View source for Mobile Servicing System

{{short description|Robotic system on board the International Space Station}}
[[File:STS-114 Steve Robinson on Canadarm2.jpg|thumb|right|300px|Astronaut [[Stephen K. Robinson]] anchored to the end of the Canadarm2 during [[STS-114]], 2005]]
[[File:Rassvet Canadarm Crop.jpg|thumb|Canadarm2 moves [[Rassvet (ISS module)|Rassvet]] to berth with the station on [[STS-132]], 2010]]

The '''Mobile Servicing System''' ('''MSS''') is a [[robot]]ic system on board the [[International Space Station]] (ISS). Launched to the ISS in 2001, it plays a key role in station assembly and maintenance; it moves equipment and supplies around the station, supports astronauts working in space, services instruments and other payloads attached to the ISS, and is used for external maintenance. Astronauts receive specialized training to perform these functions with the various systems of the MSS.

The MSS is composed of three components:

* the Space Station Remote Manipulator System (SSRMS), known as '''Canadarm2'''.
* the Mobile Remote Servicer Base System (MBS).
* the [[Dextre|Special Purpose Dexterous Manipulator]] (SPDM, also known as '''"Dextre"''' or '''"Canada hand"''').

The system can move along rails on the [[Integrated Truss Structure]] on top of the US-provided Mobile Transporter cart, which hosts the MRS Base System. The system's control software was written in the [[Ada (programming language)|Ada 95 programming language]].<ref>{{cite web | url = http://www.adacore.com/uploads/customers/CaseStudy_SpaceArm.pdf| title = Case Study: MDA - Canadian Space Arm | publisher = AdaCore | access-date=2009-10-15}}</ref>

The MSS was designed and manufactured by [[MDA (company)|MDA]] (previously divisions of MacDonald Dettwiler Associates called [[MDA Space Missions]], MD Robotics, and previously called SPAR Aerospace) for the [[Canadian Space Agency]]'s contribution to the International Space Station.

==Canadarm2==
[[File:Leroy Chiao working on Space Station Remote Manipulator System.jpg|thumb|left|250px|Astronaut
[[Leroy Chiao]] controlling Canadarm2 from the [[Destiny Laboratory Module|Destiny]] lab]]
[[File:Canadarm2 Latching End Effector and joints (ISS052e000402).jpg|thumb|The exterior of the Canadarm is clad with Kevlar fabric, while the arm itself is made from [[titanium]], pictured above [[Lake Balkhash]].]]
[[File:Melvin working on robotic computers in US lab.jpg|thumb|left|250px|[[Leland Melvin]] working on the robotic control computers]]
[[File:ISS-26 Canadarm2 and Dextre with Flex Hose Rotary Coupler.jpg|thumb|A unique view of the whole arm, MBS and Dextre, grappling containers while near the massive solar arrays]]
[[File:Cygnus 7 captured by Canadarm2.jpg|thumb|Canadarm2 captures [[Cygnus OA-5|Cygnus OA-5 ''S.S. Alan Poindexter'']] in late 2016]]
Officially known as the '''Space Station Remote Manipulator System''' (SSRMS), Canadarm2 was launched on [[STS-100]] in April 2001. This second generation arm is a larger, more advanced version of the [[Space Shuttle]]'s original [[Canadarm]]. Canadarm2 is {{convert|17.6|m|abbr=on}} when fully extended and has seven motorized joints (an 'elbow' hinge in the middle, and three rotary joints at each of the 'wrist/shoulder' ends). It has a mass of {{convert|1800|kg|abbr=on}}, a diameter of {{convert|35|cm|abbr=on}}, and is made from titanium. The arm can handle large payloads of up to {{convert|116000|kg|abbr=on}} and could assist with docking the space shuttle. It is self-relocatable and can move end-over-end to reach many parts of the Space Station in an [[Geometer moth#Caterpillars|inchworm]]-like movement. In this movement, it is limited only by the number of [[Power Data Grapple Fixture]]s (PDGFs) on the station. PDGFs located around the station provide power, data and video to the arm through either of its two Latching End Effectors (LEEs). The arm can also travel the entire length of the space station truss using the Mobile Base System.

In addition to moving itself around the station, the arm can move any object with a [[grapple fixture]]. In construction of the station the arm was used to move large segments into place. It can also capture unpiloted ships like the [[SpaceX Dragon]], the [[Cygnus (spacecraft)|''Cygnus'' spacecraft]], and Japanese [[H-II Transfer Vehicle]] (HTV), which are equipped with a standard grapple fixture that the Canadarm2 uses to capture and berth the spacecraft. The arm is also used to unberth and release the spacecraft after use.

On-board operators see what they are doing by looking at the three Robotic Work Station (RWS) LCD screens. The MSS has two RWS units: one in the [[Destiny (ISS module)|''Destiny'' module]] and the other in the [[Cupola (ISS module)|''Cupola'']]. Only one RWS controls the MSS at a time. The RWS has two sets of control joysticks: one Rotational Hand Controller (RHC) and one Translational Hand Controller (THC). In addition to this is the Display and Control Panel (DCP) and the Portable Computer System (PCS) laptop.

In recent years,{{When|date=April 2025}} the majority of robotic operations are commanded remotely by flight controllers at [[Christopher C. Kraft Jr. Mission Control Center]] or the [[Canadian Space Agency]]'s [[John H. Chapman Space Centre]]. Operators can work in shifts to accomplish objectives with more flexibility than when done by on-board crew operators, albeit at a slower pace. Astronaut operators are used for time-critical operations such as visiting vehicle captures and robotics-supported [[extra-vehicular activity]].

Some time before 12 May 2021 Canadarm2 was hit by a small piece of orbital debris, damaging its thermal blankets and one of the booms.<ref name=star2021 /> Its operation appeared to be unaffected.<ref name=star2021>{{cite news |last=Michelle |first=Star |date=31 May 2021 |title= Space Debris Has Hit And Damaged The International Space Station  |url=https://www.sciencealert.com/space-debris-has-damaged-the-international-space-station |work=Science Alert|access-date=31 May 2021}} </ref>

Canadarm 2 will also help to berth the [[Axiom Orbital Segment|Axiom Space Station]] modules to the [[ISS]].<ref>{{Cite web|title=Axiom Station Assembly Sequence — Axiom Space Axiom Space |url=https://www.axiomspace.com/axiom-station/assembly-sequence|access-date=2021-08-09|website=[[Axiom Space]]}}</ref><ref>{{Cite web|title=A Private Space Station Might Be Born From the ISS - Seeker|url=https://www.seeker.com/international-space-station-retire-private-axiom-orbit-commercializati-2214242152.html|access-date=2021-09-26|website=www.seeker.com|date=25 January 2017 |language=en}}</ref>

===Latching End Effectors===
[[File:LEE.png|right|thumb|upright=1.3|LEE drawing]]
[[File:Latching End Effector picture.jpg|right|thumb|upright=1.3|Latching end effector (LEE)]]
Canadarm2 has two LEEs, one at each end. A LEE has three snare wires to catch the [[grapple fixture]] shaft.<ref name=sts126_eva_cl>[http://www.nasa.gov/centers/johnson/pdf/290103main_sts126_eva_checklist.pdf EVA Checklist STS-126 Flight Supplement, 2008]  pages 115, 117, 118</ref> Another LEE is on the Mobile Base System's Payload ORU Accommodations (POA) unit. The POA LEE is used to temporarily hold large ISS components. One more is on the Special Purpose Dexterous Manipulator (SPDM, also known as "Dextre" or "Canada hand"). Six LEEs have been manufactured and used in various locations on the ISS.{{CN|date=January 2024}}

{| class="wikitable sortable"
|-
! S/N !! Initial location !! Current location
|-
| 201 || LEE B || POA LEE
|-
| 202 || LEE A || Earth, to be refurbished for Ground Spare
|-
| 203 || POA LEE || LEE A
|-
| 204 || Spare stored on [[ExPRESS Logistics Carrier|ELC1]] || LEE B
|-
| 205 || Earth, Ground Spare || Spare stored on exterior ISS
|-
| 301 || SPDM LEE  || SPDM LEE
|}

== Special Purpose Dexterous Manipulator ==
{{Main|Dextre}}
The Special Purpose Dexterous Manipulator or "[[Dextre]]" is a smaller two-armed robot that can attach to Canadarm2, the ISS, or the Mobile Base System. The arms and their power tools can handle delicate assembly tasks and change [[orbital replacement unit]] (ORUs) currently handled by astronauts during spacewalks. Although Canadarm2 can move around the station in an "inchworm motion", it is unable to carry anything with it unless Dextre is attached. Testing was done in the space simulation chambers of the Canadian Space Agency's [[David Florida Laboratory]] in [[Ottawa]], Ontario. The manipulator was launched to the station on 11 March 2008 on [[STS-123]].
[[file:Dextrereallyhasnohead.jpg|center|thumb|500px|Dextre and Canadarm2 docked side by side on Power Data Grapple Fixtures]]

==Mobile Base System==
[[File:STS-111 Installation of Mobile Base System.jpg|thumb|right|250px|The Mobile Base System just before Canadarm2 installed it on the Mobile Transporter during [[STS-111]]]]
The Mobile Remote Servicer Base System (MBS) is a base platform for the robotic arms. It was added to the station during [[STS-111]] in June 2002. The platform rests atop the [[Mobile Transporter]]<ref name=nst/> (installed on [[STS-110]], designed by [[Northrop Grumman#Aerospace Systems|Northrop Grumman]] in [[Carpinteria, California]]), which allows it to glide 108 metres down rails on the [[Integrated Truss Structure|station's main truss]].<ref name="mbs">{{cite web|url=https://www.asc-csa.gc.ca/eng/iss/mobile-base/|title=About the Mobile Base System|date=20 June 2018 |publisher=Government of Canada|access-date=January 2, 2023}}</ref> Canadarm2 can relocate by itself, but cannot carry at the same time. Dextre cannot relocate by itself. The MBS gives the two robotic arms the ability to travel to work sites all along the truss structure and to step off onto grapple fixtures along the way. When ''Canadarm2'' and ''Dextre'' are attached to the MBS, they have a combined mass of {{convert|4900|kg|abbr=on}}.<ref name=MSS>{{cite web|url=http://www.nasa.gov/mission_pages/station/structure/elements/mobile-servicing-system.html|title=Mobile Servicing System|first=Mark|last=Garcia|date=22 October 2018|website=NASA}}</ref> Like ''Canadarm2'' it was built by [[MD Robotics]], and it has a minimum service life of 15 years.<ref name="mbs"/><ref>{{cite web|title=A Space-Age Robot|url=https://www.technologyreview.com/2008/03/11/221407/a-space-age-robot/|publisher=MIT Technology Review|access-date=January 2, 2023}}</ref>

The MBS is equipped with four Power Data Grapple Fixtures, one at each of its four top corners. Any of these can be used as a base for the two robots, Canadarm2 and Dextre, as well as any of the payloads that might be held by them. The MBS also has two locations to attach payloads. The first is the [[Payload/Orbital Replacement Unit Accommodations]] (POA). This is a device that looks and functions much like the [[Latching End Effector]]s of Canadarm2. It can be used to park, power and command any payload with a grapple fixture, while keeping Canadarm2 free to do something else. The other attachment location is the [[MBS Common Attachment System]] (MCAS). This is another type of attachment system that is used to host scientific experiments.<ref name="MBS features">{{cite web|url=http://www.space.gc.ca/eng/missions/sts-111/mobile_design_component.asp|title=CSA - STS-111 - Mobile Base System - MBS Design|access-date=2008-03-15|publisher=Canadian Space Agency|archive-date=2008-09-21|archive-url=https://web.archive.org/web/20080921030803/http://www.space.gc.ca/eng/missions/sts-111/mobile_design_component.asp|url-status=dead}}</ref>

The MBS also supports astronauts during [[Extravehicular activity|extravehicular activities]]. It has locations to store tools and equipment, foot-restraints, handrails and safety tether attachment points as well as a camera assembly. If needed, it is even possible for an astronaut to "ride" the MBS while it moves at a top speed of about 1.5 meters per minute.<ref name=nst>
{{cite web | url = http://www.nasa.gov/missions/shuttle/f_slowtrain.html | title = The Slowest and Fastest Train in the Universe | publisher = NASA}}</ref> On either side of the MBS are the Crew and Equipment Translation Aids. These carts ride on the same rails as the MBS. Astronauts ride them manually during EVAs to transport equipment and to facilitate their movements around the station.
{{wide image|ISS Mobile Transporter railway system.jpg|1000px|Canadarm2 riding the Mobile Base System along the Mobile Transporter railway, running the length of the station's main truss}}
{{clear}}

== Enhanced ISS Boom Assembly ==
{{Main|Orbiter Boom Sensor System#Enhanced ISS Boom Assembly}}
Installed on May 27, 2011, is a {{convert|50|ft|adj=on|order=flip}} boom with handrails and inspection cameras, attached to the end of Canadarm2.
<gallery mode="packed-hover" heights="300">
file:STS-114 robot arm extension.jpg|Shuttle Remote Manipulator System (RMS) holding OBSS boom on STS-114
file:STS-120 OBSS repair.jpg|Astronaut Scott Parazynski (at right) riding the OBSS boom to repair the solar array during STS-120
</gallery>

==Other ISS robotics==
The station received a second robotic arm during [[STS-124]], the [[Japanese Experiment Module]] Remote Manipulator System (JEM-RMS). The JEM-RMS is primarily used to service the JEM Exposed Facility. An additional robotic arm, the [[European Robotic Arm]] (ERA) was launched alongside the Russian-built [[Multipurpose Laboratory Module]] on July 15, 2021.

Originally connected to ''Pirs'', the ISS also has two [[Strela (crane)|Strela]] cargo cranes. One of the cranes could be extended to reach the end of [[Zarya (ISS module)|Zarya]]. The other could extend to the opposite side and reach the end of [[Zvezda (ISS module)|Zvezda]]. The first crane was assembled in space during [[STS-96]] and [[STS-101]]. The second crane was launched alongside Pirs itself. The cranes were later moved to the docking compartment [[Poisk (ISS module)|''Poisk'']] and ''Zarya'' module.

===List of cranes===
{| class="wikitable"
!Name
!Agency or Company
!Launch

|-
|[[Canadarm 2]]
|[[Canadian Space Agency]]
|April 19, 2001

|-
|[[Dextre]]
|[[Canadian Space Agency]]
|March 11, 2008

|}

==See also==
{{Portal|Spaceflight}}
* [[MacDonald, Dettwiler and Associates|MacDonald Dettwiler and Associates (MDA)]], the manufacturers of Canadarm2
* [[Canadarm]], which was used on the [[Space Shuttle Orbiter]]s
* [[European Robotic Arm]], a third robotic arm installed on the ISS
* The Remote Manipulator System, used on the ISS module [[Kibo (ISS module)|Kibo]]
* [[Dextre]], also known as the Special Purpose Dexterous Manipulator (SPDM), used on the ISS
* [[Strela (crane)|Strela]], a crane used on the ISS to perform similar tasks as the Mobile Servicing System

==References==
{{Reflist}}

==Further reading==
* [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140008717.pdf Robotic Transfer and Interfaces for External ISS Payloads. 2014] good diagrams of SSRMS/Canadarm2

==External links==
{{Commons category|Mobile Servicing System}}
* [https://web.archive.org/web/20000106213153/http://spaceflight.nasa.gov/station/assembly/elements/mss/index.html ISS Assembly: Canadarm2 and the Mobile Servicing System]
* [http://www.asc-csa.gc.ca/eng/iss/canadarm2/success.asp Canadian Space Agency information about Canadarm2]
* [https://www.youtube.com/watch?v=IT3Vuku9CEw  Youtube animation of the Mobile Base System, Canadarm2 and Dextre working together]
* [https://www.youtube.com/watch?v=qF9IysSGg2U  Youtube animation of Canadarm2 inchworming on the station]
{{MDA Space Missions|state=autocollapse}}
{{ISS modules}}
{{Canadian Space Agency}}

[[Category:Components of the International Space Station]]
[[Category:Space robots]]
[[Category:Space program of Canada]]
[[Category:2001 in spaceflight]]
[[Category:2001 robots]]
[[Category:Robots of Canada]]
[[Category:Robotic manipulators]]

[[fr:Canadarm 2]]