Docking and berthing of spacecraft is the joining of two space vehicles. This connection can be temporary, or partially permanent such as for space station modules.
Docking specifically refers to joining of two separate free-flying space vehicles. Berthing refers to mating operations where a passive module/vehicle is placed into the mating interface of another space vehicle by using a robotic arm. Because the modern process of un-berthing requires more crew labor and is time-consuming, berthing operations are unsuited for rapid crew evacuations in the event of an emergency.
History
Docking
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 uncrewed 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 crewed Gemini 7, approaching to within , but there was no docking capability between two Gemini spacecraft. 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 and 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, as well as on Apollo 13 where the LM was used as a rescue vehicle instead of making a lunar landing.
Unlike the United States, which used manual piloted docking throughout the Apollo, Skylab, and Space Shuttle programs, the Soviet Union employed automated docking systems from the beginning of its docking attempts. The first such system, Igla, was successfully tested on October 30, 1967, when the two uncrewed Soyuz test vehicles Kosmos 186 and Kosmos 188 docked automatically in orbit. This was the first successful Soviet docking. Proceeding to crewed docking attempts, the Soviet Union first achieved rendezvous of Soyuz 3 with the uncrewed Soyuz 2 craft on October 25, 1968; docking was unsuccessfully attempted. The first crewed docking was achieved on January 16, 1969, between Soyuz 4 and Soyuz 5. This early version of the Soyuz spacecraft had no internal transfer tunnel, but two cosmonauts performed an extravehicular transfer from Soyuz 5 to Soyuz 4, landing in a different spacecraft than they had launched in.
In the 1970s, the Soviet Union upgraded the Soyuz spacecraft to add an internal transfer tunnel and used it to transport cosmonauts during the Salyut space station program with the first successful space station visit beginning on 7 June 1971, when Soyuz 11 docked to Salyut 1. The United States followed suit, docking its Apollo spacecraft to the Skylab space station in May 1973. In July 1975, the two nations cooperated in the Apollo-Soyuz Test Project, docking an Apollo spacecraft with a Soyuz using a specially designed docking module to accommodate the different docking systems and spacecraft atmospheres.
Beginning with Salyut 6 in 1978, the Soviet Union began using the uncrewed Progress cargo spacecraft to resupply its space stations in low earth orbit, greatly extending the length of crew stays. As an uncrewed spacecraft, Progress rendezvoused and docked with the space stations entirely automatically. In 1986, the Igla docking system was replaced with the updated Kurs system on Soyuz spacecraft. Progress spacecraft received the same upgrade several years later. The Kurs system is still used to dock to the Russian Orbital Segment of the International Space Station.
Berthing Berthing of spacecraft can be traced at least as far back as the berthing of payloads into the Space Shuttle payload bay.(Lyndon B. Johnson Space Center, Houston Texas, 2000) Such payloads could be either free-flying spacecraft captured for maintenance/return, or payloads temporarily exposed to the space environment at the end of the Remote Manipulator System. Several different berthing mechanisms were used during the Space Shuttle era. Some of them were features of the Payload Bay (e.g., the Payload Retention Latch Assembly), while others were airborne support equipment (e.g., the Flight Support Structure used for HST servicing missions).
Hardware
Androgyny
Docking/berthing systems may be either androgynous (ungendered) or non-androgynous (gendered), indicating which parts of the system may mate together.
Early systems for conjoining spacecraft were all non-androgynous docking system designs. Non-androgynous designs are a form of gender mating where each spacecraft to be joined has a unique design (male or female) and a specific role to play in the docking process. The roles cannot be reversed. Furthermore, two spacecraft of the same gender cannot be joined at all.
Androgynous docking (and later androgynous berthing) by contrast has an identical interface on both spacecraft. In an androgynous interface, there is a single design which can connect to a duplicate of itself. This allows system-level redundancy (role reversing) as well as rescue and collaboration between any two spacecraft. It also provides more flexible mission design and reduces unique mission analysis and training.
List of mechanisms/systems Image Name Method Internal crew transfer Notes Type Gemini Docking Mechanism Docking No Allowed the Gemini Spacecraft (active) to dock to the Agena target vehicle (passive). Non-Androgynous Apollo Docking Mechanism Docking Yes Allowed the Command/Service Module (active) to dock to the Apollo Lunar ModuleHistory of U.S. Docking Systems (10/05/2010) (passive) and the Skylab space station (passive). Was used to dock to the Docking Module adapter (passive) during the Apollo–Soyuz Test Project (ASTP), which enabled the crew to dock with a Soviet Soyuz 7K-TM spacecraft. It had a circular pass through diameter of . Non-Androgynous Original Russian probe and drogue docking system Docking No The original Soyuz probe-and-drogue docking system was used with the first generation Soyuz 7K-OK spacecraft from 1966 until 1970 in order to gather engineering data as a preparation for the Soviet space station program. The gathered data were subsequently used for the conversion of the Soyuz spacecraft – which was initially developed for the Soviet crewed lunar program – into a space station transport craft. A first docking with two uncrewed Soyuz spacecraft – the first fully automated space docking in the history of space flight – was made with the Kosmos 186 and Kosmos 188 missions on October 30, 1967. Non-Androgynous Kontakt docking system Docking No Intended to be used in the Soviet crewed lunar program to allow the Soyuz 7K-LOK ("Lunar Orbital Craft", active) to dock to the LK lunar lander (passive). Non-Androgynous SSVP-G4000 Docking Yes SSVP-G4000 is also known more vaguely as the Russian probe and drogue or simply the Russian Docking System (RDS). In Russian, SSVP stands for Sistema Stykovki i Vnutrennego Perekhoda, literally "System for docking and internal transfer". It was used for the first docking to a space station in the history of space flight, with the Soyuz 10 and Soyuz 11 missions that docked to the Soviet space station Salyut 1 in 1971. The docking system was upgraded in the mid-1980s to allow the docking of 20 ton modules to the Mir space station. It has a circular transfer passage that has a diameter of and is manufactured by RKK Energiya.
The probe-and-drogue system allows visiting spacecraft using the probe docking interface, such as Soyuz, Progress and ESA's ATV spacecraft, to dock to space stations that offer a port with a drogue interface, like the former Salyut and Mir or the current ISS space station. There are a total of four such docking ports available on the Russian Orbital Segment of ISS for visiting spacecraft; These are located on the Zvezda, Rassvet, Prichal and Poisk modules. Furthermore, the probe-and-drogue system was used on the ISS to dock Rassvet semipermanently to Zarya. Non-Androgynous APAS-75 Docking Yes Used on the Apollo-Soyuz Test Project Docking Module and Soyuz 7K-TM. There were variations in design between the American and Soviet version but they were still mechanically compatible. Androgynous APAS-89 Docking Yes Used on Mir (Kristall, Mir Docking Module), Soyuz TM-16, Buran (was planned). It had a circular transfer passage with a diameter of . Androgynous APAS-95 Docking Yes It was used for Space Shuttle dockings to Mir and ISS, On the ISS, it was also used on Zarya module, Russian Orbital Segment to interface with PMA-1 on Unity module, US Orbital SegmentNASA.gov It has a diameter of . Described as "essentially the same as" APAS-89. Androgynous (Shuttle and PMA-1), Non-Androgynous (Zarya, PMA-2 and PMA-3) SSVP-M8000 (Hybrid Docking System) Docking Yes SSVP-M8000 or more commonly known as "hybrid", is a combination of a "probe and drogue" soft-dock mechanism with an APAS-95 hard-dock collar. It began to be manufactured in 1996. It is manufactured by RKK Energiya.
Used on ISS (connects Zvezda to Zarya, Pirs, Poisk, Nauka and Nauka to Prichal) Non-Androgynous Common Berthing Mechanism Berthing Yes Used on ISS (USOS), MPLMs, HTV, SpaceX Dragon 1, Cygnus. The standard CBM has a pass through in the shape of a square with rounded edges and has a width of . The smaller hatch that Cygnus uses results in a transfer passage of the same shape but has a width of . Non-Androgynous Chinese Docking Mechanism Docking Yes Used by Shenzhou spacecraft, beginning with Shenzhou 8, to dock to Chinese space stations. The Chinese docking mechanism is based on the Russian APAS-89/APAS-95 system; some have called it a "clone". There have been contradicting reports by the Chinese on its compatibility with APAS-89/95. It has a circular transfer passage that has a diameter of . The androgynous variant has a mass of 310 kg and the non-androgynous variant has a mass of 200 kg.