Editing Apollo 6 (section)

==Preparation==
The [[S-IC]] first stage arrived by barge on March 13, 1967, and was erected in the [[Vehicle Assembly Building]] (VAB) four days later; the S-IVB third stage and [[Saturn V instrument unit|Instrument Unit]] computer both arrived on March 17. The [[S-II]] second stage was not yet ready and so the dumbbell-shaped spacer, used in preparation for Apollo 4 (which also had a delayed S-II), was substituted so testing could proceed. The spacer had the same height and mass as the S-II along with all the electrical connections. The S-II arrived May 24 and was stacked and mated into the rocket on July 7.<ref name = "moonport 6">{{cite book |last1=Benson |first1=Charles D. |last2=Faherty |first2=William Barnaby |title=Moonport: A History of Apollo Launch Facilities and Operations |url=https://www.hq.nasa.gov/office/pao/History/SP-4204/contents.html |access-date=November 3, 2022 |year=1978 |publisher=NASA |id=NASA SP-4204 |chapter=Apollo 6 - A "Less Than Perfect" Mission |chapter-url=https://www.hq.nasa.gov/office/pao/History/SP-4204/ch20-2.html |archive-date=January 23, 2008 |archive-url=https://web.archive.org/web/20080123133438/https://www.hq.nasa.gov/office/pao/History/SP-4204/contents.html |url-status=dead }} Ch. 20-2.</ref>

Apollo 6 saw the first use of the High Bay 3 of the VAB, and it was quickly discovered that its air conditioning facilities were inadequate. Portable high-capacity units were brought in to keep equipment and workers cool. There were delays in April as personnel and equipment were busy with Apollo 4, and not available for tests on Apollo 6. The S-II second stage arrived on May 25 and was erected in one of the VAB's low bays, but work on Apollo 6 continued to be plagued by delays, many occasioned by work on Apollo 4. The vehicle was erected on Mobile Service Launcher 2, but work on the launcher's arms, which would swing back at launch, proceeded slowly. Also slow to arrive was the CSM itself; the planned late-September arrival was pushed back two months.<ref name = "moonport 6" />

After Apollo 4's launch on November 9, 1967, the pace of the Apollo 6 project picked up, but there remained many problems with flight hardware.
The CSM was erected atop the launch vehicle on December 11, 1967, and the spacecraft stack was rolled out to [[Kennedy Space Center Launch Complex 39|Launch Complex 39A]] on February 6, 1968.{{sfn|Orloff & Harland 2006|p=152}} The rollout was an all-day affair and much of it was conducted in heavy rain. Because the [[crawler-transporter]] had to halt for two hours when communications failed, the vehicle did not arrive at the launch pad until it was dark. The mobile [[service structure]] could not be moved to the launch pad for two days due to high winds.{{sfn|Brooks 1979|p=247}}<ref name = "moonport 6" />

The flight readiness test concluded on March 8, 1968, and at a review held three days later, Apollo 6 was cleared for launch contingent on the successful completion of testing and some action items identified at the meeting. Launch was set for March 28, 1968, but was postponed to April 1 and then April 3 after problems with some guidance system equipment and with fueling. The [[terminal countdown demonstration test|countdown demonstration test]] began on March 24; although it was completed within a week, the launch had to be postponed one more time. On April 3, the final countdown began with liftoff scheduled for the following day.<ref name = "moonport 6" /> All subsequent problems were fixed during the built-in holds in the countdown and did not delay the mission.{{sfn|Orloff & Harland 2006|p=151}}