The International Space Station (ISS) is a modular space station 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 ISS flies 400km at speeds that defy gravity. It takes only 92 minutes to make a complete circuit of Earth, at 28 800 km/h. Astronauts working and living on the Station experience 16 sunrises and sunsets each day.
It took 10 years and more than 30 missions to assemble the station but all the efforts were worth it. The space station is approximately the size of a football field: a 460-ton, permanently crewed platform orbiting 400km above Earth. The idea of a space station was once science fiction, existing only in the imagination until it became clear in the 1940s that the construction of such a structure might be attainable. As the Space Age began in the 1950s, designs of “space planes” and stations dominated popular media. The first rudimentary station was created in 1969 by the linking of two Russian Soyuz vehicles in space, followed by other stations and developments in space technology until construction began on the ISS in 1998, aided by the first reusable spacecraft ever developed: the American shuttles. The Station can accommodate 7 members on it.
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 space and the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth’s surface. 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 many other nations. In 2018 the station’s operation authorization was extended to 2030, with funding secured until 2025. There have been calls to privatize ISS operations after that point to pursue future Moon and Mars missions, with former NASA Administrator Jim Bridenstine said: “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 pressurized 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. As of August 2021, 244 astronauts, cosmonauts, and space tourists from 19 different nations have visited the space station, many of them multiple times; this includes 153 Americans, 50 Russians, 9 Japanese, 8 Canadians, 5 Italians, and 1 Brazilian.
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 realized. In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic, and educational purposes. 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. Crews fly expeditions of several months’ duration, providing approximately 160 person-hours per week of labor with a crew of six. 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 and is as important as the Hubble Space Telescope according to NASA.
Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift. This data will be used to determine whether high-duration human spaceflight and space colonization is feasible.
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. 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 assembly of the International Space Station, a major endeavor in space architecture, began in November 1998. Russian modules launched and docked robotically, except for Rassvet. All other modules were delivered by the Space Shuttle, which required installation by ISS and Shuttle crewmembers using the Canadarm2 (SSRMS) and extra-vehicular activities (EVAs); as of 5 June 2011, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles. The beta angle of the station had to be considered at all times during construction. The first resident crew, Expedition 1, arrived in November 2000 on Soyuz TM-31. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign “Alpha”, which he and cosmonaut Krikalev preferred to the more cumbersome “International Space Station”.
The expansion schedule was interrupted by the Space Shuttle Columbia disaster in 2003 and a resulting hiatus in flights. The Space Shuttle was grounded until 2005 with STS-114 flown by Discovery. Assembly resumed in 2006 with the arrival of STS-115 with Atlantis, which delivered the station’s second set of solar arrays. The pressurized modules are Zarya, Unity, Zvezda, Destiny, Quest, Poisk, Harmony, Tranquility, Columbus, Kibo, Cupola, Rassvet, MLM outfittings, Leonardo, Bigelow Expandable Activity Module, and Nauka. There are also a lot of unpressurized elements like robotic arms and cargo cranes.
There are currently 9 available docking ports for visiting spacecraft: Harmony forward (with PMA 2 /IDA 2); Harmony zenith (with PMA 3/ IDA 3); Harmony nadir; Unity nadir; Nauka nadir; Nauka forward; Poisk zenith; Rassvet nadir; Zvezda aft.
The ISS is partially protected from the space environment by Earth’s magnetic field. From an average distance of about 70,000 km (43,000 mi) from the Earth’s surface, depending on Solar activity, the magnetosphere begins to deflect solar wind around Earth and the space station. Solar flares are still a hazard to the crew, who may receive only a few minutes’ warning. In 2005, during the initial “proton storm” of an X-3 class solar flare, the crew of Expedition 10 took shelter in a more heavily shielded part of the ROS designed for this purpose. Subatomic charged particles, primary protons from cosmic rays and solar wind, are normally absorbed by Earth’s atmosphere. When they interact in sufficient quantity, their effect is visible to the naked eye in a phenomenon called an aurora. Outside Earth’s atmosphere, ISS crews are exposed to approximately one millisievert each day (about a year’s worth of natural exposure on Earth), resulting in a higher risk of cancer.
A very important aspect of ISS safety is the debris that is floating in space at high speeds and can damage the station. For protection, ballistic panels are incorporated into the station. On the USOS, Whipple Shields are used. The US segment modules consist of an inner layer made from 1.5–5.0 cm-thick (0.59–1.97 in) aluminum, a 10 cm-thick (3.9 in) intermediate layers of Kevlar and Nextel, and an outer layer of stainless steel, which causes objects to shatter into a cloud before hitting the hull, thereby spreading the energy of impact.
The countries involved in this project are Brazil (1997-2007), Canada, Japan, Russia, United States, ESA (Belgium, Denmark, France, Germany, Italy, Netherlands, Norway, Spain, Sweden, Switzerland, and United Kingdom).
The ISS has been described as the most expensive single item ever constructed. As of 2010, the total cost was US$150 billion. This includes NASA’s budget of $58.7 billion (inflation-unadjusted) for the station from 1985 to 2015 ($72.4 billion in 2010 dollars), Russia’s $12 billion, Europe’s $5 billion, Japan’s $5 billion, Canada’s $2 billion, and the cost of 36 shuttle flights to build the station, estimated at $1.4 billion each, or $50.4 billion in total. Summing up, the whole project approximately costs $132.7 billion. Assuming 20,000 person-days of use from 2000 to 2015 by two- to six-person crews, each person-day would cost $7.5 million, less than half the inflation-adjusted $19.6 million ($5.5 million before inflation) per person-day of Sky.
More information: https://www.nasa.gov/mission_pages/station/main/index.html