On November 20th, 1998, a Russian rocket launched off with an unusual piece of cargo - Zarya ('sunrise' in Russian), the module that became the first piece of the largest manmade structure every built in space - The International Space Station (ISS). Designed to be the power source for the ISS, it orbited earth for two weeks, before being joined by Unity.

Launched by US Space Shuttle Endeavour on December 6th, 1998, Unity arrived with a crew of six American and Russian astronauts. It then proceeded to chase down the 44,000 lbs Zarya and tug it closer using the shuttle's 50-foot arm. A few days and three spacewalks later, the 26,225-lb American module that had cost $300 million USD to build, was successfully attached to the Russian module. On December 11, 1998, @ 2.54 PM, the astronauts made history by becoming the first humans to board the newly established International Space Station.

Over the years, the ISS has grown to the size of a football field with about the same amount of livable space as a conventional six-bedroom house - a good thing, given that it constantly hosts teams of astronauts from around the world, for as long as six months at a time. What's even cooler is that this large construction project that was not completed until 2011, when an upgraded permanent storage closet to give station crews more room was attached, is a never before seen International collaboration. Five different space agencies - NASA, Roscosmos, ESA, JAXA and CSA, representing a total of 15 countries have come together to make the ISS that sparkles brightly in our skies today, a reality.

Over the last 15 years, astronauts have conducted 174 spacewalks and spent a total of 1,100 hours or nearly 46 days on missions ranging from adding new modules to routine maintenance. With over 1,500 experiments conducted in the five dedicated research modules, the station has been responsible for many important scientific discoveries and breakthroughs.

Besides conducting experiments, all astronauts that reside at the ISS are living experiments themselves. That's because they allow scientists to monitor the effects of zero gravity on the human body and seek out solutions to combat them. For example, one of the biggest ailments suffered by astronauts used to be weakened bones and wasted muscles. Today, the effects have been mitigated by changing their diets and adding a gym to the ISS.

Psychological health which is as important as physical well-being, has also been improved by providing the astronauts with tiny cabins that allow for some alone time and the opportunity to talk to their loved ones in private. While these improvements are certainly important for the scientists that visit the ISS for short periods of time, they are going to be crucial for the men and women that make the long haul to Mars.

When Ronald Reagan gave NASA the mandate to build an orbital home for humans in 1984, he had envisioned it to be a place for 'peaceful, economic and scientific gain'. The ISS has certainly achieved all three goals, quite successfully!

Resources: theregister.co.uk, dailymail.co.uk,nasa.gov, mirror.co.uk