Video: Astronauts Bolt The Final American Module Onto The ISS, Completing a Dozen Years' Construction

ISS From Discovery

The International Space Station as seen from Discovery's approach.NASA

After almost 13 years, the world's most complicated construction project, the International Space Station, is almost complete. Spacewalking astronauts attached the final U.S. pressurized module, the Permanent Multipurpose Module Leonardo, thereby wrapping up the U.S. portion of station construction.

The PMM will provide additional storage for the station crew, and they might conduct experiments inside it to study fluid physics, materials science, biology and biotechnology. Other nodes may be attached later, but work on the station's pressurized living/working areas is pretty much done.

Watch it come to life in the video below.

Though the U.S. has been a leader in station construction, 15 nations have contributed modules and hardware. This international heritage is on striking display this week in particular, as four spacecraft from four space agencies — NASA, Roscosmos, JAXA and ESA — are docked with the station.

NASA wanted to use a Russian Soyuz capsule to fly around the station and snap a photo of the international parking lot, commemorating the festival of nations as well as capturing Discovery's last rendezvous with the orbiting outpost. But Russia nixed the idea because officials did not want to move the capsule, which is a new model, into an unfamiliar flight plan.

Discovery astronauts will take photos of the station when it undocks on Sunday, but the shuttle won't be in the photo.

There is one big construction project left — later this spring, space shuttle Endeavour will deliver the Alpha Magnetic Spectrometer-02, designed to detect dark matter and uncover the secrets of the origins of the universe. Beyond that, Russian craft and European cargo ships like the Johannes Kepler craft will bring new supplies and experiments to the station. It is slated to fly until at least 2020.