounzNice

That isn’t a boulder. It is a white Nylon bag. Try actually downloading and zooming in on NASA’s high-res photo. You will see that it is a Nylon bag and not a white boulder.

@philwebb59

“…without an atmosphere for the dust to ride on, it would simply fall.”

Dust would fall slower on Earth, but that don’t make it fly a longer distance, on the contrary. The resistance of atmosphere stops dust flying forward on its trajectory on Earth. On the Moon dust would not lose its energy to atmosphere resistance but would fly as any other object, a distance relative to its kinetic energy and the gravity pull, like a bullet if you will.

So the replaced soil would equal as mass to 8000 pieces of a block kept in Paris. That would WEIGHT 8000 kilograms on Earth, and about one sixth of it on the Moon. Good, just asking to get the picture of the volume of dirt you think the engine exhaust moved.

That’s still a lot of powdery soil. But you still didn’t answer the questions. Why not?

“The dirt and dust on the Moon flies MUCH easier and longer” Actually, without an atmosphere for the dust to ride on, it would simply fall. Gravity is more efficient in a vacuum: no drag, no terminal velocity, just constant acceleration.

In a vacuum there is no atmosphere for the exhaust to move out of the way. And the gas will expand in every direction possible. Unless the molecules of gas in the exhaust directly contact the dust, it will not move. So yes, the displacement pattern will look strange compared to what you would expect from a leaf blower experiment on earth.

Side issue: 8000 kg = 8000 kg = 8000 kg. I’m not using kgf. Mass is constant, weight depends on gravity.

I asked you 1) about the deep footprints right next to LEM. Do you consider this soil would not have blown away (as I would think it should looking at A11 descent footage)? And 2) about the satellite images not showing such a wide disturbed soil area everyone was expecting.

As a side issue, loose soil would fly few centimeters only at the very outmost rim of the whole effect area. And is this 8000kg you say measured soil weight on the Moon (that would equal to 48000kg on Earth)?

And if popcorn wasn’t in a bag it would be everywhere except the place where it started. Funny enough the dust is still laying directly under the nozzle.

In my video I show that 3 inches of regolith are missing out at the foot pads, probably more under the nozzle. Assuming a 3 inch thick cylinder, that works out to 8000 kg of regolith that WAS displaced. That’s your shallow bowl of a crater. The dust was blown away at a rate of 2000 to 3000 kg/sec. Some of the dust blew a few centimeters. Some of the dust blew kilometers. The deeper the hole, the more packed the dust, the more force was required to blow it away. Makes sense to me.

Some of the concrete chips fly straight back, opposite the direction of the exhaust. Why would they do that if they were being blown away by the exhaust? What you see is the effect of water turning to steam and expanding rapidly causing the concrete to explode. It is the same thing pop corn would do in your microwave if it wasn’t in a bag.