Docking and berthing of spacecraft

Docking states

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.

History

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.

The Soviet Union first achieved rendezvous of Soyuz 3 with the unmanned Soyuz 2 craft on October 25, 1968; docking was unsuccessfully attempted. The first Soviet docking was achieved on January 16, 1969, between the manned Soyuz 4 and manned 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.

In the 1970s, the Soviets upgraded the Soyuz spacecraft to add an internal transfer tunnel and used it for their Salyut space station program. The United States docked its Apollo spacecraft to its Skylab space station. In July 1975, both nations docked an Apollo spacecraft with a Soyuz in the Apollo-Soyuz Test Project, using a specially designed docking module to accommodate the different docking systems and spacecraft atmospheres.

In the 1990s, the Russians demonstrated automated docking capability to allow unmanned cargo ships to ferry supplies to their Mir space station and the International Space Station.

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.

Adapters

A docking or berthing adapter is a mechanical or electromechanical device that facilitates the connection of one type of docking or berthing interface to a different interface. While such interfaces may theoretically be docking/docking, docking/berthing, or berthing/berthing, only the first two types have been deployed in space to date. Previously launched and planned to be launched adapters are listed below:

Docking of unmanned spacecraft

For the first fifty years of spaceflight, the main objective of most docking and berthing missions was to transfer crew, construct or resupply a space station, or to test for such a mission (e.g. the docking between Kosmos 186 and Kosmos 188). Therefore, commonly at least one of the participating spacecraft was "manned", with a pressurized habitable volume (e.g. a space station or a lunar lander) being the target – the exceptions were a few fully unmanned Soviet docking missions (e.g. the dockings of Kosmos 1443 and Progress 23 to an unmanned Salyut 7 or Progress M1-5 to an unmanned Mir). Another exception were a few missions of the manned US Space Shuttles, like berthings of the Hubble Space Telescope (HST) during the five HST servicing missions.

This is changing, as a number of economically driven commercial dockings of unmanned spacecraft are planned starting as soon as 2015. In early 2011, two commercial spacecraft providers have announced plans to provide new autonomous/teleoperated unmanned resupply spacecraft for servicing other unmanned spacecraft. Notably, both of these servicing spacecraft will be intending to dock with satellites that were designed neither for docking, nor for in-space servicing.

The early business model for these services is primarily in near-geosynchronous orbit, although large delta-v orbital maneuvering services are also envisioned.

Building off of the 2007 Orbital Express mission — a U.S. government-sponsored mission to test in-space satellite servicing with two vehicles designed from the ground up for on-orbit refueling and subsystem replacement — two companies have announced new commercial satellite servicing missions that will require docking of two unmanned vehicles.

The SIS and MEV vehicles will each use a different docking technique. SIS will utilize a ring attachment around the kick motor while the Mission Extension Vehicle will use a somewhat more standard insert-a-probe-into-the-nozzle-of-the-kick-motor approach.

A prominent spacecraft that received a mechanism for unmanned dockings is the Hubble Space Telescope (HST). In 2009 the STS-125 shuttle mission added the Soft-Capture Mechanism (SCM) at the aft bulkhead of the space telescope. The SCM is meant for unpressurized dockings and will be used at the end of Hubble's service lifetime to dock an unmanned spacecraft to de-orbit Hubble. The SCM used was designed to be compatible to the NASA Docking System (NDS) interface to reserve the possibility of a Multi-Purpose Crew Vehicle docked mission. The SCM will, compared to the system used during the five HST Servicing Missions to capture and berth the HST to the Space Shuttle, significantly reduce the rendezvous and capture design complexities associated with such missions. The NDS bears some resemblance to the APAS-95 mechanism, but is not compatible with it.

Non-cooperative docking

Docking with a spacecraft (or other man made space object) that does not have an operable attitude control system might sometimes be desirable, either in order to salvage it, or to initiate a controlled de-orbit. Some theoretical techniques for docking with non-cooperative spacecraft have been proposed so far. Yet, with the sole exception of the Soyuz T-13 mission to salvage the crippled Salyut 7 space station, as of 2006, all spacecraft dockings in the first fifty years of spaceflight had been accomplished with vehicles where both spacecraft involved were under either piloted, autonomous or telerobotic attitude control. In 2007, however, a demonstration mission was flown that included an initial test of a non-cooperative spacecraft captured by a controlled spacecraft with the use of a robotic arm. Research and modeling work continues to support additional autonomous noncooperative capture missions in the coming years.

Salyut 7 space station salvage mission

Salyut 7, the tenth space station of any kind launched, and Soyuz T-13 were docked in what author David S. F. Portree describes as "one of the most impressive feats of in-space repairs in history". Solar tracking failed and due to a telemetry fault the station did not report the failure to mission control while flying autonomously. Once the station ran out of electrical energy reserves it ceased communication abruptly in February 1985. Crew scheduling was interrupted to allow Russian military commander Vladimir Dzhanibekov and technical science flight engineer Viktor Savinykh to make emergency repairs.

All Soviet and Russian space stations were equipped with automatic rendezvous and docking systems, from the first space station Salyut 1 using the IGLA system, to the Russian Orbital Segment of the International Space Station using the Kurs system. The soyuz crew found the station was not broadcasting radar or telemetry for rendezvous, and after arrival and external inspection of the tumbling station, the crew judged proximity using handheld laser rangefinders.

Dzhanibekov piloted his ship to intercept the forward port of Salyut 7, matched the station's rotation and achieved soft dock with the station. After achieving hard dock they confirmed that the station's electrical system was dead. Prior to opening the hatch, Dzhanibekov and Savinykh sampled the condition of the station's atmosphere and found it satisfactory. Attired in winter fur-lined clothing, they entered the cold station to conduct repairs. Within a week sufficient systems were brought back online to allow robot cargo ships to dock with the station. Nearly two months went by before atmospheric conditions on the space station were normalized.

Uncrewed dockings of non-cooperative space objects

Non-cooperative rendezvous and capture techniques have been theorized, and one mission has successfully been performed with uncrewed spacecraft in orbit.

A typical approach for solving this problem involves two phases. First, attitude and orbital changes are made to the "chaser" spacecraft until it has zero relative motion with the "target" spacecraft. Second, docking maneuvers commence that are similar to traditional cooperative spacecraft docking. A standardized docking interface on each spacecraft is assumed.

NASA has identified automated and autonomous rendezvous and docking — the ability of two spacecraft to rendezvous and dock "operating independently from human controllers and without other back-up, [and which requires technology] advances in sensors, software, and realtime on-orbit positioning and flight control, among other challenges" — as a critical technology to the "ultimate success of capabilities such as in-orbit propellant storage and refueling," and also for complex operations in assembling mission components for interplanetary destinations.

The Automated/Autonomous Rendezvous & Docking Vehicle (ARDV) is a proposed NASA Flagship Technology Demonstration (FTD) mission, for flight as early as 2014/2015. An important NASA objective on the proposed mission is to advance the technology and demonstrate automated rendezvous and docking. One mission element defined in the 2010 analysis was the development of a laser proximity operations sensor that could be used for non-cooperative vehicles at distances between 1 metre (3 ft 3 in) and 3 kilometers (2 mi). Non-cooperative docking mechanisms were identified as critical mission elements to the success of such autonomous missions.

Grappling and connecting to non-cooperative space objects was identified as a top technical challenge in the 2010 NASA Robotics, tele-robotics and autonomous systems roadmap.