Integrated Truss Structure
Encyclopedia
the Integrated Truss Structure (ITS) forms the backbone of the International Space Station
, with mountings for unpressurized logistics carriers, radiator
s, solar arrays, and other equipment.
plans, a variety of designs for the truss
were used, all of them intended to be shipped up as girder
s where they would be assembled and their equipment installed by astronauts on spacewalks
once it had been launched. After the 1991 redesign, NASA
switched to shorter, prefabricated pieces that were easier to install.
The first truss piece, the Z1 truss, launched aboard STS-92
in October 2000 was used as a temporary mounting position for the P6 truss and solar array until its relocation to the end of the P5 truss during STS-120. Though not a part of the main truss, the Z1 truss was the first permanent lattice-work structure for the ISS, very much like a girder, setting the stage for the future addition of the station's major trusses or backbones. It contains the control moment gyroscope
(CMG) assemblies, electrical wiring, communications equipment, and two plasma contactors designed to neutralize the static electrical charge of the space station. It is unpressurized (with the exception of a small vestibule), but features two Common Berthing Mechanism
docking ports for easy connecting and data communications. One port (nadir) is used to connect the Z1 truss to the zenith port of Unity. The other port (forward) was used to temporarily berth PMA-2
during the placing of the Destiny lab onto the Unity node during STS-98
. In October 2007, the P6 was moved to its permanent position next to P5, and the Z1 truss is now not used for connecting other elements, but solely to house the CMGs, communications equipment and the plasma contactors.
The S0 truss, (also called the Center Integrated Truss Assembly Starboard 0 Truss) forms the center backbone of the Space Station. It was attached on the top of the Destiny Laboratory Module
during STS-110
in April 2002. S0 is used to route power to the pressurized station modules and conduct heat away from the modules to the S1 and P1 Trusses. The S0 truss is not docked to the ISS, but is connected with four Module to Truss Structure (MTS) struts.
and astronauts to worksites along the space station. They each flow 290 kg (637 lb) of anhydrous
ammonia
through three heat rejection radiators. The S1 truss was launched on STS-112
in October 2002 and the P1 truss was launched on STS-113
in November 2002. Detailed design, test and construction of the S1 and P1 structures was conducted by McDonnell Douglas (now Boeing) in Huntington Beach, CA. First parts were cut for the structure in 1996, and delivery of the first truss occurred in 1999.
capability of the Space Station Freedom design was no longer needed at that location. So P2 and S2 were canceled.
The P3/P4 truss assembly was installed by the Space Shuttle
Atlantis
STS-115
mission, launched September 9, 2006, and attached to the P1 segment. The P3 and P4 segments together contain a pair of solar arrays, a radiator and a rotary joint that will aim the solar arrays, and connects P3 to P4. Upon its installation, no power was flowing across the rotary joint, so the electricity generated by the P4 solar array wings was only being used on the P4 segment, and not the rest of the station. Then in December 2006 a major electrical rewiring of the station by STS-116
routed this power to the entire grid. The S3/S4 truss assembly—a mirror-image of P3/P4—was installed on June 11, 2007 also by Space Shuttle
Atlantis
during flight STS-117
, mission 13A and mounted to the S1 truss segment.
Major P3 and S3 subsystems include the Segment-to-Segment Attach System (SSAS), Solar Alpha Rotary Joint (SARJ), and Unpressurized Cargo Carrier Attach System (UCCAS). The primary functions of the P3 truss segment are to provide mechanical, power and data interfaces to payloads attached to the two UCCAS platforms; axial indexing for solar tracking, or rotating of the arrays to follow the sun, via the SARJ; movement and work site accommodations for the Mobile Transporter. The P3/S3 primary structure is made of a hexagonal shaped aluminum structure and includes four bulkheads and six longerons. The S3 truss also supports EXPRESS Logistics Carrier
locations, first to be launched and installed in the 2009 time frame.
Major subsystems of the P4 and S4 Photovoltaic Modules (PVM) include the two Solar Array Wings (SAW), the Photovoltaic Radiator (PVR), the Alpha Joint Interface Structure (AJIS), and Modified Rocketdyne Truss Attachment System (MRTAS), and Beta Gimbal Assembly (BGA).
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The P5 and S5 trusses are connectors which support the P6 and S6 trusses, respectively. The P3/P4 and S3/S4 truss assemblies' length was limited by the cargo bay capacity of the Space Shuttle
, so these small connectors are needed to extend the truss. The P5 truss was installed on December 12, 2006 during the first EVA of mission STS-116
. The S5 truss was brought into orbit by mission STS-118
and installed on August 11, 2007.
, but SAW was folded, one half at a time, to make room for the SAWs on the P4 and S4 trusses, during STS-116
and STS-117
respectively. Shuttle mission STS-120
(assembly mission 10A) detached the P6 truss from Z1, remounted it on the P5 truss, redeployed its radiator panels and attempted to redeploy its SAWs. One SAW (2B) was deployed successfully but the second SAW (4B) developed a significant tear that temporarily stopped deployment at around 80%. This was subsequently fixed and the array is now fully deployed. A later assembly mission (the out of sequence STS-119
) mounted the S6 truss on the S5 truss, which provided a fourth and final set of solar arrays and radiators.
's main source of energy
is from three of the four large U.S.-made photovoltaic arrays currently on the station, sometimes referred to as the Solar Array Wings (SAW). The first pair of arrays are attached to the P6 truss segment, which was launched and installed on top of Z1 in late 2000 during STS-97
. The P6 segment was relocated to its final position, bolted to the P5 truss segment, in November 2007 during STS-120
. The second pair of arrays was launched and installed in September 2006 during STS-115
, but they didn't provide electricity until STS-116
in December 2006 when the station got an electrical rewiring. A third pair of arrays was installed during STS-117
in June 2007. A final pair arrived mid March 2009 on STS-119
. More solar power was to have been available via the Russia
n-built Science Power Platform
, but it was cancelled.
Each of the Solar Array Wings are 34 m (112 ft) long by 12 m (39 ft) wide, and are capable of generating nearly 32.8 kW
of DC
power. They are split into two photovoltaic blankets, with the deployment mast in between. Each blanket has 16,400 silicon
photovoltaic cells, each cell measuring 8 cm x 8 cm, grouped into 82 active panels, each consisting of 200 cells, with 4,100 diode
s.
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Each pair of blankets is folded like an accordion
for compact delivery to space. Once in orbit, the deployment mast between each pair of blankets unfolds the array to its full length. Gimbal
s, known as the Beta Gimbal Assembly (BGA) are used to rotate
the arrays so that they face the Sun to provide maximum power to the International Space Station.
). One Solar Alpha Rotary Joint (SARJ) is located between the P3 and P4 truss segments and the other is located between the S3 and S4 truss segments. When in operation, these joints continuously rotate to keep the solar array wings on the outboard truss segments oriented towards the Sun. Each SARJ is 10 feet in diameter, weighs approximately 2,500 pounds and can be rotated continuously using bearing assemblies and a servo control system. On both the port and starboard sides, all of the power flows through the Utility Transfer Assembly (UTA) in the SARJ. Roll ring assemblies allow transmission of data and power across the rotating interface so it never has to unwind. The SARJ was designed, built and tested by Lockheed Martin
and its subcontractors.
In 2007, a problem was detected in the starboard SARJ. Damage had occurred due to excessive and premature wear of a track in the joint mechanism. The SARJ was frozen during problem diagnosis, and in 2008 lubrication was applied to the track to address the issue.
The power storage system consists of a battery charge/discharge unit (BCDU) and two nickel–hydrogen battery assemblies.
The BCDU serves a dual function of charging the batteries during solar collection periods, and providing conditioned battery power to the primary power busses (via the DCSU) during eclipse periods. The BCDU has a battery charging capability of 8.4 kW and a discharge capability of 6.6 kW. The BCDU also includes provisions for battery status monitoring and protection from power circuit faults. Commanding of the BCDU is from the IEA computer.
Each battery assembly consist of 38 lightweight Nickel Hydrogen cells and associated electrical and mechanical equipment. Each battery assembly has a nameplate capacity of 81 A·hr
and 4 kW·hr
. This power is fed to the ISS via the BCDU and DCSU respectively. The batteries have a design life of 6.5 years and can exceed 38,000 charge/discharge cycles at 35% depth of discharge. Each battery measures 40” by 36” by 18” and weighs 375 pounds.
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
, with mountings for unpressurized logistics carriers, radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...
s, solar arrays, and other equipment.
History
In the initial Space Station FreedomSpace Station Freedom
Space Station Freedom was a NASA project to construct a permanently manned Earth-orbiting space station in the 1980s. Although approved by then-president Ronald Reagan and announced in the 1984 State of the Union Address, Freedom was never constructed or completed as originally designed, and after...
plans, a variety of designs for the truss
Truss
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
were used, all of them intended to be shipped up as girder
Girder
A girder is a support beam used in construction. Girders often have an I-beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams...
s where they would be assembled and their equipment installed by astronauts on spacewalks
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...
once it had been launched. After the 1991 redesign, NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
switched to shorter, prefabricated pieces that were easier to install.
Z1 truss
STS-92
STS-92 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Discovery. STS-92 marked the 100th mission of the Space Shuttle...
in October 2000 was used as a temporary mounting position for the P6 truss and solar array until its relocation to the end of the P5 truss during STS-120. Though not a part of the main truss, the Z1 truss was the first permanent lattice-work structure for the ISS, very much like a girder, setting the stage for the future addition of the station's major trusses or backbones. It contains the control moment gyroscope
Control moment gyroscope
A control momentum gyroscope is an attitude control device generally used in spacecraft attitude control systems. A CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor’s angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic...
(CMG) assemblies, electrical wiring, communications equipment, and two plasma contactors designed to neutralize the static electrical charge of the space station. It is unpressurized (with the exception of a small vestibule), but features two Common Berthing Mechanism
Common Berthing Mechanism
The common berthing mechanism is a berthing mechanism used to connect all non-Russian pressurized modules of the International Space Station....
docking ports for easy connecting and data communications. One port (nadir) is used to connect the Z1 truss to the zenith port of Unity. The other port (forward) was used to temporarily berth PMA-2
Pressurized Mating Adapter
The International Space Station uses three Pressurized Mating Adapters to interconnect spacecraft and modules with different docking mechanisms. The first two PMAs were launched with the Unity module in 1998 aboard STS-88...
during the placing of the Destiny lab onto the Unity node during STS-98
STS-98
STS-98 was a 2001 Space Shuttle mission to the International Space Station flown by Space Shuttle Atlantis. STS-98 delivered to the station the Destiny Laboratory Module...
. In October 2007, the P6 was moved to its permanent position next to P5, and the Z1 truss is now not used for connecting other elements, but solely to house the CMGs, communications equipment and the plasma contactors.
S0 truss
Destiny Laboratory Module
The Destiny module is the primary operating facility for U.S. research payloads aboard the International Space Station . It was berthed to the Unity module and activated over a period of five days in February, 2001...
during STS-110
STS-110
STS-110 was a Space Shuttle mission to the International Space Station on 8–19 April 2002 flown by Space Shuttle Atlantis. The main purpose was to install the S0 Truss segment, which forms the backbone of the truss structure on the station.- Crew :...
in April 2002. S0 is used to route power to the pressurized station modules and conduct heat away from the modules to the S1 and P1 Trusses. The S0 truss is not docked to the ISS, but is connected with four Module to Truss Structure (MTS) struts.
P1, S1 trusses
The P1 and S1 trusses (also called the Port and Starboard Side Thermal Radiator Trusses) are attached to the S0 truss, and contain carts to transport the Canadarm2Mobile Servicing System
The Mobile Servicing System , better known by its primary component Canadarm2, is a robotic system and associated equipment on the International Space Station...
and astronauts to worksites along the space station. They each flow 290 kg (637 lb) of anhydrous
Anhydrous
As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
through three heat rejection radiators. The S1 truss was launched on STS-112
STS-112
STS-112 was an 11-day space shuttle mission to the International Space Station flown by . Space Shuttle Atlantis was launched on 7 October 2002 at 19:45 UTC from the Kennedy Space Center's launch pad 39B to deliver the 28,000 pound Starboard 1 truss segment to the Space Station...
in October 2002 and the P1 truss was launched on STS-113
STS-113
STS-113 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Endeavour. During the 14-day mission in late 2002, Endeavour and its crew extended the ISS backbone with the P1 truss and exchanged the Expedition 5 and Expedition 6 crews aboard the station...
in November 2002. Detailed design, test and construction of the S1 and P1 structures was conducted by McDonnell Douglas (now Boeing) in Huntington Beach, CA. First parts were cut for the structure in 1996, and delivery of the first truss occurred in 1999.
P2, S2 trusses
The P2 and S2 trusses were planned as locations for rocket thrusters in the original design for Space Station Freedom. Since the Russian parts of the ISS also provided that capability, the reboostReboost
Reboost is the process of boosting the altitude of an artificial satellite, to increase the time until its orbit will decay and it re-enters the atmosphere...
capability of the Space Station Freedom design was no longer needed at that location. So P2 and S2 were canceled.
P3/P4, S3/S4 truss assemblies
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
Atlantis
Space Shuttle Atlantis
The Space Shuttle Atlantis is a retired Space Shuttle orbiter in the Space Shuttle fleet belonging to the National Aeronautics and Space Administration , the spaceflight and space exploration agency of the United States...
STS-115
STS-115
Note:The P3/P4 Truss segment and batteries were so heavy that the crew count was reduced from seven to six.-Crew notes:...
mission, launched September 9, 2006, and attached to the P1 segment. The P3 and P4 segments together contain a pair of solar arrays, a radiator and a rotary joint that will aim the solar arrays, and connects P3 to P4. Upon its installation, no power was flowing across the rotary joint, so the electricity generated by the P4 solar array wings was only being used on the P4 segment, and not the rest of the station. Then in December 2006 a major electrical rewiring of the station by STS-116
STS-116
-Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss....
routed this power to the entire grid. The S3/S4 truss assembly—a mirror-image of P3/P4—was installed on June 11, 2007 also by Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
Atlantis
Space Shuttle Atlantis
The Space Shuttle Atlantis is a retired Space Shuttle orbiter in the Space Shuttle fleet belonging to the National Aeronautics and Space Administration , the spaceflight and space exploration agency of the United States...
during flight STS-117
STS-117
- Crew Notes :The initial crew manifest before the Columbia accident was:Astronaut Mark Polansky was originally slated to pilot this mission, but was moved to STS-116, which he commanded...
, mission 13A and mounted to the S1 truss segment.
Major P3 and S3 subsystems include the Segment-to-Segment Attach System (SSAS), Solar Alpha Rotary Joint (SARJ), and Unpressurized Cargo Carrier Attach System (UCCAS). The primary functions of the P3 truss segment are to provide mechanical, power and data interfaces to payloads attached to the two UCCAS platforms; axial indexing for solar tracking, or rotating of the arrays to follow the sun, via the SARJ; movement and work site accommodations for the Mobile Transporter. The P3/S3 primary structure is made of a hexagonal shaped aluminum structure and includes four bulkheads and six longerons. The S3 truss also supports EXPRESS Logistics Carrier
EXPRESS Logistics Carrier
An ExPRESS logistics carrier is an unpressurized attached payload platform for the International Space Station that provides mechanical mounting surfaces, electrical power, and command and data handling services for Orbital Replacement Units as well as science experiments on the ISS...
locations, first to be launched and installed in the 2009 time frame.
Major subsystems of the P4 and S4 Photovoltaic Modules (PVM) include the two Solar Array Wings (SAW), the Photovoltaic Radiator (PVR), the Alpha Joint Interface Structure (AJIS), and Modified Rocketdyne Truss Attachment System (MRTAS), and Beta Gimbal Assembly (BGA).
P5, S5 trusses
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
, so these small connectors are needed to extend the truss. The P5 truss was installed on December 12, 2006 during the first EVA of mission STS-116
STS-116
-Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss....
. The S5 truss was brought into orbit by mission STS-118
STS-118
- Crew notes :Astronaut Clayton Anderson originally was slated to be launched to the ISS on this mission, but was moved to STS-117. His replacement was Alvin Drew....
and installed on August 11, 2007.
P6, S6 trusses
The P6 truss was the second truss segment to be added, because it contains a large Solar Array Wing (SAW) that generated essential electricity for the station, prior to activation of the SAW on the P4 truss. It was originally mounted to the Z1 truss and had its SAW extended during STS-97STS-97
STS-97 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Endeavour. The crew installed the first set of solar arrays to the ISS, prepared a docking port for arrival of the Destiny Laboratory Module, and delivered supplies for the station's crew.-Crew:-Mission...
, but SAW was folded, one half at a time, to make room for the SAWs on the P4 and S4 trusses, during STS-116
STS-116
-Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss....
and STS-117
STS-117
- Crew Notes :The initial crew manifest before the Columbia accident was:Astronaut Mark Polansky was originally slated to pilot this mission, but was moved to STS-116, which he commanded...
respectively. Shuttle mission STS-120
STS-120
-Crew notes:As commander of STS-120, Pamela Melroy became the second woman to command a space shuttle mission. Additionally, the Expedition 16 crew that received STS-120 was commanded by Peggy Whitson, the first female ISS commander...
(assembly mission 10A) detached the P6 truss from Z1, remounted it on the P5 truss, redeployed its radiator panels and attempted to redeploy its SAWs. One SAW (2B) was deployed successfully but the second SAW (4B) developed a significant tear that temporarily stopped deployment at around 80%. This was subsequently fixed and the array is now fully deployed. A later assembly mission (the out of sequence STS-119
STS-119
-Crew notes:This mission was originally scheduled to bring the Expedition 9 crew to the ISS. This crew would have consisted of:-Mission parameters:* Mass:* Orbiter liftoff: * Orbiter landing: * Perigee: * Apogee:...
) mounted the S6 truss on the S5 truss, which provided a fourth and final set of solar arrays and radiators.
Solar arrays
The International Space StationInternational Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
's main source of energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
is from three of the four large U.S.-made photovoltaic arrays currently on the station, sometimes referred to as the Solar Array Wings (SAW). The first pair of arrays are attached to the P6 truss segment, which was launched and installed on top of Z1 in late 2000 during STS-97
STS-97
STS-97 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Endeavour. The crew installed the first set of solar arrays to the ISS, prepared a docking port for arrival of the Destiny Laboratory Module, and delivered supplies for the station's crew.-Crew:-Mission...
. The P6 segment was relocated to its final position, bolted to the P5 truss segment, in November 2007 during STS-120
STS-120
-Crew notes:As commander of STS-120, Pamela Melroy became the second woman to command a space shuttle mission. Additionally, the Expedition 16 crew that received STS-120 was commanded by Peggy Whitson, the first female ISS commander...
. The second pair of arrays was launched and installed in September 2006 during STS-115
STS-115
Note:The P3/P4 Truss segment and batteries were so heavy that the crew count was reduced from seven to six.-Crew notes:...
, but they didn't provide electricity until STS-116
STS-116
-Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss....
in December 2006 when the station got an electrical rewiring. A third pair of arrays was installed during STS-117
STS-117
- Crew Notes :The initial crew manifest before the Columbia accident was:Astronaut Mark Polansky was originally slated to pilot this mission, but was moved to STS-116, which he commanded...
in June 2007. A final pair arrived mid March 2009 on STS-119
STS-119
-Crew notes:This mission was originally scheduled to bring the Expedition 9 crew to the ISS. This crew would have consisted of:-Mission parameters:* Mass:* Orbiter liftoff: * Orbiter landing: * Perigee: * Apogee:...
. More solar power was to have been available via the Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n-built Science Power Platform
Science Power Platform
The Science Power Platform was a planned Russian element of the International Space Station that was intended to be delivered to the ISS by a Russian Proton rocket or Zenit rocket but was shifted to launch by Space Shuttle as part as a tradeoff agreement on other parts of the ISS...
, but it was cancelled.
Each of the Solar Array Wings are 34 m (112 ft) long by 12 m (39 ft) wide, and are capable of generating nearly 32.8 kW
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
of DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
power. They are split into two photovoltaic blankets, with the deployment mast in between. Each blanket has 16,400 silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
photovoltaic cells, each cell measuring 8 cm x 8 cm, grouped into 82 active panels, each consisting of 200 cells, with 4,100 diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
s.
Accordion
The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist....
for compact delivery to space. Once in orbit, the deployment mast between each pair of blankets unfolds the array to its full length. Gimbal
Gimbal
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support...
s, known as the Beta Gimbal Assembly (BGA) are used to rotate
Night Glider mode
Night Glider mode is one of the procedures for orienting the solar arrays on the International Space Station.Normally the photovoltaic solar arrays of the space station track the sun...
the arrays so that they face the Sun to provide maximum power to the International Space Station.
Solar alpha rotary joint
The Alpha joint is the main rotary joint allowing the solar arrays to track the sun; in nominal operation the alpha joint rotates by 360° each orbit (however, see also Night Glider modeNight Glider mode
Night Glider mode is one of the procedures for orienting the solar arrays on the International Space Station.Normally the photovoltaic solar arrays of the space station track the sun...
). One Solar Alpha Rotary Joint (SARJ) is located between the P3 and P4 truss segments and the other is located between the S3 and S4 truss segments. When in operation, these joints continuously rotate to keep the solar array wings on the outboard truss segments oriented towards the Sun. Each SARJ is 10 feet in diameter, weighs approximately 2,500 pounds and can be rotated continuously using bearing assemblies and a servo control system. On both the port and starboard sides, all of the power flows through the Utility Transfer Assembly (UTA) in the SARJ. Roll ring assemblies allow transmission of data and power across the rotating interface so it never has to unwind. The SARJ was designed, built and tested by Lockheed Martin
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....
and its subcontractors.
In 2007, a problem was detected in the starboard SARJ. Damage had occurred due to excessive and premature wear of a track in the joint mechanism. The SARJ was frozen during problem diagnosis, and in 2008 lubrication was applied to the track to address the issue.
Power conditioning and storage
The sequential shunt unit (SSU) is designed to coarsely regulate the solar power collected during periods of insolation – when the arrays collect power during sun-pointing periods. A sequence of 82 separate strings, or power lines, leads from the solar array to the SSU. Shunting, or controlling, the output of each string regulates the amount of power transferred. The regulated voltage setpoint is controlled by a computer located on the IEA and is normally set to around 140 volts. The SSU has an overvoltage protection feature to maintain the output voltage below 200 V DC maximum for all operating conditions. This power is then passed through the BMRRM to the DCSU located in the IEA. The SSU measures 32” by 20” by 12” and weighs 185 pounds.The power storage system consists of a battery charge/discharge unit (BCDU) and two nickel–hydrogen battery assemblies.
The BCDU serves a dual function of charging the batteries during solar collection periods, and providing conditioned battery power to the primary power busses (via the DCSU) during eclipse periods. The BCDU has a battery charging capability of 8.4 kW and a discharge capability of 6.6 kW. The BCDU also includes provisions for battery status monitoring and protection from power circuit faults. Commanding of the BCDU is from the IEA computer.
Each battery assembly consist of 38 lightweight Nickel Hydrogen cells and associated electrical and mechanical equipment. Each battery assembly has a nameplate capacity of 81 A·hr
Ampere-hour
An ampere-hour or amp-hour is a unit of electric charge, with sub-units milliampere-hour and milliampere second...
and 4 kW·hr
Watt-hour
The kilowatt hour, or kilowatt-hour, is a unit of energy equal to 1000 watt hours or 3.6 megajoules.For constant power, energy in watt hours is the product of power in watts and time in hours...
. This power is fed to the ISS via the BCDU and DCSU respectively. The batteries have a design life of 6.5 years and can exceed 38,000 charge/discharge cycles at 35% depth of discharge. Each battery measures 40” by 36” by 18” and weighs 375 pounds.
Truss and solar array assembly sequence
- All truss segments are in orbit (S2 and P2 were cancelled).
| Element | Flight | Launch date | Length (m) |
Diameter (m) |
Mass (kg) |
|---|---|---|---|---|---|
| Z1 truss | 3A – STS-92 STS-92 STS-92 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Discovery. STS-92 marked the 100th mission of the Space Shuttle... |
October 11, 2000 | 4.9 | 4.2 | 8,755 |
| P6 truss – solar array | 4A – STS-97 STS-97 STS-97 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Endeavour. The crew installed the first set of solar arrays to the ISS, prepared a docking port for arrival of the Destiny Laboratory Module, and delivered supplies for the station's crew.-Crew:-Mission... |
November 30, 2000 | 73.2 | 10.7 | 15,824 |
| S0 truss | 8A – STS-110 STS-110 STS-110 was a Space Shuttle mission to the International Space Station on 8–19 April 2002 flown by Space Shuttle Atlantis. The main purpose was to install the S0 Truss segment, which forms the backbone of the truss structure on the station.- Crew :... |
April 8, 2002 | 13.4 | 4.6 | 13,971 |
| S1 truss | 9A – STS-112 STS-112 STS-112 was an 11-day space shuttle mission to the International Space Station flown by . Space Shuttle Atlantis was launched on 7 October 2002 at 19:45 UTC from the Kennedy Space Center's launch pad 39B to deliver the 28,000 pound Starboard 1 truss segment to the Space Station... |
October 7, 2002 | 13.7 | 4.6 | 14,124 |
| P1 truss | 11A – STS-113 STS-113 STS-113 was a Space Shuttle mission to the International Space Station flown by Space Shuttle Endeavour. During the 14-day mission in late 2002, Endeavour and its crew extended the ISS backbone with the P1 truss and exchanged the Expedition 5 and Expedition 6 crews aboard the station... |
November 23, 2002 | 13.7 | 4.6 | 14,003 |
| P3/P4 truss – solar array | 12A – STS-115 STS-115 Note:The P3/P4 Truss segment and batteries were so heavy that the crew count was reduced from seven to six.-Crew notes:... |
September 9, 2006 | 13.8 | 4.8 | 15,824 |
| P5 truss - spacer | 12A.1 – STS-116 STS-116 -Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss.... |
December 9, 2006 | 3.37 | 4.55 | 1,864 |
| S3/S4 truss – solar array | 13A – STS-117 STS-117 - Crew Notes :The initial crew manifest before the Columbia accident was:Astronaut Mark Polansky was originally slated to pilot this mission, but was moved to STS-116, which he commanded... |
June 8, 2007 | 73.2 | 10.7 | 15,824 |
| S5 truss - spacer | 13A.1 – STS-118 STS-118 - Crew notes :Astronaut Clayton Anderson originally was slated to be launched to the ISS on this mission, but was moved to STS-117. His replacement was Alvin Drew.... |
August 8, 2007 | 3.37 | 4.55 | 1,818 |
| P6 truss – solar array (relocation) | 10A – STS-120 STS-120 -Crew notes:As commander of STS-120, Pamela Melroy became the second woman to command a space shuttle mission. Additionally, the Expedition 16 crew that received STS-120 was commanded by Peggy Whitson, the first female ISS commander... |
October 23, 2007 | 73.2 | 10.7 | 15,824 |
| S6 truss – solar array | 15A – STS-119 STS-119 -Crew notes:This mission was originally scheduled to bring the Expedition 9 crew to the ISS. This crew would have consisted of:-Mission parameters:* Mass:* Orbiter liftoff: * Orbiter landing: * Perigee: * Apogee:... |
March 15, 2009 | 73.2 | 10.7 | 15,824 |
See also
- Science Power PlatformScience Power PlatformThe Science Power Platform was a planned Russian element of the International Space Station that was intended to be delivered to the ISS by a Russian Proton rocket or Zenit rocket but was shifted to launch by Space Shuttle as part as a tradeoff agreement on other parts of the ISS...
— the canceled truss structure of the Russian Orbital SegmentRussian Orbital SegmentThe Russian Orbital Segment is the name given to the components of the International Space Station constructed in Russia and operated by the Russian Federal Space Agency... - ISS assembly sequence
- List of manned spaceflights to the ISS
External links
- http://spaceflight.nasa.gov/station/assembly/elements/its/its_structure.htmlNASA FlashAdobe FlashAdobe Flash is a multimedia platform used to add animation, video, and interactivity to web pages. Flash is frequently used for advertisements, games and flash animations for broadcast...
ITS Interactive]