Editing Lunar Laser Ranging experiments (section)

==History==
[[Image:ALSEP AS15-85-11468.jpg|thumb|Apollo 15 LRRR]]
[[Image:Laser Ranging Retroreflector Apollo 15.svg|thumb|Apollo 15 LRRR schematic]]

The first successful lunar ranging tests were carried out in 1962 when [[Louis Smullin]] and [[Giorgio Fiocco]] from the [[Massachusetts Institute of Technology]] succeeded in observing laser pulses reflected from the Moon's surface using a laser with a 50J 0.5 millisecond pulse length.<ref>{{cite journal |last1=Smullin |first1=Louis D. |last2=Fiocco |first2=Giorgio |year=1962 |title=Optical Echoes from the Moon |journal=[[Nature (journal)|Nature]] |volume=194 |issue=4835 |pages=1267 |bibcode=1962Natur.194.1267S |doi=10.1038/1941267a0|s2cid=4145783 |doi-access=free }}</ref> Similar measurements were obtained later the same year by a Soviet team at the [[Crimean Astrophysical Observatory]] using a [[Q-switching|Q-switched]] [[ruby laser]].<ref>{{cite journal |last1=Bender |first1=P. L. |display-authors=etal |year=1973 |title=The Lunar Laser Ranging Experiment: Accurate ranges have given a large improvement in the lunar orbit and new selenophysical information |url=http://www.physics.ucsd.edu/~tmurphy/apollo/doc/Bender.pdf |journal=[[Science (journal)|Science]] |volume=182 |issue=4109 |pages=229–238 |bibcode=1973Sci...182..229B |doi=10.1126/science.182.4109.229 |pmid=17749298|s2cid=32027563 }}</ref>

Shortly thereafter, [[Princeton University]] graduate student [[James E. Faller|James Faller]] proposed placing optical reflectors on the Moon to improve the accuracy of the measurements.<ref name=":0">{{Cite journal|last=Newman|first=Michael E.|date=2017-09-26|title=To the Moon and Back … in 2.5 Seconds|url=https://www.nist.gov/nist-time-capsule/any-object-any-need-call-nist/moon-and-back-25-seconds|access-date=2021-01-27|journal=NIST|language=en}}</ref> This was achieved following the installation of a [[retroreflector]] array on July 21, 1969 by the crew of [[Apollo 11]]. Two more retroreflector arrays were left by the [[Apollo 14]] and [[Apollo 15]] missions. Successful lunar laser range measurements to the [[retroreflectors]] were first reported on Aug. 1, 1969 by the 3.1&nbsp;m telescope at [[Lick Observatory]].<ref name=":0" /> Observations from [[Air Force Cambridge Research Laboratories]] Lunar Ranging Observatory in Arizona, the [[Pic du Midi de Bigorre|Pic du Midi Observatory]] in France, the Tokyo [[National Astronomical Observatory of Japan|Astronomical Observatory]], and [[McDonald Observatory]] in Texas soon followed.

The uncrewed Soviet ''[[Lunokhod 1]]'' and ''[[Lunokhod 2]]'' rovers carried smaller arrays. Reflected signals were initially received from ''Lunokhod 1'' by the Soviet Union up to 1974, but not by western observatories that did not have precise information about location. In 2010 [[NASA]]'s [[Lunar Reconnaissance Orbiter]] located the Lunokhod 1 rover on images and in April 2010 a team from University of California ranged the array.<ref>{{cite news |last=McDonald |first=K. |date=26 April 2010 |title=UC San Diego Physicists Locate Long Lost Soviet Reflector on Moon |url=http://ucsdnews.ucsd.edu/newsrel/science/04-26SovietReflector.asp |publisher=University of California, San Diego |access-date=27 April 2010|archive-date=30 April 2010|archive-url=https://web.archive.org/web/20100430164946/http://ucsdnews.ucsd.edu/newsrel/science/04-26SovietReflector.asp|url-status=dead}}</ref> ''Lunokhod 2''{{'s}} array continues to return signals to Earth.<ref name="jwjd1">{{cite conference |url=https://ilrs.cddis.eosdis.nasa.gov/docs/williams_lw13.pdf |title=Lunar Geophysics, Geodesy, and Dynamics |conference=13th International Workshop on Laser Ranging. 7–11 October 2002. Washington, D. C. |first1=James G. |last1=Williams |first2=Jean O. |last2=Dickey |date=2002}}</ref> The Lunokhod arrays suffer from decreased performance in direct sunlight—a factor considered in reflector placement during the Apollo missions.<ref name="UniverseToday">{{cite news |title=It's Not Just The Astronauts That Are Getting Older |date=10 March 2010 |work=[[Universe Today]] |url=http://www.universetoday.com/59310/its-not-just-the-astronauts-that-are-getting-older/ |access-date=24 August 2012}}</ref>

The Apollo 15 array is three times the size of the arrays left by the two earlier Apollo missions. Its size made it the target of three-quarters of the sample measurements taken in the first 25 years of the experiment. Improvements in technology since then have resulted in greater use of the smaller arrays, by sites such as the [[Côte d'Azur Observatory]] in [[Nice]], France; and the [[Apache Point Observatory Lunar Laser-ranging Operation]] (APOLLO) at the [[Apache Point Observatory]] in [[New Mexico]].

In the 2010s several [[List of retroreflectors on the Moon|new retroreflectors]] were planned. The [[MoonLIGHT (experiment)|MoonLIGHT]] reflector, which was to be placed by the private [[MX-1E]] lander, was designed to increase measurement accuracy up to 100 times over existing systems.<ref name="Currie 2011">{{cite journal|last1=Currie|first1=Douglas|last2=Dell'Agnello|first2=Simone|last3=Delle Monache|first3=Giovanni|date=April–May 2011|title=A Lunar Laser Ranging Retroreflector Array for the 21st Century|journal=Acta Astronautica|volume=68|issue=7–8|pages=667–680|bibcode=2011AcAau..68..667C|doi=10.1016/j.actaastro.2010.09.001|url=https://www.openaccessrepository.it/record/137265 }}</ref><ref name="Tune 2015">{{cite news|last=Tune|first=Lee|date=10 June 2015|title=UMD, Italy & MoonEx Join to Put New Laser-Reflecting Arrays on Moon|work=UMD Right Now|publisher=University of Maryland|url=https://umdrightnow.umd.edu/news/umd-italy-moonex-join-put-new-laser-reflecting-arrays-moon|access-date=21 March 2018|archive-date=22 March 2018|archive-url=https://web.archive.org/web/20180322081731/https://umdrightnow.umd.edu/news/umd-italy-moonex-join-put-new-laser-reflecting-arrays-moon|url-status=dead}}</ref><ref name="MX-1">{{Cite news|last=Boyle|first=Alan|date=12 July 2017|title=Moon Express unveils its roadmap for giant leaps to the lunar surface ... and back again|work=GeekWire|url=https://www.geekwire.com/2017/moon-express-unveils-roadmap-giant-leaps-lunar-surface-back/|access-date=15 March 2018}}</ref> MX-1E was set to launch in July 2020,<ref>{{Citation|title=Moon Express Lunar Scout (MX-1E)|url=https://www.rocketlaunch.live/launch/lunar-scout|publisher=RocketLaunch.Live|access-date=27 July 2019|archive-date=27 July 2019|archive-url=https://web.archive.org/web/20190727095927/https://www.rocketlaunch.live/launch/lunar-scout|url-status=dead}}</ref> however, as of February 2020, the launch of the MX-1E has been canceled.<ref>{{cite web|title=MX-1E 1, 2, 3|url=https://space.skyrocket.de/doc_sdat/mx-1e.htm|access-date=24 May 2020}}</ref> India's [[Chandrayaan-3]] lunar lander successfully placed a sixth reflector on the Moon in August 2023.<ref name=":5" /> MoonLIGHT will be launched in early 2024 with a [[Commercial Lunar Payload Services]] (CLPS) mission.<ref>{{Cite web |title=NASA Payloads for (CLPS PRISM) CP-11 |url=https://science.nasa.gov/lunar-discovery/deliveries/cp-11}}</ref>