Editing Apollo 6 (section)

{{short description|Second test flight of the Apollo Saturn V rocket}}
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{{use mdy dates|date=September 2021}}
{{use American English|date=January 2014}}
{{Infobox spaceflight
| name                  = Apollo 6
| image                 = Apollo 6 launch.jpg
| image_caption         = Launch of Apollo 6 (identifiable by its white-painted service module) as seen from the top of the launch tower
| insignia              = <!-- Mission had no insignia; do not use Apollo program -->
| mission_type          = Uncrewed Earth orbital CSM flight ([[List of Apollo missions#Alphabetical mission types|A]])
| operator              = [[NASA]] 
| COSPAR_ID             = 1968-025A 
| SATCAT                = 3170
| mission_duration      = 9&nbsp;hours 57&nbsp;minutes 20&nbsp;seconds
| orbits_completed      = 3
| spacecraft            = {{plainlist|
*[[Apollo command and service module|Apollo CSM]]-020
* Apollo LTA-2R}}
| manufacturer          = [[North American Rockwell]]
| launch_mass           = {{plainlist|
* Total: {{convert|81,420|lb|kg|order=flip}}
* CSM: {{convert|55,420|lb|kg|order=flip}}}}
| landing_mass          =

| launch_date           = {{start-date|April 4, 1968, 12:00:01|timezone=yes}}&nbsp;UTC 
| launch_rocket         = [[Saturn V]] SA-502
| launch_site           = [[Kennedy Space Center|Kennedy]] [[Kennedy Space Center Launch Complex 39|LC-39A]]

| landing_date          = {{end-date|April 4, 1968, 21:57:21|timezone=yes}}&nbsp;UTC 
| landing_site          = {{Coord|27|40|N|157|55|W|type:event|name=Apollo 6 splashdown}}
| recovery_by           = {{USS|Okinawa|LPH-3|6}}
| previous_mission      = [[Apollo 5]]
| next_mission          = [[Apollo 7]]
| programme             = [[Apollo program]]
}}
'''Apollo 6''' (April 4, 1968), also known as '''AS-502''', was the third and final uncrewed flight in the United States' [[Apollo Program]] and the second test of the [[Saturn V]] launch vehicle. It qualified the Saturn V for use on crewed missions, and it was used beginning with [[Apollo 8]] in December 1968.

Apollo 6 was intended to demonstrate the ability of the Saturn V's third stage, the [[S-IVB]], to propel itself and the [[Apollo spacecraft]] to lunar distances. Its components began arriving at the [[Kennedy Space Center]] in early 1967. Testing proceeded slowly, often delayed by testing of the Saturn V intended for [[Apollo 4]]—the inaugural launch of the Saturn V. After that uncrewed mission launched in November 1967, there were fewer delays, but enough so that the flight was postponed from March to April 1968.

The flight plan called for, following [[trans-lunar injection]],  a direct return abort using the [[service module]]'s main engine with a flight time totaling about 10 hours but vibrations damaged some of the [[Rocketdyne J-2]] engines in the second and third stages by rupturing internal fuel lines causing a second-stage engine to shut down early. An additional second-stage engine also shut down early due to cross-wiring with the engine that had shut down. The vehicle's onboard guidance system compensated by burning the second and third stages longer, although the resulting parking orbit was more elliptical than planned. The damaged third-stage engine failed to restart for trans-lunar injection. Flight controllers elected to repeat the flight profile of the previous Apollo 4 test, achieving a high orbit and high-speed return. Despite the engine failures, the flight provided [[NASA]] with enough confidence to use the Saturn V for crewed launches; a potential third uncrewed flight was cancelled.