Editing Apollo 8 (section)

==Preparations==
===Mission schedule===

{{Main|List of Apollo missions#Alphabetical mission types|l1=List of Apollo missions}}

On September 20, 1967, NASA adopted a seven-step plan for Apollo missions, with the final step being a Moon landing. [[Apollo 4|Apollo{{nbsp}}4]] and [[Apollo 6|Apollo{{nbsp}}6]] were "A" missions, tests of the [[Saturn V|Saturn{{nbsp}}V]] launch vehicle using an uncrewed Block I production model of the command and service module (CSM) in Earth orbit. [[Apollo 5|Apollo{{nbsp}}5]] was a "B" mission, a test of the LM in Earth orbit. Apollo{{nbsp}}7, scheduled for October 1968, would be a "C" mission, a crewed Earth-orbit flight of the CSM. Further missions depended on the readiness of the LM. It had been decided as early as May 1967 that there would be at least four additional missions. Apollo{{nbsp}}8 was planned as the "D" mission, a test of the LM in a low Earth orbit in December 1968 by [[James McDivitt]], [[David Scott]], and [[Rusty Schweickart|Russell Schweickart]], while Borman's crew would fly the "E" mission, a more rigorous LM test in an elliptical medium Earth orbit as Apollo{{nbsp}}9, in early 1969. The "F" Mission would test the CSM and LM in lunar orbit, and the "G" mission would be the finale, the Moon landing.{{sfn|Brooks|Grimwood|Swenson|1979|pp=231–234}}
[[File:Apollo 8 first stage in the Vehicle Assembly Building.jpg|thumb|left|upright|The first stage of AS-503 being erected in the [[Vehicle Assembly Building]] (VAB) on February 1, 1968]]

Production of the LM fell behind schedule, and when Apollo{{nbsp}}8's LM-3 arrived at the [[Kennedy Space Center]] (KSC) in June 1968, more than a hundred significant defects were discovered, leading [[Bob Gilruth]], the director of the [[Manned Spacecraft Center]] (MSC), and others to conclude that there was no prospect of LM-3 being ready to fly in 1968.{{sfn|Brooks|Grimwood|Swenson|1979|p=256}} Indeed, it was possible that delivery would slip to February or March 1969. Following the original seven-step plan would have meant delaying the "D" and subsequent missions, and endangering the program's goal of a lunar landing before the end of 1969.{{sfn|Ertel|Newkirk|Brooks|1978|pp=237–238}} [[George Low]], the Manager of the Apollo Spacecraft Program Office, proposed a solution in August 1968 to keep the program on track despite the LM delay. Since the next CSM (designated as "CSM-103") would be ready three months before LM-3, a CSM-only mission could be flown in December 1968. Instead of repeating the "C" mission flight of Apollo{{nbsp}}7, this CSM could be sent all the way to the Moon, with the possibility of entering a lunar orbit and returning to Earth. The new mission would also allow NASA to test lunar landing procedures that would otherwise have had to wait until [[Apollo 10|Apollo{{nbsp}}10]], the scheduled "F" mission. This also meant that the medium Earth orbit "E" mission could be dispensed with. The net result was that only the "D" mission had to be delayed, and the plan for lunar landing in mid-1969 could remain on timeline.{{sfn|Brooks|Grimwood|Swenson|1979|p=257}}

On August 9, 1968, Low discussed the idea with Gilruth, Flight Director [[Chris Kraft]], and the Director of Flight Crew Operations, [[Donald Slayton]]. They then flew to the [[Marshall Space Flight Center]] (MSFC) in [[Huntsville, Alabama]], where they met with KSC Director [[Kurt Debus]], Apollo Program Director [[Samuel C. Phillips]], [[Rocco Petrone]], and [[Wernher von Braun]]. Jerry Wittenstein, deputy chief of flight mechanics, presented trajectories for the new mission.<ref>family history</ref> Kraft considered the proposal feasible from a flight control standpoint; Debus and Petrone agreed that the next Saturn V, AS-503, could be made ready by December 1; and von Braun was confident the [[pogo oscillation]] problems that had afflicted Apollo{{nbsp}}6 had been fixed. Almost every senior manager at NASA agreed with this new mission, citing confidence in both the hardware and the personnel, along with the potential for a circumlunar flight providing a significant morale boost. The only person who needed some convincing was [[James E. Webb]], the NASA administrator. Backed by the full support of his agency, Webb authorized the mission. Apollo{{nbsp}}8 was officially changed from a "D" mission to a "C-Prime" lunar-orbit mission.{{sfn|Brooks|Grimwood|Swenson|1979|pp=257–260}}

With the change in mission for Apollo 8, Slayton asked McDivitt if he still wanted to fly it. McDivitt turned it down; his crew had spent a great deal of time preparing to test the LM, and that was what he still wanted to do. Slayton then decided to swap the prime and backup crews of the D{{nbsp}}and E{{nbsp}}missions. This swap also meant a swap of spacecraft, requiring Borman's crew to use CSM-103, while McDivitt's crew would use CSM-104, since CM-104 could not be made ready by December. David Scott was not happy about giving up CM-103, the testing of which he had closely supervised, for CM-104, although the two were almost identical, and Anders was less than enthusiastic about being an LMP on a flight with no LM.{{sfn|Brooks|Grimwood|Swenson|1979|p=262}}{{sfn|Collins|2001|pp=296–298}} Instead, Apollo{{nbsp}}8 would carry the<!--LM is pronounced "LEM"--> LM test article, a [[Boilerplate (spaceflight)|boilerplate]] model that would simulate the correct weight and balance of LM-3.{{sfn|Brooks|Grimwood|Swenson|1979|pp=257–260}}

Added pressure on the Apollo program to make its 1969 landing goal was provided by the [[Soviet Union]]'s [[Zond 5|Zond{{nbsp}}5]] mission, which flew some living creatures, including [[Russian tortoise]]s, in a [[cislunar]] loop around the Moon and returned them to Earth on September 21.{{sfn|Chaikin|1994|p=76}} There was speculation within NASA and the press that they might be preparing to launch [[astronaut#Cosmonaut|cosmonauts]] on a similar [[Zond program#Circumlunar missions|circumlunar mission]] before the end of 1968.<ref name="Moon Race 1968">{{cite magazine |title=Poised for the Leap |url=http://www.time.com/time/subscriber/article/0,33009,844661-1,00.html |archive-url=https://archive.today/20130204221712/http://www.time.com/time/subscriber/article/0,33009,844661-1,00.html |url-status=dead |archive-date=February 4, 2013 |access-date=December 15, 2011 |magazine=[[Time (magazine)|Time]] |date=December 6, 1968 }}</ref>  Compounding these concerns, American reconnaissance satellites observed a mockup [[N1 (rocket)|N1]] being rolled to the pad at Baikonur on November 25, 1967.<ref>{{cite web |first=John |last=Uri |date=November 17, 2017 |title=50 Years Ago: Soviet's Moon Rocket's Rollout to Pad Affects Apollo Plans |publisher=NASA |url=https://www.nasa.gov/history/50-years-ago-soviets-moon-rockets-rollout-to-pad-affects-apollo-plans/ |access-date=January 18, 2024}}</ref>
[[File:Mating of Apollo 8 spacecraft with Saturn-V.jpg|thumb|right|Erection and mating of spacecraft 103 to Launch Vehicle AS-503 in the VAB for the Apollo{{nbsp}}8 mission]]
The Apollo 8 crew, now living in the crew quarters at Kennedy Space Center, received a visit from [[Charles Lindbergh]] and his wife, [[Anne Morrow Lindbergh]], the night before the launch.<ref>{{cite news |title=Astronauts look back 30 years after historic lunar launch |first=Richard |last=Benke |url=http://cgi.canoe.ca/SpaceArchive/981221_30.html |archive-url=https://archive.today/20121206004702/http://cgi.canoe.ca/SpaceArchive/981221_30.html |url-status=usurped |archive-date=December 6, 2012 |agency=[[Associated Press]] |newspaper=[[The Augusta Chronicle]] |publisher=[[Morris Communications]] |date=December 21, 1998 |access-date=June 28, 2013}}</ref> They talked about how, before his [[Spirit of St. Louis|1927 flight]], Lindbergh had used a piece of string to measure the distance from New York City to Paris on a globe and from that calculated the fuel needed for the flight. The total he had carried was a tenth of the amount that the Saturn V would burn every second. The next day, the Lindberghs watched the launch of Apollo{{nbsp}}8 from a nearby dune.{{sfn|Kluger|2017|pp=149–151}}

===Saturn V redesign===

The Saturn V rocket used by Apollo{{nbsp}}8 was designated AS-503, or the "03rd" model of the Saturn{{nbsp}}V ("5") rocket to be used in the Apollo-Saturn ("AS") program. When it was erected in the [[Vehicle Assembly Building]] on December 20, 1967, it was thought that the rocket would be used for an uncrewed Earth-orbit test flight carrying a [[Boilerplate (spaceflight)|boilerplate]] command and service module. Apollo{{nbsp}}6 had suffered several major problems during its April 1968 flight, including severe [[pogo oscillation]] during its first stage, two second-stage engine failures, and a third stage that failed to reignite in orbit. Without assurances that these problems had been rectified, NASA administrators could not justify risking a crewed mission until additional uncrewed test flights proved the Saturn V was ready.{{sfn|Bilstein|1996|pp=360–370}}

Teams from the MSFC went to work on the problems. Of primary concern was the pogo oscillation, which would not only hamper engine performance, but could exert significant g-forces on a crew. A task force of contractors, NASA agency representatives, and MSFC researchers concluded that the engines vibrated at a frequency similar to the frequency at which the spacecraft itself vibrated, causing a resonance effect that induced oscillations in the rocket. A system that used helium gas to absorb some of these vibrations was installed.{{sfn|Bilstein|1996|pp=360–370}}
[[File:Ap8-KSC-68PC-147.jpg|thumb|upright=1.4|left|Apollo 8 atop Saturn{{nbsp}}V being rolled out to [[Kennedy Space Center Launch Complex 39|Pad 39A]] atop the [[crawler-transporter]]]]

Of equal importance was the failure of three engines during flight. Researchers quickly determined that a leaking hydrogen fuel line ruptured when exposed to vacuum, causing a loss of fuel pressure in engine two. When an automatic shutoff attempted to close the liquid hydrogen valve and shut down engine two, it had accidentally shut down engine three's liquid oxygen due to a miswired connection. As a result, engine three failed within one second of engine two's shutdown. Further investigation revealed the same problem for the third-stage engine—a faulty igniter line. The team modified the igniter lines and fuel conduits, hoping to avoid similar problems on future launches.{{sfn|Bilstein|1996|pp=360–370}}

The teams tested their solutions in August 1968 at the MSFC. A Saturn stage IC was equipped with shock-absorbing devices to demonstrate the team's solution to the problem of pogo oscillation, while a Saturn Stage II was retrofitted with modified fuel lines to demonstrate their resistance to leaks and ruptures in vacuum conditions. Once NASA administrators were convinced that the problems had been solved, they gave their approval for a crewed mission using AS-503.{{sfn|Bilstein|1996|pp=360–370}}

The Apollo 8 spacecraft was placed on top of the rocket on September 21, and the rocket made the slow {{convert|3|mi|adj=on}} journey to the launch pad atop one of NASA's two massive [[crawler-transporter]]s on October{{nbsp}}9.<ref name="satVillust">{{cite book|last=Akens |first=David S. |title=Saturn Illustrated Chronology |url=https://history.nasa.gov/MHR-5/cover.htm |archive-url=https://web.archive.org/web/20080307132427/https://history.nasa.gov/MHR-5/app_h.htm |archive-date=March 7, 2008 |access-date=February 1, 2008 |year=1971 |publisher=[[Marshall Space Flight Center]] |location=Huntsville, AL |id=MSFC MHR-5 |chapter=Appendix H—Saturn at the Cape |chapter-url=https://history.nasa.gov/MHR-5/app_h.htm |url-status=live}}</ref> Testing continued all through December until the day before launch, including various levels of readiness testing from December{{nbsp}}5 through 11. Final testing of modifications to address the problems of pogo oscillation, ruptured fuel lines, and bad igniter lines took place on December 18, three days before the scheduled launch.{{sfn|Bilstein|1996|pp=360–370}}