International Space Station
The International Space Station (ISS) is an internationally developed research facility that is being assembled in low Earth orbit. On-orbit construction of the station began in 1998 and is scheduled for completion by 2011. The station is expected to remain in operation until at least 2015, and likely 2020.With a greater mass than that of any previous space station, the ISS can be seen from the Earth with the naked eye, and, as of 2010, is the largest artificial satellite orbiting the Earth.The ISS serves as a research laboratory that has a microgravity environment in which crews conduct experiments in biology, human biology, physics, astronomy and meteorology. The station has a unique environment for the testing of the spacecraft systems that will be required for missions to the Moon and Mars. The ISS is operated by Expedition crews, and has been continuously staffed since 2 November 2000, meaning the ISS programme has maintained an uninterrupted human presence in space for the past 9 years and 170 days, which is approaching the current record, set aboard Mir, of 9 years and 257 days. As of 18 March 2010, the crew of Expedition 23 is aboard.
The ISS is a synthesis of several space station projects that includes the American Freedom, the Soviet/Russian Mir-2, the European Columbus and the Japanese Kibō. Budget constraints led to the merger of these projects into a single multi-national programme. The ISS project began in 1994 with the Shuttle-Mir programme,and the first module of the station, Zarya, was launched in 1998 by Russia.Assembly continues, as pressurised modules, external trusses and other components are launched by American space shuttles, Russian Proton rockets and Russian Soyuz rockets.As of February 2010, the station consisted of 13 pressurised modules and an extensive integrated truss structure (ITS). Power is provided by 16 solar arrays mounted on the external truss, in addition to four smaller arrays on the Russian modules. The station is maintained at an orbit between
Operated as a joint project between the five participant space agencies, the station's sections are controlled by mission control centres on the ground operated by 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). The ownership and use of the space station is established in intergovernmental treaties and agreements that allow the Russian Federation to retain full ownership of its own modules, with the remainder of the station allocated between the other international partners.The cost of the station has been estimated by ESA as €100 billion over 30 years,and, although estimates range from 35 billion dollars to 160 billion dollars, the ISS is believed to be the most expensive object ever constructed. The financing, research capabilities and technical design of the ISS programme have been criticised because of the high cost. The station is serviced by Soyuz spacecraft, Progress spacecraft, space shuttles, the Automated Transfer Vehicle and the H-II Transfer Vehicle, and has been visited by astronauts and cosmonauts from 15 different nations.
Station statistics
NSSDC ID: 1998-067A
Call sign: Alpha
Crew: 6
Launch: 1998–2011
Launch pad: KSC LC-39,
Baikonur LC-1/5 & LC-81/23
Mass:
Length:
from PMA-2 to Zvezda
Width:
along truss, arrays extended
Height: c.
nadir–zenith, arrays forward–aft
Living volume: c.
(c. 13,200 cu ft)
Atmospheric pressure:
101.3 kPa (29.91 inHg) (1 atm)
Perigee:
Apogee:
Orbit inclination: 51.6419 degrees
Average speed: 7,706.6 m/s
(
Orbital period: c. 91 minutes
Days in orbit: 4168
(19 April 2010)
Days occupied: 3457
(19 April 2010)
Number of orbits: c. 65780
(19 April 2010)
Orbital decay: 2 km/month
Purpose
The International Space Station (ISS) is an internationally developed satellite currently being assembled in Low Earth Orbit. 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. 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 specialised unmanned spacecraft.
Crews, who fly expeditions of several months' duration, conduct scientific experiments each day (approximately 160 man-hours a week). As of the conclusion of Expedition 15, 138 major science investigations had been conducted on the ISS. Scientific findings, in fields from basic science to exploration research, are published every month.
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.
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 14 nations to live and work together in space, providing lessons for future multi-national missions.
Scientific research
Main article: Research and Science on the International Space Station
Expedition 8 Commander and Science Officer Michael Foale conducts an inspection of the Microgravity Science Glovebox.
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. 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.
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 colonisation 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). 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.
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.
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.
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.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.
Origins
Main article: Shuttle-Mir Program
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-
With the fall of the
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
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.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.
According to the plan, the ISS 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
Station structure
Assembly
Main article: Assembly of the International Space Station
The assembly of the International Space Station, a major endeavour in space architecture, began in November 1998.[2] Astronauts install each element using spacewalks. By 27 November 2009, they had completed 136, totalling 849 hours of extra-vehicular activity (EVA), all devoted to assembly and maintenance of the station. Twenty-eight of these spacewalks originated from the airlocks of docked Space Shuttles; the remaining 108 were launched from the station.
The first segment of the ISS, Zarya, was launched on 20 November 1998 on a Russian Proton rocket, followed two weeks later by Unity—the first of three node modules—which was launched aboard Space Shuttle flight STS-88. This bare two-module core of the ISS remained unmanned for the next one-and-a-half years. In July 2000 the Russian module Zvezda was added, allowing a maximum crew of three to occupy the ISS continuously. 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 embryonic station with communications, guidance, electrical grounding (on Z1), and power via solar arrays located on the P6 truss.
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.
The expansion schedule was interrupted by the destruction of the Space Shuttle Columbia on STS-
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, the Japanese Experiment Module. 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, and the third node, Tranquillity, in February 2010 during STS-130 by the Space Shuttle Endeavour, alongside the Cupola.
As of February 2010, the station consisted of thirteen pressurised modules and the complete Integrated Truss Structure. Still to be launched is the Pressurised Multipurpose Module Leonardo, the European Robotic Arm, two Russian modules and a number of external components, including the 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).
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.The ITS consists of ten separate segments forming a structure
The Alpha Magnetic Spectrometer (AMS), a particle physics experiment, is scheduled to be launched on STS-
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
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;the JEM RMS, which services the JEM Exposed Facility, 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.
The station in its complete form will have several smaller external components, such as the three External Stowage Platforms (ESPs), launched on STS-102, STS-114 and STS-118, which are used for storage of 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-
Power supply
Main article: Electrical system of the International Space Station
The source of electrical power for the ISS is the sun. Sunlight is converted into electricity by solar arrays. The Russian segment of the station uses 28 volts DC (partly provided by four solar arrays mounted directly to Zarya and Zvezda), as does the space shuttle, but in the remainder of the station, electricity provided by the US solar arrays is distributed at a voltage ranging from 130 to 180 volts DC. These arrays are arranged as four pairs of wings, and each pair is capable of generating nearly 32.8 kW of DC power.
Power is stabilised and distributed at 160 volts DC, and then is converted to the user-required 124 volts DC. The high-voltage distribution allows the use of small-diameter electrical cables and consequently reduces weight. Power can be shared between the two segments of the station using converters. The power sharing feature has become essential since the cancellation of the Russian Science Power Platform because the Russian Orbital Segment now depends on the US-built solar arrays for power.
Since the station is often not in direct sunlight, it relies on rechargeable nickel-hydrogen batteries to provide continuous power for the 35 minutes of every 90 minute orbit during which it is eclipsed by the Earth. During the sunlit part of the orbit, the batteries are recharged. The batteries have a working life of 6.5 years, and they are expected to be replaced multiple times during the anticipated 20-year life of the station.
The
Orbit control
The ISS is maintained in a near circular orbit with a minimum mean altitude of
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. This technology could allow station-keeping to be done more economically than at present.
Attitude (orientation) control
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
Communications
* Luch satellite not currently in use.
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.
The Russian Orbital Segment communicates directly with the ground via the Lira antenna mounted to Zvezda. The Lira antenna also has the capability to use the Luch data relay satellite system. This system, used for communications with Mir, fell into disrepair during the 1990s, and as a result is no longer in use, although two new Luch satellites—Luch-5A and Luch-5B—are planned for launch in 2011 to restore the operational capability of the system.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 Ku 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 Centre (MCC-H) in
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 Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers. 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.
Microgravity
At the station's orbital altitude, the gravity from the Earth is 88% of that at sea level. The state of weightlessness is caused by the constant free fall of the ISS, which, because of the equivalence principle, is indiscernible from a state of zero gravity. The environment on the station is, however, often described as microgravity, as the weightlessness is imperfect. This is caused by four separate effects:
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. This is also called the tidal force.
Life support
Main article: ISS ECLSS
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, shower, toilet, and condensation from the air. The Elektron system aboard Zvezda and a similar system in Destiny generate oxygen aboard the station. The crew has a backup option in the form of bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters. 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.
The atmosphere on board the ISS is similar to the Earth's.
Sightings
A July 2007 sighting of the International Space Station.
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.
To view the station, the following conditions need to be fulfilled, assuming the weather is clear: The station must be above the observer's horizon, and it must pass within about
The station has now become bright enough to be seen during the day under certain conditions.
Politics, utilisation and financing
Main article: International Space Station programme.
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).
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, Russian Federation, Japan, Canada and ten member states of the European Space Agency (Belgium, Denmark, France, Germany, Italy, The Netherlands, Norway, Spain, Sweden and Switzerland).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. Use of the Russian Orbital Segment is also negotiated at this level.
In addition to these main intergovernmental agreements,
Utilisation rights
The Russian part of the station is operated and controlled by the
Kibō: 51% for the JAXA, 46.7% for NASA, and 2.3% for CSA.
Destiny: 97.7% for NASA and 2.3% for CSA.
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.
Visiting spacecraft
Spacecraft 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 H-II Transfer Vehicle from the Japan Aerospace Exploration Agency have provided resupply services to the station. In addition,
As of 17 April 2010, there are four spacecraft docked with the ISS:
Soyuz TMA-17 is at Zarya's nadir port, the last spacecraft to dock there, having delivered three members of Expedition 23 to the station.
Soyuz TMA-18 is at the Poisk docking port, having delivered three members of Expedition 23 to the station.
Progress M-03M is at the Pirs docking port, having delivered supplies to the station.
Progress M-04M is at Zvezda's aft docking port, having delivered a cargo of propellant, oxygen and air, water, spare parts and other supplies to the station.
