Docking and berthing of spacecraft

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The free-flying Progress in the process of docking to the ISS
Dragon prior to being berthed to the ISS by the Canadarm2 robotic arm

Spacecraft docking and berthing mechanisms are mechanisms which are used to connect one spacecraft to another spacecraft (including space stations). In the case of berthing mechanisms, a space module without its own propulsion can be a berthing partner. The connection can be temporary for spacecraft visiting each other, or semipermanent for space station modules.

A docking mechanism is used when one spacecraft actively maneuvers under its own propulsion to connect to another spacecraft.[1][2]

A berthing mechanism is used when space station modules or spacecraft are attached to one another by using a robotic arm – instead of their own propulsion – for the final few meters of the rendezvous and attachment process. Berthing typically involves connection to a space station.[1][3]

The currently deployed mechanisms are designed to either support docking or berthing – the upcoming NASA Docking System (NDS) will be the first system designed to support both.[4]

Docking and berthing of manned spacecraft[edit]

Androgyny[edit]

Early systems for conjoining spacecraft were all non-androgynous docking system designs. Non-androgynous designs are a form of "gender mating"[2] where each spacecraft to be joined has a unique design 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, on the other hand has an identical interface design on both spacecraft, allowing system-level redundancy (role reversing) as well as rescue and collaboration between any two spacecraft vehicles. In an androgynous interface, there is a single design which can connect to a duplicate of itself. This results in more flexible mission design and reduces unique mission analysis and training.[2]

Adapters[edit]

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.

The backup Docking Module of the Apollo–Soyuz Test Project mission using the APAS-75.
One of the Pressurized Mating Adapters (PMA) that provide APAS-95 ports on the ISS, pictured here with the docked Shuttle Discovery.
A graphic showing an International Docking Adapter to be added to the PMAs.

Docking Module[edit]

The Docking Module converted NASA's "Probe and Drogue" docking system used for Apollo spacecraft to the APAS-75 system used for the 1975 Apollo–Soyuz Test Project mission.

Pressurized Mating Adapter (PMA)[edit]

The Pressurized Mating Adapter (PMA) allows spacecraft utilizing the Androgynous Peripheral Attach System (APAS-95) to dock to the ISS and is semi-permanently attached to an "active" CBM berthing port. There are three PMAs attached to the ISS, with PMA-2 and PMA-3 being available to visiting spacecraft and the PMA-1 adapter being semi-permanently attached to the Functional Cargo Block (Zarya) and Node 1 (Unity), in order to connect the Russian Orbital Segment to the rest of the station.

International Docking Adapter (IDA)[edit]

International Docking Adapters (IDA) will be attached to the Pressurized Mating Adapters PMA-2 and PMA-3 and convert their APAS-95 docking interface to the NASA Docking System (NDS).[5][6] PMA-2 and PMA-3 will be outfitted with IDAs, one in late 2014 and the other in either 2015 or 2016, and with one being attached to Node-2's (Harmony) forward CBM port and the other to its zenith CBM port. The adapter will be compatible with the International Docking System Standard (IDSS), which is an attempt by the ISS Multilateral Coordination Board to create a docking standard.[7]

Docking of unmanned spacecraft[edit]

The Soft-Capture Mechanism (SCM) added in 2009 to the Hubble Space Telescope. The SCM allows both manned and unmanned spacecraft that utilize the NASA Docking System (NDS) to dock with Hubble.

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.[8]

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[12] while the Mission Extension Vehicle will use a somewhat more standard insert-a-probe-into-the-nozzle-of-the-kick-motor approach.[8]

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.[13] The SCM will, compared to the system used during the five HST Servicing Missions to capture and berth the HST to the Space Shuttle,[citation needed] 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.[14]

Non-cooperative docking[edit]

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.[15] 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.[15] 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.[16]

Salyut 7 space station salvage mission[edit]

Main article: Soyuz T-13
Commander Vladimir Dzhanibekov (left) with Oleg Grigoryevich Makarov (right) on a 1978 Soviet postage stamp
Doctor of technical sciences Viktor Savinykh with Vladimir Kovalyonok pictured on a Soviet postage stamp commemorating a Salyut 6 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".[17] 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[18] and technical science flight engineer Viktor Savinykh[19] 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.[17]

Uncrewed dockings of non-cooperative space objects[edit]

Orbital Express: ASTRO (left) and NEXTSat (right), 2007.

Non-cooperative rendezvous and capture techniques have been theorized and, in a few instances,[16] put into practice 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.[20]

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.[21]

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.[21]

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.[22]

List of types of spacecraft docking and berthing mechanisms[edit]

Manned[edit]

Name and image Type Usage

Gemini Docking Mechanism[edit]

The passive interface of the target (left) and active of the Gemini spacecraft.
Docking mechanism
(Fixed active/passive role)


Note:
No internal crew transfer

Allowed the Gemini Spacecraft to dock to the Agena target vehicle as a preparation for the Apollo project.

Apollo Docking Mechanism[edit]

On the left the active "probe" interface used on the CSM, which docks to the passive "drogue" on the right.
Docking mechanism
(Fixed active/passive role)
Allowed the Command/Service Module (CSM) to dock to the Apollo Lunar Module[23] and the Skylab space station. Was used to dock to the Docking Module adapter during the Apollo–Soyuz Test Project (ASTP), which allowed to dock with a Soviet Soyuz 7K-TM spacecraft .

Kontakt docking system[edit]

Left the passive side designed for the lunar lander and right the active side.
Docking mechanism
(Fixed active/passive role)


Note:
No internal crew transfer

Intended to be used in the Soviet manned lunar program to allow the Soyuz 7K-LOK ("Lunar Orbital Craft") to dock to the LK lunar lander.[17]

Soyuz "probe and drogue" (original type)[edit]

Left the passive and right the active side.
Docking mechanism
(Fixed active/passive role)


Note:
No internal crew transfer, only used to gather engineering data.

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 was subsequently used for the conversion of the Soyuz spacecraft – which was initially developed for the Soviet manned lunar program – into a space station transport craft.[1]

A first docking with two unmanned 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.

Soyuz "probe and drogue" (Salyut-1 type)[edit]

On the left an active probe interface, as used to dock to a passive drogue on the right.
Docking mechanism
(Fixed active/passive role)
and
Berthing mechanism(berthing Rassvet & Zaria)
The contemporary Russian docking mechanism, the Soyuz "probe and drogue" docking system of Salyut-1 type, is in use since 1971.

The system is known in Russia as Sistema Stykovki i Vnutrennego Perekhoda (SSVP), literally "System for docking and internal transfer".[24] 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.[1] The docking system was upgraded in the mid-1980s to allow the docking of 20 ton modules to the Mir space station.[24]

The "probe and drogue" system allows visiting spacecraft using the "probe" docking interface, such as Soyuz, Progress and 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. The current implementation of the Soyuz docking interface is known as SSVP-G4000, and in total four such docking ports are available for visiting spacecraft on the ISS; These are located on the Zvezda, Rassvet, Pirs and Poisk modules.[24] Furthermore the "probe and drogue" system was used on the ISS to dock Rassvet semipermanently to Zarya.[1]

APAS-75[edit]

The spade-shaped guides of the extended active APAS-75 unit (right) and the retracted passive unit (left) interacted for gross alignment during soft docking. The active unit then retracted to bring the docking collars of both spacecraft together for hard docking.
Docking mechanism
(Androgynous)
Used on the Docking Module (ASTP) to dock a US Apollo spacecraft with a Soviet APAS-75 equipped Soyuz 7K-TM[citation needed] spacecraft in low Earth orbit (LEO) during the Apollo–Soyuz Test Project (ASTP) in 1975.[17]

APAS-89[edit]

On the left an APAS-89 in active, on the right in passive configuration.
Docking mechanism
(Androgynous)


Note:
Was fixed in passive role for Kristall[25] and Mir Docking Module[26]

The APAS-89 was, besides the Soyuz "probe and drogue" system, used on Mir to allow visiting spacecraft to dock to the space station – initially intended for the Soviet Buran space shuttle which never flew to the station,[27] it was actually used with an APAS-95 adapter by the Space Shuttle fleet after a test with Soyuz TM-16.[17]

APAS-89 ports on Mir were installed on the modules Kristall[17] and the Mir Docking Module.[28]

APAS-95[edit]

On the left an APAS-95 can be seen in active configuration, its soft dock ring with the three petals extended; On the right an APAS-95 in passive configuration.
Docking mechanism
(Androgynous)
and
Berthing mechanism(berthing Node-1 and FGB Zaria)


Note:
Is fixed in passive role for PMA-2 and PMA-3.[1]

APAS-95 was used to dock the Shuttle to the Mir space station during the Shuttle–Mir Program and then later to the ISS.[27]

APAS-95 ports, which are compatible with APAS-89, were installed on the Space Shuttles Discovery, Atlantis and Endeavour, but not on the oldest shuttle Columbia. Three Pressurized Mating Adapters (PMA) with an APAS-95 docking port are installed on the ISS, with PMA-1 semi-permanently connected to the APAS interface of Functional Cargo Block (Zarya), connecting the US Orbital Segment (USOS) and the Russian Orbital Segment (ROS); The other two PMAs are free, possibly available for visiting spacecraft.

Hybrid Docking System[edit]

On the left an active Hybrid Docking System with its probe, on the right a passive version with its drogue.
Docking mechanism
(Fixed active/passive role)
Used by some modules on the Russian Orbital Segment (ROS) of the ISS. The name "hybrid" derives from the combination of a "probe and drogue" soft-dock mechanism with an APAS-95 hard-dock collar. The implementation is known in Russia as SSVP-M8000.[24]

Connects Zvezda to Zarya, and Pirs & Poisk to Zvezda.[1]

Common Berthing Mechanism (CBM)[edit]

On the left an "active" CBM (with its micrometeorite shield still attached), on the right a "passive" CBM.
Berthing mechanism
(Fixed active/passive role)
Used for berthing of all pressurized modules on the US Orbital Segment (USOS) on the ISS.[1]

Is used by visiting cargo supply craft and modules such as MPLMs, HTV, Dragon Cargo,[29] and Cygnus. Has as of 2012 not been used to berth a manned spacecraft to the ISS.

Chinese Docking Mechanism[edit]

Left the passive and right the active configuration.
Docking mechanism
(Androgynous)


Note:
Is fixed in passive role for Tiangong-1

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. There have been contradicting reports by the Chinese on its compatibility with APAS-89/95.[30]

Used for the first time on Tiangong 1 space station and will be used on future Chinese space stations.

NASA Docking System (NDS)[edit]

Left the passive and right the active configuration.
Dual role:
Docking mechanism
(Androgynous)
and
Berthing mechanism
(Androgynous)


Note:
Will be fixed in passive role for the IDAs to be installed on PMA-2 and PMA-3.

The NASA Docking System (NDS) is intended to be used for future US spacecraft. Also known as (international) Low Impact Docking System (iLIDS or LIDS). The NDS bears some resemblance to the APAS-95 mechanism, but is not compatible with it. Can be used both for docking and berthing.

An NDS interface will be available on the two International Docking Adapters (IDA), which are intended to be installed on two of the three Pressurized Mating Adapters (PMA) on the ISS. The Soft Capture Mechanism (SCM) on the Hubble Space Telescope is compatible with the NDS.

NDS is intended to be used by Commercial Crew, Orion, and all other US vehicles.[31]

Unmanned[edit]

Name and image Type Usage

Soft Capture Mechanism (SCM)[edit]

The passive interface installed on Hubble.
Docking mechanism
(Fixed passive role)


Note:
The SCM is based on the NDS, which is androgynous.

The Soft-Capture Mechanism (SCM) was installed at the Hubble Space Telescope on STS-125 to allow for unpressurized dockings. It will be used at the end of Hubble's service lifetime to dock an unmanned spacecraft in order 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.[13] The NDS bears some resemblance to the APAS-95 mechanism, but is not compatible with it.[14]

Robotic force closure end-effector[edit]

Non-cooperative capture mechanism A robotic force closure[32] end effector was used in 2007 on the Orbital Express mission to allow a robotic arm on the ASTRO spacecraft to capture a custom-designed grapple fixture on the NEXTSat spacecraft.[16]

See also[edit]

References[edit]

  1. ^ a b c d e f g h "ISS Interface Mechanisms and their Heritage" (PDF). NASA. Retrieved 2011-11-04. 
  2. ^ a b c "International Docking Standardization" (PDF). NASA. 2009-03-17. p. 15. Retrieved 2011-03-04. "Gender Mating vs. Androgynous Mating ... Hard Docking vs. Soft Capture" 
  3. ^ "Advanced Docking/Berthing System - NASA Seal Workshop" (PDF). NASA. 2004-11-04. p. 15. Retrieved 2011-03-04. "Berthing refers to mating operations where an inactive module/vehicle is placed into the mating interface using a Remote Manipulator System-RMS." 
  4. ^ "NASA Space Flight Systems – International Low Impact Docking System (iLIDS)". 
  5. ^ Hartman, Dan (23 July 2012). "International Space Station Program Status". NASA. Retrieved 10 August 2012. 
  6. ^ Lupo, Chris (2010-06-14). "NDS Configuration and RequirementsChanges since Nov 2010". NASA. Retrieved 22 August 2011. 
  7. ^ Bayt, Rob (2011-07-26). "Commercial Crew Program: Key Drving Requirments Walkthrough". NASA. Retrieved 27 July 2011. 
  8. ^ a b c d Morring, Frank, Jr. (2011-03-22). "An End To Space Trash?". Aviation Week. Retrieved 2011-03-21. "ViviSat, a new 50-50 joint venture of U.S. Space and ATK, is marketing a satellite-refueling spacecraft that connects to a target spacecraft using the same probe-in-the-kick-motor approach as MDA, but does not transfer its fuel. Instead, the vehicle becomes a new fuel tank, using its own thrusters to supply attitude control for the target. ... [the ViviSat] concept is not as far along as MDA. ... In addition to extending the life of an out-of-fuel satellite, the company could also rescue fueled spacecraft like AEHF-1 by docking with it in its low orbit, using its own motor and fuel to place it in the right orbit, and then moving to another target." 
  9. ^ "Intelsat Picks MacDonald, Dettwiler and Associates Ltd. for Satellite Servicing". press release. CNW Group. Retrieved 2011-03-15. "MDA plans to launch its Space Infrastructure Servicing ("SIS") vehicle into near geosynchronous orbit, where it will service commercial and government satellites in need of additional fuel, re-positioning or other maintenance. ... MDA and Intelsat will work together to finalize specifications and other requirements over the next six months before both parties authorize the build phase of the program. The first refueling mission is to be available 3.5 years following the commencement of the build phase. ... The services provided by MDA to Intelsat under this agreement are valued at more than US$280 million." 
  10. ^ de Selding, Peter B. (2011-03-14). "Intelsat Signs Up for Satellite Refueling Service". Space News. Retrieved 2011-03-15. "if the MDA spacecraft performs as planned, Intelsat will be paying a total of some $200 million to MDA. This assumes that four or five satellites are given around 200 kilograms each of fuel." 
  11. ^ "ViviSat Corporate Overview". company website. ViviSat. Retrieved 2011-03-28. 
  12. ^ de Selding, Peter B. (2011-03-18). "Intelsat Signs Up for MDA’s Satellite Refueling Service". Space News. Retrieved 2011-03-20. "more than 40 different types of fueling systems ... SIS will be carrying enough tools to open 75 percent of the fueling systems aboard satellites now in geostationary orbit. ... MDA will launch the SIS servicer, which will rendezvous and dock with the Intelsat satellite, attaching itself to the ring around the satellite’s apogee-boost motor. With ground teams governing the movements, the SIS robotic arm will reach through the nozzle of the apogee motor to find and unscrew the satellite’s fuel cap. The SIS vehicle will reclose the fuel cap after delivering the agreed amount of propellant and then head to its next mission. ... Key to the business model is MDA’s ability to launch replacement fuel canisters that would be grappled by SIS and used to refuel dozens of satellites over a period of years. These canisters would be much lighter than the SIS vehicle and thus much less expensive to launch. " 
  13. ^ a b NASA (2008). "The Soft Capture and Rendezvous System". NASA. Retrieved May 22, 2009. 
  14. ^ a b Parma, George (2011-05-20). "Overview of the NASA Docking System and the International Docking System Standard". NASA. Retrieved 11 April 2012. 
  15. ^ a b Ma, Zhanhua; Ma, Ou and Shashikanth, Banavara (October 2006). "Optimal Control for Spacecraft to Rendezvous with a Tumbling Satellite in a Close Range". Proceedings of the 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems: 4109–4114. Retrieved 2011-08-09 quote=One of the most challenging tasks for satellite on-orbit servicing is to rendezvous and capture a non-cooperative satellite such as a tumbling satellite.. 
  16. ^ a b c Clark, Stephen (2007-07-04). "In-space satellite servicing tests come to an end". Spaceflight Now. Retrieved 2014-03-20. 
  17. ^ a b c d e f Portree, David (March 1995). "Mir Hardware Heritage". NASA. Retrieved 11 December 2011. 
  18. ^ "Dzhanibekov". Astronautix.com. Retrieved August 5, 2013. 
  19. ^ "Savinykh". Astronautix.com. Retrieved August 5, 2013. 
  20. ^ "Optimal Control of Rendezvous and Docking with a Non-Cooperative Satellite". New Mexico State University. Retrieved 2011-07-09. "Most of the current research and all the past missions are aiming at capturing very cooperative satellites only. In the future, we may also need to capture non-cooperative satellites such as the ones tumbling in space or not designed for being captured." 
  21. ^ a b Tooley, Craig (2010-05-25). "A New Space Enterprise of Exploration". NASA. Retrieved 2012-06-25. 
  22. ^ Ambrose, Rob (November 2010). "Robotics, Tele-Robotics and Autonomous systems Roadmap (Draft)". NASA. Retrieved 2012-06-25. "A smaller common docking system for robotic spacecraft is also needed to enable robotic spacecraft AR&D within the capture envelopes of these systems. Assembly of the large vehicles and stages used for beyond LEO exploration missions will require new mechanisms with new capture envelopes beyond any docking system currently used or in development. Development and testing of autonomous robotic capture of non-cooperative target vehicles in which the target does not have capture aids such as grapple fixtures or docking mechanisms is needed to support satellite servicing/rescue." 
  23. ^ History of U.S. Docking Systems (10/05/2010)
  24. ^ a b c d "Docking Systems". RussianSpaceWeb.com. Retrieved 2 September 2012. 
  25. ^ "Kristall module (77KST) at a glance". 
  26. ^ "Space Shuttle Mission STS-74 Press Kit". NASA. Retrieved 28 December 2011. "Atlantis will carry the Russian-built Docking Module, which has multi-mission androgynous docking mechanisms at top and bottom" 
  27. ^ a b Bart Hendrickx & Bert Vis (2007). Energiya-Buran: The Soviet Space Shuttle. Chichester, UK: Praxis Publishing Ltd. pp. 379–381. ISBN 978-0-387-69848-9. "Although Energiya's internal desginator for the Shuttle APAS is APAS-95, it is essentially the same as Buran's APAS-89" 
  28. ^ Bart Hendrickx & Bert Vis (2007). Energiya-Buran: The Soviet Space Shuttle. Chichester, UK: Praxis Publishing Ltd. pp. 379–381. ISBN 978-0-387-69848-9. "This Module was equipped with an APAS-89 docking system" 
  29. ^ Tests of new Dragon systems to begin minutes after launch, Stephen Clark, Spaceflight Now, 2012-05-21, accessed 2012-050-22.
  30. ^ "China’s First Space Station Module Readies for Liftoff". Space News. 1 August 2012. Retrieved 3 September 2012. 
  31. ^ Frank Morring, Jr., Mark Carreau (4 June 2012). "Commercial Crew Vehicles Will Use New Docking Standard". Aviation Week. Retrieved 29 September 2012. "All four companies working with partial NASA funding under Space Act Agreements (SAAs) to develop commercial crew vehicles—Blue Origin, Boeing, Sierra Nevada and SpaceX—will use the NDS to dock with the station...The NDS also will be mounted on NASA's Orion Multi-Purpose Crew Vehicle, a holdover from the old Constellation program of human exploration vehicles that is intended for human exploration beyond low Earth orbit." 
  32. ^ "Robotics Grasping and Force closure". pdf. FU Berlin. Retrieved 2014-03-20.