Editing Apollo 13 (section)

== Flight of Apollo 13 ==
[[File:Apollo 13 timeline.svg|center|framed|alt= Apollo 13's circumlunar flight trajectory, showing its distance to the Moon when the accident occurred|The [[circumlunar trajectory]] followed by Apollo&nbsp;13, drawn to scale. The accident occurred about 56 hours into the mission.]]

===Launch and translunar injection===
[[File:Apollo 13 launch (S70-34852).jpg|thumb|upright|Apollo&nbsp;13 launches from Kennedy Space Center, April 11, 1970]]
[[File:Apolo-1. CSM&LM diagram.svg|thumb|Apollo 13 spacecraft configuration during most of the journey: Click on image for key to numbered components.]]
The mission was launched at the planned time, 2:13:00&nbsp;pm [[Eastern Time Zone|EST]] (19:13:00&nbsp;UTC) on April 11. An anomaly occurred when the second-stage, center (inboard) engine shut down about two minutes early.<ref name="lver">{{cite book |author= |url=https://archive.org/details/nasa_techdoc_19900066486 |title=Saturn 5 Launch Vehicle Flight Evaluation Report: AS-508 Apollo 13 Mission |date=June 20, 1970 |publisher=[[NASA]] |publication-place=[[Marshall Space Flight Center|George C. Marshall Space Flight Center]], Huntsville, Alabama |id=MPR-SAT-FE-70-2 |access-date=May 30, 2017}}</ref>{{sfn|Benson & Faherty|1979|pp=494–499}} This was caused by severe [[pogo oscillation]]s. Starting with Apollo 10, the vehicle's guidance system was designed to shut the engine down in response to chamber pressure excursions.{{sfn|Larsen|2008|p=5-13}} Pogo oscillations had occurred on [[Titan (rocket family)|Titan rockets]] (used during the [[Project Gemini|Gemini program]]) and on previous Apollo missions,<ref>{{cite journal|last=Fenwick |first=Jim |date=Spring 1992 |title=Pogo |url=http://www.engineeringatboeing.com/articles/pogo.htm |journal=Threshold |publisher=[[Pratt & Whitney Rocketdyne]] |access-date=July 3, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20071213010936/http://www.engineeringatboeing.com/articles/pogo.htm |archive-date=December 13, 2007 }}</ref>{{sfn|Larsen|2008|pp=5-7–5-12}} but on Apollo&nbsp;13 they were amplified by an interaction with turbopump [[cavitation]].<ref>{{cite journal |last=Dotson |first=Kirk |date=Winter 2003–2004 |title=Mitigating Pogo on Liquid-Fueled Rockets |journal=Crosslink |volume=5 |issue=1 |pages=26–29 |location=El Segundo, California|publisher=[[The Aerospace Corporation]] |access-date=July 3, 2013 |url=http://aerospace.wpengine.netdna-cdn.com/wp-content/uploads/crosslink/V5N1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://aerospace.wpengine.netdna-cdn.com/wp-content/uploads/crosslink/V5N1.pdf |archive-date=2022-10-09 |url-status=live}}</ref><ref name=launch>{{cite web |url=https://history.nasa.gov/afj/ap13fj/01launch_ascent.html |title=Launch and Reaching Earth Orbit |year=2016 |editor-last=Woods |editor-first=W. David |editor-last2=Turhanov|editor-first2=Alexandr|editor-last3=Waugh|editor-first3=Lennox J. |work=Apollo 13 Flight Journal |publisher=NASA |access-date=August 5, 2019}}</ref> A fix to prevent pogo was ready for the mission, but schedule pressure did not permit the hardware's integration into the Apollo&nbsp;13 vehicle.{{sfn|Larsen|2008|p=5-13}}<ref>{{cite journal|url=https://www.universetoday.com/62672/13-things-that-saved-apollo-13-part-5-unexplained-shutdown-of-the-saturn-v-center-engine/|last=Atkinson|first=Nancy|title=13 things that saved Apollo 13, Part 5: Unexplained shutdown of the Saturn V center engine|date=April 14, 2010|journal=[[Universe Today]]|access-date=September 16, 2019}}</ref> A post-flight investigation revealed the engine was one cycle away from catastrophic failure.{{sfn|Larsen|2008|p=5-13}} The four outboard engines and the [[S-IVB]] third stage burned longer to compensate, and the vehicle achieved very close to the planned circular {{convert|190|km|mi nmi|sp=us}} [[parking orbit]], followed by a translunar injection (TLI) about two hours later, setting the mission on course for the Moon.<ref name="lver" />{{sfn|Benson & Faherty|1979|pp=494–499}}

After TLI, Swigert performed the separation and transposition maneuvers before docking the CSM ''Odyssey'' to the LM ''Aquarius'', and the spacecraft pulled away from the third stage.<ref name = "journal extraction">{{cite web|work=Apollo Lunar Flight Journal|url=https://history.nasa.gov/afj/ap13fj/03tde.html|title=Day 1: Transposition, Docking and Extraction|date=February 17, 2017|access-date=August 12, 2019|last1=Woods|first1=W. David |last2=Kemppanen |first2=Johannes|last3=Turhanov|first3=Alexander|last4=Waugh |first4=Lennox J.}}</ref> Ground controllers then sent the third stage on a course to impact the Moon in range of the Apollo 12 seismometer, which it did just over three days into the mission.{{sfn|Orloff & Harland|2006|p=367}}

The crew settled in for the three-day trip to Fra Mauro. At 30:40:50 into the mission, with the TV camera running, the crew performed a burn to place Apollo&nbsp;13 on a hybrid trajectory. The departure from a [[free-return trajectory]] meant that if no further burns were performed, Apollo&nbsp;13 would miss Earth on its return trajectory, rather than intercept it, as with a free return.<ref name = "journal midcourse">{{cite web|work=Apollo Lunar Flight Journal|url=https://history.nasa.gov/afj/ap13fj/05day2-mcc2-tv.html|title=Day 2: Midcourse correction 2 on TV|date=February 17, 2017|access-date=August 7, 2019}}</ref> A free return trajectory could only reach sites near the lunar equator; a hybrid trajectory, which could be started at any point after TLI, allowed sites with higher latitudes, such as Fra Mauro, to be reached.<ref name = "journal hybrid">{{cite web|work=Apollo Lunar Flight Journal|url=https://history.nasa.gov/afj/launchwindow/lw1.html|title=Apollo lunar landing launch window: The controlling factors and constraints|year=2009|access-date=December 2, 2019|author=Robin Wheeler}}</ref> Communications were enlivened when Swigert realized that in the last-minute rush, he had omitted to file his [[Form 1040|federal income tax return]] (due April 15), and amid laughter from mission controllers, asked how he could get an extension. He was found to be entitled to a 60-day extension for being out of the country at the deadline.{{sfn|NASA 1970|p=8}}

Entry into the LM to test its systems had been scheduled for 58:00:00; when the crew awoke on the third day of the mission, they were informed it had been moved up three hours and was later moved up again by another hour. A television broadcast was scheduled for 55:00:00; Lovell, acting as emcee, showed the audience the interiors of ''Odyssey'' and ''Aquarius''.<ref name=storm>{{cite web |url=https://history.nasa.gov/afj/ap13fj/07day3-before-the-storm.html |title=Day 3: Before the storm |year=2016 |editor-last=Woods |editor-first=W. David |editor-last2=Turhanov|editor-first2=Alexandr|editor-last3=Waugh|editor-first3=Lennox J. |work=Apollo 13 Flight Journal |publisher=NASA |access-date=August 27, 2019}}</ref> The audience was limited since none of the television networks were carrying the broadcast,{{sfn|Houston, Heflin & Aaron|2015|p=206}} forcing Marilyn Lovell (Jim Lovell's wife) to go to the VIP room at Mission Control if she wanted to watch her husband and his crewmates.{{sfn|Chaikin|1995|pp=285–287}}
{{clear}}

=== Accident ===
{{For|the cause of the accident|Apollo 13#Investigation and response}}

About six and a half minutes after the TV broadcast{{snd}}approaching 56:00:00{{snd}}Apollo&nbsp;13 was about {{convert|180000|nmi|mi km}} from Earth.<ref name = "journal Houston">{{cite web|work=Apollo Lunar Flight Journal|url=https://history.nasa.gov/afj/ap13fj/08day3-problem.html|title=Day 3: 'Houston, we've had a problem'|date=May 30, 2017|access-date=August 18, 2019|last1=Woods|first1=W. David|last2=Kemppanen|first2=Johannes|last3=Turhanov|first3=Alexander|last4=Waugh|first4=Lennox J.}}</ref> Haise was completing the shutdown of the LM after testing its systems while Lovell stowed the TV camera. [[Jack Lousma]], the [[Flight controller#CAPCOM|CAPCOM]], sent minor instructions to Swigert, including changing the [[orientation (geometry)|attitude]] of the craft to facilitate photography of [[Comet Bennett]].<ref name = "journal Houston" />{{sfn|Chaikin|1995|p=292}}

The pressure sensor in one of the SM's oxygen tanks had earlier appeared to be malfunctioning, so [[Seymour Liebergot|Sy Liebergot]] (the [[Flight controller#Electrical, environmental, and consumables manager (EECOM)|EECOM]], in charge of monitoring the CSM's electrical system) requested that the stirring fans in the tanks be activated. Normally this was done once daily; a stir would [[Thermal destratification|destratify]] the contents of the tanks, making the pressure readings more accurate.<ref name = "journal Houston" /> The Flight Director, Kranz, had Liebergot wait a few minutes for the crew to settle down after the telecast,{{sfn|Houston, Heflin & Aaron|2015|p=207}} then Lousma relayed the request to Swigert, who activated the switches controlling the fans,<ref name = "journal Houston" /> and after a few seconds turned them off again.{{sfn|Chaikin|1995|p=292}}

{{Listen|filename=Apollo13-wehaveaproblem.ogg|title=Houston, we've had a problem.|description=Swigert and Lovell reporting the incident on April 14, 1970 [2:59] "[[Houston, we have a problem|Houston, we've had a problem]]"|format=[[Ogg]]}}

Ninety-five seconds after Swigert activated those switches,{{sfn|Houston, Heflin & Aaron|2015|p=207}} the astronauts heard a "pretty large bang", accompanied by fluctuations in electrical power and the firing of the attitude control thrusters.{{sfn|Orloff & Harland|2006|p=368}}{{sfn|Orloff|2000|pp=152–157}} Communications and telemetry to Earth were lost for 1.8&nbsp;seconds, until the system automatically corrected by switching the [[directional antenna|high-gain]] [[Unified S-band|S-band]] antenna, used for translunar communications, from narrow-beam to wide-beam mode.{{sfn|Accident report|p=4-44}} The accident happened at 55:54:53 (03:08 UTC on April 14; 10:08 PM EST, April 13). Swigert reported 26&nbsp;seconds later, [[Houston, we have a problem|"Okay, Houston, we've had a problem here,"]] echoed at 55:55:42 by Lovell, "Houston, we've had a problem. We've had a Main&nbsp;B Bus undervolt."<ref name = "journal Houston" /> William Fenner was the [[Flight controller|guidance officer]] (GUIDO) who was the first to report a problem in the control room to Kranz.<ref name = "journal Houston" />

Lovell's initial thought on hearing the noise was that Haise had activated the LM's cabin-repressurization valve, which also produced a bang (Haise enjoyed doing so to startle his crewmates), but Lovell could see that Haise had no idea what had happened. Swigert initially thought that a [[meteoroid]] might have struck the LM, but he and Lovell quickly realized there was no leak.{{sfn|Chaikin|1995|p=293}} The "Main Bus&nbsp;B undervolt" meant that there was insufficient [[voltage]] produced by the SM's three [[fuel cell]]s (fueled by hydrogen and oxygen piped from their respective tanks) to the second of the SM's two electric power distribution systems. Almost everything in the CSM required power. Although the [[Bus (computing)|bus]] momentarily returned to normal status, soon both buses A and B were short on voltage. Haise checked the status of the fuel cells and found that two of them were dead. Mission rules forbade entering lunar orbit unless all fuel cells were operational.{{sfn|Chaikin|1995|pp=293–294}}

In the minutes after the accident, there were several unusual readings, showing that tank{{nbsp}}2 was empty and tank{{nbsp}}1's pressure slowly falling, that the [[Apollo Guidance Computer|computer on the spacecraft]] had reset and that the high-gain antenna was not working. Liebergot initially missed the worrying signs from tank{{nbsp}}2 following the stir, as he was focusing on tank{{nbsp}}1, believing that its reading would be a good guide to what was present in tank{{nbsp}}2, as did controllers supporting him in the "back room".  When Kranz questioned Liebergot on this, he initially responded that there might be false readings due to an instrumentation problem; he was often teased about that in the years to come.<ref name = "Cass 1">{{cite web|last=Cass|first=Stephen|title=Apollo 13, we have a solution|url=https://spectrum.ieee.org/apollo-13-we-have-a-solution|date=April 1, 2005|access-date=October 13, 2022|website=IEEE}}</ref> Lovell, looking out the window, reported "a gas of some sort" venting into space, making it clear that there was a serious problem.{{sfn|Houston, Heflin & Aaron|2015|p=215}}

Since the fuel cells needed oxygen to operate, when Oxygen Tank{{nbsp}}1 ran dry, the remaining fuel cell would shut down, meaning the CSM's only significant sources of power and oxygen would be the CM's batteries and its oxygen "surge tank". These would be needed for the final hours of the mission, but the remaining fuel cell, already starved for oxygen, was drawing from the surge tank. Kranz ordered the surge tank isolated, saving its oxygen, but this meant that the remaining fuel cell would die within two hours, as the oxygen in tank{{nbsp}}1 was consumed or leaked away.{{sfn|Chaikin|1995|pp=293–294}} The volume surrounding the spacecraft was filled with myriad small bits of debris from the accident, complicating any efforts to use the stars for navigation.{{sfn|Chaikin|1995|p=299}} The mission's goal became simply getting the astronauts back to Earth alive.<ref name = "Cass 2" />

=== Looping around the Moon ===
[[File:Direct Abort Trajectory - Lunar Landing Symposium, MSC Jun66.jpg|upright=1.2|thumb|This depiction of a direct abort (from a 1966 planning report) contemplates returning from a point much earlier in the mission, and closer to Earth, than where the Apollo&nbsp;13 accident occurred.]]
[[File:NASA-Apollo13-ViewsOfMoon-20200224.webm|thumb|upright=1.18|NASA – Apollo 13 Lunar Mission – Views Of The Moon (2:24)]]
The lunar module had charged batteries and full oxygen tanks for use on the lunar surface, so Kranz directed that the astronauts power up the LM and use it as a "lifeboat"<ref name = "Cass 1" />{{snd}}a scenario anticipated but considered unlikely.{{sfn|Lovell & Kluger|2000|pp=83–87}} Procedures for using the LM in this way had been developed by LM flight controllers after a training simulation for Apollo 10 in which the LM was needed for survival, but could not be powered up in time.<ref name = "Cass 2" /> Had Apollo&nbsp;13's accident occurred on the return voyage, with the LM already jettisoned, the astronauts would have died,<ref name="LM-ALSEP">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1970-029C|title=Apollo 13 Lunar Module/ALSEP|website=NASA Space Science Data Coordinated Archive|access-date=October 31, 2009}}</ref> as they would have following an explosion in lunar orbit, including one while Lovell and Haise walked on the Moon.<ref name = "Yahoo 50th" />

A key decision was the choice of return path. A "direct abort" would use the SM's main engine (the [[Apollo command and service module#Service propulsion system|Service Propulsion System]] or SPS) to return before reaching the Moon. However, the accident could have damaged the SPS, and the fuel cells would have to last at least another hour to meet its power requirements, so Kranz instead decided on a longer route: the spacecraft would swing around the Moon before heading back to Earth. Apollo&nbsp;13 was on the hybrid trajectory which was to take it to Fra Mauro; it now needed to be brought back to a free return. The LM's [[Descent propulsion system|Descent Propulsion System]] (DPS), although not as powerful as the SPS, could do this, but new software for Mission Control's computers needed to be written by technicians as it had never been contemplated that the CSM/LM spacecraft would have to be maneuvered from the LM. As the CM was being shut down, Lovell copied down its guidance system's orientation information and performed hand calculations to transfer it to the LM's guidance system, which had been turned off; at his request Mission Control checked his figures.<ref name = "Cass 2">{{cite web|last=Cass|first=Stephen|title=Houston, we have a solution, part 2|url=https://spectrum.ieee.org/apollo-13-we-have-a-solution-part-2|date=April 1, 2005|website=IEEE|access-date=August 31, 2019}}</ref>{{sfn|Chaikin|1995|pp=297–298}} At 61:29:43.49 the DPS burn of 34.23&nbsp;seconds took Apollo&nbsp;13 back to a free return trajectory.{{sfn|Orloff & Harland|2006|p=369}}

[[File:Mare Moscoviense AS13-60-8648.jpg|thumb|The Apollo&nbsp;13 crew photographed the Moon out of the [[Apollo Lunar Module|Lunar Module]].]]
The change would get Apollo&nbsp;13 back to Earth in about four days' time{{snd}}though with splashdown in the [[Indian Ocean]], where NASA had few recovery forces. Jerry Bostick and other [[Flight controller#FDO|Flight Dynamics Officers]] (FIDOs) were anxious both to shorten the travel time and to move splashdown to the [[Pacific Ocean]], where the main recovery forces were located. One option would shave 36 hours off the return time, but required jettisoning the SM; this would expose the CM's heat shield to space during the return journey, something for which it had not been designed. The FIDOs also proposed other solutions. After a meeting involving NASA officials and engineers, the senior individual present, [[Johnson Space Center|Manned Spaceflight Center]] director [[Robert R. Gilruth]], decided on a burn using the DPS, that would save 12&nbsp;hours and land Apollo&nbsp;13 in the Pacific. This "PC+2" burn would take place two hours after [[pericynthion]], the closest approach to the Moon.<ref name = "Cass 2" />  At pericynthion, Apollo&nbsp;13 set the record (per the ''Guinness Book of World Records''), which still stands, for the furthest distance from Earth by a crewed spacecraft: {{convert|400171|km|mi nmi|sp=us}} from Earth at 7:21&nbsp;pm EST, April 14 (00:21:00&nbsp;UTC April 15).{{sfn|Glenday|2010|p=13}}{{NoteTag|The record was set because the Moon was nearly at [[Apsis|its furthest from Earth]] during the mission. Apollo&nbsp;13's unique free return trajectory caused it to go approximately {{convert|100|km|-1|sp=us}} further from the [[Far side (Moon)|lunar far side]] than other Apollo lunar missions, but this was a minor contribution to the record.{{sfn|Adamo|2009|p=37}} A reconstruction of the trajectory by astrodynamicist Daniel Adamo in 2009 records the furthest distance as {{convert|400046|km|sp=us}} at 7:34&nbsp;pm&nbsp;EST (00:34:13&nbsp;UTC). Apollo 10 holds the record for second-furthest at a distance of {{convert|399806|km|sp=us}}.{{sfn|Adamo|2009|p=41}}}}

While preparing for the burn, the crew was told that the S-IVB had impacted the Moon as planned, leading Lovell to quip, "Well, at least something worked on this flight."<ref name = "journal leaving" />{{sfn|Cooper|2013|pp=84–86}} Kranz's White team of mission controllers, who had spent most of their time supporting other teams and developing the procedures urgently needed to get the astronauts home, took their consoles for the PC+2 procedure.{{sfn|Houston, Heflin & Aaron|2015|pp=221–222}} Normally, the accuracy of such a burn could be assured by checking the alignment Lovell had transferred to the LM's computer against the position of one of the stars astronauts used for navigation, but the light glinting off the many pieces of debris accompanying the spacecraft made that impractical. The astronauts accordingly used the one star available whose position could not be obscured{{snd}}the Sun. Houston also informed them that the Moon would be centered in the commander's window of the LM as they made the burn, which was almost perfect{{snd}}less than 0.3 meters (1 foot) per second off.<ref name = "journal leaving" /> The burn, at 79:27:38.95, lasted four minutes and 23&nbsp;seconds.{{sfn|Orloff & Harland|2006|p=391}} The crew then shut down most LM systems to conserve consumables.<ref name = "journal leaving">{{cite web|work=Apollo Lunar Flight Journal|url=https://history.nasa.gov/afj/ap13fj/13day4-leaving-moon.html|title=Day 4: Leaving the Moon|date=February 17, 2017|access-date=September 7, 2019}}</ref>

=== Return to Earth ===
[[File:Apollo13 apparatus.jpg|thumb|Swigert with the rig improvised to adapt the CM's [[lithium hydroxide]] canisters for use in the LM]]

The LM carried enough oxygen, but that still left the problem of [[carbon dioxide scrubber|removing carbon dioxide]], which was absorbed by canisters of [[lithium hydroxide]] pellets. 
The LM's stock of canisters, meant to accommodate two astronauts for 45 hours on the Moon, was not enough to support three astronauts for the return journey to Earth.{{sfn|Houston, Heflin & Aaron|2015|p=224}} The CM had enough canisters, but they were of a different shape and size to the LM's, hence unable to be used in the LM's equipment. Engineers on the ground devised a way to bridge the gap, using plastic covers ripped from procedure manuals, duct tape, and other items available on the spacecraft.<ref>{{cite news|url=https://www.newspapers.com/clip/36237422/detroit_free_press/|title=Astronauts Beat Air Crisis By Do-It-Yourself Gadget|newspaper=Detroit Free Press|location=Detroit, Michigan|date=April 16, 1970|page=12–C|last1=Pothier|first1=Richard|via=Newspapers.com}}</ref>{{sfn|Barell|2016|p=154}} NASA engineers referred to the improvised device as "the mailbox".<ref>{{Cite web|last=Smith|first=Yvette|date=2015-09-24|title=Putting a Square Peg in a Round Hole|url=http://www.nasa.gov/image-feature/putting-a-square-peg-in-a-round-hole|access-date=2021-05-20|website=NASA}}</ref> The procedure for building the device was read to the crew by CAPCOM [[Joseph P. Kerwin|Joseph Kerwin]] over the course of an hour, and was built by Swigert and Haise; carbon dioxide levels began dropping immediately. Lovell later described this improvisation as "a fine example of cooperation between ground and space".{{sfn|Cortright|1975|pp=257–262}}

[[File:Apollo 13 Hasselblad image from film magazine 62-JJ (cropped).jpg|thumb|left|Lovell tries to rest in the frigid spacecraft]]

The CSM's electricity came from fuel cells that produced water as a byproduct, but the LM was powered by [[Silver-oxide battery|silver-zinc batteries]] which did not, so both electrical power and water (needed for equipment cooling as well as drinking) would be critical. LM power consumption was reduced to the lowest level possible;{{sfn|Mission Operations Report 1970|pp=III‑17, III-33, III-40}} Swigert was able to fill some drinking bags with water from the CM's water tap,<ref name = "journal leaving" /> but even assuming rationing of personal consumption, Haise initially calculated they would run out of water for cooling about five hours before reentry. This seemed acceptable because the systems of Apollo 11's LM, once jettisoned in lunar orbit, had continued to operate for seven to eight hours even with the water cut off. In the end, Apollo&nbsp;13 returned to Earth with {{convert|28.2|lb|order=flip}} of water remaining.{{sfn|Cortright|1975|pp=254–257}} The crew's ration was 0.2&nbsp;liters (6.8&nbsp;fl&nbsp;oz) of water per person per day; the three astronauts lost a total of {{convert|31|lb|order=flip}} among them, and Haise developed a [[urinary tract infection]].<ref name = "mission summary">{{cite web|last=Jones|first=Eric M.|date=January 4, 2006|url=https://history.nasa.gov/alsj/a13/a13.summary.html|title=The frustrations of Fra Mauro: Part I|work=Apollo Lunar Surface Journal|access-date=September 7, 2019}}</ref>{{sfn|Cortright|1975|pp=262–263}} This infection was probably caused by the reduced water intake, but microgravity and effects of cosmic radiation might have impaired his immune system's reaction to the pathogen.<ref>{{cite journal |last1=Kennedy |first1=A.R. |date=2014 |title=Biological effects of space radiation and development of effective countermeasures |journal=Life Sciences in Space Research |volume= 1|issue=1 |pages=10–43 |doi=10.1016/j.lssr.2014.02.004|pmid=25258703 |pmc=4170231 |bibcode=2014LSSR....1...10K }}</ref>

[[File:Apollo 13 Houston, We've Got a Problem.ogv|thumb|''Apollo 13: Houston, We've Got a Problem'' (1970) — Documentary about the mission by NASA (28:21)]]

Inside the darkened spacecraft, the temperature dropped as low as {{convert|38|F|order=flip}}.<ref>{{Cite web|last=Mars|first=Kelli|date=2020-04-16|title=50 Years Ago: Apollo 13 Crew Returns Safely to Earth|url=http://www.nasa.gov/feature/50-years-ago-apollo-13-crew-returns-safely-to-earth|access-date=2021-05-20|website=NASA}}</ref> Lovell considered having the crew don their spacesuits, but decided this would be too hot. Instead, Lovell and Haise wore their lunar EVA boots and Swigert put on an extra coverall. All three astronauts were cold, especially Swigert, who had got his feet wet while filling the water bags and had no lunar overshoes (since he had not been scheduled to walk on the Moon). As they had been told not to discharge their urine to space to avoid disturbing the trajectory, they had to store it in bags. Water condensed on the walls, though any condensation that may have been behind equipment panels{{sfn|Cortright|1975|pp=257–263}} caused no problems, partly because of the extensive electrical insulation improvements instituted after the [[Apollo 1]] fire.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/constellation/main/A13_panel.html|title=Generation Constellation Learns about Apollo 13|last=Siceloff|first=Steven|date=September 20, 2007|work=[[Constellation program|Constellation Program]]|publisher=NASA|access-date=September 7, 2019}}</ref> Despite all this, the crew voiced few complaints.<ref name = "Cass 3">{{cite web|last=Cass|first=Stephen|title=Houston, we have a solution, part 3|url=https://spectrum.ieee.org/apollo-13-we-have-a-solution-part-3|date=April 1, 2005|website=IEEE|access-date=September 8, 2019}}</ref>

Flight controller [[John Aaron]], along with Mattingly and several engineers and designers, devised a procedure for powering up the command module from full shutdown{{snd}}something never intended to be done in flight, much less under Apollo&nbsp;13's severe power and time constraints.<ref>{{cite journal|last=Leopold|first=George|date=March 17, 2009|title=Power engineer: Video interview with Apollo astronaut Ken Mattingly|journal=[[EE Times]]|publisher=UMB Tech|url=https://www.eetimes.com/power-engineer-video-interview-with-apollo-astronaut-ken-mattingly/|access-date=August 14, 2010}}</ref> The astronauts implemented the procedure without apparent difficulty: Kranz later credited all three astronauts having been test pilots, accustomed to having to work in critical situations with their lives on the line, for their survival.<ref name = "Cass 3" />

Recognizing that the cold conditions combined with insufficient rest would hinder the time-critical startup of the command module prior to reentry, at 133 hours into flight Mission Control gave Lovell the okay to fully power up the LM to raise the cabin temperature, which included restarting the LM's guidance computer.  Having the LM's computer running enabled Lovell to perform a navigational sighting and calibrate the LM's Inertial Measurement Unit (IMU).  With the lunar module's computer aware of its location and orientation, the command module's computer was later calibrated in a reverse of the normal procedures used to set up the LM, shaving steps from the restart process and increasing the accuracy of the [[Apollo PGNCS|PGNCS]]-controlled reentry.<ref>{{cite web|url=https://www.history.nasa.gov/afj/ap13fj/25day6-thelastcoursecorrection.html|title=Apollo Flight Journal: Day 6 Part 4|publisher=NASA|access-date=May 17, 2021|archive-date=January 18, 2022|archive-url=https://web.archive.org/web/20220118020508/https://www.history.nasa.gov/afj/ap13fj/25day6-thelastcoursecorrection.html|url-status=dead}}</ref>

=== Reentry and splashdown ===

Despite the accuracy of the transearth injection, the spacecraft slowly drifted off course, necessitating a correction. As the LM's guidance system had been shut down following the PC+2 burn, the crew was told to use [[solar terminator|the line between night and day]] on the Earth to guide them, a technique used on NASA's Earth-orbit missions but never on the way back from the Moon.<ref name = "Cass 3" /> This DPS burn, at 105:18:42 for 14&nbsp;seconds, brought the projected entry flight path angle back within safe limits. Nevertheless, yet another burn was needed at 137:40:13, using the LM's [[reaction control system]] (RCS) thrusters, for 21.5&nbsp;seconds. The SM was jettisoned less than half an hour later, allowing the crew to see the damage for the first time, and photograph it. They reported that an entire panel was missing from the SM's exterior, the fuel cells above the oxygen tank shelf were tilted, that the high-gain antenna was damaged, and there was a considerable amount of debris elsewhere.{{sfn|Orloff & Harland|2006|pp=370–371}} Haise could see possible damage to the SM's engine bell, validating Kranz's decision not to use the SPS.<ref name = "Cass 3" /> The crew then moved out of the LM back into the CM and reactivated its life support systems.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1970-029C |title=Apollo 13 Lunar Module / EASEP |publisher=[[NASA Space Science Data Coordinated Archive]] |access-date=July 9, 2024}}</ref> 

[[File:Apollo13 splashdown.jpg|thumb|left|alt=Spaceship contacts ocean under parachute|Apollo&nbsp;13 splashes down in the South Pacific on April 17, 1970]]

The last problem to be solved was how to separate the lunar module a safe distance away from the command module just before reentry. The normal procedure, in lunar orbit, was to release the LM and then use the service module's RCS to pull the CSM away, but by this point, the SM had already been released. [[Grumman]], manufacturer of the LM, assigned a team of [[University of Toronto]] engineers, led by senior scientist [[Bernard Etkin]], to solve the problem of how much air pressure to use to push the modules apart. The astronauts applied the solution, which was successful.<ref name="G&M">{{cite news|title=Bernard Etkin helped avert Apollo 13 tragedy|url=https://www.theglobeandmail.com/technology/science/bernard-etkin-helped-avert-apollo-13-tragedy/article19735265/#dashboard/follows/|access-date=September 7, 2019|newspaper=The Globe and Mail}}</ref> The LM reentered Earth's atmosphere and was destroyed, the remaining pieces falling in the deep ocean.<ref name="LM-ALSEP" /><ref name=impact>{{cite web|url=https://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_impact.html|title=Impact Sites of Apollo LM Ascent and SIVB Stages|website=NASA Space Science Data Coordinated Archive|access-date=August 27, 2019}}</ref> Apollo&nbsp;13's final midcourse correction had addressed the concerns of the Atomic Energy Commission, which wanted the cask containing the plutonium oxide intended for the SNAP-27 RTG to land in a safe place. The impact point was over the [[Tonga Trench]] in the Pacific, one of its deepest points, and the cask sank {{convert|10|km|mi nmi|sp=us|0}} to the bottom. Later helicopter surveys found no radioactive leakage.<ref name = "Cass 3" />

Ionization of the air around the command module during reentry would typically cause a four-minute communications blackout. Apollo&nbsp;13's shallow reentry path lengthened this to six minutes, longer than had been expected; controllers feared that the CM's heat shield had failed.<ref>{{cite magazine|title=Did Ron Howard exaggerate the reentry scene in the movie Apollo 13?|first=Joe|last=Pappalardo|url=http://www.airspacemag.com/need-to-know/did-ron-howard-exaggerate-the-reentry-scene-in-the-movie-apollo-13-17639496/|magazine=[[Air & Space/Smithsonian]]|publisher=[[Smithsonian Institution]]|location=Washington, D.C.|date=May 1, 2007|access-date=September 8, 2019}}</ref> ''Odyssey'' regained radio contact and splashed down safely in the South Pacific Ocean, {{Coord|21|38|24|S|165|21|42|W|type:event|name=Apollo 13 splashdown}},{{sfn|Apollo 13 Mission Report 1970|p=1-2}} southeast of [[American Samoa]] and {{convert|6.5|km|mi nmi|abbr=on}} from the recovery ship, [[USS Iwo Jima (LPH-2)|USS ''Iwo Jima'']].{{sfn|Orloff & Harland|2006|p=371}} Although fatigued, the crew was in good condition except for Haise, who had developed a serious urinary tract infection because of insufficient water intake.{{sfn|Cortright|1975|pp=262–263}} The crew stayed overnight on the ship and flew to [[Pago Pago]], [[American Samoa]], the next day. They flew to Hawaii, where President [[Richard Nixon]] awarded them the [[Presidential Medal of Freedom]], the highest civilian honor.<ref>{{cite news|url=https://www.newspapers.com/clip/39764154/the_philadelphia_inquirer/|title=Heroes of Apollo 13 Welcomed by President and Loved Ones|agency=Associated Press|newspaper=The Philadelphia Inquirer|location=Philadelphia, Pennsylvania|date=April 19, 1970|via=Newspapers.com|page=1}}</ref> They stayed overnight, and then were flown back to Houston.{{sfn|Apollo 13 Mission Report 1970|p=10-5}}

En route to Honolulu, President Nixon stopped at Houston to award the Presidential Medal of Freedom to the Apollo&nbsp;13 Mission Operations Team.<ref name="nixon">{{cite web|title=Behind the Scenes of Apollo 13|url=https://www.nixonfoundation.org/2016/04/behind-scenes-apollo-13/|website=Richard Nixon Foundation|access-date=June 27, 2019|date=April 11, 2016}}</ref> He originally planned to give the award to NASA administrator [[Thomas O. Paine]], but Paine recommended the mission operations team.<ref>{{cite web|url=https://www.presidency.ucsb.edu/node/241054|title=Remarks on Presenting the Presidential Medal of Freedom to Apollo 13 Mission Operations Team in Houston.|publisher=The American Presidency Project|access-date=December 27, 2017}}</ref>