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hilly said..
Not really they did not use those to land. They are for take off.
Finally, one or more of three 67.2-inch (1.71 m) probes extending from footpads on the legs of the lander touched the surface, activating the contact indicator light which signaled the commander to manually shut off the descent engine, allowing the LM to settle onto the surface. On touchdown, the probes would be bent as much as 180 degrees, or even break off.
So the decent engine was used to slow them down until the probes projecting 1.71m down from the underside of the landing feet, contacted the surface, signalling for a manual shut down of the engine...
Couple of things on this:
- the nozzle is pretty big (you can see it there under the lander in the middle) and the outlet of which is set around, say 400mm above the bottom of the feet, this would put the nozzle about 2.1m above the surface when the probes touched.
- the lander was firing through the decent to slow them down, so it was still firing (and decending) before the probes touched.
- the manual shut off would not have been instantaneous, you have the reaction time of the commander or whoever it was that flicked the off switch. As well as that, the thrust shut off would not have been instant like a light switch, there would be some wind down before full shut down.
- from the above we can safely assume that there was still enough thrust coming from the decent engine for some time after the probes touched as the lander continued to descend and settle.
- lets say the probes retracted slightly as the lander descended and there was still thrust coming from the engine, at 1.71m surely there would have been enough thrust to kick up some moon dust and make a mark on the surface.
As Imax said, the dust falling at 1/4 rate of fall to that of Earth - there is no dust on the lander feet or any other surface, it's all shiny and clean...
Where's the dust and descent engine mark?