| ronaldo |
06-18-2007 03:29 PM |
Quote:
Originally Posted by Mr.Sexbankroll
(Post 12619361)
I didn't believe in the theory till i read something pointing out the lack of a blast crater under the lander
http://ginacobb.typepad.com/photos/u..._on_moon_1.jpg
Pretty steady "sandy" surface eh?
If that actually landed, it sure the hell wouldn't look like this :1orglaugh:1orglaugh
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1. No blast crater or any sign of dust scatter as was seen in the 16mm movies of each landing [3], p. 75.
No crater should be expected. The Descent Propulsion System was throttled very far down during the final stages of landing. The Lunar Module was no longer rapidly decelerating, so the descent engine only had to support the module's own weight, which by then was greatly diminished by the near exhaustion of the descent propellants, and the Moon's lower gravity. At the time of landing, the engine's thrust divided by the cross-sectional area of the engine bell is only about 10 kilopascals (1.5 PSI)[11], p. 164, and that is reduced by the fact that the engine was in a vacuum, causing the exhaust to spread out. (By contrast, the thrust of the first stage of the Saturn V was 3.2 MPa (459 PSI), over the area of the engine bell.) Rocket exhaust gases expand much more rapidly after leaving the engine nozzle in a vacuum than in an atmosphere. The effect of an atmosphere on rocket plumes can be easily seen in launches from Earth; as the rocket rises through the thinning atmosphere, the exhaust plumes broaden very noticeably. Rocket engines designed for vacuum operation have longer bells than those designed for use at the Earth's surface, but they still cannot prevent this spreading. The Lunar Module's exhaust gases therefore expanded rapidly well beyond the landing site. Even if they hadn't, a simple calculation will show that the pressure at the end of the descent engine bell was much too low to carve out a crater. However, the descent engines did scatter a considerable amount of very fine surface dust as seen in 16mm movies of each landing, and as Neil Armstrong said as the landing neared ("...kicking up some dust..."). This significantly impaired visibility in the final stages of landing, and many mission commanders commented on it. Photographs do show slightly disturbed dust beneath the descent engine. And finally, the landers were generally moving horizontally as well as vertically until right before landing, so the exhaust would not be focused on any one surface spot for very long, and the compactness of the lunar soil below a thin surface layer of dust also make it virtually impossible for the descent engine to blast out a "crater".[11], pp. 163?165
http://en.wikipedia.org/wiki/Apollo_...ax_accusations
That'll be fun to read when I have some more time. |
