Editing Apollo 10 (section)

=== Background ===
{{for|a fuller overview of this subject|Apollo program}}

By 1967, NASA had devised a [[List of Apollo missions#Alphabetical mission types|list of mission types]], designated by letters, that needed to be flown before a landing attempt, which would be the "G" mission. The early uncrewed flights were considered "A" or "B" missions, while [[Apollo 7]], the crewed-flight test of the [[Apollo Command and Service Module|Command and Service Module]] (CSM), was the "C" mission. The first crewed orbital test of the [[Apollo Lunar Module|Lunar Module]] (LM) was accomplished on [[Apollo 9]], the "D" mission. [[Apollo 8]], flown to the Moon's orbit without an LM, was considered a "C-prime" mission, but its success gave NASA the confidence to skip the "E" mission, which would have tested the full Apollo spacecraft in medium or high Earth orbit. Apollo 10, the dress rehearsal for the lunar landing, was to be the "F" mission.<ref name="drew" />{{sfn|Brooks|pp=234–235}}

NASA considered skipping the "F" mission as well and attempting the first lunar landing on Apollo 10. Some within the agency advocated for this, feeling it was senseless to bring astronauts so close to the lunar surface, only to turn away. Although the lunar module intended for Apollo 10 was too heavy to perform the lunar mission, the one intended for [[Apollo 11]] could be substituted by delaying Apollo 10 a month from its May 1969 planned launch.{{sfn|Chaikin|pp=151–152}} NASA official [[George Mueller (engineer)|George Mueller]] favored a landing attempt on {{nowrap|Apollo 10}}; he was known for his aggressive approach to moving the [[Apollo program]] forward.<ref name="Hamish">{{Cite web |last=Lindsay |first=Hamish |title=Apollo 10 |url=https://honeysucklecreek.net/msfn_missions/Apollo_10_mission/hl_apollo10.html |access-date=July 2, 2022 |publisher=Colin Hackellar}}</ref> However, Director of Flight Operations [[Christopher C. Kraft]] and others opposed this, feeling that new procedures would have to be developed for a rendezvous in lunar orbit and that NASA had incomplete information regarding the Moon's [[Mass concentration (astronomy)|mass concentration]]s, which might throw off the spacecraft's trajectory. Lieutenant General [[Samuel C. Phillips|Sam Phillips]], the Apollo Program Manager, listened to the arguments on both sides and decided that having a dress rehearsal was crucial.{{sfn|Chaikin|pp=151–152}}