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  Mercury - Gemini - Apollo
  Apollo lunar module surface sensing probes

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Author Topic:   Apollo lunar module surface sensing probes
NJ CO
New Member

Posts: 2
From: Greenwich, NJ, US
Registered: Mar 2008

posted 09-01-2014 06:08 PM     Click Here to See the Profile for NJ CO     Edit/Delete Message   Reply w/Quote
Regarding the Apollo lunar module landing probes, I'm sure we're all aware that a switch triggered the contact light once the probe struck the lunar surface.

But photos show that the probes actually dug into the surface and some photos show that they even stuck up a bit. Nowadays, I'm sure we'd use a rope-like probe that simply coils and/or lays right under or near a foot pad...

My question is: The landing probes appear to be rigid and tubular in make-up.

If the probes are as mentioned, and a bit longer than say a rake handle, how is it that the lunar module was not affected, meaning tilted to one side or another? If the LM came straight down, how could three probes (as in Apollo 11) not get in the way?

Not the most technical in the way of posting, but just one of those things I've wondered and not really found the answer, although I'm sure I will here.

space1
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Posts: 590
From: Danville, Ohio, USA
Registered: Dec 2002

posted 09-01-2014 06:48 PM     Click Here to See the Profile for space1   Click Here to Email space1     Edit/Delete Message   Reply w/Quote
The probes were relatively fragile aluminum tubes that would be like toothpicks with the "heavy" Lunar Module above them. As far as I know they had no measurable effect on landing dynamics.

I'm not so sure we would do it so differently today. The kind of rope-like probe you describe would not be rigid enough. You need to know exactly where the sensor is relative to the landing pad. We might prefer something that would retract while making contact, but the Apollo Lunar Module lunar surface sensing probe was a good lightweight solution at 2.52 pounds.

schnappsicle
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Posts: 189
From: Houston, TX, USA
Registered: Jan 2012

posted 09-03-2014 05:25 AM     Click Here to See the Profile for schnappsicle   Click Here to Email schnappsicle     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by NJ CO:
But photos show that the probes actually dug into the surface and some photos show that they even stuck up a bit.

You bring up an interesting point. I've also wondered why some stick up (as in the Apollo 12 plus-Y probe) while the Apollo 11 plus-Y probe lays flat. If I had to guess, it probably has something to do with Buzz's comment just before landing that they were "drifting forward". Also, Armstrong landed with the engine still running while Conrad cut off the engine as soon as the contact light came on. In other words, Eagle had a relatively gentler landing than Intrepid. Also Eagle landed in a relatively flat area, while Intrepid landed on a very slight slope. Lastly, Conrad stated that the plus-Y probe hit the ground first and tilted Intrepid to Conrad's left before settling down to the surface. All that may have contributed to Intrepid's plus-Y probe sticking up in a dangerous position.

I agree, something probably should be done to the probes with regard to future landings. It might be that they snap off at the footpads or something. Whenever I look at the photos Bean took of Intrepid's probes after landing, I'm amazed one of the astronauts didn't run into one of them and puncture his suit.

Lou Chinal
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Posts: 1041
From: Staten Island, NY
Registered: Jun 2007

posted 09-03-2014 09:45 AM     Click Here to See the Profile for Lou Chinal   Click Here to Email Lou Chinal     Edit/Delete Message   Reply w/Quote
That was discussed. Unfortunately the design was already frozen. The Apollo 9 LM Spider had four probes. By the time Apollo 11 flew the one on the front landing strut had been removed for that very reason.

NJ CO
New Member

Posts: 2
From: Greenwich, NJ, US
Registered: Mar 2008

posted 09-03-2014 04:00 PM     Click Here to See the Profile for NJ CO     Edit/Delete Message   Reply w/Quote
Thanks for the informative replies. Been around this site in "lurker mode" for some years, and again, many thanks.

Along with most of the missions, I have the Apollo 12 mission report book (purchased back when we had only dial up internet rather to now viewing it in seconds...), and I certainly missed the tilting of the lander Conrad mentioned. Makes sense in that these things look sort of on the sturdier side to me, the way they dig into the surface and protrude upwards without appearing to be bent or crimped.

But again, I'm sure they were designed to perform the way they did, and worked beautifully too, no matter how much it might curiously confuse a dumb prison guard from New Jersey 40 plus years later...

All times are CT (US)

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