Bouncing lasers off the moon without a mirror

[jnb]

The title should give away where this is going so let's not turn this into a conspiracy argument.

I was doing a presentation recently and talking about the moon because an audience member had asked about it. At that point someone else in the audience piped up with a comment that made it obvious that he didn't believe people had landed on the moon. Normally I don't engage in those conversations because if someone is ignoring the scientific evidence there is no point presenting a scientific argument, social ones yes but not science at that point. However I did mention about the laser reflectors because on our site (Herstmonceux) we have a piece of kit that is regularly used for laser ranging so context made it appropriate. He countered that laser reflections could be done and measured off the surface without the aid of a mirror. I ignored that and moved on because the whole thing would have been a distraction.

Question - is it possible to measure lunar distances by using laser ranging off the surface without the use of the mirrors?

 

[RikM]

I wouldn't have thought it possible. The surface isn't reflective enough; you would loose the beam colimation from bouncing off the individual grains of soil. If you had a powerful enough laser maybe in theory but I don't think it's a practical reality.

[SilverAstro]

40 minutes ago, jnb said:

Question - is it possible to measure lunar distances by using laser ranging off the surface without the use of the mirrors?

I have no qualifications in the area but something rings a bell about needing a specular reflection (maybe to maintain coherence?) to get measurable inteference. No Idea where I might have read that ! (Ah I see Rick is having similar thoughts as I type )

Other thoughts :  need an impossibly powerful laser. If a powerful enough laser was available why did they waste lift on taking retroreflectors. So, well done on ignoring any further disputation with the guy, I like your style, if the whole world & NASA has not persuaded him then you'll just be wasting breath trying to do it alone !!

 

[Zakalwe]

Most of these conspiracy theory nutjobs tend to focus on one area that they believe "proves" their point. You are right that giving them the evidence doesn't normally work as they will handwave it away. The Dunning-Kruger effect is strong in them!

Laser Ranging is possible without the Lunar Laser Ranging equipment. Smullin and Fiocco from MIT and Graysuk from the Crimean Astrophysical Observatory both carried out the first ranging experiments in 1962. The accuracy of these experiments was improved after the Apollo Lunar Laser Ranging kit was left on the surface. Please see the attached pdf authored by PL Bender.

Bender.pdf

[Zakalwe]

Smullin and Fiocco's work was published in Nature, edition 194 in 1962, titled "Optical echoes from the Moon"

 

http://www.nature.com/nature/journal/v194/n4835/pdf/1941267a0.pdf

[RikM]

Surprising  

[SilverAstro]

Interesting !

[Zakalwe]

Its important to note that some conspiracy theory nutjobs try to use this as "evidence" that the Apollo Lunar Ranging experiments are all part of the "hoax". Their thinking (for lack of a better word. If they actually did some thinking then they wouldn't be conspiracy nutjobs) goes along the lines of "Lunar ranging was carried out before Apollo, therefore the evidence from the LLR can be handwaved away". What they fail to appreciate is that Lunar ranging was extremely difficult prior to Apollo- the 1962 MIT demonstration had to use the most powerful laser available at the time (a 50 joule Raytheon device) and the very best available photomultipliers.  Their calculations showed that they would only receive 12.5 photons back per pulse. After the LLR reflectors were left by Apollo 11, 14 and 15 laser ranging became a much more powerful tool and has yielded solid science for 40+ years.

 

http://physics.ucsd.edu/~tmurphy/apollo/apollo.html

http://physics.ucsd.edu/~tmurphy/apollo/basics.html

[The Head Gardener]

I don't suppose you could get him to watch Series 3, episode 23 of The Big Bang Theory - The Lunar Excitation?

Sorry (tongue firmly in cheek ? )

Jayne

 

[cjdawson]

Don't forget to ask the Nutjobs why the USSR didn't jump up and down and out the "hoax moon landings"  after all, it was the middle of the cold war and I'm sure that nothing would have been more fun than to watch the american dogs squirm    Who needs to fight them with a scientific one

[Zakalwe]

1 hour ago, cjdawson said:

Don't forget to ask the Nutjobs why the USSR didn't jump up and down and out the "hoax moon landings"  after all, it was the middle of the cold war and I'm sure that nothing would have been more fun than to watch the american dogs squirm    Who needs to fight them with a scientific one

They normally respond with garbage about the USSR need for American grain. Which ignores the dates of those particular transactions...

Threads like this tend to descend into breaches of the CoC and end up getting locked. If the nutjob gentleman in question really wants to debate his views then send him over to Apollohoax.net and we'll see how long he lasts.

[saac]

2 hours ago, Zakalwe said:

They normally respond with garbage about the USSR need for American grain. Which ignores the dates of those particular transactions...

Threads like this tend to descend into breaches of the CoC and end up getting locked. If the nutjob gentleman in question really wants to debate his views then send him over to Apollohoax.net and we'll see how long he lasts.

No, no, no  and no Zakalwe, you are way off there.  The reason the Russians did not blow the hoax was because of chemtrails.  The Americans used high altitude aircraft to disperse mind altering chemicals into the atmosphere above Russia.

 

Oops, got to go  - two black limousines have just puled up at the front door, donning tin foil hat now and placing hard-drive in the microwave. 

 

Jim

 

 

[Zakalwe]

[GuLinux]

This post reminded me of this: http://what-if.xkcd.com/13/

Not exactly the same, but it shows that given the low moon albedo, it's pretty hard to point a laser at its surface, and see anything from here...

[symesie04]

Confused i thought the Russians said nothing as America had promised to share the Stargate with them?

[Zakalwe]

2 hours ago, GuLinux said:

This post reminded me of this: http://what-if.xkcd.com/13/

Not exactly the same, but it shows that given the low moon albedo, it's pretty hard to point a laser at its surface, and see anything from here...

I love XKCD!

The problem is exacerbated by the atmosphere causing the laser pulses to diverge.

 

[Ouroboros]

I have often thought that some of the best counter arguments to moon-landing deniers  is the sheer impossibility of making a conspiracy work with the large number of people and organisations involved.  It's not just the people either: it's the paper trail, the government  funding of the programme, the minutes of congressional meetings and board meetings in most of America's large aerospace corporations, the project planning meetings, the purchasing and delivery of equipment and so it goes on and on ....

In order to fake it you'd have to do all that and yet not actually go to the moon, just make tens of thousands of people think that's what they were doing. In fact you might as well just do it for real. 

[SilverAstro]

2 hours ago, Ouroboros said:

it's the paper trail, / large aerospace corporations, / the project planning meetings, . In fact you might as well just do it for real. 

So true. Tell me about it !,,, been there done that may still have some of the paper trail in the attic, and that was just to get one small spacecraft (Giotto) to fly past Halley !

[Zakalwe]

On 22/08/2016 at 15:42, Ouroboros said:

I have often thought that some of the best counter arguments to moon-landing deniers  is the sheer impossibility of making a conspiracy work with the large number of people and organisations involved.  It's not just the people either: it's the paper trail, the government  funding of the programme, the minutes of congressional meetings and board meetings in most of America's large aerospace corporations, the project planning meetings, the purchasing and delivery of equipment and so it goes on and on ....

In order to fake it you'd have to do all that and yet not actually go to the moon, just make tens of thousands of people think that's what they were doing. In fact you might as well just do it for real. 

 

 

 

[Ouroboros]

Brilliant. I'd not seen that before.  As funny as the sketch they did on homeopathic medicine. 

[Delasaurus]

Have a look at this

 

http://scienceblogs.com/startswithabang/2013/07/24/why-observatories-shoot-lasers-at-the-universe/