Assembly of the International Space Station

The process of assembling the International Space Station (ISS) has been under way since the 1990s. Zarya, the first ISS module, was launched by a Proton rocket on 20 November 1998. The STS-88 shuttle mission followed two weeks after Zarya was launched, bringing Unity, the first of three node modules, and connecting it to Zarya. This bare 2-module core of the ISS remained unmanned for the next one and a half years, until in July 2000 the Russian module Zvezda was added, allowing a maximum crew of two astronauts or cosmonauts to be on the ISS permanently.

The ISS has a planned pressurized volume of approximately 1,000 cubic meters, a mass of approximately 400,000 kilograms, approximately 100 kilowatts of power output, a truss 108.4 meters long, modules 74 meters long, and a crew of six. Building the complete station will require more than 40 assembly flights. As of March 2011, 26 Space Shuttle flights have docked with ISS to add elements, and 9 other Shuttle flights have flown logistics-servicing missions to ISS without adding major external elements. These 35 Shuttle missions include 9 SpaceHab and 10 MPLM logistics-servicing missions in various combinations. The last two planned Shuttle flights are due to add one of the two final elements of ISS, followed by one last Proton launch with the planned delivery of the ERA. Other assembly flights have consisted of modules lifted by the Russian Proton rocket or in the case of Pirs and Poisk by a Soyuz-U rocket.

Some of the larger modules include:

The space station is located in orbit around the Earth at an altitude of approximately 410 km (250 mi), a type of orbit usually termed low Earth orbit (the actual height varies over time by several kilometers due to atmospheric drag and reboosts). It orbits Earth in a period of about 90 minutes; by August 2007 it had completed more than 50,000 orbits since launch of Zarya on 20 November 1998.

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