Editing Apollo 10 (section)

==Mission highlights==
[[File:Apollo-10-Lancering.jpg|thumb|upright|Launch of Apollo 10 on May 18, 1969]]

===Launch and outbound trip===
Apollo 10 launched from KSC on May 18, 1969, at 16:49:00&nbsp;[[UTC]] (12:49:00&nbsp;[[Eastern Daylight Time|EDT]], local time at the launch site), at the start of a 4.5-hour [[launch window]]. The launch window was timed to secure optimal lighting conditions at Apollo Landing Site 2 at the time of the LM's closest approach to the site days later. The launch followed a countdown that had begun at 01:00:00&nbsp;UTC on May 17. Because preparations for Apollo 11 had already started at LC-39A, Apollo 10 launched from LC-39B, becoming the only Apollo flight to launch from that pad<ref name="launch">{{Cite web |date=February 6, 2022 |title=Day 1, part 1: Countdown, launch and climb to orbit |url=https://history.nasa.gov/afj/ap10fj/as10-day1-pt1.html |access-date=June 20, 2022 |website=Apollo 10 Lunar Flight Journal |publisher=[[NASA]]}}</ref> and the only one to be controlled from its Firing Room 3.<ref name="Hamish" /><ref>{{Cite web |last=Neufeld |first=Michael |date=May 22, 2020 |title=Launch Complex 39: From Saturn to Shuttle to SpaceX and SLS |url=https://airandspace.si.edu/stories/editorial/launch-complex-39-saturn-shuttle-spacex-and-sls |access-date=July 12, 2022 |publisher=[[National Air and Space Museum]]}}</ref>

Problems that arose during the countdown were dealt with during the built-in holds and did not delay the mission.{{sfn|Orloff & Harland|p=256}} On the day before launch, Cernan had been [[Traffic stop|stopped for speeding]] while returning from a final visit with his wife and child. Lacking identification and under orders to tell no one who he was, Cernan later attested in his autobiography that he had feared being arrested. Launch pad leader [[Gunther Wendt]], who had pulled over nearby after recognizing Cernan, explained the situation to the police officer, who then released Cernan despite the officer's skepticism that Cernan was an astronaut.{{sfn|Cernan|pp=238–239}}

[[File:Apollo 10 Mission Control.jpg|thumb|left|Mission Control in Houston during an Apollo 10 telecast]]
The crew experienced a somewhat rough ride on the way to orbit due to [[pogo oscillation]]s.{{sfn|Cernan|pp=201–202}} About 12 minutes after liftoff, the spacecraft entered a [[low Earth orbit]] with a high point of {{convert|100.32|nmi|km|abbr=off|disp=out|sp=us}} (100.32&nbsp;nautical&nbsp;miles; {{convert|100.32|nmi|mi|abbr=off|disp=out}}) and a low point of {{convert|99.71|nmi|km|abbr=off|disp=out|sp=us}} (99.71&nbsp;nautical&nbsp;miles; {{convert|99.71|nmi|mi|abbr=off|disp=out}}).{{sfn|Orloff|2004|p=286}} All appeared to be normal during the systems review period in Earth orbit, and the crew restarted the [[S-IVB]] third stage to achieve [[trans-lunar injection]] (TLI) and send them towards the Moon. The vehicle shook again while executing the TLI burn, causing Cernan to be concerned that they might have to abort. However, the TLI burn was completed without incident.{{sfn|Cernan|pp=203–204}} Young then performed the [[transposition, docking, and extraction]] maneuver, separating the CSM from the S-IVB stage, turning around, and docking its nose to the top of the lunar module (LM), before separating from the S-IVB. Apollo 10 was the first mission to carry a [[color television]] camera inside the spacecraft, and mission controllers in Houston watched as Young performed the maneuver. Soon thereafter, the large television audience was treated to color views of the Earth.{{sfn|Brooks|pp=303–304}} One problem that was encountered was that the [[mylar]] cover of the CM's hatch had pulled loose, spilling quantities of fiberglass insulation into the tunnel, and then into both the CM and LM.{{sfn|Mission Report|pp=9-4, 9-8}} The S-IVB was fired by ground command and sent into solar orbit with a period of 344.88 days.{{sfn|Orloff & Harland|p=260}}

The crew settled in for the voyage to the Moon. They had a light workload, and spent much of their time studying the flight plan or sleeping. They made five more television broadcasts back to Earth, and were informed that more than a billion people had watched some part of their activities.{{sfn|Brooks|pp=304–306}} In June 1969, the crew would accept a special [[Emmy Award]] on behalf of the first four Apollo crews for their television broadcasts from space.<ref>{{Cite news |last=Gent |first=George |date=June 9, 1969 |title=N.B.C.'s 'Teacher, Teacher' Voted Best TV Drama |url=https://www.nytimes.com/1969/06/09/archives/nbcs-teacher-teacher-voted-best-tv-drama.html |url-access=subscription |work=[[The New York Times]] |page=94}}</ref> One slight course correction was necessary;{{sfn|Brooks|pp=304–306}} this occurred at 26:32:56.8 into the mission and lasted 7.1 seconds. This aligned Apollo 10 with the trajectory Apollo 11 was expected to take.{{sfn|Orloff & Harland|p=260}} One issue the crew encountered was bad-tasting food, as Stafford apparently used a double dose of chlorine in their drinking water, which had to be placed in their dehydrated food to reconstitute it.<ref name="drew" />

===Lunar orbit===
[[File:Apollo 10 Lunar Orbit Profile.png|thumb|300px|Lunar orbit profile of the Apollo 10 mission, as artist-depicted in the NASA press kit for the mission]]

====Arrival and initial operations====
At 75:55:54 into the mission, {{convert|95.1|nmi|km|abbr=off|disp=out|sp=us}} (95.1&nbsp;nautical&nbsp;miles; {{convert|95.1|nmi|mi|abbr=off|disp=out}}) above the far side of the Moon, the CSM's [[service propulsion system]] (SPS) engine was fired for 356.1 seconds to slow the spacecraft into a lunar orbit of {{convert|170.0|by|60.2|nmi|km|abbr=off|disp=out|sp=us}} (170&nbsp;by&nbsp;60.2&nbsp;nautical&nbsp;miles; {{convert|170.0|by|60.2|nmi|mi|abbr=off|disp=out}}). This was followed, after two orbits of the Moon, with a 13.9-second firing of the SPS to circularize the orbit to {{convert|61.0|by|59.2|nmi|km|abbr=off|disp=out|sp=us}} (61&nbsp;by&nbsp;59.2&nbsp;nautical&nbsp;miles; {{convert|61.0|by|59.2|nmi|mi|abbr=off|disp=out}}) at 80:25:08.1.{{sfn|Orloff & Harland|p=260}} Within the first couple of hours after the initial lunar orbit insertion burn and following the circularization burn, the crew turned to tracking planned landmarks on the surface below to record observations and take photographs. In addition to ALS-1, ALS-2, and ALS-3, the crew of Apollo 10 observed and photographed features on the near and far sides of the Moon, including the craters [[Coriolis (crater)|Coriolis]], [[King (crater)|King]], and [[Papaleksi (crater)|Papaleksi]].<ref>{{Cite web |title=Apollo 10 Day 4, part 13: Acclimatising in lunar orbit |url=https://history.nasa.gov/afj/ap10fj/as10-day4-pt13.html |access-date=June 27, 2022 |website=Apollo 10 Lunar Flight Journal |publisher=NASA}}</ref> Shortly after the circularization burn, the crew partook in a scheduled half-hour color-television broadcast with descriptions and video transmissions of views of the lunar surface below.{{sfn|Orloff|2004|pp=72–79}}

About an hour after the second burn, the LM crew of Stafford and Cernan entered the LM to check out its systems.{{sfn|Orloff & Harland|p=260}} They were met with a blizzard of fiberglass particles from the earlier problem, which they cleaned up with a vacuum cleaner as best they could. Stafford had to help Cernan remove smaller bits from his hair and eyebrows.{{sfn|Chaikin|p=156}} Stafford later commented that Cernan looked like he just came out of a [[chicken coop]], and that the particles made them itch and got into the air conditioning system, and they were scraping it off the filter screens for the rest of the mission.<ref name="Hamish" /> This was merely an annoyance, but the particles may have gotten into the docking ring joining the two craft and caused it to misalign slightly. Mission Control determined that this was still within safe limits.{{sfn|French & Burgess|pp=1374–1376}}

====The flight of ''Snoopy''====
[[File:AS10-34-5158 - Apollo 10 - Apollo 10 Mission image - Landing Site 2 - NARA - 16682380.jpg|thumb|right|Photograph of ALS-2 taken by Apollo 10]]
After Stafford and Cernan checked out ''Snoopy'', they returned to ''Charlie Brown'' for a rest. Then they re-entered ''Snoopy'' at 95:02 and undocked it from the CSM three hours later at 98:11:57.{{sfn|Orloff|2004|pp=72–79}} Young, who remained in the CSM, became the first person to fly solo in lunar orbit.<ref name="Neal">{{Cite news |last=Neal |first=Valerie |date=January 19, 2018 |title=John W. Young, an Astronaut's Astronaut (1930-2018) |url=https://airandspace.si.edu/stories/editorial/john-w-young-astronaut-1930-2018 |access-date=July 2, 2022 |publisher=[[National Air and Space Museum]]}}</ref> After undocking, Stafford and Cernan deployed the LM's landing gear and inspected the LM's systems. About 35 minutes after the initial separation, the CSM performed an 8.3-second burn with its RCS thrusters to separate itself from the LM by about {{Convert|30|ft}}, after which Young visually inspected the LM from the CSM. The CSM performed another separation burn, this time separating the two spacecraft by about {{convert|2|nmi|km|abbr=off|disp=out|sp=us}} (2&nbsp;nautical&nbsp;miles; {{convert|2|nmi|mi|abbr=off|disp=out}}).{{sfn|Orloff|2004|pp=72–79}} The LM crew then performed the descent orbit insertion maneuver by firing their descent engine for 27.4 seconds at 99:46:01.6, and tested their craft's landing radar as they approached the {{convert|50000|ft|m|adj=on|abbr=off|sp=us|order=flip}} altitude where the subsequent Apollo 11 mission would begin powered descent to land on the Moon.{{sfn|Orloff & Harland|pp=259–260}} Previously, the LM's landing radar had only been tested under terrestrial conditions.{{sfn|Press Kit|p=8}} While the LM executed these maneuvers, Young monitored the location and status of the LM from the CSM, standing by to rescue the LM crew if necessary.{{sfn|Chaikin|p=158}} Cernan and Stafford surveyed ALS-2, coming within {{convert|8.4|nmi|km|abbr=off|disp=out|sp=us}} (8.4&nbsp;nautical&nbsp;miles; {{convert|8.4|nmi|mi|abbr=off|disp=out}}) of the surface at a point 15 degrees to its east, then performed a phasing burn at 100:58:25.93, thrusting for just under 40 seconds to allow a second pass at ALS-2, when the craft came within {{convert|7.8|nmi|km|abbr=off|disp=out|sp=us}} (7.8&nbsp;nautical&nbsp;miles; {{convert|7.8|nmi|mi|abbr=off|disp=out|0}}) of the Moon, its closest approach.{{sfn|Orloff & Harland|pp=259–260}} Reporting on his observations of the site from the LM's low passes, Stafford indicated that ALS-2 seemed smoother than he had expected{{sfn|Chaikin|p=158}} and described its appearance as similar to the desert surrounding [[Blythe, California]];{{sfn|Wilhelms|p=191}} but he observed that Apollo 11 could face rougher terrain downrange if it approached off-target.{{sfn|Chaikin|p=158}} Based upon Apollo 10's observations from relatively low altitude, NASA mission planners became comfortable enough with ALS-2 to confirm it as the target site for Apollo 11.{{sfn|Wilhelms|p=192}}

[[File:AS10-34-5087.jpg|thumb|left|LM ''Snoopy'' containing Stafford and Cernan, as inspected by Young after separation from ''Charlie Brown'']]
The next action was to prepare to separate the LM ascent stage from the descent stage, to jettison the descent stage, and fire the [[Ascent Propulsion System]] to return the ascent stage towards the CSM. As Stafford and Cernan prepared to do so, the LM began to gyrate out of control.{{sfn|Chaikin|p=159}} Alarmed, Cernan exclaimed, "Son of a bitch!" into a [[hot mic]] being broadcast live, which, combined with other language used by the crew during the mission, generated some complaints back on Earth.<ref>{{Cite news |last=Simmons |first=Roger |date=May 28, 2019 |title=Foul-mouthed Apollo astronauts got space program in trouble 50 years ago |url=https://www.orlandosentinel.com/space/apollo-11-anniversary/os-ne-apollo-11-cursing-astronautps-20190528-xpfrowxpdve37acs4kbsnn43fe-story.html |access-date=June 26, 2022 |work=[[Orlando Sentinel]]}}</ref> Stafford discarded the descent stage about five seconds after the tumbling began{{sfn|Orloff|2004|pp=72–79}} and fought to regain control manually, suspecting that there might have been an "open thruster", or a thruster stuck firing.{{sfn|Cernan|p=218}} He did so in time to orient the spacecraft to rejoin ''Charlie Brown''.{{sfn|Chaikin|p=159}} The problem was traced to a switch controlling the mode of the abort guidance system; it was to be moved as part of the procedure, but both of the crew members switched it, thus returning it to the original position. Had they fired ''Snoopy'' in the wrong direction, they might have missed the rendezvous with ''Charlie Brown'' or crashed into the Moon.{{sfn|French & Burgess|pp=1385–1391}} Once Stafford had regained control of the LM ascent stage, which took about eight seconds,{{sfn|Chaikin|p=159}} the pair fired the ascent engine at the lowest point of the LM's orbit, mimicking the [[orbital insertion]] maneuver after launch from the lunar surface in a later landing mission. ''Snoopy'' coasted on that trajectory for about an hour before firing the engine once more to further fine-tune its approach to ''Charlie Brown''.{{sfn|Orloff|2004|pp=72–79}}

[[File:Apollo 10 Earthrise.ogv|thumb|right|Earthrise video captured by Apollo 10 crew]]
''Snoopy'' rendezvoused with and re-docked with ''Charlie Brown'' at 106:22:02, just under eight hours after undocking.{{sfn|Orloff|2004|pp=72–79}} The docking was telecast live in color from the CSM.<ref>{{Cite web |last=Gohd |first=Chelsea |date=May 18, 2019 |title=Snoopy to the Moon! Apollo 10 Commander Looks Back on Historic Flight 50 Years Ago |url=https://www.space.com/apollo-10-commander-thomas-stafford-memories-50th-anniversary.html |access-date=June 26, 2022 |publisher=[[Space.com]] |language=en}}</ref><ref>{{Cite web |date=April 15, 2022 |title=John Young: Not just the commander of Apollo 16 |url=https://universemagazine.com/en/john-young-not-just-the-commander-of-apollo-16/ |access-date=June 26, 2022 |magazine=Universe Magazine}}</ref> Once Cernan and Stafford had re-entered ''Charlie Brown'', ''Snoopy'' was sealed off and separated from ''Charlie Brown.'' The rest of the LM's ascent-stage engine fuel was burned to send it on a trajectory past the Moon and into a [[heliocentric orbit]].<ref name="nasa_apollo10">{{Cite web |date=July 8, 2009 |editor-last=Ryba |editor-first=Jeanne |title=Apollo 10 |url=http://www.nasa.gov/mission_pages/apollo/missions/apollo10.html |access-date=June 26, 2013 |publisher=NASA}}</ref><ref name="disposition">{{Cite web |title=Current locations of the Apollo Command Module Capsules (and Lunar Module crash sites) |url=http://nssdc.gsfc.nasa.gov/planetary/lunar/apolloloc.html |access-date=27 December 2014 |website=Apollo: Where are they now? |publisher=NASA}}</ref>

It was the only Apollo LM to meet this fate. The Apollo 11 ascent stage would be left in lunar orbit to crash randomly, while ascent stages of later Apollo mission (12, 14, 15 and 17) were steered into the Moon to obtain readings from [[seismometers]] placed nearby on the surface, with two exceptions: Apollo 13's ascent stage, which the crew used as a "life boat" to get safely back to Earth before releasing it to burn up in Earth's atmosphere, and [[Apollo 16]]'s, which NASA lost control of after jettison.<ref name="disposition" />

===Return to Earth===
[[File:Apollo 10 Helicopter Recovery - GPN-2000-001143.jpg|thumb|[[Helicopter 66]] post-splashdown crew recovery operations in the Pacific Ocean]]
After ejecting the LM ascent stage, the crew slept and performed photography and observation of the lunar surface from orbit. Though the crew located 18 landmarks on the surface and took photographs of various surface features, crew fatigue necessitated the cancellation of two scheduled television broadcasts. Thereafter, the main Service Propulsion System engine of the CSM re-ignited for about 2.5 minutes to set Apollo 10 on a trajectory towards Earth, achieving such a trajectory at 137:39:13.7. As it departed lunar orbit, Apollo 10 had orbited the Moon 31 times over the span of about 61 hours and 37 minutes.{{sfn|Orloff|2004|pp=72–79}}

During their journey back to Earth, the crew performed some observational activities which included star-Earth horizon sightings for navigation. The crew also performed a scheduled test to gauge the reflectivity of the CSM's [[Directional antenna|high-gain antenna]] and broadcast six television transmissions of varying durations to show views inside the spacecraft and of the Earth and Moon from the crew's vantage point.{{sfn|Orloff|2004|pp=72–79}} Cernan reported later that he and his crewmates became the first to "successfully shave in space" during the return trip, using a [[safety razor]] and thick [[Shaving cream|shaving gel]], as such items had been deemed a safety hazard and prohibited on earlier flights.{{sfn|Cernan|p=220}} The crew fired the engine of the CSM for the only mid-course-correction burn required during the return trip at 188:49:58, a few hours before separation of the CM from the SM. The burn lasted about 6.7 seconds.{{sfn|Orloff|2004|pp=72–79}}

As the spacecraft rapidly approached Earth on the final day of the mission, the Apollo 10 crew traveled faster than any humans before or since, relative to Earth: 39,897&nbsp;km/h (11.08&nbsp;km/s or 24,791&nbsp;mph).<ref>{{Cite news |last=Wall |first=Mike |date=April 23, 2019 |title=The Most Extreme Human Spaceflight Records |url=https://www.space.com/11337-human-spaceflight-records-50th-anniversary.html |access-date=June 26, 2022 |publisher=[[Space.com]] |language=en}}</ref><ref>{{Cite web |last=Granath |first=Bob |date=February 24, 2015 |title=Apollo 10 Anniversary Catapults Next Step |url=http://www.nasa.gov/content/apollo-10-was-moon-landing-rehearsal-eft-1-preps-for-trips-beyond |access-date=April 29, 2020 |website=NASA}}</ref> This is because the return trajectory was designed to take only 42 hours rather than the normal 56.{{sfn|Stafford & Cassutt|p=458}} The Apollo 10 crew also traveled farther than any humans before or since from their (Houston) homes: {{convert|408950|nmi|km|abbr=off|disp=out|sp=us}} (408,950&nbsp;nautical&nbsp;miles; {{convert|408950|nmi|mi|abbr=off|disp=out}}) (though the Apollo 13 crew was 200&nbsp;km farther away from Earth as a whole).<ref>{{Cite web |last=Holtkamp |first=Gerhard |date=June 6, 2009 |title=Far Away From Home |url=http://www.scilogs.eu/en/blog/spacetimedreamer/2009-06-06/far-away-from-home |url-status=dead |archive-url=https://web.archive.org/web/20111031132720/http://www.scilogs.eu/en/blog/spacetimedreamer/2009-06-06/far-away-from-home |archive-date=October 31, 2011 |access-date=20 September 2011 |website=SpaceTimeDreamer |publisher=SciLogs |type=Blog |df=mdy-all}}</ref>

At 191:33:26, the CM (which contained the crew) separated from the SM in preparation for [[Atmospheric reentry|reentry]], which occurred about 15 minutes later at 191:48:54.5.{{sfn|Orloff|2004|pp=72–79}} [[Splashdown (spacecraft landing)|Splashdown]] of the CM occurred about 15 minutes after reentry in the Pacific Ocean about {{convert|400|nmi|km|abbr=off|disp=out|sp=us}} (400&nbsp;nautical&nbsp;miles; {{convert|400|nmi|mi|abbr=off|disp=out}}) east of [[American Samoa]] on May 26, 1969, at 16:52:23 UTC and mission elapsed time 192:03:23.{{sfn|Orloff|2004|pp=72–79}} The astronauts were recovered by {{USS|Princeton|CV-37|6}}. They spent about four hours aboard, during which they took a congratulatory phone call from President [[Richard Nixon]].<ref name="clear" /> As they had not made contact with the lunar surface, Apollo 10's crew were not required to [[Mobile quarantine facility|quarantine]] like the first landing crews would be.{{sfn|Cernan|p=222}} They were flown to [[Pago Pago International Airport]] in [[Tafuna, American Samoa|Tafuna]] for a greeting reception, before boarding a [[Lockheed C-141 Starlifter|C-141]] cargo plane to [[Ellington Air Force Base]] near [[Houston]].<ref name="clear">{{Cite web |date=May 23, 2019 |title=50 Years Ago: Apollo 10 Clears the Way for the first Moon Landing |url=https://www.nasa.gov/feature/50-years-ago-apollo-10-clears-the-way-for-the-first-moon-landing |access-date=June 26, 2022 |publisher=[[NASA]]}}</ref>