[酷图] 不断扩建中的国际空间站。

Credit: STS-113 Shuttle Crew, NASA
Explanation: The International Space Station (ISS) will be the largest human-made object ever to orbit the Earth. 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 trusses to keep it rigid and to route electricity and liquid coolants. These trusses are huge, extending over 15 meters long, and with masses over 10,000 kilograms. Pictured above at the end of last month, astronaut Michael Lopez-Alegria works to install the Port-One Truss. On the right is the end of Canadarm2, the robotic remote control arm of the ISS.

                               
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