International Space Station

The International Space Station on 7 March 2011 as seen from the departing Space Shuttle Discovery during STS-133.
ISS Insignia
Station statistics
COSPAR ID	1998-067A
Call sign	Alpha
Crew	6 Expedition 27
Launch	1998–2012
Launch pad	LC-81/23, Baikonur LC-1/5 KSC LC-39,
Mass	417,289 kg (919,960 lb)
Length	51 m (167.3 ft) from PMA-2 to Zvezda
Width	109 m (357.5 ft) along truss, arrays extended
Height	c. 20 m (c. 66 ft) nadir–zenith, arrays forward–aft (27 November 2009)[dated info]
Pressurised volume	837 m3 (29,600 cu ft) (21 March 2011)
Atmospheric pressure	101.3 kPa (29.91 inHg, 1 atm)
Perigee	352 km (190 nmi) AMSL (21 March 2011)
Apogee	355 km (192 nmi) AMSL (21 March 2011)
Orbital inclination	51.6 degrees
Average speed	7,706.6 m/s (27,743.8 km/h, 17,239.2 mph)
Orbital period	91 minutes
Days in orbit	4548 (4 May)
Days occupied	3835 (4 May)
Number of orbits	71388 (4 May)
Orbital decay	2 km/month
Statistics as of 9 March 2011 (unless noted otherwise)
References: [1][2][3][4][5][6]
Configuration
Station elements as of March 2011[update] (exploded view)

The International Space Station (ISS) is an internationally developed research facility that is being assembled in low Earth orbit. The objective of the ISS, as defined by NASA, is to develop and test technologies for exploration spacecraft systems, develop techniques to maintain crew health and performance on missions beyond low Earth orbit, and gain operational experience that can be applied to exploration missions.^[7] The objective of the ISS, for the RKA, another significant partner of the ISS project, is a continuation of the "permanent Soviet human presence in low-Earth orbit".^[7]

On-orbit construction of the station began in 1998 and is scheduled for completion by mid-2012. The station is expected to remain in operation until at least 2015, and likely 2020.^[8][9] With a greater cross-sectional area than that of any previous space station, the ISS can be seen from Earth with the naked eye.^[10] The ISS is by far the largest artificial satellite that has ever orbited Earth.^[11] The ISS serves as a research laboratory that has a microgravity environment in which crews conduct experiments in biology, chemistry, medicine, physiology and physics, as well as astronomical and meteorological observations.^[12][13][14] The station provides a unique environment for the testing of the spacecraft systems that will be required for missions to the Moon and Mars.^[15] The ISS is operated by Expedition crews of six astronauts and cosmonauts, with the station programme maintaining an uninterrupted human presence in space since the launch of Expedition 1 on 31 October 2000, a total of &000000000000001000000010 years and &0000000000000185000000185 days. The programme thus holds the current record for the longest uninterrupted human presence in space, surpassing the previous record of 3,644 days, set aboard Mir.^[16] As of 16 March 2011 (2011 -03-16)^[update], the crew of Expedition 27 is aboard.^[17]

The ISS is a synthesis of several space station projects that include the American Freedom, the Soviet/Russian Mir-2, the European Columbus and the Japanese Kibō.^[18][19] Budget constraints led to the merger of these projects into a single multi-national programme.^[18] The ISS project began in 1994 with the Shuttle-Mir programme,^[20] and the first module of the station, Zarya, was launched in 1998 by Russia.^[18] Assembly continues, as pressurised modules, external trusses, and other components are launched by American space shuttles and Russian Proton and Soyuz rockets.^[19] As of March 2011^[update], the station consists of fifteen pressurised modules and an extensive integrated truss structure (ITS). Power is provided by sixteen solar arrays mounted on the external truss, in addition to four smaller arrays on the Russian modules.^[21] The station is maintained at an orbit between 278 km (173 mi) and 460 km (286 mi) altitude, and travels at an average speed of 27,743.8 km/h (17,239.2 mph), completing 15.7 orbits per day.^[22]

The stations sections are operated by their builders, the American National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), the Russian Federal Space Agency (RKA), the Japan Aerospace Exploration Agency (JAXA) and the Canadian Space Agency (CSA).^[23][24] The ownership and use of the space station is established in intergovernmental treaties and agreements^[25] that allow the Russian Federation to retain full ownership of its own modules in the Russian Orbital Segment,^[26] with the US Orbital Segment, the remainder of the station, allocated between the other international partners.^[25] The cost of the station has been estimated by ESA as €100 billion over 30 years;^[27] estimates range from 35 to 160 billion US dollars.^[28] The financing, research capabilities and technical design of the ISS programme have been criticised because of the high cost.^[29][30] The station is serviced by Soyuz spacecraft, Progress spacecraft, space shuttles, the Automated Transfer Vehicle and the H-II Transfer Vehicle,^[24] and has been visited by astronauts and cosmonauts from 15 different nations.^[11]

Contents 1 Purpose 1.1 Scientific research 2 Origins 3 Station structure 3.1 Assembly 3.2 Pressurised modules 3.2.1 Scheduled to be launched 3.2.2 Cancelled modules 3.3 Unpressurised elements 3.4 Power supply 3.5 Orbit control 3.6 Communications 3.7 Microgravity 3.8 Life support 3.9 Sightings 4 Politics, utilisation and financing 4.1 Legal aspects 4.2 Challenges Resulting from the Iran Nonproliferation Act of 2000 4.3 Utilisation rights 4.4 Costs 4.5 Criticism 4.6 End of mission and deorbit plans 5 Life on board 5.1 Crew schedule 5.2 Sleeping in space 5.3 Hygiene 5.4 Food and drink 5.5 Exercise 6 Station operations 6.1 Expeditions 6.2 Visiting spacecraft 6.2.1 Docking 6.2.2 Currently docked 6.2.3 Scheduled to be docked in 2011 6.3 Mission control centres 6.4 Safety aspects 6.4.1 Anomalies 6.4.1.1 Cooling loop A failure 6.4.2 Orbital debris 6.4.3 Radiation 7 See also 8 References 9 External links

[edit] Purpose

According to the original Memorandum of Understanding between NASA and RSA, the International Space Station is intended to be:^[26]

• a laboratory in space
• a permanent observatory
• a transportation node
• a servicing depot
• a factory
• a staging base for possible future missions

• a human mission to Mars
• a human mission to survey the asteroids
• a permanent Lunar base
• Robotic planetary probes

Primarily a research laboratory, the ISS offers an advantage over spacecraft such as NASA's Space Shuttle because it is a long-term platform in the space environment, where extended studies are conducted.^[11][31] The presence of a permanent crew affords the ability to monitor, replenish, repair, and replace experiments and components of the spacecraft itself. Scientists on Earth have swift access to the crew's data and can modify experiments or launch new ones, benefits generally unavailable on unmanned spacecraft.^[31]

Crews, who fly expeditions of several months duration, conduct scientific experiments each day (approximately 160 man-hours a week).^[12][32] As of the conclusion of Expedition 15, 138 major science investigations had been conducted on the ISS.^[33] Scientific findings, in fields from basic science to exploration research, are published every month.^[15]

The ISS provides a location in the relative safety of Low Earth Orbit to test spacecraft systems that will be required for long-duration missions to the Moon and Mars. This provides experience in the maintenance, repair, and replacement of systems on-orbit, which will be essential in operating spacecraft further from Earth. Mission risks are reduced, and the capabilities of interplanetary spacecraft are advanced.^[15]

Part of the crew's mission is educational outreach and international cooperation. The crew of the ISS provide opportunities for students on Earth by running student-developed experiments, making educational demonstrations, and allowing for student participation in classroom versions of ISS experiments, NASA investigator experiments, and ISS engineering activities. The ISS programme itself, with the international cooperation that it represents, allows more than 20 nations to live and work together in space, providing lessons for future multi-national missions.^[24][34]

[edit] Scientific research

The ISS provides a platform to conduct experiments that require one or more of the unusual conditions present on the station. The primary fields of research include human research, space medicine, life sciences, physical sciences, astronomy and meteorology.^{[12][13][14][35][36]} The 2005 NASA Authorization Act designated the American segment of the International Space Station as a national laboratory with the goal of increasing the use of the ISS by other federal agencies and the private sector.^[37] Research on the ISS improves knowledge about the effects of long-term space exposure on the human body. Subjects currently under study include muscle atrophy, bone loss, and fluid shift. The data will be used to determine whether space colonization and lengthy human spaceflight are feasible. As of 2006, data on bone loss and muscular atrophy suggest that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise (such as the six-month journey time required to fly to Mars).^[38][39] Large scale medical studies are conducted aboard the ISS via the National Space and Biomedical Research Institute (NSBRI). Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity study in which astronauts (including former ISS Commanders Leroy Chiao and Gennady Padalka) perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician onboard the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.^[40][41][42]

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate microgravity's effects on the growth of three-dimensional, human-like tissues, and the unusual protein crystals that can be formed in space.^[13]

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of superconductivity.^[13]

The study of materials science is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground.^[43] Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve our knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine aerosols, ozone, water vapour, and oxides in Earth's atmosphere, as well as cosmic rays, cosmic dust, antimatter, and dark matter in the universe.^[13]

[edit] Origins

The International Space Station represents a union of several national space station projects that originated during the Cold War. In the early 1980s, NASA planned to launch a modular space station called Freedom as a counterpart to the Soviet Salyut and Mir space stations, while the Soviets were planning to construct Mir-2 in the 1990s as a replacement for Mir.^[18] Because of budget and design constraints, Freedom never progressed past mock-ups and minor component tests.

With the fall of the Soviet Union and the end of the Space Race, Freedom was nearly cancelled by the United States House of Representatives. The post-Soviet economic chaos in Russia led to the cancellation of Mir-2, though only after its base block, DOS-8, had been constructed.^[18] Similar budgetary difficulties were faced by other nations with space station projects, which prompted the American government to negotiate with European states, Russia, Japan, and Canada in the early 1990s to begin a collaborative project.^[18]

In June 1992 American president George H. W. Bush and Russian president Boris Yeltsin agreed to cooperate on space exploration. The resulting Agreement between the United States of America and the Russian Federation Concerning Cooperation in the Exploration and Use of Outer Space for Peaceful Purposes called for a short, joint space programme, with one American astronaut deployed to the Russian space station Mir and two Russian cosmonauts deployed to a Space Shuttle.^[18]

In September 1993, American Vice-President Al Gore, Jr., and Russian Prime Minister Viktor Chernomyrdin announced plans for a new space station, which eventually became the International Space Station.^[44] They also agreed, in preparation for this new project, that the United States would be heavily involved in the Mir programme as part of an agreement that later included Space Shuttle orbiters docking with Mir.^[20]

According to the plan, the International Space Station programme would combine the proposed space stations of all participant agencies: NASA's Freedom, the RSA's Mir-2 (with DOS-8 later becoming Zvezda), ESA's Columbus, and the Japanese Kibō laboratory. When the first module, Zarya, was launched in 1998, the station was expected to be completed by 2003. Delays have led to a revised estimated completion date of 2011.^[45]

The Russian Orbital Segment is the eleventh Soviet-Russian space station. Mir and the ISS are successors to the Salyut and Almaz stations. Salyut 6 included Soviet crews and cosmonauts from Czechoslovakia, Hungary, Bulgaria,Poland, Romania, Cuba, Mongolia, Vietnam, and East Germany. Salyut 7 included crew from India and France during its almost 9-year lifespan. Mir was visited by crews from a dozen nations during the station's 15-year lifespan, and ISS expands on this international co-operation with crew from more than 14 nations.^[18]

[edit] Station structure

[edit] Assembly

The assembly of the International Space Station, a major endeavour in space architecture, began in November 1998.^[2] Russian modules launch and dock robotically, with the exception of Rassvet. All other modules were delivered by space shuttle, and required installation by ISS and shuttle crewmembers using the SSRMS and EVAs; as of 9 March 2011 (2011 -03-09)^[update], they had completed 155, totalling approximately 973 hours of EVA activity. 127 of these spacewalks originated from the station, the remaining 28 were launched from the airlocks of docked space shuttles.^[1]

The first segment of the ISS, Zarya, was launched on 20 November 1998 on an autonomous Russian Proton rocket. It provided propulsion, orientation control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module Unity was launched aboard Space Shuttle flight STS-88 and attached to Zarya by astronauts using EVA's. This module has two (PMAs) one connects permanently to Zarya, the other allowed the space shuttle to dock to the space station. At this time, the Russian station MIR was still inhabited. The ISS remained unmanned for two years, during which time MIR was de-orbited. On July 12, 2000 Zvezda was launched into orbit. Preprogrammed commands onboard deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the already-orbiting Zarya and Unity. As the passive “target” vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya/Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, a kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.^[46][47]

The first resident crew, Expedition 1, arrived in November 2000 on Soyuz TM-31, midway between the flights of STS-92 and STS-97. These two Space Shuttle flights each added segments of the station's Integrated Truss Structure, which provided the station with Ku-band communication for U.S. television, additional attitude support needed for the additional weight of the USOS, and substantial solar arrays supplementing the stations existing 4 solar arrays.^[48]

Over the next two years the station continued to expand. A Soyuz-U rocket delivered the Pirs docking compartment. The Space Shuttles Discovery, Atlantis, and Endeavour delivered the Destiny laboratory and Quest airlock, in addition to the station's main robot arm, the Canadarm2, and several more segments of the Integrated Truss Structure.^[49]

The expansion schedule was interrupted by the destruction of the Space Shuttle Columbia on STS-107 in 2003, with the resulting hiatus in the Space Shuttle programme halting station assembly until the launch of Discovery on STS-114 in 2005.^[50]

The official resumption of assembly was marked by the arrival of Atlantis, flying STS-115, which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on STS-116, STS-117, and STS-118. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the Harmony node and Columbus European laboratory were added. These were followed shortly after by the first two components of Kibō. In March 2009, STS-119 completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of Kibō was delivered in July 2009 on STS-127, followed by the Russian Poisk module. The third node, Tranquility, was delivered in February 2010 during STS-130 by the Space Shuttle Endeavour, alongside the Cupola, closely followed in May 2010 by the penultimate Russian module, Rassvet, delivered by Space Shuttle Atlantis on STS-132. The last pressurised module of the USOS, Leonardo, was brought to the station by Discovery on her final flight, STS-133.

As of March 2011^[update], the station consisted of fifteen pressurised modules and the Integrated Truss Structure. Still to be launched are the Russian Multipurpose Laboratory Module Nauka and a number of external components, including the European Robotic Arm and Alpha Magnetic Spectrometer (AMS-02). Assembly is expected to be completed by 2011, by which point the station will have a mass in excess of 400 metric tons (440 short tons).^[2][45]

[edit] Pressurised modules

When completed in late 2011, the ISS will consist of sixteen pressurised modules with a combined volume of around 1,000 cubic metres (35,000 cu ft).^[51] These modules include laboratories, docking compartments, airlocks, nodes and living quarters. Fifteen of these components are already in orbit, with the remaining one awaiting launch. Each module was or will be launched either by the Space Shuttle, Proton rocket or Soyuz rocket.^[49]

Module	Assembly mission	Launch date	Launch system	Nation	Isolated view	Notes
Zarya (lit. dawn) (FGB)	1A/R	November 20,1998	Proton-K	Russia (builder) USA (financier)		[52]
	The first component of the ISS to be launched, Zarya provided electrical power, storage, propulsion, and guidance during initial assembly. The module now serves as a storage compartment, both inside the pressurised section and in the externally mounted fuel tanks.
Unity (Node 1)	2A	4 December 1998	Space Shuttle Endeavour, STS-88	USA		[53]
	The first node module, connecting the American section of the station to the Russian section (via PMA-1), and providing berthing locations for the Z1 truss, Quest airlock, Destiny laboratory, Tranquility node and the PMM Leonardo.
Zvezda (lit. star) (service module)	1R	12 July 2000	Proton-K	Russia		[54]
	The station's service module, which provides the main living quarters for resident crews, environmental systems and attitude & orbit control. The module also provides docking locations for Soyuz spacecraft, Progress spacecraft and the Automated Transfer Vehicle, and its addition rendered the ISS permanently habitable for the first time.
Destiny (US laboratory)	5A	7 February 2001	Space Shuttle Atlantis, STS-98	USA		[55]
	The primary research facility for US payloads aboard the ISS, Destiny is intended for general experiments. The module houses 24 International Standard Payload Racks, some of which are used for environmental systems and crew daily living equipment. Destiny also serves as the mounting point for most of the station's Integrated Truss Structure.
Quest (joint airlock)	7A	12 July 2001	Space Shuttle Atlantis, STS-104	USA		[56]
	The primary airlock for the ISS, Quest hosts spacewalks with both US EMU and Russian Orlan spacesuits. Quest consists of two segments; the equipment lock, that stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before EVAs, to avoid decompression sickness (known as "the bends") in the low pressure suits.
Pirs (lit. pier) (docking compartment)	4R	14 September 2001	Soyuz-U, Progress M-SO1	Russia		[57]
	Pirs provides the ISS with additional docking ports for Soyuz and Progress spacecraft, and allows egress and ingress for spacewalks by cosmonauts using Russian Orlan spacesuits, in addition to providing storage space for these spacesuits.
Harmony (node 2)	10A	23 October 2007	Space Shuttle Discovery, STS-120	Europe (builder) USA (operator)		[58]
	The second of the station's node modules, Harmony is the utility hub of the ISS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to the module, and American Space Shuttle Orbiters dock with the ISS via PMA-2, attached to Harmony's forward port. In addition, the module serves as a berthing port for the Italian Multi-Purpose Logistics Modules during shuttle logistics flights.
Columbus (European laboratory)	1E	7 February 2008	Space Shuttle Atlantis, STS-122	Europe		[59][60]
	The primary research facility for European payloads aboard the ISS, Columbus provides a generic laboratory as well as facilities specifically designed for biology, biomedical research and fluid physics. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the European Technology Exposure Facility (EuTEF), Solar Monitoring Observatory, Materials International Space Station Experiment, and Atomic Clock Ensemble in Space. A number of expansions are planned for the module to study quantum physics and cosmology.
Kibō Experiment Logistics Module (lit. hope and wish JEM–ELM)	1J/A	11 March 2008	Space Shuttle Endeavour, STS-123	Japan		[61]
	Part of the Kibō Japanese Experiment Module laboratory, the ELM provides storage and transportation facilities to the laboratory with a pressurised section to serve internal payloads.
Kibō Pressurised Module (JEM–PM)	1J	31 May 2008	Space Shuttle Discovery, STS-124	Japan		[61][62]
	Part of the Kibō Japanese Experiment Module laboratory, the PM is the core module of Kibō to which the ELM and Exposed Facility are berthed. The laboratory is the largest single ISS module and contains a total of 23 racks, including 10 experiment racks. The module is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, and communications research. The PM also serves as the mounting location for an external platform, the Exposed Facility (EF), that allows payloads to be directly exposed to the harsh space environment. The EF is serviced by the module's own robotic arm, the JEM–RMS, which is mounted on the PM.
Poisk (lit. 'search') (mini-research module 2)	5R	10 November 2009	Soyuz-U, Progress M-MIM2	Russia		[63][64]
	One of the Russian ISS components, Poisk is used for docking of Soyuz and Progress ships, as an airlock for spacewalks and as an interface for scientific experiments.
Tranquility (node 3)	20A	8 February 2010	Space Shuttle Endeavour, STS-130	Europe (builder) USA (operator)		[65][66]
	The third and last of the station's US nodes, Tranquility contains an advanced life support system to recycle waste water for crew use and generate oxygen for the crew to breathe. The node also provides four berthing locations for more attached pressurised modules or crew transportation vehicles, in addition to the permanent berthing location for the station's Cupola.
Cupola	20A	8 February 2010	Space Shuttle Endeavour, STS-130	Europe (builder) USA (operator)		[67]
	The Cupola is an observatory module that provides ISS crew members with a direct view of robotic operations and docked spacecraft, as well as an observation point for watching the Earth. The module comes equipped with robotic workstations for operating the SSRMS and shutters to protect its windows from damage caused by micrometeorites. It features a 80-centimetre (31 in) round window, the largest window on the station.
Rassvet (lit. dawn) (mini-research module 1)	ULF4	14 May 2010	Space Shuttle Atlantis, STS-132	Russia		[45]
	Rassvet is being used for docking and cargo storage aboard the station.
Leonardo (Permanent Multipurpose Module)	ULF5	24 February 2011	Space Shuttle Discovery, STS-133	Italy (Builder) USA (Operator)		[68][69][70]
	The Leonardo PMM will house spare parts and supplies, allowing longer times between resupply missions and freeing space in other modules, particularly Columbus. The PMM was created by converting the Italian Leonardo Multi-Purpose Logistics Module into a module that could be permanently attached to the station. The arrival of the PMM module marked the completion of the US Orbital Segment.

[edit] Scheduled to be launched

Module	Assembly mission	Launch date	Launch system	Nation	Isolated view	Notes
Nauka (lit. 'science') (Multipurpose Laboratory Module)	3R	May 2012[71]	Proton-M	Russia		[45][72]
	The MLM will be Russia's primary research module as part of the ISS and will be used for general microgravity experiments, docking, and cargo logistics. The module provides a crew work and rest area, and will be equipped with a backup attitude control system that can be used to control the station's attitude. Based on the current assembly schedule, the arrival of Nauka will complete construction of the Russian Orbital Segment and it will be the last major component added to the station.

[edit] Cancelled modules

Several modules planned for the station have been cancelled over the course of the ISS programme, whether for budgetary reasons, because the modules became unnecessary, or following a redesign of the station after the 2003 Columbia disaster. The cancelled modules include:

• The US Centrifuge Accommodations Module for experiments in varying levels of artificial gravity.^[73]
• The US Habitation Module, which would have served as the station's living quarters. The sleep stations are now spread throughout the station.^[74]
• The US Crew Return Vehicle would have served as the station's lifeboat; a service now provided by one Soyuz spacecraft for every three crew members aboard.^[75]
• The US Interim Control Module and ISS Propulsion Module were intended to replace functions of Zvezda in case of a launch failure.^[76]
• The Russian Universal Docking Module, to which the cancelled Russian Research modules and spacecraft would have docked.^[77]
• The Russian Science Power Platform would have provided the Russian Orbital Segment with a power supply independent of the ITS solar arrays.^[77]
• Two Russian Research Modules that were planned to be used for scientific research.^[78]

[edit] Unpressurised elements

In addition to the pressurised modules, the ISS features a large number of external components. The largest component is the Integrated Truss Structure (ITS), to which the station's main solar arrays and thermal radiators are mounted.^[21] The ITS consists of ten separate segments forming a structure 108.5 m (356 ft) long.^[2]

The Alpha Magnetic Spectrometer (AMS), a particle physics experiment, is scheduled to be launched on STS-134 in 2011, and will be mounted externally on the ITS. The AMS will measure cosmic rays and look for evidence of dark matter and antimatter.^[79]

The ITS serves as a base for the main remote manipulator system called the Mobile Servicing System (MSS). This consists of the Mobile Base System (MBS), the Canadarm2, and the Special Purpose Dexterous Manipulator. The MBS rolls along rails built into some of the ITS segments to allow the arm to reach all parts of the US segment of the station.^[80] The MSS is due to have its reach increased by an Orbiter Boom Sensor System, scheduled for installation during the STS-133 mission.^[81]

Two other remote manipulator systems are present in the station's final configuration. The European Robotic Arm, which will service the Russian Orbital Segment, will be launched alongside the Multipurpose Laboratory Module.^[82] The Japanese Experiment Module's Remote Manipulator System(JFM RMS) , which services the JEM Exposed Facility,^[83] was launched on STS-124 and is attached to the JEM Pressurised Module. In addition to these robotic arms, there are two Russian Strela cargo cranes used for moving spacewalking cosmonauts and parts around the exterior of the Russian Orbital Segment.^[84]

The station in its complete form has several smaller external components, such as the three External Stowage Platforms (ESPs), launched on STS-102, STS-114 and STS-118, which are used to store spare parts. Four ExPrESS Logistics Carriers (ELCs) will allow experiments to be deployed and conducted in the vacuum of space, and will provide the necessary electricity and computing to process experimental data locally. ELCs 1 and 2 were delivered on STS-129 in November 2009, and ELCs 3 and 4 are scheduled for delivery on STS-134 in November 2010 and STS-133 in September 2010.^[45][85] There are two exposure facilities mounted directly to laboratory modules: the JEM Exposed Facility serves as an external 'porch' for the Japanese Experiment Module complex,^[86] and a facility on the European Columbus laboratory provides power and data connections for experiments such as the European Technology Exposure Facility^[87][88] and the Atomic Clock Ensemble in Space.^[89] A remote sensing instrument, SAGE III-ISS, is due to be delivered to the station in 2014 aboard a Dragon capsule.^[90]

[edit] Power supply

Photovoltaic (PV) arrays power the ISS. The Russian segment of the station, like the space shuttle and most aircraft, uses 28 volt DC partly provided by four solar arrays mounted directly to Zarya and Zvezda. The rest of the station uses 130–180 V DC from the US PV array arranged as four wing pairs. Each wing produces nearly 32.8 kW.^[21]

Power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The higher distribution voltage allows smaller, lighter conductors. The two station segments share power with converters, essential since the Columbia disaster forced the cancellation of the Russian Science Power Platform and Jaxa centrifuge modules.^{[91] [92]}

The station uses rechargeable nickel-hydrogen batteries for continuous power during the 35 minutes of every 90 minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the earth. They have a 6.5 year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.^[93]

The US solar arrays normally track the sun to maximise power generation. Each array is about 375 m² (450 yd²) in area and 58 metres (63 yd) long. In the complete configuration, the solar arrays track the sun by rotating the alpha gimbal once per orbit while the beta gimbal follows slower changes in the angle of the sun to the orbital plane. The Night Glider mode aligns the solar arrays parallel to the velocity vector at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.^[94]

[edit] Orbit control

The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 278 km (173 mi) and a maximum of 460 km (286 mi). It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes 15.7 orbits per day.^[95] The normal maximum altitude is 425 km (264 mi) to allow Soyuz rendezvous missions. As the ISS constantly loses altitude because of a slight atmospheric drag, it needs to be boosted to a higher altitude several times each year.^[31][96] This boost can be performed by the station's two main engines on the Zvezda service module, a docked space shuttle, a Progress resupply vessel, or by ESA's ATV. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.^[96]

In December 2008 NASA signed an agreement with the Ad Astra Rocket Company which may result in the testing on the ISS of a VASIMR plasma propulsion engine.^[97] This technology could allow station-keeping to be done more economically than at present.^[98][99] The station's navigational position and velocity, or state vector, is independently established using the US Global Positioning System (GPS) and a combination of state vector updates from Russian Ground Sites and the Russian GLONASS system.

The attitude (orientation) of the station is independently determined by a set of sun, star and horizon sensors on Zvezda and the US GPS with antennas on the S0 truss and a receiver processor in the US lab. The attitude knowledge is propagated between updates by rate sensors.^[24] Attitude control is maintained by either of two mechanisms; normally, a system of four control moment gyroscopes (CMGs) keeps the station oriented, with Destiny forward of Unity, the P truss on the port side, and Rassvet on the Earth-facing (nadir) side. When the CMG system becomes 'saturated'—when the set of CMGs exceed their operational range or cannot track a series of rapid movements—they can lose their ability to control station attitude.^[100] In this event, the Russian attitude control system is designed to provide desaturating thruster firings, taking over automatically whilst the CMG system is reset. This automatic attitude control safing has only occurred once, during Expedition 10.^[101] When a space shuttle is docked to the station, it can also be used to maintain station attitude. This occurs during portions of every mated shuttle ISS mission. Shuttle control was used exclusively during STS-117 as the S3/S4 truss was installed.^[102]

[edit] Communications

Radio communications provide telemetry and scientific data links between the station and Mission Control Centres. Radio links are also used during rendezvous and docking procedures and for audio and video communication between crewmembers, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.^[103]

The Russian Orbital Segment communicates directly with the ground via the Lira antenna mounted to Zvezda.^[24][104] The Lira antenna also has the capability to use the Luch data relay satellite system.^[24] This system, used for communications with Mir, fell into disrepair during the 1990s, and as a result is no longer in use,^{[18][24][105]} although two new Luch satellites—Luch-5A and Luch-5B—are planned for launch in 2011 to restore the operational capability of the system.^[106] Another Russian communications system is the Voskhod-M, which enables internal telephone communications between Zvezda, Zarya, Pirs, Poisk and the USOS, and also provides a VHF radio link to ground control centres via antennas on Zvezda's exterior.^[107]

The US Orbital Segment (USOS) makes use of two separate radio links mounted in the Z1 truss structure: the S band (used for audio) and K_u band (used for audio, video and data) systems. These transmissions are routed via the US Tracking and Data Relay Satellite System (TDRSS) in geostationary orbit, which allows for almost continuous real-time communications with NASA's Mission Control Center (MCC-H) in Houston.^{[19][24][103]} Data channels for the Canadarm2, European Columbus laboratory and Japanese Kibō modules are routed via the S band and K_u band systems, although the European Data Relay Satellite System and a similar Japanese system will eventually complement the TDRSS in this role.^[19][108] Communications between modules are carried on an internal digital wireless network.^[109]

UHF radio is used by astronauts and cosmonauts conducting EVAs. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and K_u band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers.^[24] Automated spacecraft are fitted with their own communications equipment; the ATV uses a laser attached to the spacecraft and equipment attached to Zvezda, known as the Proximity Communications Equipment, to accurately dock to the station.^[110][111]

[edit] Microgravity

At the station's orbital altitude, the gravity from the Earth is 88% of that at sea level. While the constant free fall of the ISS offers a perceived sensation of weightlessness, the environment onboard is not one of weightlessness or zero-gravity, instead often being described as microgravity. This state of perceived weightlessness is not perfect, however, being disturbed by five separate effects:^[112]

• The drag resulting from the residual atmosphere.
• Vibratory acceleration caused by mechanical systems and the crew on board the ISS.
• Orbital corrections by the on-board gyroscopes or thrusters.
• The spatial separation from the real centre of mass of the ISS. Any part of the ISS not at the exact centre of mass will tend to follow its own orbit. However, as each point is physically part of the station, this is impossible, and so each component is subject to small accelerations from the forces which keep them attached to the station as it orbits.^[112] This is also called the tidal force.
• The differences in orbital plane between different locations aboard the ISS.

[edit] Life support

The ISS Environmental Control and Life Support System (ECLSS) provides or controls atmospheric pressure, fire detection and suppression, oxygen levels, waste management and water supply. The highest priority for the ECLSS is the ISS atmosphere, but the system also collects, processes, and stores waste and water produced and used by the crew—a process that recycles fluid from the sink, toilet, and condensation from the air. The Elektron system aboard Zvezda and a similar system in Destiny generate oxygen aboard the station.^[113] The crew has a backup option in the form of bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters.^[114] Carbon dioxide is removed from the air by the Vozdukh system in Zvezda. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by activated charcoal filters.^[114]

The atmosphere on board the ISS is similar to the Earth's.^[115] Normal air pressure on the ISS is 101.3 kPa (14.7 psi);^[116] the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the Apollo 1 crew.^[117]

[edit] Sightings

Because of the size of the ISS (about that of an American football field) and the large reflective area offered by its solar panels, ground based observation of the station is possible with the naked eye if the observer is in the right location at the right time. In many cases, the station is one of the brightest naked-eye objects in the sky, although it is visible only for periods ranging from two to five minutes.^[10]

If the following conditions are fulfilled (assuming the weather is clear), the station will appear as a very bright object in the sky: The station must be above the observer's horizon, and it must pass within about 2,000 kilometres (1,200 mi) of the observation site (the closer the better). It must be dark enough at the observer's location for stars to be visible, and the station must be in sunlight rather than in the Earth's shadow. It is common for the third condition to begin or end during what would otherwise be a good viewing opportunity. In the evening, as the station moves further from the dusk, going from west to east it will appear to suddenly fade and disappear. In the reverse situation, it may suddenly appear in the sky as it approaches the dawn.^[10][118] With the station's maximum theoretical brightness at approximately magnitude −5.9 (with a typical maximum of −3.8), it is bright enough to be spotted during broad daylight conditions without optical aid.^{[119][120][121]}

The ISS orbits at an inclination of 51 degrees, and so it is not visible in extreme northern or southern regions of the earth. Russia's next space station is expected to orbit with an inclination of approximately 70 degrees to allow observation to and from all Russian territory, which is currently not possible, a side effect of the low inclination necessary to allow American space shuttles to reach the current station. ^[122]

Internet users can find simple instructions for viewing the ISS without equipment, using the non-profit website Heavens-Above.^[123]

[edit] Politics, utilisation and financing

[edit] Legal aspects

The ISS is a joint project of several space agencies: the US National Aeronautics and Space Administration (NASA), the Russian Federal Space Agency (RKA), the Japan Aerospace Exploration Agency (JAXA), the Canadian Space Agency (CSA) and the European Space Agency (ESA).^[23]

As a multinational project, the legal and financial aspects are complex. Issues of concern include the ownership of modules, station utilisation by participant nations, and responsibilities for station resupply. Obligations and rights are established by the Space Station Intergovernmental Agreement (IGA). This international treaty was signed on 28 January 1998 by the primary nations involved in the Space Station project; the United States of America, Russia, Japan, Canada and eleven member states of the European Space Agency (Belgium, Denmark, France, Germany, Italy, The Netherlands, Norway, Spain, Sweden, Switzerland, and the United Kingdom).^[25] A second layer of agreements was then achieved, called Memoranda of Understanding (MOU), between NASA and ESA, CSA, RKA and JAXA. These agreements are then further split, such as for the contractual obligations between nations, and trading of partners' rights and obligations.^[25] Use of the Russian Orbital Segment is also negotiated at this level.^[26]

In addition to these main intergovernmental agreements, Brazil originally joined the programme as a bilateral partner of the United States by a contract with NASA to supply hardware.^[124] In return, NASA would provide Brazil with access to its ISS facilities on-orbit, as well as a flight opportunity for one Brazilian astronaut during the course of the ISS programme. However, due to cost issues, the subcontractor Embraer was unable to provide the promised ExPrESS pallet, and Brazil left the programme.^[125] Italy has a similar contract with NASA to provide comparable services, although Italy also takes part in the programme directly via its membership in ESA.^[126] The Chinese, who have their own space station, Project 921-2, scheduled for launch late in 2011, have reportedly expressed interest in the project, especially if it would be able to work with the RKA. Chinese manned spacecraft and space stations have Russian compatible docking systems. However, as of December 2010^[update] China remains uninvolved.^[127][128] The heads of both the South Korean and Indian space agency ISRO announced at the first plenary session of the 2009 International Astronautical Congress that their nations intend to join the ISS programme, with talks due to begin in 2010. The heads of agency also expressed support for extending ISS lifetime.^[129] European countries not part of the programme will be allowed access to the station in a three-year trial period, ESA officials say.^[130]

[edit] Challenges Resulting from the Iran Nonproliferation Act of 2000

On March 14, 2000 President Bill Clinton signed the Iran Nonproliferation Act of 2000 (INA), which created a problem for NASA in its financial dealings with the Russian space agency. Section 6 of the Act "prohibits the U.S. Government from making payments in connection with the ISS to the Russian space agency, organizations or entities under its control, or any other element of the Russian government, after January 1, 1999, unless the President makes a determination that Russia's policy is to oppose proliferation to Iran, that Russia is demonstrating a sustained commitment to seek out and prevent the transfer of WMD (weapons of mass destruction) and missile systems to Iran, and that neither the Russian space agency nor any entity reporting to it has made such transfers for at least one year prior to such determination." ^[131] Section 6 incorporated a "crew safety exception" which was intended to prevent "imminent loss of life" and also allowed for payments involving Russia's Service Module and docking hardware that was already in process when the Act was being debated. At an October 12, 2000 House International Relations Committee hearing, NASA was criticized for its broad interpretation of the word “imminent” in the crew safety exception.^[132] In 2006 Russia was no longer obligated to provide transportation of American astronauts aboard the Soyuz spacecraft without payment. With this deadline looming, in 2005 Congress amended the INA to exempt Soyuz flights from the Section 6 ban. The exemption was renewed in 2008 and is in effect through 2016. ^[133]

[edit] Utilisation rights

The Russian part of the station is operated and controlled by the Russian Federation's space agency and provides Russia with the right to nearly one-half of the crew time for the ISS. The allocation of remaining crew time (three to four crew members of the total permanent crew of six) and hardware within the other sections of the station has been assigned as follows:

• Columbus: 51% for the ESA, 46.7% for NASA, and 2.3% for CSA.^[25]
• Kibō: 51% for the JAXA, 46.7% for NASA, and 2.3% for CSA.^[108]
• Destiny: 97.7% for NASA and 2.3% for CSA.^[134]
• Crew time, electrical power and rights to purchase supporting services (such as data upload and download and communications) are divided 76.6% for NASA, 12.8% for JAXA, 8.3% for ESA, and 2.3% for CSA.^{[25][108][134]}

[edit] Costs

The cost estimates for the ISS range from 35 billion to 160 billion dollars.^[28] ESA, the one agency which actually presents potential overall costs, estimates €100 billion for the entire station over 30 years.^[27] A precise cost estimate for the ISS is unclear, as it is difficult to determine which costs should be attributed to the ISS programme, or how the Russian contribution should be measured.^[28]

[edit] Criticism

Critics of the ISS contend that the time and money spent on the ISS could be better spent on other projects—whether they be robotic spacecraft missions, space exploration, investigations of problems on Earth, colonisation of Mars, or just tax savings.^[29][30] Some critics, such as Robert L. Park, argue that little scientific research was convincingly planned for the ISS, and that the primary feature of a space-based laboratory, its microgravity environment, can be studied less expensively with a "vomit comet".^{[29][135][136]}

The research capabilities of the ISS have been criticised, particularly following the cancellation of the ambitious Centrifuge Accommodations Module, which, alongside other equipment cancellations, means scientific research performed on the station is generally limited to experiments which do not require any specialised apparatus. For example, in the first half of 2007, ISS research dealt primarily with human biological responses to living and working in space, covering topics like kidney stones, circadian rhythm, and the effects of cosmic rays on the nervous system.^{[137][138][139]} Other criticisms hinge on the technical design of the ISS, including the high inclination of the station's orbit, which leads to a higher cost for US-based launches to the station.^[140]

[edit] End of mission and deorbit plans

NASA had planned to deorbit the ISS in the first quarter of 2016.^[141] However, the plan to end the ISS programme in 2015, as determined in 2004 by then-President George W. Bush, has been rejected by the current Obama administration. With the new budget announced on 1 February 2010, the administration aims to extend the lifetime through 2020.^[9] The Augustine Commission, which reviewed NASA's human space flight program, recommended in its final report of 23 October 2009 the extension of the ISS programme to at least 2020.^[142] In particular, Leroy Chiao, a former space station commander and space shuttle astronaut who sat on the advisory panel, stated in a CNN interview: “You've got all of these different countries working together on this common project in space. And if we go ahead and stop [...] it is going to break up that framework. The different countries around the world will lose confidence in the US as a leader in space exploration." NASA officials received confirmation from the Obama administration on the future direction of the ISS in particular and the human spaceflight programme in general on 1 February 2010, with a budget proposing an extension to the ISS programme until at least 2020,^[9][143] with talks between ISS partners suggesting that the station could conceivably remain operational until 2025 or 2028.^[144][145]

The Multilateral Coordination Board (MCB) of the ISS international partners, in a videoconference on 21 September 2010, learned that the Japanese and Russian governments have approved operation continuing to 2020. The European Space Agency (ESA) has since also approved the extension.^[146] The Canadian Space Agency (CSA) is working with its government to confirm the extension of operations beyond 2016, while NASA continues working with the US Congress on extension plans.^[147]

NASA has the responsibility to deorbit the ISS. Although Zvezda has a propulsion system used for station-keeping, it is not powerful enough for a controlled deorbit. Options for controlled deorbit of the ISS include the use of a modified European ATV or a specially constructed deorbit vehicle.^[148][149]

According to a 2009 report, RKK Energia is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the Orbital Piloted Assembly and Experiment Complex. The modules under consideration for removal from the current ISS include the Multipurpose Laboratory Module (MLM), currently scheduled to be launched at the end of 2011, with other Russian modules which are currently planned to be attached to the MLM until 2015, although still currently unfunded. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from Mir, a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.^[150]

Russia and ISS partners in a 2011 statement said that work is being done to make sure other modules can be used beyond 2015. The first Russian module was launched in 1998, and the 30th anniversary of that module's launch has been chosen as a target date for certification of all components of the ISS. Russia has plans to keep the station on orbit until 2028. ^[151]

[edit] Life on board

[edit] Crew schedule

The time zone used on board the ISS is Coordinated Universal Time (UTC). The windows are covered at night hours to give the impression of darkness because the station experiences 16 sunrises and sunsets a day. During visiting space shuttle missions, the ISS crew will mostly follow the shuttle's Mission Elapsed Time (MET), which is a flexible time zone based on the launch time of the shuttle mission.^[152][153] Because the sleeping periods between the UTC time zone and the MET usually differ, the ISS crew often has to adjust its sleeping pattern before the space shuttle arrives and after it leaves to shift from one time zone to the other in a practice known as sleep shifting.^[154]

A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.^[155]

[edit] Sleeping in space

The station provides crew quarters for each member of permanent Expedition crews, with two 'sleep stations' in the Russian Orbital Segment and four more, due to be installed in Tranquility, currently spread around the USOS. The American quarters are private, approximately person-sized soundproof booths. A crewmember can sleep in them in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop.^{[156][157][158]} Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment.^[159] It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.^[158]

[edit] Hygiene

The ISS does not feature a shower, although it was planned as part of the now cancelled Habitation Module. Instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.^[159]

There are two space toilets on the ISS, both of Russian design, located in Zvezda and Tranquility.^[156] These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal.^[158] A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal.^[156][160] Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct “urine funnel adapters” attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.^[157]

[edit] Food and drink

Most of the food eaten by station crews is frozen, refrigerated or canned. Menus are prepared by the astronauts, with the help of a dietitian, before the astronauts' flight to the station.^[157] As the sense of taste is reduced in orbit because of fluid shifting to the head, spicy food is a favourite of many crews.^[158] Each crewmember has individual food packages and cooks them using the onboard galley, which features two food warmers, a refrigerator, and a water dispenser that provides both heated and unheated water.^[156] Drinks are provided in dehydrated powder form, and are mixed with water before consumption.^[156][157] Drinks and soups are sipped from plastic bags with straws, while solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food which does float away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.^[157]

[edit] Exercise

The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. Other significant effects include fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. These effects begin to reverse quickly upon return to the Earth.^[38]

To prevent some of these adverse physiological effects, the station is equipped with two treadmills (including the COLBERT), the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises, and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.^[156][158] Astronauts use bungee cords to strap themselves to the treadmill.^[161] Researchers believe that exercise is a good countermeasure for the bone and muscle density loss that occurs when humans live for a long time without gravity.^[162]

[edit] Station operations

[edit] Expeditions

Each permanent station crew is given a sequential expedition number. Expeditions have an average duration of half a year, and they commence following the official handover of the station from one Expedition commander to another. Expeditions 1 through 6 consisted of three person crews, but the Columbia accident led to a reduction to two crew members for Expeditions 7 to 12. Expedition 13 saw the restoration of the station crew to three, and the station has been permanently staffed as such since. While only three crew members are permanently on the station, several expeditions, such as Expedition 16, have consisted of up to six astronauts or cosmonauts, who are flown to and from the station on separate flights.^[163][164]

On 27 May 2009, Expedition 20 began. Expedition 20 was the first ISS crew of six. Before the expansion of the living volume and capabilities from STS-115 the station could only host a crew of three. Expedition 20s crew was lifted to the station in two separate Soyuz-TMA flights launched at two different times (each Soyuz-TMA can hold only three people): Soyuz TMA-14 on 26 March 2009 and Soyuz TMA-15 on 27 May 2009. However, the station would not be permanently occupied by six crew members all year. For example, when the Expedition 20 crew (Roman Romanenko, Frank De Winne and Bob Thirsk) returned to Earth in November 2009, for a period of about two weeks only two crew members (Jeff Williams and Max Surayev) were aboard. This increased to five in early December, when Oleg Kotov, Timothy Creamer and Soichi Noguchi arrived on Soyuz TMA-17. It decreased to three when Williams and Surayev departed in March 2010, and finally returned to six in April 2010 with the arrival of Soyuz TMA-18, carrying Aleksandr Skvortsov, Mikhail Korniyenko and Tracy Caldwell Dyson.^[163][164]

The International Space Station is the most-visited spacecraft in the history of space flight. As of 15 December 2010 (2010 -12-15)^[update], it had received 297 visitors (196 different people).^[11][165] Mir had 137 visitors (104 different people).^[18]

[edit] Visiting spacecraft

Spacecraft (or 'visiting vehicles') from four different space agencies visit the ISS, serving a variety of purposes. The Automated Transfer Vehicle from the European Space Agency, the Russian Roskosmos Progress spacecraft and the HTV from the Japan Aerospace Exploration Agency have provided resupply services to the station. In addition, Russia supplies a Soyuz spacecraft used for crew rotation and emergency evacuation, which is replaced every six months. Finally, the US services the ISS through its Space Shuttle programme, providing resupply missions, assembly and logistics flights, and crew rotation. As of 9 March 2011 (2011 -03-09)^[update], there have been 25 Soyuz, 41 Progress, 2 ATV, 2 HTV and 35 space shuttle flights to the station.^[1] Expeditions require, on average, 2,722 kg of supplies, and as of 9 March 2011 (2011 -03-09)^[update], crews had consumed a total of around 22,000 meals.^[1] Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year,^[166] with the ATV and HTV planned to visit annually from 2010 onwards.

Following the retirement of the Space Shuttle, a number of other spacecraft are expected to fly to the station. Two, the Orbital Sciences Cygnus and SpaceX Dragon, will fly under NASA's Commercial Orbital Transportation Services and Commercial Resupply Services contracts, delivering cargo to the station until at least 2015.^[167][168]

[edit] Docking

Spacecraft from Russia and Europe are able to dock themselves without human intervention. American craft are manually docked, Japanese craft are berthed with the use of manually controlled robot arms. Russian and European Supply craft can remain at the ISS for 4-6 months, allowing great flexibility in crew time for loading and unloading of supplies and trash. Japanese spacecraft berth for 1-2 months. American space shuttles can remain in space for up to 14 days, the longest docking being 11 days.

The American Manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialized training and planning, making the process more labor-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardizations that provide significant cost benefits in repetitive routine operations. ^[169] The Russian approach allows assembly of space stations orbiting other worlds in preparation for manned missions. The Nauka module of the ISS will be used in the 12th Russian(/Soviet) space station, OPSEK, whose main goal is supporting deep space exploration.

[edit] Currently docked

As of 29 April 2011 (2011 -04-29)^[update], there are 4 spacecraft docked with the ISS.

	Spacecraft	Mission	Docking port	Date docked (UTC)	Notes
	Soyuz TMA-20	Expedition 26/27	Rassvet	17 December 2010 20:12	Scheduled to undock on 23 May 2011[170]
	Johannes Kepler	ATV-2	Zvezda aft	24 February 2011 15:59	Scheduled to undock on 20 June 2011[171]
	Soyuz TMA-21	Expedition 27/28	Poisk	7 April 2011 00:09	[citation needed]
	Progress M-10M	ISS Progress 42	Pirs	29 April 2011 14:29	[172]

From 26 February 2011 to 7 March 2011 (the docked phase of STS-133), all four major Governmental partners (USA, ESA, Japan and Russia) had their current visiting vehicles (Space Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS at one time, the only time in history this has, and will, occur.

[edit] Scheduled to be docked in 2011

	Spacecraft	Mission	Docking port	Date of scheduled docking (UTC)	Notes
	Space Shuttle Endeavour	STS-134/ULF6	Harmony forward (PMA-2)	NET 12 May 2011	Launch is scheduled for 10 May 2011[173]
	Soyuz TMA-02M	Expedition 28/29	Rassvet	NET 1 June 2011	Launch is scheduled for 30 May 2011.
	Progress M-11M	ISS Progress 43	TBD	NET 25 June 2011	Launch is scheduled for 23 June 2011
	Space Shuttle Atlantis	STS-135/ULF7	Harmony forward (PMA-2)	NET 30 June 2011	Launch is scheduled for 28 June 2011
	Progress M-12M	ISS Progress 44	TBD	NET 1 August 2011	Launch is scheduled for 30 August 2011
	Soyuz TMA-22	Expedition 29/30	Poisk	NET 2 October 2011	Launch is scheduled for 30 September 2011.
	Dragon C3	COTS Demo 3	Harmony nadir	NET 10 October 2011	Launch is scheduled for 8 October 2011
	Progress M-13M	ISS Progress 45	TBD	NET 28 October 2011	Launch is scheduled for 26 October 2011
	Dragon C4	ISS Dragon Cargo 1	TBD	NET 9 December 2011	Launch is scheduled for 7 December 2011
	Cygnus 1	ISS Cygnus 1	TBD	NET 16 December 2011	Launch is scheduled for 14 December 2011
	Progress M-14M	ISS Progress 46	TBD	NET 29 December 2011	Launch is scheduled for 27 December 2011
	Soyuz TMA-03M	Expedition 30/31	TBD	NET December 2011	Launch is scheduled for December 2011.

The docking of STS-135 will be the last time that Space Shuttle will dock with the ISS.

[edit] Mission control centres

The components of the ISS are operated and monitored by their respective space agencies at control centres across the globe, including:

• NASA's Mission Control Center at Lyndon B. Johnson Space Center in Houston, Texas, serves as the primary control facility for the US segment of the ISS and also controls the Space Shuttle missions that visit the station.^[24]
• NASA's Payload Operations and Integration Center at Marshall Space Flight Center in Huntsville, Alabama, serves as the centre that coordinates all payload operations in the US Segment.^[24]
• Roskosmos's Mission Control Center at Korolyov, Moscow Oblast, controls the Russian Orbital Segment of the ISS, in addition to individual Soyuz and Progress missions.^[24]
• ESA's Columbus Control Centre at the German Aerospace Centre (DLR) in Oberpfaffenhofen, Germany, controls the European Columbus research laboratory.^[24]
• ESA's ATV Control Centre, at the Toulouse Space Centre (CST) in Toulouse, France, controls flights of the unmanned European Automated Transfer Vehicle.^[24]
• JAXA's JEM Control Centre and HTV Control Centre at Tsukuba Space Centre (TKSC) in Tsukuba, Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the unmanned Japanese HTV respectively.^[24]
• CSA's MSS Control at Saint-Hubert, Quebec, Canada, controls and monitors the Mobile Servicing System, or Canadarm2.^[24]

[edit] Safety aspects

[edit] Anomalies

Since construction started, the ISS programme has had to deal with several major incidents, unexpected problems and failures. These incidents have impacted the station's assembly timeline, led to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons, had these problems not been resolved.

The first major impact to station operations came with the Space Shuttle Columbia disaster on 1 February 2003 (during STS-107), which resulted in a two-and-a-half-year suspension of the US Space Shuttle programme, followed by another one-year suspension following STS-114 (because of continued foam shedding on the external tank). This halted station assembly plans and reduced the station's operational capabilities, as, due to a lack of logistics, caretaker crews of just two astronauts were launched from Expedition 7 until Expedition 12.^[174] The Columbia disaster was followed by a number of smaller issues aboard the station, including an air leak from the USOS in 2004,^[175] the venting of smoke from an Elektron oxygen generator in 2006,^[176] and the failure of the computers in the ROS in 2007 during STS-117 which left the station without thruster, Elektron, Vozdukh and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.^[177]

These issues with internal station equipment were then followed by a spate of issues with external components; during STS-120 on 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly.^[178] An emergency EVA was carried out by Scott Parazynski, assisted by Douglas Wheelock, to repair the array, an activity which was considerably more dangerous than most EVAs due to the short planning time and the risk of electric shock from the arrays themselves.^[179] The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and STS-123 showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic race ring at the heart of the joint, and so the joint was locked to prevent further damage.^[180] Repairs to the joint were carried out during STS-126 with lubrication of both joints and the replacement 11 of 12 trundle bearings on the joint.^[181][182]

More recently, problems have been noted with the station's engines and cooling. In 2009, the engines on Zvezda were issued an incorrect command which caused excessive vibrations to propagate throughout the station structure which persisted for over two minutes.^[183] While no damage to the station was immediately reported, some components may have been stressed beyond their design limits. Further analysis confirmed that the station was unlikely to have suffered any structural damage, and it appears that "structures will still meet their normal lifetime capability". Further evaluations are under way.^[184] 2009 also saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in Soyuz imagery in September 2008, but was not thought to be serious.^[185] The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.^[185]

[edit] Cooling loop A failure

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems.^{[186][187][188]} The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module.^[189][190] A third EVA was required to restore Loop A to normal functionality.^[191][192]

The station's cooling system is largely built by the American company Boeing,^[193] which is also the manufacturer of the failed pump.^[194]

[edit] Orbital debris

At the low altitudes at which the ISS orbits there is a variety of space debris, consisting of everything from entire spent rocket stages and defunct satellites, to explosion fragments, paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites, small needles, and many other objects.^[195] These objects, in addition to natural micrometeoroids,^[196] pose a threat to the station as they have the ability to puncture the pressurised modules and cause damage to other parts of the station.^[197][198] Micrometeoroids also pose a risk to spacewalking astronauts, as such objects could puncture their spacesuits, causing them to depressurise.^[199]

Space debris objects are tracked remotely from the ground, and the station crew can be notified of many objects with sufficient size to cause damage on impact. This allows for a Debris Avoidance Manoeuvre (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance.^[197] Eight DAMs had been performed prior to March 2009,^[200] the first seven between October 1999 and May 2003.^[201] Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years.^[201][202] There were two DAMs in 2009, on 22 March and 17 July.^[203] If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their Soyuz spacecraft, so that they would be able to evacuate in the event it was damaged by the debris. This partial station evacuation has occurred twice, on 6 April 2003 and 13 March 2009.^[197]

[edit] Radiation

Without the protection of the Earth's atmosphere, astronauts are exposed to higher levels of radiation from a steady flux of cosmic rays. The station's crews are exposed to about 1 millisievert of radiation each day, which is about the same as someone would get in a year on Earth, from natural sources.^[204] This results in a higher risk of astronauts' developing cancer. High levels of radiation can cause damage to the chromosomes of lymphocytes. These cells are central to the immune system and so any damage to them could contribute to the lowered immunity experienced by astronauts. Over time lowered immunity results in the spread of infection between crew members, especially in such confined areas. Radiation has also been linked to a higher incidence of cataracts in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level, but data is scarce and longer-term exposure will result in greater risks.^[38]

Despite efforts to improve radiation shielding on the ISS compared to previous stations such as Mir, radiation levels within the station have not been vastly reduced, and it is thought that further technological advancement will be required to make long-duration human spaceflight further into the Solar System a possibility.^[204]

It should be noted, however, that the radiation levels experienced on ISS are about 5 times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level^{[dubious – discuss]} of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers, however, experience this level of radiation for no more than 15 hours for the longest transcontinental flights. For example, on a 12 hour flight an airline passenger would experience 0.1 millisievert of radiation, or a rate of 0.2 millisieverts per day, only 1/5 the rate experienced by an astronaut in LEO.^[205]

[edit] See also

• Bigelow Commercial Space Station
• Orbital Technologies Commercial Space Station
• Rotating wheel space station
• Space stations and habitats in popular culture
• Stanford torus

[edit] References

[edit] External links

Official International Space Station webpages of the participating space agencies

• NASA
• RSC Energia
• Russian Federal Space Agency
• Canadian Space Agency
• European Space Agency
• Japanese Space Agency
• Italian Space Agency

Interactive and multimedia

• ISS in telescope
• NASA's ISS interactive reference guide
• NASA's ISS image gallery search page
• Current position of the ISS
• ISS and satellite tracking website
• ISS Webcam
• Animation showing ISS assembly sequence
• ISS real-time tracking information
• Free App for iPhone/iPod touch to predict ISS sightings
• Free App for iPhone/iPad to follow ISS operations and status

Experiments and science

• ESA – Columbus
• JAXA – Space Environment Utilization and Space Experiment
• NASA – Station Science
• RSC Energia – Science Research on ISS Russian Segment

Media articles

• How It Works magazine - ISS nears completion

v · d · eComponents of the International Space Station Overview Assembly · Expeditions · Spacewalks · ISS Program · Scientific Research · Major Incidents Major components in orbit Zarya (Functional Cargo Block) · Zvezda (Service Module) · Unity (Node 1) · Harmony (Node 2) · Tranquility (Node 3) · Destiny (Laboratory) · Columbus (Laboratory) · Kibō (PM, ELM-PS, EF) · Quest (Airlock) · Pirs (Airlock / Docking Module) · Rassvet (MRM 1) · Poisk (MRM 2) · Leonardo (PMM) · Cupola · Integrated Truss Structure (ITS) Subsystems in orbit Canadarm2 (MSS) · Dextre (SPDM) · Strela crane · Kibō Remote Manipulator System · External Stowage Platforms (ESPs) · ExPRESS Logistics Carriers (ELCs) 1,2,4 · Pressurized Mating Adapters (PMAs) · Electrical System · Life Support System Launched periodically Multi-Purpose Logistics Modules (MPLMs) · Kibō (ELM-ES) Scheduled for Shuttle ExPRESS Logistics Carrier (ELC) 3 · Alpha Magnetic Spectrometer · OBSS Scheduled for Proton Nauka (Multipurpose Laboratory Module) · European Robotic Arm (ERA) Not currently scheduled ExPRESS Logistics Carrier (ELC) 5 · Interim Control Module (ICM)  · Node 4 Cancelled Propulsion Module · Centrifuge Accommodations Module (CAM) · Habitation Module · Crew Return Vehicle (CRV/ACRV) · Science Power Platform (SPP) · Universal Docking Module (UDM) · Russian Research Module (RM) Support vehicles Current: Space Shuttle · Soyuz · Progress · Automated Transfer Vehicle (ATV) · H-II Transfer Vehicle (HTV) Future: Dragon · Cygnus · Orion  · Rus  · CST-100 Mission control centers MCC-H (NASA) · TsUP (RKA) · Col-CC (ESA) · ATV-CC (ESA) · JEM-CC (JAXA) · HTV-CC (JAXA) · MSS-CC (CSA) Book:International Space Station  · Category:International Space Station  · Portal:Spaceflight

v · d · eExpeditions to the International Space Station Completed: Expedition 1 • Expedition 2 • Expedition 3 • Expedition 4 • Expedition 5 • Expedition 6 • Expedition 7 • Expedition 8 • Expedition 9 • Expedition 10 • Expedition 11 • Expedition 12 • Expedition 13 • Expedition 14 • Expedition 15 • Expedition 16 • Expedition 17 • Expedition 18 • Expedition 19 • Expedition 20 • Expedition 21 • Expedition 22 • Expedition 23 • Expedition 24 • Expedition 25 • Expedition 26 Current: Expedition 27 Planned: Expedition 28 • Expedition 29 • Expedition 30 • Expedition 31 • Expedition 32 • Expedition 33 • Expedition 34 • Expedition 35 • Expedition 36 • Expedition 37 • Expedition 38 • Expedition 39 Book:Expeditions to the ISS  · Category:Expeditions to the ISS  · Portal:Spaceflight

v · d · eHuman spaceflights to the International Space Station Current Soyuz TMA-20 · Soyuz TMA-21 Planned STS-134 · Soyuz TMA-02M · STS-135 · Soyuz TMA-22 · Soyuz TMA-03M · Soyuz TMA-04M · Soyuz TMA-05M · Soyuz TMA-06M · Soyuz TMA-07M · Soyuz TMA-08M · Soyuz TMA-09M · Soyuz TMA-10M · Soyuz TMA-11M Completed STS-88 · STS-96 · STS-101 · STS-106 · STS-92 · Soyuz TM-31 · STS-97 · STS-98 · STS-102 · STS-100 · Soyuz TM-32 · STS-104 · STS-105 · Soyuz TM-33 · STS-108 · STS-110 · Soyuz TM-34 · STS-111 · STS-112 · Soyuz TMA-1 · STS-113 · Soyuz TMA-2 · Soyuz TMA-3 · Soyuz TMA-4 · Soyuz TMA-5 · Soyuz TMA-6 · STS-114 · Soyuz TMA-7 · Soyuz TMA-8 · STS-121 · STS-115 · Soyuz TMA-9 · STS-116 · Soyuz TMA-10 · STS-117 · STS-118 · Soyuz TMA-11 · STS-120 · STS-122 · STS-123 · Soyuz TMA-12 · STS-124 · Soyuz TMA-13 · STS-126 · STS-119 · Soyuz TMA-14 · Soyuz TMA-15 · STS-127 · STS-128 · Soyuz TMA-16 · STS-129 · Soyuz TMA-17 · STS-130 · Soyuz TMA-18 · STS-131 · STS-132 · Soyuz TMA-19 · Soyuz TMA-01M · STS-133

v · d · eSpace stations and habitats Active International Space Station (ISS) · Genesis I1 and II1 (private, Bigelow Aerospace) Defunct Soviet Union and Russia Salyut (Salyut 1 · DOS-22 · Salyut 21, 3 · Cosmos 5571 · Salyut 33 · Salyut 4 · Salyut 53 · Salyut 6 · Salyut 7) · Polyus2 · Mir United States Skylab Cancelled Manned Orbiting Laboratory · Skylab B · Galaxy ISS-incorporated Space Station Freedom (USOS) · Columbus · Mir-2 (ROS) Developmental China Project 921-2 (Tiangong 1 · Tiangong 2 · Tiangong 3) Bigelow Aerospace Sundancer · BA 330  · Bigelow Commercial Space Station Excalibur Almaz Almaz commercial Russia OPSEK · LOS Proposed Rotating wheel · Bernal sphere · O'Neill cylinder · Stanford torus · Wet workshop · Space habitat · Industrial Space Facility · Orbital Technologies Commercial Space Station  · Bigelow Aerospace BA-2100 1 Never inhabited 2 Failed launch 3 Part of the Almaz military program

v · d · eUnited States government human spaceflight programs Active Space Shuttle · ISS (joint) Previous X-15 (suborbital) · Mercury · Gemini · Apollo · Skylab · Apollo-Soyuz Test Project (with USSR)  · Shuttle-Mir (with Russia) Canceled MISS · Orion (nuclear) · Dyna-Soar · Manned Orbiting Laboratory · National Aero-Space Plane · Space Station Freedom (now ISS) · Orbital Space Plane · Project Constellation

v · d · eSoviet and Russian government manned space programs Active Soyuz • ISS (joint) Past Vostok • Voskhod • Salyut • Apollo-Soyuz Test Project (joint) • Mir • Shuttle-Mir programme (joint) Cancelled Zond (lunar Soyuz 7K-L1) • N1-L3 (Moon landing program) • TMK (Mars flyby program) • Spiral • Almaz (incorporated into Salyut program) / TKS spacecraft • Energia / Buran • Kliper

v · d · eSpaceflight General spaceflight History (Space Race, Accidents and incidents) · Astrodynamics Applications Earth observation satellites (Spy satellites, weather satellites) · Space exploration · Space tourism · Satellite navigation · Space architecture · Space colonization Human spaceflight General Astronaut  · Life support system Hazards Weightlessness (space adaptation syndrome)  · cosmic radiation Major projects Vostok · Mercury · Voskhod · Gemini · Soyuz · Apollo · Space Shuttle · Shenzhou · Mir · ISS · Constellation Other Extra-vehicular activity Spacecraft Launch vehicle · Space Shuttle · Robotic spacecraft · Spacecraft propulsion · Rocket Destinations Sub-orbital · Orbital (Geosynchronous orbit, Geocentric orbit)  · Interplanetary spaceflight · Interstellar travel · Intergalactic travel Space launch Expendable and Reusable systems · Escape velocity · Direct ascent · Non-rocket spacelaunch · Spaceport · Launch pad Main agencies ESA · NASA  · RKA  · CNES  · CNSA · JAXA Other Private spaceflight · Space weather · Lagrangian point · Space and survival