Spacecraft docking and berthing mechanisms

Docking and berthing of spacecraft is the joining of two space vehicles. This connection can be temporary, or such as for space station modules.

Docking specifically refers to joining of two separate free-flying space vehicles.Berthing refers to mating operations where an inactive module/vehicle is placed into the mating interface of another space vehicle by using a robotic arm. Because the modern process of un-berthing is manually laborious, berthing operations are seen as unsuited for rapid crew evacuations in the event of an emergency.

A docking/berthing connection is referred to as either "soft" or "hard". Typically, a spacecraft first initiates a soft dock by making contact and latching its docking connector with that of the target vehicle. Once the soft connection is secured, if both spacecraft are pressurized, they may proceed to a hard dock where the docking mechanisms airtightly seal together, enabling interior hatches to be safely opened so that crew and cargo can be transferred.

Spacecraft docking capability depends on space rendezvous, the ability of two spacecraft to find each other and station-keep in the same orbit. This was first developed by the United States for Project Gemini. It was planned for the crew of Gemini 6 to rendezvous and manually dock under the command of Wally Schirra, with an unmanned Agena Target Vehicle in October 1965, but the Agena vehicle exploded during launch. On the revised mission Gemini 6A, Schirra successfully performed a rendezvous in December 1965 with the manned Gemini 7, but there was no docking capability. The first docking with an Agena was successfully performed under the command of Neil Armstrong on Gemini 8 on March 16, 1966. Manual dockings were performed on three subsequent Gemini missions in 1966.

The Apollo program depended on lunar orbit rendezvous to achieve its objective of landing men on the Moon. This required first a transposition, docking, and extraction maneuver between the Apollo Command/Service Module (CSM) mother spacecraft and the Lunar Module (LM) landing spacecraft, shortly after both craft were sent out of Earth orbit on a path to the Moon. Then after completing the lunar landing mission, two astronauts in the LM had to rendezvous and dock with the CSM in lunar orbit, in order to be able to return to Earth. The spacecraft were designed to permit intra-vehicular crew transfer through a tunnel between the nose of the Command Module and the roof of the Lunar Module. These maneuvers were first demonstrated in low Earth orbit on March 7, 1969, on Apollo 9, then in lunar orbit in May 1969 on Apollo 10, then in six lunar landing missions.

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