QUOTE(turbonium @ Jul 24 2007, 01:00 AM)

Hey MID
I'd like to respond to some of the points you've raised here.
First of all, I won't go over the argument about whether or not the LM could (or should) have produced a blast crater within the substrate. For now, let's assume you are correct - that no such blast crater would (and therefore did not) result from the landings, and that only the few inches of lunar surface dust below the LM descent engine would (and therefore did) blow up and away.
OK, let's just say I'm right about that aspect!
(I like that)...
QUOTE
But even at that, I do not see any evidence - in either the photos or videos - that any of the surface dust has been blown away from below any of the LM's.
Well, there is evidence in a couple of forms. We'll get into that in a minute.
QUOTE
You contend that the dust "flew out for a very long distance" before it fell back to the surface. What is the "very long distance", in terms of feet or meters? Was it blown a different distance for each of the missions?
Dunno!
That's really not possible for me to say. I would need to know the specifics about the energy imparted to the surface dust (exhaust gas velocity), the velocity imparted initially to the dust, and the specific angle that the dust sprayed out in that radial pattern around the LM on its ballistic trajectory in order to get a rough calculation on the distance in a 1/6g field.
I should imagine that 100 FPS + may be a reasonable estimate of the outward velocity of the dust. According to the crews it shot out in a sheet like radial pattern for quite some distance out toward the horizon, and Neil Armstrong indicated in the AS-11 technical debrief that it was moving at a "great speed"
I would think that it disappeared from sight a couple hundred meters from the LM, probably still falling in it's arc. I don't think the actual distance is relevant. It was a ways off.
QUOTE
1. If the "dust moves out in radial sheets" away from the LM, then why is this not even remotely evident in any of the photos or videos? Removing a few inches of dust from a large perimeter below and around the LM would certainly be noticeable in many of the close-up, hi-res images. But, I haven't seen anything of the sort.
Because, the end of the dust "sheet" flew out from the LM upon engine cutdown, exactly like the rest of the dust did. The last of the dust flew away from the LM at somewhat of an upward angle to the surface (again, I don't know, save to say it was between 1 and 90 degrees!). Nothing fell close to the LM because it was moving at a fairly high rate of speed away from the LM. I have often equated the visual to what you would see if squirting a garden hose out into an arc away from you, and then suddenly cutting off the valve. The end of the water stream vanishes along the same arc, and no water falls on you, or near you. It follows the impulse of the thrust it was given.
It should be understood that the engine blast was enough to effect the dust layer some distance up off the surface, but only enough to scatter part of the dust. Underneath the engine bell, especially as they got close, was the area where most of the dust would be blown from. At touchdown, or at cutoff some distance above the surface, generally, the engine was throttled down to 25% or less of its rated thrust, and the LM was generally translating slightly forward, or perhaps translated a bit to one side and forward. The main area effected by this dust was right below the bell. As you moved out from the bell, less of the surface dust was effected, and generally, out in front of the LM (where the +Z strut (the ladder strut) was), the ground had very little effect at all. The effect was primarily observed under the LM where the engine bell was, and somewhat aft of the direction of movement.
Additionally, different sites had different depths of soft soil on the surface. Thus, some landings, like Apollo 11's, removed virtually everything immediately under the LM, and others cut through a bit less of the depth (later missions tended to touch down by shutting their engines down betweeen 6 and 8 feet up and plopping down onto the surface to effect a crush in the honeycomb shocks of the landing gear, reducing the distance from the bottom step of the ladder to the foot pad).
QUOTE
2. If there is no dust on the LM footpads because it was blown far away before settling back to the surface, then why would there be so much dust mere inches away from the footpads that the astronauts were able to make deep footprints in it?
Same reasons. The dust outside of the immediate area underneath the LM, especially in the +Z direction, was essentially undisturbed. The footpads, you must note, were approximately 15 feet from the engine bell. There was little effect in that area, if any.
QUOTE
3. How could the astronauts leave such noticeable footprints everywhere, and the rover could leave such noticeable tire tracks everyywhere, but the much stronger force of the LM descent engine leave no evidence of disturbing any dust?
As Swanny asked....Who said the force was much greater? The LM DPS engine had an estimated pressure of about 1.5 psi at the low thrust it was producing in the terminal landing phase. Not really all so much.
Further, you should understand that the force of a diffuse gas will not produce the same impression as a solid mass concentrated in a very small area.
A foot, for instance, in an Apollo lunar overshoe, was pressing into the ground with a pressure of about the same value, and an LRV, which sat on the surface with about the same pressure. However, there is a difference between a difuse gas blowing on something and a solid object pressing into it.
A little demonstration I've often advised is this. Using corn starch (which has similar self-adherent qualities to lunar dust), fill a pan or something with a little layer of the stuff. Blow on it with a light but concentrated stream toward the center of the layer.
You'll notice that where the air is concentrated, your blow more dust away than to the perimieter of the layer. You'll get some of the outer material to move, but far less than where the "exhaust" is focused (You're also gonna make a mess, so be prepapred to clean up!).
After you do this, note that there's no really definitive impression made in the corn starch from your breath, but you can certainly see where you've disturbed it. You could tell that it was sheared by air. Now, just touch your finger lightly to the corn starch, and you'll notice that it leaves a definite and clear imprint in the stuff. Just a light touch coimpacts the corn starch and leaves a fingerprint in it.
This is exactly why a foot, or an LRV wheel, or a landing probe, or any other solid object, leaves a clear print in the dust, while the engine blast itself leaves a characteristic shearing pattern in it.
QUOTE
MID, I'd like to give you (or anyone else) an opportunity to show solid evidence of the "dust" craters you claim were created by the landers. Or, at very least, any evidence that you feel indicates that dust was blown away by the landers.
Turb, I have specifically said that there werre no craters created by the LM DPS thrust. The dust was blown away radially to one degree or another, and left no craters...merely what is called a "scouring" pattern beneath and around the base of the LM, to one degree or another.
Now, evidence of this first comes from pilot reports, like this one, made by Neil Armstrong at Tranquility Base, approximately 1 and 1/2 minutes after he became the first human being to set foot (or boot) upon the Moon:
"Okay.
The descent engine did not leave a crater of any size. It has about a one foot clearance on the ground. We're essentially on a very level place here.
I can see some evidence of rays eminating from the descent engine, but a very insignificant amount."
Of course, one may not "buy" this...but it was in the plan to observe the LM in detail and the surroundings, and in fact, photos were taken on AS-11, AS-12 and AS-14, specifically designed to document the effects of the DPS on the lunar surface.
For instance:
AS11-40-5921
This is under Eagle's engine bell. You can clearly see the radial scouring pattern eminating from the engine bell. In fact, it's cutting into the substrate and evidence of the hard substrate fully exposed is evident here. But there is no crater.
AS12-47-6908
Under the butt of Apollo 12's LM, "Intrepid".
Clearly, you can see the scour of the LM DPS in a radial pattern beneath the bell. This engine was cut down higher over the surface, and as is clearly visible, much of the surface matter is still present, but obviously affected by the exhaust.
AS14-66-9262

Clearly, the Apollo LM, "Antares" left obvious scour on the surface. In fact, in this shot, you can clearly see the direction of motion at landing (the -Z strut shows some forward motion, as does the scouring pattern.
That is about as solid as evidence gets of exactly what I've maintained that the LM DPS exhaust did to the surface.
You can also consult the following photos, which all clearly show scour, scatter, and various cobbling patterns caused by the DPS exhaust gas:
AS11-40-5858, AS11-40-5892, AS12-47-6904 through 6911, and AS14-66-9261 through 9268...all of which were taken to document DPS engine effects on the lunar surface.
Now Turb, you can see human appendages, shades, curtains, chairs, and TV monitors, and evidence of stagehands in a mere few seconds of obscure, blurred, out of focus Apollo 12 color TV camera movement.
Please don't tell me that in these clear Hassleblad photos, which clearly indicate the obvious, that you do not see the patterns caused by the DPS engine on the lunar surface. The proof of what I've told you is right here, clear as day.
I trust this will be sufficient!
M~