Editing Galileo project (section)

===''Galileo'' Optical Experiment===
During the second Earth flyby, another experiment was performed. Optical communications in space were assessed by detecting light pulses from powerful lasers with ''Galileo''{{'s}} CCD. The experiment, dubbed ''Galileo'' Optical Experiment or GOPEX,<ref name="GOPEX">{{cite web |url=http://lasers.jpl.nasa.gov/PAPERS/GOPEX/gopex_s2.pdf |title=GOPEX SPIE 1993 (Edited) |publisher=NASA/Jet Propulsion Laboratory |access-date=May 15, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110721050447/http://lasers.jpl.nasa.gov/PAPERS/GOPEX/gopex_s2.pdf |archive-date=July 21, 2011}}</ref> used two separate sites to beam laser pulses to the spacecraft, one at [[Table Mountain Observatory]] in California and the other at the [[Starfire Optical Range]] in [[New Mexico]]. The Table Mountain site used a [[Nd:YAG laser]] operating at a [[nonlinear optics#Frequency doubling|frequency-doubled]] wavelength of 532&nbsp;nm, with a repetition rate of 15 to 30&nbsp;Hertz and a pulse power [[full width at half maximum]] (FWHM) in the tens of megawatts range, which was coupled to a {{convert|0.6|m|ft|abbr=on}} [[Cassegrain reflector]] telescope for transmission to ''Galileo''. The Starfire range site used a similar setup with a larger {{convert|1.5|m|ft|abbr=on}} transmitting telescope. Long-exposure (~0.1 to 0.8&nbsp;s) images using ''Galileo''{{'s}} 560&nbsp;nm centered green filter produced images of Earth clearly showing the laser pulses even at distances of up to {{convert|6|e6km|e6mi|abbr=unit}}.<ref name="GOPEX" />

Adverse weather conditions, restrictions placed on laser transmissions by the U.S. [[Space Defense Operations Center]] ([[Cheyenne Mountain Complex|SPADOC]]) and a pointing error caused by the scan platform on the spacecraft not being able to change direction and speed as quickly as expected (which prevented laser detection on all frames with less than 400&nbsp;ms exposure times) contributed to a reduction in the number of successful detections of the laser transmission to 48 of the total 159 frames taken.<ref name="GOPEX" /> Nonetheless, the experiment was considered a resounding success and the data acquired were used to design laser downlinks to send large volumes of data very quickly from spacecraft to Earth. The scheme was studied in 2004 for a data link to a future Mars-orbiting spacecraft.<ref name="lasers">{{cite news |url=https://www.space.com/534-nasa-test-laser-communications-mars-spacecraft.html |title=NASA To Test Laser Communications With Mars Spacecraft |publisher=[[Space.com]] |date=November 15, 2004 |access-date=January 19, 2021 |archive-date=November 8, 2021 |archive-url=https://web.archive.org/web/20211108200952/https://www.space.com/534-nasa-test-laser-communications-mars-spacecraft.html |url-status=live }}</ref> On December 5, 2023, NASA's [[Deep Space Optical Communications]] experiment on the ''[[Psyche (spacecraft)|Psyche]]'' spacecraft used infrared lasers for two-way communication between Earth and the spacecraft.<ref>{{cite press release |title=NASA's Deep Space Optical Comm Demo Sends, Receives First Data |date= |publisher=NASA |url=https://www.jpl.nasa.gov/news/nasas-deep-space-optical-comm-demo-sends-receives-first-data |access-date=April 2, 2024 |archive-date=April 2, 2024 |archive-url=https://web.archive.org/web/20240402195233/https://www.jpl.nasa.gov/news/nasas-deep-space-optical-comm-demo-sends-receives-first-data |url-status=live }}</ref><ref>{{cite news |title=Pew! Pew! Pew! NASA's 1st successful two-way laser experiment is a giant leap for moon and Mars communications |first=Andrew |last=Jones |date=December 20, 2023 |publisher=[[Space.com]] |url=https://www.space.com/nasa-laser-communication-1st-two-way-link-iss |access-date=2 April 2024 |archive-date=April 2, 2024 |archive-url=https://web.archive.org/web/20240402195233/https://www.space.com/nasa-laser-communication-1st-two-way-link-iss |url-status=live }}</ref>