The International Space Station will be operational until 2020s as NASA, Roscosmos, and partners in Japan, Europe, and Canada have reached consensus regarding the matter. "The international partners have been discussing extending the mission through 2028. At this point, there's no reason we wouldn't do that, said NASA spokesperson Joshua Buck.

However, the Space Station will be directed for a controlled fall towards the earth after the stipulated time, which if not done will result in an eventual uncontrolled fall of the Space Station from its orbit at some point of time in future, endangering life on earth, reports National Geographic.

Space surveillance is a critical part of U.S.'s mission and involves detecting, tracking, cataloging and identifying man-made objects orbiting Earth, which consist of active/inactive satellites, spent rocket bodies, or fragmentation debris. Of the 8000 objects of varying sizes under surveillance, 500 are functional spacecrafts.

The ISS orbits earth at a height of about 200 miles (322 kilometers), and in velocities about 17,500 miles (28,163 kilometers) an hour.

Objects will fall out of their orbits in the event of them attaining greater of lesser velocities than the optimal. Since ISS's orbit isn't a vacuum, it will slow down bombarding into the molecules present in its orbiting space, which means scientists will have to constantly boost the Space Station's orbit velocity, using propellants, in order to prevent it from falling out.

"You can't just leave something you want up there or you'll lose it. It's going to require boosting," said aerospace engineer and reentry specialist William Ailor of the Aerospace Corporation, a federally funded research and development center based in El Segundo, California, according to a National Geographic report.

To keep ISS, which weighs about 920,000 pounds (417,305 kilograms), secure in its orbit, high amounts of propellants will have to be used for indefinite period which is simply not practical. If in case the propellants aren't used and the ISS is left to spin above earth, nobody will be able to predict when and where the debris will fall.

Similar to what Roscosmos did for Mir, which, prior to the ISS, was the biggest human-made object in space, ISS will be slowed down de-orbiting it from space for a controlled fall.

Mir's debris fall captured from South Pacific island: 

Space Station's Fall:

The station controllers will dock an unmanned vehicle to the forward end of the laboratory, followed by burning its propellant to the maximum and sinking the entire complex into the atmosphere.

ISS will traverse the outer atmosphere at hypersonic speeds compressing and colliding with air and emitting infrared radiation.

"You're converting all of that kinetic energy from the spacecraft's orbit into heat to slow it down," Ailor said, adding that "the things that [will disintegrate] first are the flimsiest components, like solar panels."

Bigger modules will heat up and begin to melt as the ISS continues to fall. The space station's joints will start to disintegrate and deceleration up to eight times stronger than Earth's gravity will rip the components to shreds, as can be seen in the Mir's de-orbiting video.

"A spacecraft is essentially all broken apart by 120,000 feet [36,576 meters] or so. Surviving pieces are now cooling and continue to slow down," Ailor said. "Most fragments go subsonic at 60,000 to 80,000 feet [18,288 to 24,384 meters], then fall straight down-pianos falling out of a window is a good analogy."

About 40 percent of the ISS's mass will fall on earth's surface and the pieces that survive will either be those dense enough to not fully melt or break apart, or those shielded by components that resisted atmospheric reentry.

"When debris was recovered from space shuttle Columbia, things survived reentry that were never designed to," Ailor said. "They even found living organisms in a biological experiment that" the shuttle was bringing back to Earth.