Milestone moments from 15 years of the ISS (pictures)

On November 20, 1998, when some of us were adjusting to life in a college dorm, the first part of the International Space Station launched from Kazakhstan atop a Russian Proton rocket. Astronauts aboard the space shuttle Endeavour would connect a second module two weeks later, beginning a multiyear construction process for one of the largest and most complex projects ever requiring broad international cooperation. Full assembly of the ISS was finally completed in 2011. In its first 15 years, more than 1,500 science experiments have been conducted at the ISS, with 68 partnering countries and astronauts representing 15 nations making 139 flights to the station.

On December 4, 1998, the space shuttle Endeavour lifted off, carrying American astronaut Bob Cabana, Russian cosmonaut Sergei Krikalev, and NASA's Unity module, which was to be connected to the already orbiting Russian Zarya control module. Endeavour's on-board camera captured the first two parts of the International Space Station after they were joined in the shuttle's cargo bay. Cabana and Krikalev then entered together to become the first crew members of the ISS.

The first crew to live aboard the ISS for an extended period of time was the trio of astronaut Bill Shepherd and cosmonauts Yuri Gidzenko and Sergei Krikalev, who moved into their new digs in November of 2000 and stayed for several months. They performed a wide array of setup and unpacking activities and hosted visiting shuttle flights.

In February of 2001, the US research laboratory module dubbed "Destiny" was added to the ISS. In 2005, it was recognized as the newest laboratory to be added to America's National Lab system, alongside the likes of Los Alamos and Lawrence Livermore. Today research facilities aboard the ISS have been made available to students and some commercial uses.

Wealthy engineer Dennis Tito (at right) boarded a Soyuz rocket bound for the ISS on April 28, 2001, and became the first private citizen to go to space. Tito spent $20 million on the flight and a six-day stay aboard the space station. Since then, Space Adventures -- the company that booked Tito's space trip -- has gone on to book several other space tourists.

In 2003, the Space Shuttle Columbia disaster put the entire shuttle program on hiatus. During the more than two-year halting of shuttle flights, the ISS was dependent on Russian Soyuz flights, and waste began to accumulate aboard the station, hindering some operations.

Space shuttle Discovery marked NASA's "return to flight" after the Columbia disaster. The spacecraft made a supply run to the ISS in July of 2005, more than two years since a shuttle had last docked with the station. In this image, the underside of Discovery is shown in orbit alongside the station's robotic arm.

So far, more than 1,500 experiments have been performed at the ISS, including raising butterfiles and spiders in zero gravity. Students on Earth compared the life cycle of monarch butterflies raised on terra firma to imagery (shown here) of butterflies on the ISS.

In 2009, three astronauts from Russia, Belgium, and Canada boarded the International Space Station, doubling its crew size to six for the first time. The expansion of the crew size had been long awaited and came with the central benefit of boosting potential man hours for science research by more than three times.

In 2011, more than 25 years after President Reagan first called for the construction of the space station, the ISS was completed. It is about the length and width of a football field and weighs almost a million pounds (or would on Earth). The interior of the ISS includes 13,396 cubic feet of habitable space. The entire station is powered by 8 solar arrays generating 84 kilowatts.

In a twist worthy of a Hollywood plot line, the ISS crew was forced to take shelter in the station's Soyuz "lifeboats" shortly after the station was completed. A piece of space junk passed near the ISS but caused no damage.

History was made again at the International Space Station in May of 2012 when the first commercial cargo ship completed a successful test flight to dock with the ISS. The SpaceX Dragon capsule carried more than 1,000 pounds of low-priority supplies to deliver to its client, NASA, which awarded Elon Musk's company a $1.6 billion contract for at least 12 missions.

Of the many experiments performed aboard the ISS, some of the coolest have to be those that involve fire in zero gravity. You can get the full details here on why flames in space are more like floating fireballs that give off formaldehyde. Three cheers for space science!

This month, in advance of its 15th birthday, the ISS received a special visitor: The Olympic torch made a stop at the station and went for a brief spacewalk on its way to the 2014 Olympics in Sochi, Russia. Looking further ahead, the International Space Station is scheduled to remain in operation until at least 2020, but there has been some talk of trying to extend that date to 2028, possibly giving us another 15 years of epic space science -- and perhaps a few more cool music videos along the way.