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Is it possible for anyone to use that reflector to calculate the earth-moon distance? What kind of laser is used for this? Do we know the precise location of th

Is it possible for anyone to use that reflector to calculate the earth-moon distance? What kind of laser is used for this? Do we know the precise location of the reflector?

swatkat 13y ago
Lunar Ranging Retro Reflector: http://physics.ucsd.edu/~tmurphy/apollo/lrrr.html http://physics.ucsd.edu/~tmurphy/apollo/lrrr.html Retro Reflector coordinates: http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.html http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.htm... Experiment: http://physics.ucsd.edu/~tmurphy/apollo/basics.html http://physics.ucsd.edu/~tmurphy/apollo/basics.html http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf
brazzy 13y ago
> Is it possible for anyone to use that reflector to calculate the earth-moon distance? Sure - anyone who has a strong enough laser and sensitive enough detection rig to measure the returned signal. What could prevent them? > What kind of laser is used for this? These: http://ilrs.gsfc.nasa.gov/network/stations/active/MDOL_sitelog.html#5.%20%20%20Laser%20System%20Information http://ilrs.gsfc.nasa.gov/network/stations/active/MDOL_sitel... It's actually not all that powerful (probably still strong enough to be subject to all kinds of regulations though). The most cost and effort seems to go into the optics (read: telescops) for targeting and detection. > Do we know the precise location of the reflector? Of course: http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.html http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.htm...
- deleted 13y ago
  [deleted]
soneca 13y ago
They did it here: http://www.youtube.com/watch?v=-e5CtbbZL-k http://www.youtube.com/watch?v=-e5CtbbZL-k
exDM69 13y ago
There is a Mythbusters episode about moon landing hoax conspiracy theories where the hosts visited an observatory to test the lunar retro reflectors. The laser they used was pretty big (don't know/remember the numbers) but the more impressive part was the detector. Despite the huge laser, just a handful of photons make it there and back and twice through the atmosphere. Overall it didn't look like something you do on your back yard with off the shelf equipment, but it might be doable by a motivated hackerspace crew with a lot of time and some money on their hands.
- jacquesm 13y ago
  best issue a 'notice to airmen' if you go this route, pointing multiple-tens-of-watt lasers skyward is going to get you into a lot of trouble if you're not careful about it.
  - exDM69 13y ago
    Yes, better report to the authorities before you go waving a huge laser at the moon. In my home country, owning a laser this big requires a permit in the first place. You would definitely need to report it to the local aviation authority, who would re-route flights and notify aviators. A few weeks ago there was a music festival with some big laser decorations and they actually changed the approach path to the largest airport in the country for the weekend.
  - ars 13y ago
    The laser is an extremely short pulse, I doubt you would be able to see it as more than a tiny flash.
  - lutusp 13y ago
    The lasers used in the lunar ranging experiments are pulsed, in much the same way radar is pulsed, so even though the laser's peak power is very high, the average power could be less than a watt and accomplish the desired objective. The other thing about this experiment is that it relies on autocorrelation to avoid a need for very much power. Autocorrelation depends on knowing the departure times of the outgoing laser energy and accumulating many samples at the expected return time, which is predictably and reliably related to the transmission time. This integration technique produces a clear return signal that would be lost in noise if only one sample were collected. http://en.wikipedia.org/wiki/Autocorrelation http://en.wikipedia.org/wiki/Autocorrelation In principle, if someone was patient and had good enough equipment, one could detect the reflection of a very small outgoing power level by collecting hundreds or thousands of samples. Autocorrelation is an amazing technique.

Is it possible for anyone to use that reflector to calculate the earth-moon distance? What kind of laser is used for this? Do we know the precise location of the reflector?

swatkat 13y ago

Lunar Ranging Retro Reflector: http://physics.ucsd.edu/~tmurphy/apollo/lrrr.html http://physics.ucsd.edu/~tmurphy/apollo/lrrr.html Retro Reflector coordinates: http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.html http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.htm... Experiment: http://physics.ucsd.edu/~tmurphy/apollo/basics.html http://physics.ucsd.edu/~tmurphy/apollo/basics.html http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf

brazzy 13y ago

> Is it possible for anyone to use that reflector to calculate the earth-moon distance? Sure - anyone who has a strong enough laser and sensitive enough detection rig to measure the returned signal. What could prevent them? > What kind of laser is used for this? These: http://ilrs.gsfc.nasa.gov/network/stations/active/MDOL_sitelog.html#5.%20%20%20Laser%20System%20Information http://ilrs.gsfc.nasa.gov/network/stations/active/MDOL_sitel... It's actually not all that powerful (probably still strong enough to be subject to all kinds of regulations though). The most cost and effort seems to go into the optics (read: telescops) for targeting and detection. > Do we know the precise location of the reflector? Of course: http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.html http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_tables.htm...

deleted 13y ago
[deleted]

soneca 13y ago

They did it here: http://www.youtube.com/watch?v=-e5CtbbZL-k http://www.youtube.com/watch?v=-e5CtbbZL-k

exDM69 13y ago

There is a Mythbusters episode about moon landing hoax conspiracy theories where the hosts visited an observatory to test the lunar retro reflectors. The laser they used was pretty big (don't know/remember the numbers) but the more impressive part was the detector. Despite the huge laser, just a handful of photons make it there and back and twice through the atmosphere. Overall it didn't look like something you do on your back yard with off the shelf equipment, but it might be doable by a motivated hackerspace crew with a lot of time and some money on their hands.

jacquesm 13y ago
best issue a 'notice to airmen' if you go this route, pointing multiple-tens-of-watt lasers skyward is going to get you into a lot of trouble if you're not careful about it.
- exDM69 13y ago
  Yes, better report to the authorities before you go waving a huge laser at the moon. In my home country, owning a laser this big requires a permit in the first place. You would definitely need to report it to the local aviation authority, who would re-route flights and notify aviators. A few weeks ago there was a music festival with some big laser decorations and they actually changed the approach path to the largest airport in the country for the weekend.
- ars 13y ago
  The laser is an extremely short pulse, I doubt you would be able to see it as more than a tiny flash.
- lutusp 13y ago
  The lasers used in the lunar ranging experiments are pulsed, in much the same way radar is pulsed, so even though the laser's peak power is very high, the average power could be less than a watt and accomplish the desired objective. The other thing about this experiment is that it relies on autocorrelation to avoid a need for very much power. Autocorrelation depends on knowing the departure times of the outgoing laser energy and accumulating many samples at the expected return time, which is predictably and reliably related to the transmission time. This integration technique produces a clear return signal that would be lost in noise if only one sample were collected. http://en.wikipedia.org/wiki/Autocorrelation http://en.wikipedia.org/wiki/Autocorrelation In principle, if someone was patient and had good enough equipment, one could detect the reflection of a very small outgoing power level by collecting hundreds or thousands of samples. Autocorrelation is an amazing technique.