Editing Apollo program (section)

==Choosing a mission mode==
{{see also|Moon landing}}
[[File:John C. Houbolt - GPN-2000-001274.jpg|right|thumb|[[John Houbolt]] explaining the [[Lunar orbit rendezvous|LOR]] concept]]
[[File:Apollo Direct Ascent.png|thumb|right|Early Apollo configuration for [[Direct ascent|Direct Ascent]] and [[Earth orbit rendezvous|Earth Orbit Rendezvous]], 1961]]

Once Kennedy had defined a goal, the Apollo mission planners were faced with the challenge of designing a spacecraft that could meet it while minimizing risk to human life, limiting cost, and not exceeding limits in possible technology and astronaut skill.  Four possible mission modes were considered:
* '''[[Direct ascent|Direct Ascent]]:''' The spacecraft would be launched as a unit and travel directly to the lunar surface, without first going into lunar orbit. A {{convert|50000|lb|kg|adj=on}} Earth return ship would land all three astronauts atop a {{convert|113000|lb|kg|adj=on}} descent propulsion stage,<ref name="Nova_scale">Using the Apollo 11 lunar lander's mass ratio of {{convert|22667|lb|kg|adj=on}} descent stage to {{convert|10042|lb|kg|adj=on}} ascent stage, scaled up to Nova's {{convert|163000|lb|kg|adj=on}} payload.</ref> which would be left on the Moon. This design would have required development of the extremely powerful [[Saturn C-8]] or [[Nova (rocket)|Nova]] launch vehicle to carry a {{convert|163000|lb|kg|adj=on}} payload to the Moon.{{sfn|Brooks|Grimwood|Swenson|1979|loc=[http://www.hq.nasa.gov/office/pao/History/SP-4205/ch2-6.html Ch. 2.6, "Influences on Booster Determination"]}}
* '''[[Earth orbit rendezvous|Earth Orbit Rendezvous]] (EOR):''' Multiple rocket launches (up to 15 in some plans) would carry parts of the Direct Ascent spacecraft and propulsion units for [[Trans-lunar injection|translunar injection]] (TLI). These would be assembled into a single spacecraft in Earth orbit.
* '''Lunar Surface Rendezvous:''' Two spacecraft would be launched in succession. The first, an automated vehicle carrying propellant for the return to Earth, would land on the Moon, to be followed some time later by the crewed vehicle. Propellant would have to be transferred from the automated vehicle to the crewed vehicle.{{sfn|Brooks|Grimwood|Swenson|1979|loc=Chapter 3.2: [http://www.hq.nasa.gov/office/pao/History/SP-4205/ch3-2.html ''Early Reaction to LOR'']. pp. 61–67}}
* '''[[Lunar Orbit Rendezvous]] (LOR):''' This turned out to be the winning configuration, which achieved the goal with [[Apollo 11]] on July 20, 1969: a single [[Saturn V]] launched a {{convert|96886|lb|kg|adj=on}} spacecraft that was composed of a {{convert|63608|lb|kg|adj=on}} [[Apollo command and service module]] which remained in orbit around the Moon and a {{convert|33278|lb|kg|adj=on}} two-stage [[Apollo Lunar Module]] spacecraft which was flown by two astronauts to the surface, flown back to dock with the command module and was then discarded.<ref>{{cite book |last1=Orloff |first1=Richard W. |title=Apollo by the Numbers: A Statistical Reference. Launch Vehicle/Spacecraft Key Facts – 2nd table |date=September 2004 |publisher=NASA History Division |location=Washington DC |isbn=016-050631-X |url=https://history.nasa.gov/SP-4029/Apollo_18-12_Launch_Vehicle-Spacecraft_Key_Facts.htm |access-date=August 8, 2018}}</ref> Landing the smaller spacecraft on the Moon, and returning an even smaller part ({{convert|10042|lb|disp=or}}) to lunar orbit, minimized the total mass to be launched from Earth, but this was the last method initially considered because of the perceived risk of rendezvous and docking.

In early 1961, direct ascent was generally the mission mode in favor at NASA. Many engineers feared that rendezvous and docking, maneuvers that had not been attempted in [[Geocentric orbit|Earth orbit]], would be nearly impossible in [[lunar orbit]]. LOR advocates including [[John Houbolt]] at Langley Research Center emphasized the important weight reductions that were offered by the LOR approach. Throughout 1960 and 1961, Houbolt campaigned for the recognition of LOR as a viable and practical option. Bypassing the NASA hierarchy, he sent a series of memos and reports on the issue to Associate Administrator Robert Seamans; while acknowledging that he spoke "somewhat as a voice in the wilderness", Houbolt pleaded that LOR should not be discounted in studies of the question.{{sfn|Brooks|Grimwood|Swenson|1979|loc=Ch. 3.4: [http://www.hq.nasa.gov/office/pao/History/SP-4205/ch3-4.html "Early Reaction to LOR"]. p. 71}}

{{anchor|Nicholas E. Golovin}}
Seamans's establishment of an ad hoc committee headed by his special technical assistant Nicholas E. Golovin in July 1961, to recommend a [[launch vehicle]] to be used in the Apollo program, represented a turning point in NASA's mission mode decision.<ref name="hansen21">[[#Hansen|Hansen 1999]], p. 32</ref> This committee recognized that the chosen mode was an important part of the launch vehicle choice, and recommended in favor of a hybrid EOR-LOR mode. Its consideration of LOR—as well as Houbolt's ceaseless work—played an important role in publicizing the workability of the approach. In late 1961 and early 1962, members of the Manned Spacecraft Center began to come around to support LOR, including the newly hired deputy director of the Office of Manned Space Flight, [[Joseph Francis Shea|Joseph Shea]], who became a champion of LOR.<ref name="hansen24">[[#Hansen|Hansen 1999]], pp. 35–39</ref> The engineers at Marshall Space Flight Center (MSFC), who were heavily invested in direct ascent, took longer to become convinced of its merits, but their conversion was announced by Wernher von Braun at a briefing on June 7, 1962.{{sfn|Brooks|Grimwood|Swenson|1979|loc=Ch. 3.6: [http://www.hq.nasa.gov/office/pao/History/SP-4205/ch3-6.html "Settling the Mode Issue"]. pp. 81–83}}

But even after NASA reached internal agreement, it was far from smooth sailing. Kennedy's [[President's Science Advisory Committee|science advisor]] [[Jerome Wiesner]], who had expressed his opposition to human spaceflight to Kennedy before the President took office,<ref>{{Cite report |title=Managing NASA in the Apollo Era |chapter=2: The Lunar Landing Decision and Its Aftermath |url=https://history.nasa.gov/SP-4102/ch2.htm|access-date=2023-02-12 |website=history.nasa.gov}}</ref> and had opposed the decision to land people on the Moon, hired Golovin, who had left NASA, to chair his own "Space Vehicle Panel", ostensibly to monitor, but actually to second-guess NASA's decisions on the [[Saturn V]] launch vehicle and LOR by forcing Shea, Seamans, and even Webb to defend themselves, delaying its formal announcement to the press on July 11, 1962, and forcing Webb to still hedge the decision as "tentative".{{sfn|Brooks|Grimwood|Swenson|1979|loc=[http://www.hq.nasa.gov/office/pao/History/SP-4205/ch3-7.html Ch. 3.7, "Casting the Die"]}}

Wiesner kept up the pressure, even making the disagreement public during a two-day September visit by the President to [[Marshall Space Flight Center]]. Wiesner blurted out "No, that's no good" in front of the press, during a presentation by von Braun. Webb jumped in and defended von Braun, until Kennedy ended the squabble by stating that the matter was "still subject to final review". Webb held firm and issued a [[request for proposal]] to candidate Lunar Excursion Module (LEM) contractors. Wiesner finally relented, unwilling to settle the dispute once and for all in Kennedy's office, because of the President's involvement with the October [[Cuban Missile Crisis]], and fear of Kennedy's support for Webb. NASA announced the selection of [[Grumman]] as the LEM contractor in November 1962.{{sfn|Brooks|Grimwood|Swenson|1979|loc=[http://www.hq.nasa.gov/office/pao/History/SP-4205/ch4-4.html Ch. 4.4, "Pressures by PSAC"]}}

Space historian James Hansen concludes that:
{{blockquote|Without NASA's adoption of this stubbornly held minority opinion in 1962, the United States may still have reached the Moon, but almost certainly it would not have been accomplished by the end of the 1960s, President Kennedy's target date.<ref>[[#Hansen|Hansen 1999]], p. 42</ref>}}

The LOR method had the advantage of allowing the lander spacecraft to be used as a "lifeboat" in the event of a failure of the command ship. Some documents prove this theory was discussed before and after the method was chosen. In 1964 an MSC study concluded, "The [[Apollo Lunar Module|LM]] [as lifeboat]{{nbsp}}... was finally dropped, because no single reasonable [[Apollo command and service module|CSM]] failure could be identified that would prohibit use of the [[Apollo command and service module#Service propulsion system|SPS]]."<ref>{{cite book |last = Letterman |first = John B. |title = Survivors: True Tales of Endurance: 500 Years of the Greatest Eyewitness Accounts |page=404 |publisher = Simon & Schuster |date = 2003 |location = New York |isbn = 0-7432-4547-4 |url = https://archive.org/details/survivorstruetal00lett |chapter=Explosion on Apollo 13; April 1970: From the Earth to the Moon and Back |quote=Lovell writes, 'Naturally, I'm glad that view didn't prevail, and I'm thankful that by the time of Apollo 10, the first lunar mission carrying the LM, the LM as a lifeboat was again being discussed.'}}</ref> Ironically, just such a failure happened on [[Apollo 13]] when an oxygen tank explosion left the CSM without electrical power. The lunar module provided propulsion, electrical power and life support to get the crew home safely.<ref name="KSC-Apollo_13">{{cite web |url=http://science.ksc.nasa.gov/history/apollo/apollo-13/apollo-13.html |last=Dumoulin |first=Jim |title=Apollo-13 (29) |work=Historical Archive for Manned Missions |publisher=NASA |date=June 29, 2001 |access-date=September 12, 2012 |archive-date=August 19, 2011 |archive-url=https://web.archive.org/web/20110819103041/http://science.ksc.nasa.gov/history/apollo/apollo-13/apollo-13.html |url-status=dead }}</ref>