Space capsule

A space capsule is an often manned spacecraft which has a simple shape for the main section, without any wings or other features to create lift during atmospheric reentry. Capsules have been used in most of the manned space programs to date, including the world's first manned spacecraft Vostok and Mercury, as well as in later Soviet Voskhod, Soyuz, Zond/L1, L3, TKS, US Gemini, Apollo Command Module, Chinese Shenzhou and US, Russian and Indian manned spacecraft currently being developed. A capsule is the specified form for the Orion Multi-Purpose Crew Vehicle.

A manned space capsule must have everything necessary for everyday life, including air, water and food. The space capsule must also protect astronauts from the cold and radiation of space. A capsule must be well insulated and have a system that controls the inside temperature and environment. It also must have a way that the astronauts would not be knocked around during launch or reentry. Additionally, since the inside will be weightless, there must be a way for the astronauts to stay in their seats during the flight. For this each seat has a system of straps and buckles. One of the most important things that a space capsule must have is a way to communicate with people back on Earth, or mission control.

Space capsules have typically been smaller than 5 meters (16 feet) in diameter, although there is no engineering limit to larger sizes. As the capsule is both volumetrically efficient and structurally strong, it is typically possible to construct small capsules of performance comparable in all but lift-to-drag ratio to a lifting body or delta wing form for less cost. This has been especially pronounced in the case of the Soyuz manned spacecraft. Most space capsules have used an ablative heat shield for reentry and been non-reusable. The Orion Multi-Purpose Crew Vehicle appears likely, as of December 2005, to be a ten-times reusable capsule with a replaceable heat shield. There is no limit, save for lack of engineering experience, on using high-temperature ceramic tiles or ultra-high temperature ceramic sheets on space capsules.

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