When the International Space Station (ISS) ends its useful life, in 2030, NASA will lower it in a controlled manner so that its remains fall on a remote point in the Pacific Ocean known as Point Nemo, the most isolated place on any coast on the planet. However, in recent days a question has arisen on the internet: why not take advantage and launch it directly against the Sun? After all, he would disappear there forever. The idea seems logical. But physics says exactly the opposite. In fact, it is much more difficult to send a spacecraft to the Sun than to send it to Mars. According to NASAreaching our star requires about 55 times more energy than a mission to the red planet. The reason has very little to do with distance and a lot to do with speed.
When we think of the Earth we usually imagine it motionless, with the Sun waiting for us in a straight line about 150 million kilometers away. But our planet is not still for a single moment. The Earth rotates around the Sun at about 107,000 kilometers per hour and everything under its “gravitational umbrella” including the International Space Station, shares exactly that speed. Here appears one of the most difficult concepts to imagine in orbital mechanics. To fall towards the Sun it is not enough to point a rocket in that direction. First, the enormous lateral speed with which the Earth moves around our star would have to be almost completely eliminated.
It’s something like trying to drop a rock from the window of a car driving on the highway. Even if you release it vertically, the stone will continue to move forward because it maintains the speed of the vehicle. Exactly the same thing happens with the Earth (and the ISS). Our intuition tells us that the Sun should immediately attract any object we send into space. The reason is the same that keeps a satellite around the Earth. If an object moves quickly enough to one side while gravity pulls it downward, the two movements compensate and the result is an orbit.
To make the ISS “fall” towards the Sun, those more than 100,000 kilometers per hour of orbital speed would have to be stopped first. And that requires a gigantic amount of fuel. The surprising thing is that, From an energy point of view, it is easier to send a ship out of the solar system than to crash it into the Sun. Precisely for this reason the Parker Solar Probe, the spacecraft that has ever come closest to the Sun (at 6 million km, 20 times less than the distance that separates us), could not head directly towards it.
For all these reasons, when the time comes to retire the International Space Station it will not make sense to try to send it to the Sun. It will be enough to slightly reduce its orbital speed around the Earth for the atmosphere to do the rest of the work. Atmospheric friction will progressively slow down the station until it causes its controlled re-entry over the South Pacific. where the fragments that survive the intense warming will fall far from any population.