ISS

The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving 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 station serves as a microgravity and space environment research laboratory in which scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.

The ISS programme evolved from the Space Station ''Freedom'', a 1984 American proposal to construct a permanently crewed Earth-orbiting station, and the contemporaneous Soviet/Russian '' Mir-2'' proposal from 1976 with similar aims. The ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian '' Salyut'', Almaz, and '' Mir'' stations and the American Skylab. It is the largest artificial object in the solar system and the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth's surface. It maintains an orbit with an average altitude of by means of reboost manoeuvres using the engines of the '' Zvezda'' Service Module or visiting spacecraft. The ISS circles the Earth in roughly 93 minutes, completing orbits per day.

The station is divided into two sections: the Russian Orbital Segment (ROS) is operated by Russia, while the United States Orbital Segment (USOS) is run by the United States as well as by the other states. The Russian segment includes six modules. The US segment includes ten modules, whose support services are distributed 76.6% for NASA, 12.8% for JAXA, 8.3% for ESA and 2.3% for CSA.

Roscosmos had previously endorsed the continued operation of ROS through 2024, having proposed using elements of the segment to construct a new Russian space station called OPSEK. However, continued cooperation has been rendered uncertain by the 2022 Russian invasion of Ukraine and subsequent international sanctions on Russia, who theoretically, may lower, redirect, or cut funding from their side of the space station due to the sanctions set on them.

The first ISS component was launched in 1998, and the first long-term residents arrived on 2 November 2000 after being launched from the Baikonur Cosmodrome on 31 October 2000. The station has since been continuously occupied for , the longest continuous human presence in low Earth orbit, having surpassed the previous record of held by the ''Mir'' space station. The latest major pressurised module, ''Nauka'', was fitted in 2021, a little over ten years after the previous major addition, ''Leonardo'' in 2011. Development and assembly of the station continues, with an experimental inflatable space habitat added in 2016, and several major new Russian elements scheduled for launch starting in 2021. In January 2022, the station's operation authorization was extended to 2030, with funding secured within the United States through that year. There have been calls to privatize ISS operations after that point to pursue future Moon and Mars missions, with former NASA Administrator Jim Bridenstine stating: "given our current budget constraints, if we want to go to the moon and we want to go to Mars, we need to commercialize low Earth orbit and go on to the next step."

The ISS consists of pressurised habitation modules, structural trusses, photovoltaic solar arrays, thermal 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 station is serviced by a variety of visiting spacecraft: the Russian Soyuz and Progress, the SpaceX Dragon 2, and the Northrop Grumman Space Systems Cygnus, and formerly the European Automated Transfer Vehicle (ATV), the Japanese H-II Transfer Vehicle, and SpaceX Dragon 1. The Dragon spacecraft allows the return of pressurised cargo to Earth, which is used, for example, to repatriate scientific experiments for further analysis. , 251 astronauts, cosmonauts, and space tourists from 20 different nations have visited the space station, many of them multiple times.

History

Purpose

The ISS was originally intended to be a laboratory, observatory, and factory while providing transportation, maintenance, and a low Earth orbit staging base for possible future missions to the Moon, Mars, and asteroids. However, not all of the uses envisioned in the initial memorandum of understanding between NASA and Roscosmos have been realised. In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic, and educational purposes.

Scientific research

The ISS provides a platform to conduct scientific research, with power, data, cooling, and crew available to support experiments. Small uncrewed spacecraft can also provide platforms for experiments, especially those involving zero gravity and exposure to space, but space stations offer a long-term environment where studies can be performed potentially for decades, combined with ready access by human researchers.

The ISS simplifies individual experiments by allowing groups of experiments to share the same launches and crew time. Research is conducted in a wide variety of fields, including astrobiology, astronomy, physical sciences, materials science, space weather, meteorology, and human research including space medicine and the life sciences. Scientists on Earth have timely access to the data and can suggest experimental modifications to the crew. If follow-on experiments are necessary, the routinely scheduled launches of resupply craft allows new hardware to be launched with relative ease. Crews fly expeditions of several months' duration, providing approximately 160 person-hours per week of labour with a crew of six. However, a considerable amount of crew time is taken up by station maintenance.

Perhaps the most notable ISS experiment is the Alpha Magnetic Spectrometer (AMS), which is intended to detect dark matter and answer other fundamental questions about our universe. According to NASA, the AMS is as important as the Hubble Space Telescope. Currently docked on station, it could not have been easily accommodated on a free flying satellite platform because of its power and bandwidth needs. On 3 April 2013, scientists reported that hints of dark matter may have been detected by the AMS. According to the scientists, "The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays".

The space environment is hostile to life. Unprotected presence in space is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the solar wind, in addition to cosmic rays), high vacuum, extreme temperatures, and microgravity. (see Space Environment on page 122) Some simple forms of life called extremophiles, as well as small invertebrates called tardigrades can survive in this environment in an extremely dry state through desiccation.

Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift. These data will be used to determine whether high duration human spaceflight and space colonisation are feasible. In 2006, data on bone loss and muscular atrophy suggested 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 interval required to travel to Mars.

Medical studies are conducted aboard the ISS on behalf of the National Space Biomedical Research Institute (NSBRI). Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity study in which astronauts 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 on board 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.

In August 2020, scientists reported that bacteria from Earth, particularly '' Deinococcus radiodurans'' bacteria, which is highly resistant to environmental hazards, were found to survive for three years in outer space, based on studies conducted on the International Space Station. These findings supported the notion of panspermia, the hypothesis that life exists throughout the Universe, distributed in various ways, including space dust, meteoroids, asteroids, comets, planetoids or contaminated spacecraft.

Remote sensing of the Earth, astronomy, and deep space research on the ISS have dramatically increased during the 2010s after the completion of the US Orbital Segment in 2011. Throughout the more than 20 years of the ISS program researchers aboard the ISS and on the ground have examined aerosols, ozone, lightning, and oxides in Earth's atmosphere, as well as the Sun, cosmic rays, cosmic dust, antimatter, and dark matter in the universe. Examples of Earth-viewing remote sensing experiments that have flown on the ISS are the Orbiting Carbon Observatory 3, ISS-RapidScat, ECOSTRESS, the Global Ecosystem Dynamics Investigation, and the Cloud Aerosol Transport System. ISS-based astronomy telescopes and experiments include SOLAR, the Neutron Star Interior Composition Explorer, the Calorimetric Electron Telescope, the Monitor of All-sky X-ray Image (MAXI), and the Alpha Magnetic Spectrometer.

Freefall

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 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 connected these items experience small forces that keep the station moving as a rigid body.

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 the 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.

Investigating the physics of fluids in microgravity will provide better models of the behaviour of fluids. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. Examining reactions that are slowed by low gravity and low temperatures will improve our 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 low gravity on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve knowledge about energy production and lead to economic and environmental benefits.

Exploration

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 operations, maintenance as well as repair and replacement activities on-orbit. This will help develop essential skills in operating spacecraft farther from Earth, reduce mission risks, and advance the capabilities of interplanetary spacecraft. Referring to the MARS-500 experiment, a crew isolation experiment conducted on Earth, ESA states that "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations". Sergey Krasnov, the head of human space flight programmes for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS.

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programmes of research and exploration of the Solar system, including the Moon and Mars." A crewed mission to Mars may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India and South Korea be invited to join the ISS partnership. NASA chief Charles Bolden stated in February 2011, "Any mission to Mars is likely to be a global effort". Currently, US federal legislation prevents NASA co-operation with China on space projects.

Education and cultural outreach

The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, and email. ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms. In one lesson, students can navigate a 3D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.

The Japanese Aerospace Exploration Agency (JAXA) aims to inspire children to "pursue craftsmanship" and to heighten their "awareness of the importance of life and their responsibilities in society". Through a series of education guides, students develop a deeper understanding of the past and near-term future of crewed space flight, as well as that of Earth and life. In the JAXA "Seeds in Space" experiments, the mutation effects of spaceflight on plant seeds aboard the ISS are explored by growing sunflower seeds that have flown on the ISS for about nine months. In the first phase of ''Kibō'' utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.

Cultural activities are another major objective of the ISS programme. Tetsuo Tanaka, the director of JAXA's Space Environment and Utilization Center, has said: "There is something about space that touches even people who are not interested in science."

Amateur Radio on the ISS (ARISS) is a volunteer programme that encourages students worldwide to pursue careers in science, technology, engineering, and mathematics, through amateur radio communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from nine co