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The International Space Station (ISS) is a Space Station

International Space Station

The International Space Station (ISS) is a space station (habitable artificial satellite) in low Earth orbit. The ISS programme is a joint project between five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The ownership and use of the space station is established by intergovernmental treaties and agreements.

The ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology, and other fields. The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars. The ISS maintains an orbit with an average altitude of 400 kilometres (250 mi) by means of reboost manoeuvres using the engines of the Zvezda module or visiting spacecraft. It circles the Earth in roughly 92 minutes and completes 15.5 orbits per day.
The station is divided into two sections, the Russian Orbital Segment (ROS), which is operated by Russia, and the United States Orbital Segment (USOS), which is shared by many nations. Roscosmos has endorsed the continued operation of ISS through 2024, but had previously proposed using elements of the Russian segment to construct a new Russian space station called OPSEK. As of December 2018, the station is expected to operate until 2030.
International Space Station
International Space Station
The International Space Station on May 23, 2010, as seen from STS-132

The nations initially participating in the ISS programme.
International Space Station
ISS Logo
Station statistics
COSPAR ID1998-067A
SATCAT no.25544
Call signAlphaStation
CrewFully crewed: 6
Currently aboard: 6 (Expedition 61)
Launch20 November 1998; 21 years ago
Launch pad
  • Baikonur 1/5 and 81/23
  • Kennedy LC-39 and CCAFS SLC-41 (future)
Mass419,725 kg (925,335 lb)
Length73.0 m (239.4 ft)
Width109.0 m (357.5 ft)
Pressurised volume915.6 m3 (32,333 cu ft)
Atmospheric pressure101.3 kPa (14.7 psi; 1.0 atm) oxygen 21%, nitrogen 79%
Perigee altitude408 km (253.5 mi) AMSL
Apogee altitude410 km (254.8 mi) AMSL
Orbital inclination51.64°
Orbital speed7.66 km/s
(27,600 km/h; 17,100 mph)
Orbital period92.68 minutes
Orbits per day15.54
Orbit epoch14 May 2019 13:09:29  UTC
Days in orbit21 years, 2 months, 2 days
(22 January 2020)
Days occupied19 years, 2 months, 20 days
(22 January 2020)
No. of orbits116,178 as of May 2019
Orbital decay2 km/month
Statistics as of 9 March 2011
(unless noted otherwise)
International Space Station
The first ISS component was launched in 1998, with the first long-term residents arriving on 2 November 2000. Since then, the station has been continuously occupied for 19 years and 81 days. This is the longest continuous human presence in low Earth orbit, having surpassed the previous record of 9 years and 357 days held by Mir. The latest major pressurised module was fitted in 2011, with an experimental inflatable space habitat added in 2016. Development and assembly of the station continues, with several major new Russian elements scheduled for launch starting in 2020. The ISS is the largest human-made body in low Earth orbit and can often be seen with the naked eye from Earth. The ISS consists of pressurised habitation modules, structural trusses, solar arrays, radiators, docking ports, experiment bays and robotic arms. Major ISS modules have been launched by Russian Proton and Soyuz rockets and US Space Shuttles.

The ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian Salyut, Almaz, and Mir stations as well as Skylab from the US. The station is serviced by a variety of visiting spacecraft: the Russian Soyuz and Progress, the US Dragon and Cygnus, the Japanese H-II Transfer Vehicle, and formerly the European Automated Transfer Vehicle. The Dragon spacecraft allows the return of pressurised cargo to Earth (downmass), which is used for example to repatriate scientific experiments for further analysis. The Soyuz return capsule has minimal downmass capability next to the astronauts.

The ISS has been visited by astronauts, cosmonauts and space tourists from 19 different nations. As of September 2019, 239 people from 19 countries had visited the space station, many of them multiple times. The United States sent 151 people, Russia sent 47, nine were Japanese, eight Canadian, five Italian, four French, three German, and one each from Belgium, Brazil, Denmark, Kazakhstan, Malaysia, the Netherlands, South Africa, South Korea, Spain, Sweden, the United Arab Emirates, and the United Kingdom.

Free fall

Gravity at the altitude of the ISS is approximately 90% as strong as at Earth's surface, but objects in orbit are in a continuous state of freefall, resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:

Drag from the residual atmosphere.
Vibration from the movements of mechanical systems and the crew.
Actuation of the on-board attitude control moment gyroscopes.
Thruster firings for attitude or orbital changes.
Gravity-gradient effects, also known as tidal effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a rigid body.

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