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{{about|Orbital replacement units of the ISS|Orbital replacement units of the Hubble Space Telescope|Orbital replacement unit (HST)}}
'''Orbital Replacement Units''' ('''ORUs''') are key elements of the [[International Space Station]] that can be readily replaced when the unit either passes its design life or fails. Examples of ORUs are: pumps, storage tanks, controller boxes, antennas, and battery units. Such units are replaced either by astronauts during EVA or by the [[Dextre]] (SPDM) robotic arm. All are stored on the three [[External Stowage Platform]]s (ESPs) or the four [[ExPRESS Logistics Carrier]]s (ELCs) mounted on the [[Integrated Truss Structure]] (ITS).
'''Orbital replacement units''' (or '''on-orbit replaceable unit'''<ref name=RTIEIP2014/>{{rp|21}}) ('''ORUs''') are key elements of the [[International Space Station]] that can be readily replaced when the unit either passes its design life or fails. ORUs are parts of the main systems and subsystems of the external elements of the ISS, none are intended to be installed inside the pressurised modules. Examples of ORUs are: pumps, storage tanks, controller boxes, antennas, and battery units. Such units are replaced either by astronauts during EVA or by the [[Dextre]] (SPDM) robotic arm. All are stored on the three [[external stowage platform]]s (ESPs) or the four [[ExPRESS Logistics Carrier]]s (ELCs) mounted on the [[Integrated Truss Structure]] (ITS).
[[Image:ISS Unpressurized Platforms.png|right|500px|thumb|Location of ESPs and ELCs on the [[International Space Station]].]]
[[Image:ISS Unpressurized Platforms.png|right|500px|thumb|Location of ESPs and ELCs on the [[International Space Station]].]]


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[[File:Truss breakdown.png|thumb|500px|right|ISS [[Integrated Truss Structure]] detailing all Orbital Replacement Units in situ]]
[[File:Truss breakdown.png|thumb|500px|right|ISS [[Integrated Truss Structure]] detailing all Orbital Replacement Units in situ]]


While spare parts/ORUs were routinely brought up and down during the ISS life-time via Space Shuttle resupply missions, there was a heavy emphasis once the Station was considered complete.
While spare parts/ORUs were routinely brought up and down during the ISS life-time via Space Shuttle resupply missions, there was a heavy emphasis{{clarify|date=December 2019}} once the Station was considered complete.


Several Shuttle missions were dedicated to the delivery of ORUs using support carrier structures/pallets of which some remained in the cargo bay, some that were deployed and retrieved and other pallets that were designed to be removed from the payload bay by RMS and placed onto the station.
Several Shuttle missions were dedicated to the delivery of ORUs using support carrier structures/pallets of which some remained in the cargo bay, some that were deployed and retrieved and other pallets that were designed to be removed from the payload bay by RMS and placed onto the station.


Deployable pallet flights included [[STS-102]]<ref name="STS-102">{{cite web|url=http://www.shuttlepresskit.com/STS-102/spk-102.pdf|title=STS-102 Presskit}}</ref> with [[External Stowage Platform]] ESP-1, [[STS-114]]<ref name="STS-114">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/106790main_EVA_114_F_A.pdf|title=EVA Checklist: STS-114 Flight Supplement}}</ref> with ESP-2, [[STS-118]]<ref name="STS-118">{{cite web|url=http://www.shuttlepresskit.com/STS-118/spk-118.pdf|title=STS-118 Presskit }}</ref> with ESP-2, [[STS-129]]<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=October 30, 2009}}</ref> with [[ExPRESS Logistics Carrier]] ELC-1 and ELC-2, [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-131|date=February 2011|publisher=NASA}}</ref> with ELC-4 and [[STS-134]]<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> with ELC-3.
Deployable pallet flights included [[STS-102]]<ref name="STS-102">{{cite web|url=http://www.shuttlepresskit.com/STS-102/spk-102.pdf|title=STS-102 Presskit}}</ref> with [[External Stowage Platform]] ESP-1, [[STS-114]]<ref name="STS-114">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/106790main_EVA_114_F_A.pdf|title=EVA Checklist: STS-114 Flight Supplement}}</ref> with ESP-2, [[STS-118]]<ref name="STS-118">{{cite web|url=http://www.shuttlepresskit.com/STS-118/spk-118.pdf|title=STS-118 Presskit }}</ref> with ESP-2, [[STS-129]]<ref name="EVA129">{{cite web|url=http://www.nasa.gov/centers/johnson/pdf/404493main_EVA_129_F_E1.pdf|title=EVA Checklist: STS-129 Flight Supplement|author=L. D. Welsch|publisher=NASA|date=October 30, 2009}}</ref> with [[ExPRESS Logistics Carrier]] ELC-1 and ELC-2, [[STS-133]]<ref name="STS-133">{{cite web|url=http://www.nasa.gov/pdf/491387main_STS-133%20Press%20Kit.pdf|title=Space Shuttle Mission: STS-133|date=February 2011|publisher=NASA}}</ref> with ELC-4 and [[STS-134]]<ref name="STS-134">{{cite web|url=http://www.nasa.gov/pdf/538352main_sts134_presskit_508.pdf|title=Space Shuttle Mission: STS-134|publisher=NASA|date=April 2011}}</ref> with ELC-3.


Other modes of ORU delivery included:
Other modes of ORU delivery included:
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Payload bay sidewall mounted ORUs, such as BCDUs, were regularly carried and transported to the ISS via EVAs.
Payload bay sidewall mounted ORUs, such as BCDUs, were regularly carried and transported to the ISS via EVAs.


Also, three flights of the [[Integrated Cargo Carrier]] (ICC) which remained in the cargo bay on flights [[STS-102]], [[STS-105]] and [[STS-121]]; one use of the ICC-Lite on [[STS-122]] (a shortened version of the ICC); two uses of the ICC-Vertical Light Deployable on [[STS-127]] as ICC-VLD and [[STS-132]] as ICC-VLD2, which were deployed and retrieved during the mission; and five uses of the Lightweight MPESS Carrier (LMC) on [[STS-114]], [[STS-126]], [[STS-128]], [[STS-131]] and [[STS-135]], the LMC was not designed to be deployed and remained in the shuttle payload bay throughout the flight.
Also, three flights of the [[Integrated Cargo Carrier]] (ICC) which remained in the cargo bay on flights [[STS-102]], [[STS-105]] and [[STS-121]]; one use of the ICC-Lite on [[STS-122]] (a shortened version of the ICC); two uses of the ICC-Vertical Light Deployable on [[STS-127]] as ICC-VLD and [[STS-132]] as ICC-VLD2, which were deployed and retrieved during the mission; and five uses of the [[Lightweight MPESS Carrier]] (LMC) on [[STS-114]], [[STS-126]], [[STS-128]], [[STS-131]] and [[STS-135]], the LMC was not designed to be deployed and remained in the shuttle payload bay throughout the flight.


To date other than the Space Shuttle missions, only one other mode of transportation of ORUs was utilised by the station, the Japanese cargo vessel [[Kounotori 2|HTV-2]] delivered an FHRC and CTC-4 via its Exposed Pallet (EP),<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=January 20, 2011}}</ref> and [[Kounotori 4|HTV-4]] delivered a Main Bus Switching Unit (MBSU) and a Utility transfer assembly (UTA).<ref>{{cite web |url=http://iss.jaxa.jp/en/htv/mission/htv-4/presskit/htv4_presskit_a.pdf |title=HTV4 (KOUNOTORI 4) Mission Press Kit |publisher=Japan Aerospace Exploration Agency |date=August 2, 2013 |accessdate=June 19, 2015}}</ref>
To date other than the Space Shuttle missions, only one other mode of transportation of ORUs was utilised by the station, the Japanese cargo vessel [[Kounotori 2|HTV-2]] delivered an FHRC and CTC-4 via its Exposed Pallet (EP),<ref name="HTV2">{{cite web|url=http://iss.jaxa.jp/en/htv/mission/htv-2/library/presskit/htv2_presskit_en.pdf|title=HTV2: Mission Press Kit|publisher=Japan Aerospace Exploration Agency|date=January 20, 2011}}</ref> and [[Kounotori 4|HTV-4]] delivered a Main Bus Switching Unit (MBSU) and a Utility transfer assembly (UTA).<ref>{{cite web |url=http://iss.jaxa.jp/en/htv/mission/htv-4/presskit/htv4_presskit_a.pdf |title=HTV4 (KOUNOTORI 4) Mission Press Kit |publisher=Japan Aerospace Exploration Agency |date=August 2, 2013 |access-date=June 19, 2015}}</ref>


===Modes of ORU transport to the ISS===
===Modes of ORU transport to the ISS===
<center>
<gallery class="center">
<gallery>
File:MBSU on the payload bay sidewall STS-120.png|Main Bus Switching Unit (MBSU) ORU on the payload bay sidewall during STS-120
File:MBSU on the payload bay sidewall STS-120.png|Main Bus Switching Unit (MBSU) ORU on the payload bay sidewall during STS-120
File:S133e010583.jpg|ESP-2 platform mounted to the Quest module (pallet deployed)
File:S133e010583.jpg|ESP-2 platform mounted to the Quest module (pallet deployed)
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File:Mplm in shuttle.jpg|ICC in the forward end of the payload bay STS-102 (retained in the payload bay throughout the flight)
File:Mplm in shuttle.jpg|ICC in the forward end of the payload bay STS-102 (retained in the payload bay throughout the flight)
</gallery>
</gallery>
</center>
<gallery class="center">
<center>
<gallery>
File:Columbus exposed facilities on LCC-lite carrier.jpg|ICC-Lite payload structure STS-122 (retained in the payload bay throughout the flight)
File:Columbus exposed facilities on LCC-lite carrier.jpg|ICC-Lite payload structure STS-122 (retained in the payload bay throughout the flight)
File:STS-127 ICC.jpg|ICC-VLD on the RMS during STS-127 (pallet deployed and retrieved)
File:STS-127 ICC.jpg|ICC-VLD on the RMS during STS-127 (pallet deployed and retrieved)
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File:FHRC and CTC4 on the HTV-2 EP image.png|HTV-2 Exposed Pallet with FHRC and CTC4 during preflight (pallet deployed and retrieved)
File:FHRC and CTC4 on the HTV-2 EP image.png|HTV-2 Exposed Pallet with FHRC and CTC4 during preflight (pallet deployed and retrieved)
</gallery>
</gallery>
</center>


===Types of ORUs===
===Types of ORUs===
Orbital replacement units are parts of the main systems and subsystems of the external elements of the ISS. Affecting the control of the cooling system, the movement and control of the solar arrays and SARJ as well as the flow of power throughout the station from solar arrays to the heat rejection system as part of the [[External Active Thermal Control System]] (EATCS). As well as storage tanks for oxygen as part of the station [[Environmental Control and Life Support System]] (ECLSS). ORUs, can be hardware such as radiators, or simply batteries or communication antennas. Essentially any element that can readily be removed and replaced when required.
Orbital replacement units are parts of the main systems and subsystems of the external elements of the ISS. Affecting the control of the cooling system, the movement and control of the solar arrays and SARJ as well as the flow of power throughout the station from solar arrays to the heat rejection system as part of the [[External Active Thermal Control System]] (EATCS). As well as storage tanks for oxygen as part of the station [[Environmental Control and Life Support System]] (ECLSS). ORUs can be hardware such as radiators, or simply batteries or communication antennas, essentially any element that can readily be removed and replaced when required.


The replaceable modular nature of the station allows its life to be extended well beyond its initial design life, theoretically.
The replaceable modular nature of the station allows its life to be extended well beyond its initial design life, theoretically.


===ORUs and robotic arms===
===ORUs and robotic arms===
ORUs to be handled by [[Dextre]] have attachments designed to be gripped with the ORU/Tool Changeout Mechanisms on the end of each arm. The H‐fixture is for massive objects, the most common is a Micro‐fixture(also known as a Micro‐square) and the Micro‐Conical Fitting is used in tight spaces.
ORUs to be handled by [[Dextre]] have attachments designed to be gripped with the ORU/Tool Changeout Mechanisms (OTCM) on the end of each arm. The H‐fixture is for massive objects and/or to stabilize [[Dextre]], the most common is a Micro‐fixture (also known as a Micro‐square) and the Micro‐Conical Fitting is used in tight spaces.
A Modified Truncated Cone(MTC) Target is used to visually line up Dexter's arm to grab a fixture.<ref>http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140008717.pdf</ref> Any ORU with a [[Grapple Fixture|grapple fixture]] can be moved by the [[Canadarm2]].
A Modified Truncated Cone (MTC) Target is used to visually line up Dexter's arm to grab a fixture.<ref name=RTIEIP2014>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140008717.pdf Robotic Transfer and Interfaces for External ISS Payloads. 2014]</ref> Any ORU with a [[Grapple Fixture|grapple fixture]] can be moved by the [[Canadarm2]].


==Orbital replacement unit (ORU) spares==
==Orbital replacement unit (ORU) spares==
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* Flex Hose Rotary Coupler (FHRC) weight approx. 900&nbsp;lb × 1 unit each on S1 & P1 Truss. The FHRC provides the transfer of liquid ammonia across the Thermal Radiator Rotary Joint (TRRJ) between the P1 (FHRC SN1001) & S1 (FHRC SN1002) truss segments and the Heat Rejection System Radiators (HRSRs).
* Flex Hose Rotary Coupler (FHRC) weight approx. 900&nbsp;lb × 1 unit each on S1 & P1 Truss. The FHRC provides the transfer of liquid ammonia across the Thermal Radiator Rotary Joint (TRRJ) between the P1 (FHRC SN1001) & S1 (FHRC SN1002) truss segments and the Heat Rejection System Radiators (HRSRs).


Three spares – ESP-2 FRAM-7 (keel side) FHRC SN1003,<ref name="STS-114"/> ESP-3 FRAM-2 (top side) FHRC SN1004,<ref>http://www.nasa.gov/centers/johnson/pdf/290103main_sts126_eva_checklist.pdf</ref> ELC-4 FRAM-5 (keel side) FHRC SN0005 delivered by HTV-2.<ref name="HTV2"/>
Three spares – ESP-2 FRAM-7 (keel side) FHRC SN1003,<ref name="STS-114"/> ESP-3 FRAM-2 (top side) FHRC SN1004,<ref name=sts126_eva_cl>[http://www.nasa.gov/centers/johnson/pdf/290103main_sts126_eva_checklist.pdf EVA Checklist STS-126 Flight Supplement, 2008]</ref> ELC-4 FRAM-5 (keel side) FHRC SN0005 delivered by HTV-2.<ref name="HTV2"/>


* Pump Module (PM) weight 780&nbsp;lb x 1 unit each on S1 (current PM SN0006) & P1 (original PM SN0001 still in situ) Trusses. The PM is part of the station’s complex External Active Thermal Control System (ETCS), which provides vital cooling to internal and external avionics, crew members, and payloads. The station has two independent cooling loops. The external loops use an ammonia-based coolant and the internal loops use water cooling.
* Pump Module (PM) weight 780&nbsp;lb x 1 unit each on S1 (current PM SN0006) & P1 (original PM SN0001 still in situ) Trusses. The PM is part of the station's complex External Active Thermal Control System (ETCS), which provides vital cooling to internal and external avionics, crew members, and payloads. The station has two independent cooling loops. The external loops use an ammonia-based coolant and the internal loops use water cooling.


Four original spares (two unused Pump Modules remain) - ELC-1 FRAM-7 (keel side) PM SN0007,<ref name="EVA129"/> ELC-2 FRAM-6 (keel side) PM SN0005<ref name="EVA129"/> Two utilised - ESP-2 FRAM-1 (top side) PM SN0004 (was installed here during STS-121, then removed by the Exp 24 crew to replace the failed original PM SN0002 on the S1 truss. That failed unit was returned to earth by the STS-135 crew); ESP-3 FRAM-3 (top side) PM SN0006 (was swapped with failed PM SN0004 from S1 truss by Exp 38 crew Dec. 2013, then stored on the MT POA). The ISS-41 EVA-27 crew relocated this unit from the POA to ESP-2 FRAM-1 in Oct. 2014.
Four original spares. Two unused Pump Modules remain – ELC-1 FRAM-7 (keel side) PM SN0007,<ref name="EVA129"/> ESP-2 FRAM-1 (top side) PM SN0005.<ref name="EVA129"/><ref>{{cite web|title=ISS Daily Summary Report – 03/06/15|url=https://blogs.nasa.gov/stationreport/2015/03/page/17/|website=ISS On-Orbit Status Report|access-date=30 March 2018}}</ref> Two utilised – ELC-2 FRAM-6 (keel side) PM SN0004 (Installed on ESP-2 FRAM-1 during STS-121, then removed by the Exp 24 crew to replace the failed original PM SN0002 on the S1 truss. SN0002 was returned to earth by the STS-135 crew. SN0004 replaced by PM SN0006 and moved to MT POA by Exp 38 crew in Dec. 2013. Relocated to ESP-2 FRAM-1 by ISS-41 EVA-27 in Oct. 2014. Swapped positions with SN0005 by SPDM in Mar. 2015.); ESP-3 FRAM-3 (top side) PM SN0006 (Installed on ESP-3 FRAM-3 during STS-127, swapped with failed PM SN0004 from S1 truss by Exp 38 crew Dec. 2013).


* Ammonia Tank Assembly (ATA) weight 1,702&nbsp;lb x 1 unit each on S1 (now ATA SN0004) & P1 (now ATA SN0002) trusses. The primary function of the ATA is to store the ammonia used by the external thermal control system (ETCS). The major components in the ATA include two ammonia storage tanks, isolation valves, heaters, and various temperature, pressure, and quantity sensors. There is one ATA per loop located on the zenith side of the Starboard 1 (Loop A) and Port 1 (Loop B) truss segments. The ATA contains two flexible, chambers incorporated into its ammonia tanks that expand as pressurized nitrogen expels liquid ammonia out of them.
* Ammonia Tank Assembly (ATA) weight 1,702&nbsp;lb x 1 unit each on S1 (now ATA SN0004) & P1 (now ATA SN0002) trusses. The primary function of the ATA is to store the ammonia used by the external thermal control system (ETCS). The major components in the ATA include two ammonia storage tanks, isolation valves, heaters, and various temperature, pressure, and quantity sensors. There is one ATA per loop located on the zenith side of the Starboard 1 (Loop A) and Port 1 (Loop B) truss segments. The ATA contains two flexible, chambers incorporated into its ammonia tanks that expand as pressurized nitrogen expels liquid ammonia out of them.


Two spares – ELC-1 FRAM-9 (keel side),<ref name="EVA129"/> ELC-3 FRAM-5 (keel side)<ref name="STS-134"/> Also note - other than these two spares, two other Shuttle missions brought up new ATAs and then returned the failed ATAs: [[STS-128]] ATA SN0004 up/SN0002 down (P1 truss original ATA) and [[STS-131]] SN0002 up/SN0003 down (S1 truss original ATA).
Two spares – ELC-1 FRAM-9 (keel side),<ref name="EVA129"/> ELC-3 FRAM-5 (keel side)<ref name="STS-134"/> Also note – other than these two spares, two other Shuttle missions brought up new ATAs and then returned the failed ATAs: [[STS-128]] ATA SN0004 up/SN0002 down (P1 truss original ATA) and [[STS-131]] SN0002 up/SN0003 down (S1 truss original ATA).


* Nitrogen Tank Assembly (NTA) weight 550&nbsp;lb each × 1 unit each on S1 (now NTA SN0005) & P1 truss (now NTA SN0004). The NTA provides a high-pressure gaseous nitrogen supply to control the flow of ammonia out of the ATA.
* Nitrogen Tank Assembly (NTA) weight 550&nbsp;lb each × 1 unit each on S1 (now NTA SN0005) & P1 truss (now NTA SN0004). The NTA provides a high-pressure gaseous nitrogen supply to control the flow of ammonia out of the ATA.


Two spares – ELC-1 FRAM-6 (keel side) NTA SN0002 (refurbished)<ref name="EVA129"/> ELC-2 FRAM-9 (keel side) NTA SN0003 (refurbished)<ref name="EVA129"/> Also note - other than these two spares, two other Shuttle missions replaced NTAs. [[STS-122]] delivered new NTA SN0004 and then returned the depleted P1 Truss NTA SN0003. [[STS-124]] swapped the new NTA SN0005 from ESP-3 FRAM 2 with the depleted NTA SN0002 from the S1 Truss. The [[STS-126]] crew returned this depleted NTA.
Two spares – ELC-1 FRAM-6 (keel side) NTA SN0002 (refurbished)<ref name="EVA129"/> ELC-2 FRAM-9 (keel side) NTA SN0003 (refurbished)<ref name="EVA129"/> Also note – other than these two spares, two other Shuttle missions replaced NTAs. [[STS-122]] delivered new NTA SN0004 and then returned the depleted P1 Truss NTA SN0003. [[STS-124]] swapped the new NTA SN0005 from ESP-3 FRAM 2 with the depleted NTA SN0002 from the S1 Truss. The [[STS-126]] crew returned this depleted NTA.


* High-Pressure Gas Tank Assembly (HPGTA) weight 1,240&nbsp;lb x 5 units on quest. High-pressure oxygen and nitrogen gas tanks on board the ISS provide support for EVA and contingency metabolic support for the crew. This high-pressure O2 and N2 is brought to the ISS by the high-pressure gas tanks (HPGT) and is replenished by the Space Shuttle.
* High-Pressure Gas Tank Assembly (HPGTA) weight 1,240&nbsp;lb x 5 units on quest. High-pressure oxygen and nitrogen gas tanks on board the ISS provide support for EVA and contingency metabolic support for the crew. This high-pressure O2 and N2 is brought to the ISS by the high-pressure gas tanks (HPGT) and is replenished by the Space Shuttle.
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Three units – CTC-3 formerly on ELC-2 FRAM-2 (top side),<ref name="EVA129"/> was later moved to ESP-2 FRAM-3 via SPDM. CTC-2 on ELC-4 FRAM-2 (keel side),<ref name="HTV2"/> CTC-5 on ELC-3 FRAM-1 (top side)<ref name="STS-134"/>
Three units – CTC-3 formerly on ELC-2 FRAM-2 (top side),<ref name="EVA129"/> was later moved to ESP-2 FRAM-3 via SPDM. CTC-2 on ELC-4 FRAM-2 (keel side),<ref name="HTV2"/> CTC-5 on ELC-3 FRAM-1 (top side)<ref name="STS-134"/>


* Pitch/Roll-Joint (P/R‐J) x 2 units on the SSRMS. A Wrist joint with several degrees of freedom, designed to be replaced on orbit if required.
* Pitch/Roll-Joint (P/R‐J) x 2 units on the [[Space Station Remote Manipulator System|SSRMS]]. A Wrist joint with several degrees of freedom, designed to be replaced on orbit if required.


Two spares – ESP-3 FRAM-1 (top side),<ref name="STS-118"/> ESP-2 FRAM-5 (keel side)<ref name="STS-114"/>
Two spares – ESP-3 FRAM-1 (top side),<ref name="STS-118"/> ESP-2 FRAM-5 (keel side)<ref name="STS-114"/>
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* Main Bus Switching Unit (MBSU) weight 220&nbsp;lb × 4 units on S0 Truss. The MBSUs act as the distribution hub for the EPS system. The four MBSUs on board the ISS are all located on the starboard zero (S0) truss. Each of MBSU receives primary power from two power channels and distributes it downstream to the DDCUs.
* Main Bus Switching Unit (MBSU) weight 220&nbsp;lb × 4 units on S0 Truss. The MBSUs act as the distribution hub for the EPS system. The four MBSUs on board the ISS are all located on the starboard zero (S0) truss. Each of MBSU receives primary power from two power channels and distributes it downstream to the DDCUs.


Two spares – ESP-2 FRAM-4 (top side), ESP-2 FRAM-6 (keel side). First spare launched with ESP-2 (FRAM-4) on [[STS-114]], July 2005. Second spare launched on [[STS-120]], October 2007, installed on ESP-2 FRAM-6. First spare swapped for failed 1A/1B MBSU by [[Expedition 32]] crew in August 2012; the failed MBSU was initially stored on ESP-2 FRAM-4, then moved to ELC-2 FRAM-1 in January 2013. Third spare delivered by [[Kounotori 4|HTV-4]] in August 2013, installed on ESP-2 FRAM-4. 2A/2B MBSU failed and was replaced by [[Dextre]] with third spare in May 2017. Failed 2A/2B unit was brought inside via [[Kibō (ISS module)|JEM]] airlock in August 2017, repaired, returned to ESP-2 FRAM-4 in November 2017. 3A/3B MBSU failed in April 2019 and was replaced in May by the repaired former 2A/2B MBSU, with the 3A/3B unit stored on ESP-2 FRAM-4. Former 1A/1B unit brought inside and repaired in August 2019, then swapped into ESP-2 FRAM-4 for the former 3A/3B unit, which was brought inside in September 2019 and returned to Earth on board [[SpaceX CRS-19]].
Two spares – ESP-2 FRAM-4 (top side),<ref name="STS-114"/> ELC-2 FRAM-7 (placed via SPDM, delivered by HTV-4 Aug. 2013). The MBSU on ESP-2 FRAM-6 (keel side) was added by STS-120 crew, then swapped with a failed unit from the S0 truss by the Exp 32 crew in late 2012.


* Utility Transfer Assembly (UTA) a processor that allows power, signals and data to flow across the SARJ by roll rings incorporated within.
* Utility Transfer Assembly (UTA) a processor that allows power, signals and data to flow across the SARJ by roll rings incorporated within.


Two spares - ESP-2 FRAM-8 (keel side)<ref name="STS-114"/> ELC-4 FRAM-4 (keel side) Utility Transfer Assembly (delivered by HTV-4 EP via SPDM Aug. 2013)
Two spares – ESP-2 FRAM-8 (keel side)<ref name="STS-114"/> ELC-4 FRAM-4 (keel side) Utility Transfer Assembly (delivered by HTV-4 EP via SPDM Aug. 2013)


* Pump Flow Control Subassembly (PFCS) weight 235&nbsp;lb Each external loop contains a pump and flow control system (PFCS) which contains most of the controls and mechanical systems that drive the EATCS. There are 2 pumps per PFCS which circulate ammonia throughout the external coolant loops. There are 2 on each IEA x4 & 2 each on P6/S6 Spacers x 12 active units in total.
* Pump Flow Control Subassembly (PFCS) weight 235&nbsp;lb Each external loop contains a pump and flow control system (PFCS) which contains most of the controls and mechanical systems that drive the EATCS. There are 2 pumps per PFCS which circulate ammonia throughout the external coolant loops. There are 2 on each IEA (x4) for a total of 8 active units.
Five original spares, now Four spares - ESP-1 FRAM-1<ref name="STS-102"/> Plus the original 4 spares, 2 on ITS-S6, 2 on ITS-P6, one of which was swapped out for a faulty unit during an Exp 35 EVA May 11, 2013.
Three original spares, now two available spares – ESP-1 FRAM-1<ref name="STS-102"/> plus 2 on ITS-P6 that were initially used by the Early External Active Thermal Control System (EEATCS). One EEATCS spare on ITS-P6 swapped out for a leaky unit on the 2B power channel during an Exp 35 EVA May 11, 2013. Other EEATCS spare developed electrical fault and was replaced by an additional spare launched on [[SpaceX CRS-14]].


<center>
<gallery class="center">
<gallery>
File:01 FHRC sts126 fhrc.jpg|Flex hose rotary coupler (FHRC)
File:01 FHRC sts126 fhrc.jpg|Flex hose rotary coupler (FHRC)
File:FHRC without MLI cover STS-128.png|FHRC without MLI cover and in situ on the TRRJ
File:FHRC without MLI cover STS-128.png|FHRC without MLI cover and in situ on the TRRJ
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File:ATA.png|ATA drawing (cover removed)
File:ATA.png|ATA drawing (cover removed)
</gallery>
</gallery>
</center>


<center>
<gallery class="center">
<gallery>
File:03 NTA.jpg|Nitrogen tank assembly (NTA)
File:03 NTA.jpg|Nitrogen tank assembly (NTA)
File:NTA.png|NTA drawing (cover removed)
File:NTA.png|NTA drawing (cover removed)
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File:STS-134 Cargo Transportation Container.jpg|Inside a CTC box
File:STS-134 Cargo Transportation Container.jpg|Inside a CTC box
</gallery>
</gallery>
</center>


<center>
<gallery class="center">
<gallery>
File:Pitch Roll Joint PRJ.png|Pitch/roll joint (P/R J)
File:Pitch Roll Joint PRJ.png|Pitch/roll joint (P/R J)
File:Pitch Roll Joint.tiff|P/R J drawing
File:Pitch Roll Joint.tiff|P/R J drawing
Line 140: Line 132:
File:SASA.png|SASA drawing
File:SASA.png|SASA drawing
</gallery>
</gallery>
</center>


<center>
<gallery class="center">
<gallery>
File:DCSU image.png|Direct-current switching unit (DCSU)
File:DCSU image.png|Direct-current switching unit (DCSU)
File:DCSU art.png|DCSU drawing
File:DCSU art.png|DCSU drawing
Line 155: Line 145:
File:Utility Transfer Assembly UTA.png|Utility Transfer Assembly UTA preflight
File:Utility Transfer Assembly UTA.png|Utility Transfer Assembly UTA preflight
</gallery>
</gallery>
</center>


===Single spares===
===Single spares===
Line 162: Line 151:
The TUS reel assembly (TUS-RA) is basically a large spool much like a garden hose reel that pays out cable when the MT moves away and rolls it back up as the MT returns to the center of the truss. This is the same TUS-RA retrieved during [[STS-121]]. It was replaced and this failed unit was returned to earth and refurbished to later fly on ELC-2.
The TUS reel assembly (TUS-RA) is basically a large spool much like a garden hose reel that pays out cable when the MT moves away and rolls it back up as the MT returns to the center of the truss. This is the same TUS-RA retrieved during [[STS-121]]. It was replaced and this failed unit was returned to earth and refurbished to later fly on ELC-2.


* Latching end effector (LEE) weight 415&nbsp;lbs. at ELC-1 FRAM-1 (top side)<ref name="EVA129"/> x 3 units on ISS
* [[Latching End Effector]] (LEE) weight 415&nbsp;lbs. at ELC-1 FRAM-1 (top side)<ref name="EVA129"/> x 3 units on ISS (Two on [[Canadarm2]] and one on [[Dextre]] (SPDM) body)
⚫
* [[Special Purpose Dexterous Manipulator|Special-purpose dextrous manipulator]] (SPDM) arm at ELC-3 FRAM-2 (top side)<ref name="STS-134"/> x 2 arms on SPDM
The SSRMS has two identical grapple end points called LEE that enable it to reattach either end to the station as its new base.

⚫
* Special-purpose dextrous manipulator (SPDM) arm at ELC-3 FRAM-2 (top side)<ref name="STS-134"/> x 2 arms on SPDM
* Heat Rejection System Radiator (HRSR) weight 2,475&nbsp;lbs. at ELC-4 (top side)<ref name="STS-133"/> x 3 units each on S1 & P1 Truss
* Heat Rejection System Radiator (HRSR) weight 2,475&nbsp;lbs. at ELC-4 (top side)<ref name="STS-133"/> x 3 units each on S1 & P1 Truss
The Heat Rejection Subsystem (HRS) consists of a base, eight panels, torque panel, torque arm, an interconnected fluid system, a scissors-type deployment mechanism and a computer controlled motor/cable deployment system. Part of the station’s external active thermal control system (EATCS), the HRS radiator rejects thermal energy via radiation.
The Heat Rejection Subsystem (HRS) consists of a base, eight panels, torque panel, torque arm, an interconnected fluid system, a scissors-type deployment mechanism and a computer controlled motor/cable deployment system. Part of the station's external active thermal control system (EATCS), the HRS radiator rejects thermal energy via radiation.


* Linear Drive Unit (LDU) weight 255&nbsp;lbs. at ESP-3 FRAM-4 (top side)<ref name="STS-118"/> x 1 on the MT
* Linear Drive Unit (LDU) weight 255&nbsp;lbs. at ESP-3 FRAM-4 (top side)<ref name="STS-118"/> x 1 on the MT
Line 174: Line 161:
* Space-to-Ground ANTenna (SGANT) weight 194&nbsp;lbs. at ESP-3 FRAM-5 (keel side) x 2 units on Z1 Truss
* Space-to-Ground ANTenna (SGANT) weight 194&nbsp;lbs. at ESP-3 FRAM-5 (keel side) x 2 units on Z1 Truss
* Plasma Contactor Unit (PCU) weight 350&nbsp;lbs. at ELC-1 FRAM-2 (top side)<ref name="EVA129"/> x 2 units on the Truss
* Plasma Contactor Unit (PCU) weight 350&nbsp;lbs. at ELC-1 FRAM-2 (top side)<ref name="EVA129"/> x 2 units on the Truss
Plasma Contactor Unit (PCU) is used to disperse the electrical charge that builds up by providing an electrically conductive “ground path” to the plasma environment surrounding the ISS. This prevents the electrical discharges and provides a means of controlling crew shock hazard during EVA. There are two PCUs located on the ISS Zenith 1 Truss, both of which are operated during EVA.
Plasma Contactor Unit (PCU) is used to disperse the electrical charge that builds up by providing an electrically conductive "ground path" to the plasma environment surrounding the ISS. This prevents the electrical discharges and provides a means of controlling crew shock hazard during EVA. There are two PCUs located on the ISS Zenith 1 Truss, both of which are operated during EVA.


<center>
<gallery class="center">
<gallery>
File:TUS-RAb.png|Trailing umbilical system-reel assembly (TUS-RA)
File:TUS-RAb.png|Trailing umbilical system-reel assembly (TUS-RA)
File:TUS-RA.png|TUS-RA drawing
File:TUS-RA.png|TUS-RA drawing
Line 185: Line 171:
File:SPDM Arm artwork.png|SPDM Arm drawing
File:SPDM Arm artwork.png|SPDM Arm drawing
</gallery>
</gallery>
</center>


<center>
<gallery class="center">
<gallery>
Image:HRSR.png|Heat rejection system radiator (HRSR)
Image:HRSR.png|Heat rejection system radiator (HRSR)
File:HRS.png|HRSR drawing
File:HRS.png|HRSR drawing
Line 196: Line 180:
File:SGANT drawing.tif|SGANT drawing
File:SGANT drawing.tif|SGANT drawing
</gallery>
</gallery>
</center>


<center>
<gallery class="center">
<gallery>
File:PCU.png|Plasma contactor unit (PCU)
File:PCU.png|Plasma contactor unit (PCU)
File:PCU drawing.png|PCU drawing
File:PCU drawing.png|PCU drawing
</gallery>
</gallery>
</center>


==See also==
==See also==
⚫
*[[International Space Station]] (ISS)
⚫
*[[Integrated truss structure]] (ITS)
*[[Electrical system of the International Space Station]]
*[[Electrical system of the International Space Station]]
*[[Life support system|Environmental control and life support system]] (ECLSS)
*[[Life support system|Environmental control and life support system]] (ECLSS)
⚫
*[[ExPRESS Logistics Carrier]] (ELCs) [[STS-129]] ELC-1 & 2, [[STS-133]] ELC-3, [[STS-134]] ELC-4
⚫
*[[External stowage platform]] (ESPs) [[STS-102]] ICC & ESP-1, [[STS-114]] ESP-2 & LMC, [[STS-118]] ESP-3
*[[Integrated cargo carrier]]s (ICCs) [[STS-105]] ICC, [[STS-121]] ICC, [[STS-122]] ICC-Lite, [[STS-126]] LMC, [[STS-127]] ICC-VLD, [[STS-128]] LMC, [[STS-131]] LMC, [[STS-132]] ICC-VLD2, [[STS-135]] LMC
*[[Integrated cargo carrier]]s (ICCs) [[STS-105]] ICC, [[STS-121]] ICC, [[STS-122]] ICC-Lite, [[STS-126]] LMC, [[STS-127]] ICC-VLD, [[STS-128]] LMC, [[STS-131]] LMC, [[STS-132]] ICC-VLD2, [[STS-135]] LMC
⚫
*[[Integrated Truss Structure]] (ITS)
⚫
*[[External Stowage Platform]] (ESPs) [[STS-102]] ICC & ESP-1, [[STS-114]] ESP-2 & LMC, [[STS-118]] ESP-3
⚫
*[[Scientific research on the International Space Station]]
⚫
*[[ExPRESS logistics carrier]] (ELCs) [[STS-129]] ELC-1 & 2, [[STS-133]] ELC-3, [[STS-134]] ELC-4
*[[Scientific research on the ISS]]


==References==
==References==

Latest revision as of 03:15, 21 May 2023

This article is about Orbital replacement units of the ISS. For Orbital replacement units of the Hubble Space Telescope, see Orbital replacement unit (HST).

Orbital replacement units (or on-orbit replaceable unit[1]: 21 ) (ORUs) are key elements of the International Space Station that can be readily replaced when the unit either passes its design life or fails. ORUs are parts of the main systems and subsystems of the external elements of the ISS, none are intended to be installed inside the pressurised modules. Examples of ORUs are: pumps, storage tanks, controller boxes, antennas, and battery units. Such units are replaced either by astronauts during EVA or by the Dextre (SPDM) robotic arm. All are stored on the three external stowage platforms (ESPs) or the four ExPRESS Logistics Carriers (ELCs) mounted on the Integrated Truss Structure (ITS).

Location of ESPs and ELCs on the International Space Station.

Introduction

[edit]
ISS Integrated Truss Structure detailing all Orbital Replacement Units in situ

While spare parts/ORUs were routinely brought up and down during the ISS life-time via Space Shuttle resupply missions, there was a heavy emphasis[clarification needed] once the Station was considered complete.

Several Shuttle missions were dedicated to the delivery of ORUs using support carrier structures/pallets of which some remained in the cargo bay, some that were deployed and retrieved and other pallets that were designed to be removed from the payload bay by RMS and placed onto the station.

Deployable pallet flights included STS-102[2] with External Stowage Platform ESP-1, STS-114[3] with ESP-2, STS-118[4] with ESP-2, STS-129[5] with ExPRESS Logistics Carrier ELC-1 and ELC-2, STS-133[6] with ELC-4 and STS-134[7] with ELC-3.

Other modes of ORU delivery included:

Payload bay sidewall mounted ORUs, such as BCDUs, were regularly carried and transported to the ISS via EVAs.

Also, three flights of the Integrated Cargo Carrier (ICC) which remained in the cargo bay on flights STS-102, STS-105 and STS-121; one use of the ICC-Lite on STS-122 (a shortened version of the ICC); two uses of the ICC-Vertical Light Deployable on STS-127 as ICC-VLD and STS-132 as ICC-VLD2, which were deployed and retrieved during the mission; and five uses of the Lightweight MPESS Carrier (LMC) on STS-114, STS-126, STS-128, STS-131 and STS-135, the LMC was not designed to be deployed and remained in the shuttle payload bay throughout the flight.

To date other than the Space Shuttle missions, only one other mode of transportation of ORUs was utilised by the station, the Japanese cargo vessel HTV-2 delivered an FHRC and CTC-4 via its Exposed Pallet (EP),[8] and HTV-4 delivered a Main Bus Switching Unit (MBSU) and a Utility transfer assembly (UTA).[9]

Modes of ORU transport to the ISS

[edit]
  • Main Bus Switching Unit (MBSU) ORU on the payload bay sidewall during STS-120
    Main Bus Switching Unit (MBSU) ORU on the payload bay sidewall during STS-120
  • ESP-2 platform mounted to the Quest module (pallet deployed)
    ESP-2 platform mounted to the Quest module (pallet deployed)
  • ELC-3 in the grasp of Endeavour's robotic arm STS-134 (pallet deployed)
    ELC-3 in the grasp of Endeavour's robotic arm STS-134 (pallet deployed)
  • ICC in the forward end of the payload bay STS-102 (retained in the payload bay throughout the flight)
    ICC in the forward end of the payload bay STS-102 (retained in the payload bay throughout the flight)
  • ICC-Lite payload structure STS-122 (retained in the payload bay throughout the flight)
    ICC-Lite payload structure STS-122 (retained in the payload bay throughout the flight)
  • ICC-VLD on the RMS during STS-127 (pallet deployed and retrieved)
    ICC-VLD on the RMS during STS-127 (pallet deployed and retrieved)
  • LMC at the back of the payload bay STS-131 (retained in the payload bay throughout the flight)
    LMC at the back of the payload bay STS-131 (retained in the payload bay throughout the flight)
  • HTV-2 Exposed Pallet with FHRC and CTC4 during preflight (pallet deployed and retrieved)
    HTV-2 Exposed Pallet with FHRC and CTC4 during preflight (pallet deployed and retrieved)

Types of ORUs

[edit]

Orbital replacement units are parts of the main systems and subsystems of the external elements of the ISS. Affecting the control of the cooling system, the movement and control of the solar arrays and SARJ as well as the flow of power throughout the station from solar arrays to the heat rejection system as part of the External Active Thermal Control System (EATCS). As well as storage tanks for oxygen as part of the station Environmental Control and Life Support System (ECLSS). ORUs can be hardware such as radiators, or simply batteries or communication antennas, essentially any element that can readily be removed and replaced when required.

The replaceable modular nature of the station allows its life to be extended well beyond its initial design life, theoretically.

ORUs and robotic arms

[edit]

ORUs to be handled by Dextre have attachments designed to be gripped with the ORU/Tool Changeout Mechanisms (OTCM) on the end of each arm. The H‐fixture is for massive objects and/or to stabilize Dextre, the most common is a Micro‐fixture (also known as a Micro‐square) and the Micro‐Conical Fitting is used in tight spaces. A Modified Truncated Cone (MTC) Target is used to visually line up Dexter's arm to grab a fixture.[1] Any ORU with a grapple fixture can be moved by the Canadarm2.

Orbital replacement unit (ORU) spares

[edit]

(Weight, description and current location of the spare on the station)

[edit]

Multiple spares

[edit]
  • Flex Hose Rotary Coupler (FHRC) weight approx. 900 lb × 1 unit each on S1 & P1 Truss. The FHRC provides the transfer of liquid ammonia across the Thermal Radiator Rotary Joint (TRRJ) between the P1 (FHRC SN1001) & S1 (FHRC SN1002) truss segments and the Heat Rejection System Radiators (HRSRs).

Three spares – ESP-2 FRAM-7 (keel side) FHRC SN1003,[3] ESP-3 FRAM-2 (top side) FHRC SN1004,[10] ELC-4 FRAM-5 (keel side) FHRC SN0005 delivered by HTV-2.[8]

  • Pump Module (PM) weight 780 lb x 1 unit each on S1 (current PM SN0006) & P1 (original PM SN0001 still in situ) Trusses. The PM is part of the station's complex External Active Thermal Control System (ETCS), which provides vital cooling to internal and external avionics, crew members, and payloads. The station has two independent cooling loops. The external loops use an ammonia-based coolant and the internal loops use water cooling.

Four original spares. Two unused Pump Modules remain – ELC-1 FRAM-7 (keel side) PM SN0007,[5] ESP-2 FRAM-1 (top side) PM SN0005.[5][11] Two utilised – ELC-2 FRAM-6 (keel side) PM SN0004 (Installed on ESP-2 FRAM-1 during STS-121, then removed by the Exp 24 crew to replace the failed original PM SN0002 on the S1 truss. SN0002 was returned to earth by the STS-135 crew. SN0004 replaced by PM SN0006 and moved to MT POA by Exp 38 crew in Dec. 2013. Relocated to ESP-2 FRAM-1 by ISS-41 EVA-27 in Oct. 2014. Swapped positions with SN0005 by SPDM in Mar. 2015.); ESP-3 FRAM-3 (top side) PM SN0006 (Installed on ESP-3 FRAM-3 during STS-127, swapped with failed PM SN0004 from S1 truss by Exp 38 crew Dec. 2013).

  • Ammonia Tank Assembly (ATA) weight 1,702 lb x 1 unit each on S1 (now ATA SN0004) & P1 (now ATA SN0002) trusses. The primary function of the ATA is to store the ammonia used by the external thermal control system (ETCS). The major components in the ATA include two ammonia storage tanks, isolation valves, heaters, and various temperature, pressure, and quantity sensors. There is one ATA per loop located on the zenith side of the Starboard 1 (Loop A) and Port 1 (Loop B) truss segments. The ATA contains two flexible, chambers incorporated into its ammonia tanks that expand as pressurized nitrogen expels liquid ammonia out of them.

Two spares – ELC-1 FRAM-9 (keel side),[5] ELC-3 FRAM-5 (keel side)[7] Also note – other than these two spares, two other Shuttle missions brought up new ATAs and then returned the failed ATAs: STS-128 ATA SN0004 up/SN0002 down (P1 truss original ATA) and STS-131 SN0002 up/SN0003 down (S1 truss original ATA).

  • Nitrogen Tank Assembly (NTA) weight 550 lb each × 1 unit each on S1 (now NTA SN0005) & P1 truss (now NTA SN0004). The NTA provides a high-pressure gaseous nitrogen supply to control the flow of ammonia out of the ATA.

Two spares – ELC-1 FRAM-6 (keel side) NTA SN0002 (refurbished)[5] ELC-2 FRAM-9 (keel side) NTA SN0003 (refurbished)[5] Also note – other than these two spares, two other Shuttle missions replaced NTAs. STS-122 delivered new NTA SN0004 and then returned the depleted P1 Truss NTA SN0003. STS-124 swapped the new NTA SN0005 from ESP-3 FRAM 2 with the depleted NTA SN0002 from the S1 Truss. The STS-126 crew returned this depleted NTA.

  • High-Pressure Gas Tank Assembly (HPGTA) weight 1,240 lb x 5 units on quest. High-pressure oxygen and nitrogen gas tanks on board the ISS provide support for EVA and contingency metabolic support for the crew. This high-pressure O2 and N2 is brought to the ISS by the high-pressure gas tanks (HPGT) and is replenished by the Space Shuttle.

One spare – ELC-3 FRAM-6 (keel side),[7] one depleted tank ELC-2 FRAM-4 (top side)[5] Note the depleted tank was swapped with the original HPGTA launched on ELC-2 at FRAM-4.

  • Cargo Transport Container (CTC) each can weigh between 1,000 and 1,300 lb A container used to transport smaller ORUs such as Remote Power Control Modules in bulk, which may also be used during EVA or by the SPDM. NASA purchased 5 CTCs for such deliveries.

Three units – CTC-3 formerly on ELC-2 FRAM-2 (top side),[5] was later moved to ESP-2 FRAM-3 via SPDM. CTC-2 on ELC-4 FRAM-2 (keel side),[8] CTC-5 on ELC-3 FRAM-1 (top side)[7]

  • Pitch/Roll-Joint (P/R‐J) x 2 units on the SSRMS. A Wrist joint with several degrees of freedom, designed to be replaced on orbit if required.

Two spares – ESP-3 FRAM-1 (top side),[4] ESP-2 FRAM-5 (keel side)[3]

  • Control Moment Gyroscope (CMG) weight 600 lb × 4 units on Z1 Truss (two CMGs have been replaced, one by the STS-114 crew and a second by STS-118 crew). A CMG consists of a single-piece 25-inch diameter, 220-pound stainless steel flywheel that rotates at a constant speed of 6,600 rpm and develops an angular momentum of 3,600 ft-lb-sec (4,880 N-m-s) about its spin axis. The CMGs can also be used to perform attitude maneuvers. The CMGs rely on electrical power provided by the solar powered electrical subsystem.

Two spares – ELC-1 FRAM-5 (top side) CMG SN104,[5] ELC-2 FRAM-5 (top side) CMG SN102[5] Note: STS-118 crew delivered a CMG on ESP-3, swapping it for a failed unit on the ITS-Z1 truss. That failed unit was placed on ESP-2 FRAM-5 until it was returned by STS-122.[12]

  • S-band Antenna Support Assembly (SASA) weight 256 lb each × 2 active units and one other spare on ISS. The SASA consists of the assembly contingency radio frequency group (RFG, or ACRFG), SASA boom and avionics wire harness.

Two spares – ELC-3 FRAM-4 (top side),[7] ELC-3 FRAM-7 (keel side)[7]

  • Direct Current Switching Unit (DCSU) weight 218 lb x 2 units each on the 4 IEAs. The DCSU routes battery power to the MBSU distribution bus to satisfy power demands. In addition to primary power distribution, the DCSU has the additional responsibilities of routing secondary power to components on the PV modules.

Three spares – ESP-1 FRAM-2,[2] ESP-2 FRAM-2 (top side),[3] ELC-2 FRAM-2 (top side)[3]

  • Battery Charge/Discharge Unit (BCDU) weight 235 lb × 6 each on each of the 4 IEAs. The BCDU is a bidirectional power converter that serves a dual function of charging the batteries during solar collection periods (isolation) and providing conditioned battery power to the primary power buses during eclipse periods.

Two spares – ESP-3 FRAM-6 (keel side),[4] ELC-1 FRAM-4 (top side)[5]

  • Main Bus Switching Unit (MBSU) weight 220 lb × 4 units on S0 Truss. The MBSUs act as the distribution hub for the EPS system. The four MBSUs on board the ISS are all located on the starboard zero (S0) truss. Each of MBSU receives primary power from two power channels and distributes it downstream to the DDCUs.

Two spares – ESP-2 FRAM-4 (top side), ESP-2 FRAM-6 (keel side). First spare launched with ESP-2 (FRAM-4) on STS-114, July 2005. Second spare launched on STS-120, October 2007, installed on ESP-2 FRAM-6. First spare swapped for failed 1A/1B MBSU by Expedition 32 crew in August 2012; the failed MBSU was initially stored on ESP-2 FRAM-4, then moved to ELC-2 FRAM-1 in January 2013. Third spare delivered by HTV-4 in August 2013, installed on ESP-2 FRAM-4. 2A/2B MBSU failed and was replaced by Dextre with third spare in May 2017. Failed 2A/2B unit was brought inside via JEM airlock in August 2017, repaired, returned to ESP-2 FRAM-4 in November 2017. 3A/3B MBSU failed in April 2019 and was replaced in May by the repaired former 2A/2B MBSU, with the 3A/3B unit stored on ESP-2 FRAM-4. Former 1A/1B unit brought inside and repaired in August 2019, then swapped into ESP-2 FRAM-4 for the former 3A/3B unit, which was brought inside in September 2019 and returned to Earth on board SpaceX CRS-19.

  • Utility Transfer Assembly (UTA) a processor that allows power, signals and data to flow across the SARJ by roll rings incorporated within.

Two spares – ESP-2 FRAM-8 (keel side)[3] ELC-4 FRAM-4 (keel side) Utility Transfer Assembly (delivered by HTV-4 EP via SPDM Aug. 2013)

  • Pump Flow Control Subassembly (PFCS) weight 235 lb Each external loop contains a pump and flow control system (PFCS) which contains most of the controls and mechanical systems that drive the EATCS. There are 2 pumps per PFCS which circulate ammonia throughout the external coolant loops. There are 2 on each IEA (x4) for a total of 8 active units.

Three original spares, now two available spares – ESP-1 FRAM-1[2] plus 2 on ITS-P6 that were initially used by the Early External Active Thermal Control System (EEATCS). One EEATCS spare on ITS-P6 swapped out for a leaky unit on the 2B power channel during an Exp 35 EVA May 11, 2013. Other EEATCS spare developed electrical fault and was replaced by an additional spare launched on SpaceX CRS-14.

  • Flex hose rotary coupler (FHRC)
    Flex hose rotary coupler (FHRC)
  • FHRC without MLI cover and in situ on the TRRJ
    FHRC without MLI cover and in situ on the TRRJ
  • Pump module (PM)
    Pump module (PM)
  • PM drawing
    PM drawing
  • Ammonia tank assembly (ATA)
    Ammonia tank assembly (ATA)
  • ATA drawing (cover removed)
    ATA drawing (cover removed)
  • Nitrogen tank assembly (NTA)
    Nitrogen tank assembly (NTA)
  • NTA drawing (cover removed)
    NTA drawing (cover removed)
  • HPGT being installed onto the ISS
    HPGT being installed onto the ISS
  • HPGTs on the SL pallet drawing
    HPGTs on the SL pallet drawing
  • Cargo transportation container (CTC-2)
    Cargo transportation container (CTC-2)
  • Inside a CTC box
    Inside a CTC box
  • Pitch/roll joint (P/R J)
    Pitch/roll joint (P/R J)
  • P/R J drawing
    P/R J drawing
  • Control moment gyroscope (CMG)
    Control moment gyroscope (CMG)
  • CMG drawing (cover removed)
    CMG drawing (cover removed)
  • S-Band antenna support assembly (SASA)
    S-Band antenna support assembly (SASA)
  • SASA drawing
    SASA drawing
  • Direct-current switching unit (DCSU)
    Direct-current switching unit (DCSU)
  • DCSU drawing
    DCSU drawing
  • Battery charge/discharge unit (BCDU)
    Battery charge/discharge unit (BCDU)
  • BCDU drawing
    BCDU drawing
  • Main bus switching unit (MBSU)
    Main bus switching unit (MBSU)
  • MBSU drawing
    MBSU drawing
  • Pump flow control subassembly (PFCS)
    Pump flow control subassembly (PFCS)
  • PFCS MLI removed
    PFCS MLI removed
  • Utility transfer assembly (UTA) right-hand corner of this photo
    Utility transfer assembly (UTA) right-hand corner of this photo
  • Utility Transfer Assembly UTA preflight
    Utility Transfer Assembly UTA preflight

Single spares

[edit]
  • Mobile transporter trailing umbilical system-reel assembly (MT TUS-RA) weight 354 lbs. at ELC-2 FRAM-8 (keel side)[5] x 1 unit on MT

The TUS reel assembly (TUS-RA) is basically a large spool much like a garden hose reel that pays out cable when the MT moves away and rolls it back up as the MT returns to the center of the truss. This is the same TUS-RA retrieved during STS-121. It was replaced and this failed unit was returned to earth and refurbished to later fly on ELC-2.

The Heat Rejection Subsystem (HRS) consists of a base, eight panels, torque panel, torque arm, an interconnected fluid system, a scissors-type deployment mechanism and a computer controlled motor/cable deployment system. Part of the station's external active thermal control system (EATCS), the HRS radiator rejects thermal energy via radiation.

  • Linear Drive Unit (LDU) weight 255 lbs. at ESP-3 FRAM-4 (top side)[4] x 1 on the MT

The LDU provides drive and stopping forces for the mobile transporter along the integrated truss structure rail.

  • Space-to-Ground ANTenna (SGANT) weight 194 lbs. at ESP-3 FRAM-5 (keel side) x 2 units on Z1 Truss
  • Plasma Contactor Unit (PCU) weight 350 lbs. at ELC-1 FRAM-2 (top side)[5] x 2 units on the Truss

Plasma Contactor Unit (PCU) is used to disperse the electrical charge that builds up by providing an electrically conductive "ground path" to the plasma environment surrounding the ISS. This prevents the electrical discharges and provides a means of controlling crew shock hazard during EVA. There are two PCUs located on the ISS Zenith 1 Truss, both of which are operated during EVA.

  • Trailing umbilical system-reel assembly (TUS-RA)
    Trailing umbilical system-reel assembly (TUS-RA)
  • TUS-RA drawing
    TUS-RA drawing
  • Latching end effector (LEE)
    Latching end effector (LEE)
  • LEE drawing
    LEE drawing
  • Special-purpose dextrous manipulator (SPDM) arm
    Special-purpose dextrous manipulator (SPDM) arm
  • SPDM Arm drawing
    SPDM Arm drawing
  • Heat rejection system radiator (HRSR)
    Heat rejection system radiator (HRSR)
  • HRSR drawing
    HRSR drawing
  • Linear drive unit (LDU) carried by an astronaut
    Linear drive unit (LDU) carried by an astronaut
  • LDU drawing (cover removed)
    LDU drawing (cover removed)
  • Space-to-ground antenna (SGANT)
    Space-to-ground antenna (SGANT)
  • SGANT drawing
    SGANT drawing
  • Plasma contactor unit (PCU)
    Plasma contactor unit (PCU)
  • PCU drawing
    PCU drawing

See also

[edit]

References

[edit]
  1. ^ a b Robotic Transfer and Interfaces for External ISS Payloads. 2014
  2. ^ a b c "STS-102 Presskit" (PDF).
  3. ^ a b c d e f "EVA Checklist: STS-114 Flight Supplement" (PDF).
  4. ^ a b c d "STS-118 Presskit" (PDF).
  5. ^ a b c d e f g h i j k l m n L. D. Welsch (October 30, 2009). "EVA Checklist: STS-129 Flight Supplement" (PDF). NASA.
  6. ^ a b "Space Shuttle Mission: STS-133" (PDF). NASA. February 2011.
  7. ^ a b c d e f g "Space Shuttle Mission: STS-134" (PDF). NASA. April 2011.
  8. ^ a b c "HTV2: Mission Press Kit" (PDF). Japan Aerospace Exploration Agency. January 20, 2011.
  9. ^ "HTV4 (KOUNOTORI 4) Mission Press Kit" (PDF). Japan Aerospace Exploration Agency. August 2, 2013. Retrieved June 19, 2015.
  10. ^ EVA Checklist STS-126 Flight Supplement, 2008
  11. ^ "ISS Daily Summary Report – 03/06/15". ISS On-Orbit Status Report. Retrieved 30 March 2018.
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