Editing Apollo 16 (section)

===Launch and outward journey===
[[File:Apollo 16 lift-off.jpg|thumb|right|upright=1.3|Launch of Apollo 16]]
The Apollo 16 mission launched from the Kennedy Space Center in Florida at 12:54&nbsp;pm EST on April 16, 1972.<ref name=launch /> The launch was nominal; the crew experienced vibration similar to that on previous missions. The first and second stages of the Saturn{{nbsp}}V (the S-IC and [[S-II]]) performed nominally; the spacecraft entered [[Low Earth orbit|orbit]] around Earth just under 12 minutes after lift-off.

After reaching orbit, the crew spent time adapting to the [[weightlessness|zero-gravity]] environment and preparing the spacecraft for [[trans-lunar injection]] (TLI), the burn of the third-stage rocket that would propel them to the Moon. In Earth orbit, the crew faced minor technical issues, including a potential problem with the environmental control system and the [[S-IVB]] third stage's attitude control system, but eventually resolved or compensated for them as they prepared to depart towards the Moon.

After two orbits, the rocket's third stage reignited for just over five minutes, propelling the craft towards the Moon at about {{convert|22000|mph|km/h|abbr=on|order=flip}}.<ref>{{cite web|title=Apollo 16: Day One Part Three: Second Earth Orbit and Translunar Injection|date=May 8, 2006|url=https://history.nasa.gov/ap16fj/03_Day1_Pt3.htm|work=Apollo 16 Flight Journal|publisher=[[NASA]]|archive-url=https://web.archive.org/web/20111021204204/http://history.nasa.gov/ap16fj/03_Day1_Pt3.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt}}</ref> Six minutes after the burn of the S-IVB, the command and service modules (CSM), containing the crew, separated from the rocket and traveled {{convert|15|m|ft|abbr=on|sp=us|order=flip}} away from it before turning around and retrieving the lunar module from inside the expended rocket stage. The maneuver, performed by Mattingly and known as [[transposition, docking, and extraction]], went smoothly.<ref>{{cite web|title=Apollo 16: Day One Part Four: Transposition, Docking and Ejection|url=https://history.nasa.gov/afj/ap16fj/03_Day1_Pt3.html|work=Apollo 16 Flight Journal|date=February 7, 2020|access-date=September 23, 2021|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]|archive-date=October 23, 2012|archive-url=https://web.archive.org/web/20121023155334/http://history.nasa.gov/ap16fj/03_Day1_Pt3.htm|url-status=live}}</ref><ref name="fullsummary">{{cite web|title=Apollo 16 Flight Summary|url=https://history.nasa.gov/afj/ap16fj/a16summary.html|work=Apollo 16 Flight Journal|date=January 19, 2019|access-date=November 27, 2011|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]|archive-date=July 21, 2019|archive-url=https://web.archive.org/web/20190721143418/https://history.nasa.gov/afj/ap16fj/a16summary.html|url-status=live}}</ref>

Following transposition and docking, the crew noticed the exterior surface of the Lunar Module was giving off particles from a spot where the LM's skin appeared torn or shredded; at one point, Duke estimated they were seeing about five to ten particles per second. Young and Duke entered the Lunar Module through the docking tunnel connecting it with the command module to inspect its systems, at which time they did not spot any major issues.

Once on course towards the Moon, the crew put the spacecraft into a rotisserie "barbecue" mode in which the craft rotated along its long axis three times per hour to ensure even heat distribution about the spacecraft from the Sun. After further preparing the craft for the voyage, the crew began the first sleep period of the mission just under 15 hours after launch.<ref>{{cite web|title=Apollo 16: Day 1 Part 5: Settling into Translunar Coast|url=https://history.nasa.gov/afj/ap16fj/05_Day1_Pt5.html|work=Apollo 16 Flight Journal|date=February 7, 2020|access-date=September 23, 2021|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]|archive-date=October 28, 2012|archive-url=https://web.archive.org/web/20121028074016/http://history.nasa.gov/ap16fj/05_Day1_Pt5.htm|url-status=live}}</ref>
[[File:AS16-118-18885.jpg|left|thumb|upright=1.3|Earth from Apollo 16 during the trans-lunar coast, showing the US at center]]
By the time [[Christopher C. Kraft Jr. Mission Control Center|Mission Control]] issued the wake-up call to the crew for flight day two, the spacecraft was about {{convert|98000|nmi|km|sp=us|order=flip}} away from the Earth, traveling at about {{convert|5322|ft/s|km/s|abbr=on|sp=us|order=flip}}. As it was not due to arrive in lunar orbit until flight day four,<ref name=moonarrival>{{cite web|title=Apollo 16: Day Four Part One – Arrival at the Moon|url=https://history.nasa.gov/afj/ap16fj/10_Day4_Pt1.html|work=Apollo 16 Flight Journal|date=February 7, 2020|access-date=September 23, 2021|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]|archive-date=October 21, 2012|archive-url=https://web.archive.org/web/20121021002834/http://history.nasa.gov/ap16fj/10_Day4_Pt1.htm|url-status=live}}</ref> flight days two and three were largely preparatory, consisting of spacecraft maintenance and scientific research. On day two, the crew performed an [[electrophoresis]] experiment, also performed on Apollo 14,<ref name = "two" /> in which they attempted to demonstrate that electrophoretic separation in their near-weightless environment could be used to produce substances of greater purity than would be possible on Earth. Using two different sizes of [[polystyrene]] particles, one size colored red and one blue, separation of the two types via electrophoresis was achieved, though electro-osmosis in the experiment equipment prevented the clear separation of two particle bands.{{sfn|Press Kit|p=103}}<ref>{{cite web|first=R.S.|last=Snyder|title=Electrophoresis Demonstration on Apollo 16|publisher=[[NASA]]|date=November 1972|url=https://ntrs.nasa.gov/api/citations/19730009430/downloads/19730009430.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/api/citations/19730009430/downloads/19730009430.pdf |archive-date=2022-10-09 |url-status=live|pages=30–32}}</ref>

The remainder of day two included a two-second mid-course correction burn performed by the CSM's [[service propulsion system]] (SPS) engine to tweak the spacecraft's trajectory. Later in the day, the astronauts entered the Lunar Module for the second time to further inspect the landing craft's systems. The crew reported they had observed additional paint peeling from a portion of the LM's outer aluminum skin. Despite this, the crew discovered that the spacecraft's systems were performing nominally. Following the LM inspection, the crew reviewed checklists and procedures for the following days in anticipation of their arrival and the [[Lunar orbit|Lunar Orbit Insertion]] (LOI) burn. Command Module Pilot Mattingly reported "[[gimbal lock]]", meaning that the system to keep track of the craft's [[attitude (aircraft)|attitude]] was no longer accurate. Mattingly had to realign the guidance system using the Sun and Moon. At the end of day two, Apollo 16 was about {{convert|140000|nmi|km|order=flip|sp=us}} away from Earth.<ref name = "two" >{{cite web|title=Apollo 16: Day Two Part Two: LM Entry and Checks|url=https://history.nasa.gov/ap16fj/07_Day2_Pt2.htm|work=Apollo 16 Flight Journal|archive-url=https://web.archive.org/web/20111021203814/http://history.nasa.gov/ap16fj/07_Day2_Pt2.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]}}</ref>

When the astronauts were awakened for flight day three, the spacecraft was about {{convert|157000|nmi|km|sp=us|order=flip}} away from the Earth. The velocity of the craft steadily decreased, as it had not yet reached the lunar sphere of gravitational influence. The early part of day three was largely housekeeping, spacecraft maintenance and exchanging status reports with Mission Control in Houston. The crew performed the Apollo light flash experiment, or ALFMED, to investigate "light flashes" that were seen by Apollo lunar astronauts when the spacecraft was dark, regardless of whether their eyes were open. This was thought to be caused by the penetration of the [[Human eye|eye]] by [[cosmic ray]] particles.<ref>{{cite web|title=Apollo 16: Day Three Part One: ALFMED Experiment|url=https://history.nasa.gov/ap16fj/08_Day3_Pt1.htm|work=Apollo 16 Flight Journal|archive-url=https://web.archive.org/web/20111021203834/http://history.nasa.gov/ap16fj/08_Day3_Pt1.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]}}</ref><ref name=alfmed>{{cite web|title=Apollo Light Flash Investigations (AP009)|url=http://lsda.jsc.nasa.gov/scripts/experiment/exper.aspx?exp_index=380|work=Life Sciences Data Archive|publisher=[[NASA]]|access-date=July 22, 2013|archive-date=December 31, 2020|archive-url=https://web.archive.org/web/20201231213212/https://lsda.jsc.nasa.gov/Experiment/exper/380|url-status=live}}</ref> During the second half of the day, Young and Duke again entered the Lunar Module to power it up and check its systems, and perform housekeeping tasks in preparation for the lunar landing. The systems were found to be functioning as expected. Following this, the crew donned their space suits and rehearsed procedures that would be used on landing day. Just before the end of flight day three at 59 hours, 19 minutes, 45 seconds after liftoff, while {{convert|178673|nmi|km|sp=us|order=flip}} from the Earth and {{convert|33821|nmi|km|sp=us|order=flip}} from the Moon, the spacecraft's velocity began increasing as it accelerated towards the Moon after entering the lunar sphere of influence.<ref>{{cite web|title=Apollo 16: Day Three Part Two: Lunar Module Activation and Checkout|url=https://history.nasa.gov/ap16fj/09_Day3_Pt2.htm|work=Apollo 16 Flight Journal|archive-url=https://web.archive.org/web/20111021204136/http://history.nasa.gov/ap16fj/09_Day3_Pt2.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]}}</ref>

After waking up on flight day four, the crew began preparations for the LOI maneuver that would brake them into orbit.<ref name="moonarrival"/> At an altitude of {{convert|11142|nmi|km|sp=us|order=flip}} the [[scientific instrument module]] (SIM) bay cover was jettisoned. At just over 74 hours into the mission, the spacecraft passed behind the Moon, temporarily losing contact with Mission Control. While over the [[far side of the Moon|far side]], the SPS burned for 6{{nbsp}}minutes and 15 seconds, braking the spacecraft into an orbit with a low point (pericynthion) of 58.3 and a high point (apocynthion) of 170.4 nautical miles (108.0 and 315.6&nbsp;km, respectively).<ref>{{cite web|title=Apollo 16: Day Four Part Two; Lunar Orbit Insertion, Rev One and Rev Two|url=https://history.nasa.gov/ap16fj/11_Day4_Pt2.htm|work=Apollo 16 Flight Journal|archive-url=https://web.archive.org/web/20111021203744/http://history.nasa.gov/ap16fj/11_Day4_Pt2.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]}}</ref> After entering lunar orbit, the crew began preparations for the Descent Orbit Insertion (DOI) maneuver to further modify the spacecraft's orbital trajectory. The maneuver decreased the craft's pericynthion to {{convert|10.7|nmi|km|sp=us|order=flip}}. The remainder of flight day four was spent making observations and preparing for activation of the Lunar Module, undocking, and landing the following day.<ref>{{cite web|title=Apollo 16: Day Four Part Three: Descent Orbit Insertion, Revs Three to Nine|url=https://history.nasa.gov/ap16fj/12_Day4_Pt3.htm|work=Apollo 16 Flight Journal|archive-url=https://web.archive.org/web/20111021155928/http://history.nasa.gov/ap16fj/12_Day4_Pt3.htm|archive-date=October 21, 2011|url-status=dead|editor-first=David|editor-last=Woods|editor2-first=Tim|editor2-last=Brandt|publisher=[[NASA]]}}</ref>