MoonFaker: Exhibit D: Critique #11B: LLR After Reflectors

Uploaded by philwebb59 on 18.06.2010

In 1965, Robert Dicke proposed putting an array of corner cube reflectors on the moon
to test Einstein's General Theory of Relativity.
Retro-Reflectors with a high coefficient of luminous intensity, cousins to the yellow
reflectors you see on highways, reflect a majority of the photons shot at them, virtually
straight back at the source.
The laser beam is still spread out over a 30-million [square] meter area.
So, each square meter of reflector area would only receive an average of 1 out of every
30-million photons from each burst, but it would send almost every photon that hit it
straight back to earth.
So, the number of photons returned from that reflector would be much greater than what
they would have with no reflector.
And since all the photons would reflect from the exact same spot, there should be less
variation in the round trip time.
Reflectors were originally proposed for the Surveyor missions starting in 1966, but since
the corner cubes and the two-axis robots to align them were not ready before the program
was over, none were flown.
It wasn’t until the Apollo missions that the reflectors could finally hitch a ride.
To explain the effect that the reflectors have on Lunar Laser Ranging, let’s compare
the 1962 LLR method to the current configuration of the Apache Point Observatory, or APO.
The APO pulse width is 5-million times tighter, the power is 10-thousand times greater, the
number of photons emitted is 650 times less (but each photon has more energy, so theoretically
there’s less deflection through the [earth’s] atmosphere), and the capture window is 25-thousand
times shorter.
But, the most impressive number is the return density - the number of photons received divided
by the number of photons transmitted, which is 400 times higher than they achieved in 1962.
But, is this increase due to there being reflectors on the moon, or simply due to the technological
advances of the equipment being used here on earth?
This graph should answer that question.
Rather than counting the number of pulses returned in a 500us window, like they did
in 1962, the APO system operates in single-shot mode.
It catalogs the time-of-flight for the first photon received during each 20ns exposure window.
The window size and energy of each pulse is set so that they see an average of about one
photon for every three pulses from the Apollo 15 reflector, thus reducing the chance of
capturing multiple photons from the reflector in the same window which would skew the data.
The exposure window is divided into 100ps wide bins.
Each 100ps bar in this graph represents a three cm step in the distance to the moon.
If a random photon arrives early, the photon from the reflector is ignored.
If no photon arrives from the reflector, then a random photon may, or may not, be detected
later on.
After a large number, say 10-thousand consecutive bursts in one session, the time-of-flight
for photons from the reflector will have a greater density than the returns from elsewhere.
The variation is due mostly to the pulse width of the transmission burst and the slowing
of the photons as they pass through the earth’s atmosphere.
Without a reflector, you wouldn’t be able to get this many photons grouped this tightly,
because you would have about 400-times fewer photons returning from that exact distance.
And the Coup de grâce, so to speak, is that the Apollo 15 reflector (with 300 corner cubes)
returns 3 times more photons than the Apollo 11 or Apollo 14 reflectors (with 100 corner
cubes each).
Three times more reflector area, three times more signal.
But, what about LRO?
Well, the LOLA instrument onboard LRO is a basic laser altimeter, just like the ones
flown in earthbound aircraft and on the shuttle.
At an average altitude of only 50 km from the lunar surface, compared to 385-thousand
km for earth bound lasers, and due to the lack of any significant atmosphere on the
moon, the return density of the photons for LOLA is limited only by the surface absorption
of 1064nm photons.
LOLA splits the beam from the 1064nm diode pumped YAG laser into five beams.
Each 5 meter spot illuminated by these beams is 1.5-million times smaller than the area
covered by earthbound lasers.
Instead of counting a trickle of individual photons like MIT or clocking the first photon
returned like APO, LOLA receives a packet of thousands of photons in the same general
shape as the transmission burst.
This enables LOLA to perform digital signal processing on the return signal, just like
they do with laser altimeters on earth.
Not only can LOLA measure its altitude with 10 cm accuracy by average time of flight,
but she can also determine surface roughness by the pulse spreading, and surface reflectance
by the transmit/return energy ratio (comparing the areas under the curves).
She can also calculate the local slope of the lunar surface by comparing the signals
from each of the five beams.
Suggesting that LLR and laser altimetry are the same because they both use lasers, is
like saying radiotelegraphy and color TV are the same because they both use radio waves.
It’s apples and oranges.
Because we have documented evidence that the US and USSR were bouncing laser beams off
the moon long before they put up their respective reflectors, I find the MythBusters results
rather hard to swallow.
The MIT experiment showed that by shooting a laser beam at the moon, the number of photons
of a specific wavelength that you receive from the moon increased by 40%.
Applying that to the APO system, that means that if you get an average of 6 photons per
100 ps bin in your 20 ns window, without shooting the laser, you would expect an average of
8.5 photons per bin with a laser.
These photons will be evenly distributed over your 20 ns window because they are bouncing
off different surfaces, from different distances, spread out over the entire 30-million square
meter area lit up by the laser.
In single-shot mode, this effectively raises your noise floor by 40%.
This is what the MythBusters demonstrated by pointing the APO laser off target, or away
from the reflector.
They simply didn’t receive a differentiable count of photons clustered around a narrow
range of 100 ps buckets during their exposure window.
Never do they reveal these newspaper clippings that we’ve just looked at.
And despite this historical evidence, [Adam] Savage and [Jamie] Hyneman claim that they
received no return signal when they fired their laser beam at a bare spot on the moon.
With this in mind, there can be only two possibilities.
Either the MythBusters were lying or the readouts were electronically set in NASA’s favor.
The fact remains, if it is impossible to bounce lasers back to earth off the moon’s bare
surface, as is claimed in the show, how could the US and Soviets had got the data they released
long before the Apollo 11?
Of course, there couldn’t be a THIRD possibility - that Jarrah simply doesn’t understand LLR.
Did the MythBusters cheat?
Geiger mode vs. time-of-flight - it’s apples and oranges time again.
Regardless of whether anyone successfully bounced lasers off the moon’s surface in
1962 or not, you can’t successfully use modern sensing techniques, unless you have
reflectors on the moon.
Regardless of how Jarrah misrepresents the DATA, the Myth Busters got it right.
So, LLR as it is today proves that there ARE manmade objects, retro-reflectors, sitting
on the moon’s surface, exactly where NASA said manned missions took place.
So what?
Their existence still doesn’t prove we actually sent astronauts up there.
After all, the Soviets were able to place two reflectors on the moon using unmanned
Yet, there is nothing about LLR that contradicts that manned missions took place.
If other evidence were to actually corroborate the possibility that NASA used robots to deploy
their reflectors, this claim might carry a little more weight.
But, by itself, it’s simply a bare assertion fallacy.
Lick Observatory was able to locate the reflector left by Apollo 11 within two weeks after it
was deployed and McDonald Observatory obtained returns from the Apollo 14 reflector the same
day it was deployed.
Signals were also returned from the Apollo 15 reflector a few days after deployment.
Lunokhod 2 is also used for nighttime observations and now that APO has confirmed LRO’s discovery
of Lunokhod 1 in April, 2010, both Soviet reflectors are working again.
The finding of Lunokhod 1 makes it more difficult for conspiracists to claim that the images
of manmade objects found on the moon by LRO are all photoshopped.
So, at the end of the day, we have examined three different methods for using lasers to
measure distance, Geiger mode, one-shot mode, and altimeter (or packet) mode.
We have shown that modern methods of lunar laser ranging could not be possible without
there actually being reflectors on the moon.
And by comparing the LRO images of the Soviet and Apollo sites it becomes rather evident
that robots were not used to deploy the US reflectors.
I think we’ve sufficiently destroyed Jarrah’s misconceptions regarding Lunar Laser Ranging.
Next stop, my favorite, mission telecommunications.
Ciao moon hoax conspirators, wherever you are.