(CNN) It was 1998 when a Russian Proton rocket flew the Zarya module up to orbit, the first piece of what would become the International Space Station (ISS).
Seventeen years later, after playing host to 15 and a half years of continuous human habitation for astronauts from 18 different countries, the ISS has just completed its 100,000th orbit around the Earth.
NASA announced the milestone Monday, explaining that the 2.6 billion miles it's traveled is equal to 10 round trips to Mars or nearly the journey to Neptune.
The International Space Station was built in collaboration by 16 countries -- the United States, Canada, Japan, Russia, Brazil, Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland and the United Kingdom.
Circling the Earth every 90 minutes, its inhabitants (222 so far) are treated to a spectacular sunrise or sunset every 45 minutes.
It has as much pressurized living and working space as a Boeing 747 passenger jet. It weighs nearly one million pounds (450,000 kilograms) and is about the size of a football field.
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The ISS has been a part of innumerable space studies including the Twins Study -- which saw astronaut Scott Kelly spend a record 340-day mission to study longer-term effects of space on the human body -- to the Veggie Study which successfully grew lettuce on board last August.
Right now, the crew is measuring the grip strength of mice for the Rodent Research experiment, to figure a way to prevent the weakening of muscles and bones that occurs after extended durations in space.
Retired NASA astronaut Leroy Chiao, now a Space Foundation Special Advisor for Human SpaceFlight said the ISS is the key to the next space frontier: putting people on Mars.
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"The biggest technical challenges are biomedical -- how to keep astronauts healthy on the way to and back from Mars as well as staying on the surface," Chiao said.
"There are a lot of different things that occur to the human body in space but most importantly once you get out of the Earth's magnetic atmosphere, you're exposed to a lot more radiation than you are here on Earth and even the lower atmosphere."
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"Bottom line, we as human beings, as a species we love to explore. That's what we are, its part of the human experience," Chiao said.
As astronaut Jeff Williams, currently aboard the ISS, said in an anniversary message: "100,000 orbits, the journey continues."