A Large Space Station Over Earth.

The International Space Station is the largest object ever constructed by humans in space. The station perimeter now extends over roughly the area of a football field , although only a small fraction of this is composed of modules habitable by humans. The station is so large that it could not be launched all at once -- it is being built piecemeal with large sections added continually by flights of the Space Shuttle . To function, the ISS needs huge trusses , some over 15 meters long and with masses over 10,000 kilograms, to keep it rigid and to route electricity and liquid coolants. Pictured above , part of the immense space station was photographed out of a window by a member of the visiting Space Shuttle Discovery STS-131 crew. Visible in the foreground is Japan's Kibo research module , while a large truss is visible toward the left. On the far right, a crescent Earth slices through the blackness of space.