page_title: Space capsule
section_title: Apollo
hierarchical_section_title: Space capsule / History / Apollo
caption_attribution_description: English: The Apollo 15 Service Module as viewed from the Apollo Lunar Module. Image has been cropped and rotated. Polski: Apollo 15, widok modułu dowodzenia/serwisowego z modułu księżycowego. Zdjęcie po obcięciu krawędzi i obróceniu oryginalnego zdjęcia. Русский: Служебный модуль миссии «Аполлон 15», как он был виден с лунного модуля после отстыковки. Данное изображение прошло выкадровку и повёрнуто относительно снимка.
context_page_description: A space capsule is an often-crewed spacecraft that uses a blunt-body reentry capsule to reenter the Earth's atmosphere without wings. Capsules are distinguished from satellites primarily by the ability to survive reentry and return a payload to the Earth's surface from orbit. Capsule-based crewed spacecraft such as Soyuz or Orion are often supported by a service or adapter module, and sometimes augmented with an extra module for extended space operations. Capsules make up the majority of crewed spacecraft designs, although one crewed spaceplane, the Space Shuttle, has flown in orbit.
  Current examples of crewed space capsules include Soyuz, Shenzhou, Orion, Starliner, and Dragon 2. Examples of new crew capsules currently in development include Orel and Gaganyaan. Historic examples of crewed capsules include Vostok, Mercury, Voskhod, Gemini, and Apollo. A crewed space capsule must be able to sustain life in an often demanding thermal and radiation environment in the vacuum of space. It may be expendable or reusable.
context_section_description: The Apollo spacecraft was first conceived in 1960 as a three-man craft to follow Project Mercury, with an open-ended mission. It could be used to ferry astronauts to an Earth-orbiting space station, or for flights around or orbiting the Moon, and possibly landing on it. NASA solicited feasibility study designs from several companies in 1960 and 1961, while Faget and the Space Task Group worked on their own design using a conical/blunt-body capsule (Command Module) supported by a cylindrical Service Module providing electrical power and propulsion. NASA reviewed the entrants' designs in May 1961, but when President John F. Kennedy proposed a national effort to land a man on the Moon during the 1960s, NASA decided to reject the feasibility studies and proceed with Faget's design, focused on the lunar landing mission. The contract to build Apollo was awarded to North American Aviation.
  The Apollo Command/Service Module (CSM) was originally designed to take three men directly to the surface of the Moon, atop a large landing stage with legs. The Command Module sized out at 12 feet 10 inches (3.91 m) in diameter, by 11 feet 1.5 inches (3.39 m) long. The Service Module was 13 feet (4.0 m) long, with a total vehicle length of 36 feet 2.5 inches (11.04 m) including the engine bell. The hypergolic propellant service propulsion engine was sized at 20,500 pounds-force (91,000 N) to lift the CSM off the lunar surface and send it back to Earth. This required a single-launch vehicle much larger than the Saturn V, or else multiple Saturn V launches to assemble it in Earth orbit before sending it to the Moon.
  Early on, it was decided to use the lunar orbit rendezvous method, using a smaller Lunar Excursion Module (LEM) to ferry two of the men between lunar orbit and the surface. The reduction in mass allowed the lunar mission to be launched with a single Saturn V. Since significant development work had started on the design, it was decided to continue with the existing design as Block I, while a Block II version capable of rendezvous with the LEM would be developed in parallel. Besides addition of a docking tunnel and probe, Block II would employ equipment improvements based on lessons learned from the Block I design. Block I would be used for uncrewed test flights and a limited number of Earth orbit crewed flights. Though the service propulsion engine was now bigger than required, its design was not changed since significant development was already in progress; however, the propellant tanks were downsized slightly to reflect the modified fuel requirement. Based on astronaut preference, the Block II CM would replace the two-piece plug door hatch cover, chosen to avoid an accidental hatch opening such as had happened on Gus Grissom's Mercury-Redstone 4 flight, with a one-piece, outward-opening hatch to make egress easier at the end of the mission.
  The Mercury-Gemini practice of using a prelaunch atmosphere of 16.7 pounds per square inch (1,150 mbar) pure oxygen proved to be disastrous in combination with the plug-door hatch design. While participating in a pre-launch test on the pad on January 27, 1967, in preparation for the first crewed launch in February, the entire crew of Apollo 1—Grissom, Edward H. White, and Roger Chaffee—were killed in a fire that swept through the cabin. The plug door made it impossible for the astronauts to escape or be removed before their deaths. An investigation revealed the fire was probably started by a spark from a frayed wire, and fed by combustible materials that should not have been in the cabin. The crewed flight program was delayed while design changes were made to the Block II spacecraft to replace the pure oxygen pre-launch atmosphere with an air-like nitrogen/oxygen mixture, eliminate combustible materials from the cabin and the astronauts' space suits, and seal all electrical wiring and corrosive coolant lines.
  The Block II spacecraft weighed 63,500 pounds (28,800 kg) fully fueled, and was used in four crewed Earth and lunar orbital test flights, and seven crewed lunar landing missions. A modified
caption: The Apollo 15 command and service module in orbit around the Moon taken from Falcon, the misson's Apollo Lunar Module
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