page_title: Plug door
section_title: Spacecraft
hierarchical_section_title: Plug door / Spacecraft
caption_attribution_description: English: Picture of an Apollo block I Command Module with open outer hatch. Image ID: s66-57577. Picture appears on page 226 of the NASA official history Chariots for Apollo, NASA SP-4205 https://history.nasa.gov/SP-4205.pdf Polski: Zdjęcie kabiny modułu dowodzenia statku kosmicznego Apollo/Saturn 204 z otwartą zewnętrzną cześcią włazu
context_page_description: A plug door is a door designed to seal itself by taking advantage of pressure difference on its two sides and is typically used on aircraft with cabin pressurization. The higher pressure on one side forces the usually wedge-shaped door into its socket, making a good seal and preventing it from being opened until the pressure is released. Non-plug doors rely on the strength of the locking mechanism to keep the door shut.
context_section_description: An inward opening plug hatch design was used on the Block I Apollo Command Module, because the explosive-release hatch of Gus Grissom's Mercury capsule Liberty Bell 7 prematurely blew at the end of the flight, causing the capsule to sink in the Atlantic Ocean and nearly resulting in Grissom's drowning. The Apollo cabin was pressurized at launch to 2 pounds per square inch (14 kPa) above standard sea level pressure, which sealed the hatch. A cabin fire during a 1967 Apollo 1 ground test raised the pressure even higher (29 pounds per square inch (200 kPa)), and made the hatch impossible to remove for the crew to escape. This killed Grissom along with his entire crew, Edward H. White and Roger Chaffee. Because of this, NASA decided to change to a quick-release, outward opening hatch on the Command Module.
  Plug hatches were retained for the CM docking hatch and the two hatches on the Apollo Lunar Module, as the risk of fire in the low-pressure (5 pounds per square inch (34 kPa)) in-space atmosphere was much lower. Plug doors were also used as the outer hatch doors on the Space Shuttle. Currently, they are used on the International Space Station, as well as on the hatch between the Orbital Module and Descent Module of the Russian Soyuz spacecraft.
caption: Apollo 1 plug hatch in place, with external heat shield hatch open
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