Rover Footage Filmed on Earth Nov 16, 2007 16:03:41 GMT -4
Post by sts60 on Nov 16, 2007 16:03:41 GMT -4
rocky said:In this video the idea that the soil kicked up by the rover encounters atmosphere is discussed. It's pointed out that the soil clumps when it encounters atmosphere. I can see he clumps.
I think he's right about the soil encountering atmosphere. It would not have clumped in mid-air if it had been on the moon.
Apologies for the thread necromancy, but as part of working on a lunar power source study, I was looking at Apollo LRV experience with containment of the dust ejected by the wheels, and found this (note: 8 MB PDF) study, in which an LRV tire was driven around inside a vacuum chamber over simulated lunar soil, all at 1/6 G in a "Vomit Comet" flight.
J. D. Halajian at Grumman Aircraft had conducted a study to try to explain the behavior of dust as a cohesive soil on the moon when it should have behaved as a cohesionless soil since no moisture is present on the moon's surface. It is well known that moisture is required on earth for fine-grained soil to exhibit the very complex physicochemical soil mechanics phenomenon known as cohesion.
My goodness! If rocky's mad research skillz hadn't been confined completely to YouTube and random HB sites, he could have waved this around triumphantly.
Of course, later on the study points out:
In the reduced pressure of the moon, there was no possibility of there being any moisture, yet the soil exhibited apparent cohesion. Why? Vacuum conditions on the moon seem to cause all surface impurities on the individual soil grains to "boil off" leaving a "clean body." This clean body effect is what seems to cause the apparent cohesion. At the start of this test program a vacuum of several tors* had been planned. Due to flight limitations this had to be abandoned and a pressure of 2-5 mm of mercury was the best that could be hoped for. This does not nearly approach hard vacuum cbnditions even though over 99 per cent of the air is evacuated. It was found that during the test program, whenever the pressure was less than 5 mmHg, the LSS started to exhibit apparent cohesion. "Clumps" of LSS would be thrown up by the wheel and remain as a coherent mass until it struck some solid object, such as the chamber wall. It would then splatter upon impact. A lot of these clumps would stick to the sides of the chamber.
Now, I have read that the lunar soil is so clumpy because of a lot of jagged particulates - which have been cited as an inhalation hazard for future long-stay crews as they bring the stuff into airlocks. I suppose the truth is some combination of the two. If anybody knows any more about it, please chime in.
* Note: 760 torr ~ 1 atmosphere; 1 torr = 1 mm Hg pressure.