The International Space Station (ISS) is a space station, or a habitable artificial satellite in low Earth orbit. It is a modular structure whose first component was launched in 1998. Now the largest artificial body in orbit, it can often be seen at the appropriate time with the naked eye from Earth. The ISS consists of pressurised modules, external trusses, solar arrays and other components. ISS components have been launched by American Space Shuttles as well as Russian Proton and Soyuz rockets. In 1984 the ESA was invited to participate in Space Station Freedom. In 1993, after the USSR ended, the United States and Russia merged Mir-2 and Freedom together
The ISS is arguably the most expensive single item ever constructed. As of 2010 the cost is estimated to be $150 billion. It includes NASA’s budget of $58.7 billion for the station from 1985 to 2015 ($72.4 billion dollars in 2010), Russia’s $12 billion ISS budget, Europe’s $5 billion, Japan’s $5 billion, and Canada’s $2 billion plus the cost of 36 shuttle flights to build the station—estimated at $1.4 billion each, $50.4 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 Skylab.