Even halfway toward completion, the ISS was already the largest space station ever built. It has a long, narrow main truss, with several modules branching horizontally outward, and several sets of solar panels to provide electric power to the station’s many systems. The length of the ISS solar panel arrays alone is 239 feet (73 meters), or about five tractor-trailers placed end-to-end. Major pieces of ISS were originally designed to be parts of other, separate space missions—such as the American space station Freedom, the Russian space station Mir 2, the European Columbus program, and the Japanese Kibo experiment module—and were then adapted for inclusion into ISS.