Editing Apollo program (section)

===Command and service module===
{{main|Apollo command and service module}}
[[File:Apollo CSM lunar orbit.jpg|thumb|upright=1.2|left|[[Apollo 15]] [[Apollo command and service module|CSM]] ''Endeavour'' in lunar orbit|alt=The cone-shaped command module, attached to the cylindrical service module, orbits the Moon with a panel removed, exposing the scientific instrument module]]

The [[Apollo command and service module#Command module (CM)|command module]] (CM) was the conical crew cabin, designed to carry three astronauts from launch to lunar orbit and back to an Earth ocean landing. It was the only component of the Apollo spacecraft to survive without major configuration changes as the program evolved from the early Apollo study designs. Its exterior was covered with an [[ablative heat shield]], and had its own [[reaction control system]] (RCS) engines to [[Spacecraft attitude control|control its attitude]] and steer its [[atmospheric entry]] path. Parachutes were carried to slow its descent to splashdown. The module was {{convert|11.42|ft|m}} tall, {{convert|12.83|ft|m}} in diameter, and weighed approximately {{convert|12250|lb|kg}}.<ref name="ABTN_LV2" />

[[File:NASM-NASM2013-02663.jpg|thumb|Original cockpit of the command module of Apollo 11 with three seats, photographed from above. It is located in the [[National Air and Space Museum]]; the very high resolution image was produced in 2007 by the [[Smithsonian Institution]].]]
A cylindrical [[Apollo service module|service module]] (SM) supported the command module, with a service propulsion engine and an RCS with propellants, and a [[fuel cell]] power generation system with [[liquid hydrogen]] and [[liquid oxygen]] reactants. A high-gain [[S band|S-band]] antenna was used for long-distance communications on the lunar flights. On the extended lunar missions, an orbital scientific instrument package was carried. The service module was discarded just before reentry. The module was {{convert|24.6|ft|m}} long and {{convert|12.83|ft|m}} in diameter. The initial lunar flight version weighed approximately {{convert|51300|lb|kg}} fully fueled, while a later version designed to carry a lunar orbit scientific instrument package weighed just over {{convert|54000|lb|kg}}.<ref name="ABTN_LV2"/>

[[North American Aviation]] won the contract to build the CSM, and also the second stage of the Saturn V launch vehicle for NASA. Because the CSM design was started early before the selection of lunar orbit rendezvous, the service propulsion engine was sized to lift the CSM off the Moon, and thus was oversized to about twice the thrust required for translunar flight.<ref>[[#Wilford|Wilford 1969]], p. 167</ref> Also, there was no provision for docking with the lunar module. A 1964 program definition study concluded that the initial design should be continued as Block I which would be used for early testing, while Block II, the actual lunar spacecraft, would incorporate the docking equipment and take advantage of the lessons learned in Block I development.<ref name="SummaryReport">{{cite web |url=https://history.nasa.gov/apsr/Apollopt2-2.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://history.nasa.gov/apsr/Apollopt2-2.pdf |archive-date=2022-10-09 |url-status=live |title=Apollo Program Summary Report |date=April 1975 |publisher=NASA |location=Houston, TX |pages=3–66 to 4–12 |id=JSC-09423 |access-date=August 1, 2013}}</ref>