The reason the ISS station doesn’t burn up in space

Flying through Earth’s orbit are thousands of satellites and two active space stations, including the International Space Station (ISS), which weighs as much as 77 elephants. The ISS is home to scientists and researchers around the world as they contribute to discoveries in the fields of medicine, microbiology, Earth and space sciences… The ISS travels very fast around the Earth at a speed of 8 km/s, meaning it could fly from Atlanta to London in 14 minutes. But at the same time, small pieces of rock called meteorites also hurtle through space and burn up when exposed to Earth’s atmosphere. Why can the ISS station continuously orbit the Earth intact while the meteorite burns?

To answer the question of why the ISS station can stay in orbit for decades without being damaged, we first need to understand why meteorites burn up when they pass through Earth’s atmosphere. Meteors are small pieces of rock and metal that orbit the Sun. They can move at speeds of 12 – 40 km/s. That’s fast enough to fly across the entire United States in about 5 minutes. Occasionally, a meteorite’s trajectory crosses the Earth and the meteorite enters the atmosphere, where it burns up and breaks into pieces.

Although invisible, the atmosphere is filled with particles, mainly nitrogen and oxygen. The higher above ground level, the lower the density of particles in the atmosphere. The atmosphere consists of several layers. If something flies from space into Earth’s atmosphere, it must pass through each layer before reaching the ground. The meteorite burned up in the mesosphere 48 – 80 km above the ground. Even when the air aloft is very thin, meteorites still collide with particles as they pass by.

When meteorites rush through the atmosphere at very high speeds, they are destroyed by a process that causes them to heat up and break up. Meteorites press airborne particles together like bulldozers. This process creates a lot of pressure and heat. Air particles hit the meteorite at super fast speeds, much faster than the speed of sound, causing atoms to break and create many cracks in the meteorite. High pressure and hot air entered the crack, causing the meteorite to shatter and burn as it fell through the sky.

The ISS does not fly through the mesosphere. Instead, the ISS flies in a much higher and less dense atmosphere called the thermosphere, 80 – 708 km above the Earth’s surface. The Kármán Line, the boundary between the atmosphere and space, is located in the thermosphere, at an altitude of 100 km above the earth’s surface. Meanwhile, the ISS station flies at an altitude of 402 km.

The thermosphere has too few particles to transfer heat. At the altitude of the ISS, the atmosphere is so thin that to collect enough seeds equivalent to the mass of an apple, you would need a box the size of Lake Superior. As a result, the ISS does not experience interactions with airborne particles and the high temperatures and pressures that meteorites flying closer to Earth encounter, so the station does not burn up.

Even though it did not catch fire, the ISS still experienced large temperature fluctuations. As it orbits Earth, the station is alternately exposed to direct sunlight and darkness. Temperatures can reach up to 121 degrees Celsius when the station is exposed to sunlight, then drop to -156 degrees Celsius when in darkness in orbit. Station design engineers carefully selected materials to account for these temperature fluctuations. The space inside the station is maintained at a comfortable temperature for astronauts.

NASA plans to maintain the operation of the ISS until 2030. When all astronauts have returned to Earth, the ISS will leave orbit on its own or use a specially designed spacecraft. During the reentry process, the station will fly through the mesosphere, many of its parts will heat up and break up.