If the Roman Empire were able to launch a satellite into a relatively high Low Earth orbit – say about 1200 km (750 miles) in altitude – this satellite would only now be able to fall close to Earth. And if the dinosaurs launched a satellite in the farthest geostationary orbit – 36,000 km (23,000 miles) or higher – it could still be there today.
Although our satellites * really * only launched since 1957, the examples show how long objects can stay in orbit. With the growing problem of space debris accumulating in the Earth’s orbit, many experts have stressed for years that satellite operators need to figure out how to remove the abandoned satellites at the end of their lives in a responsible manner.
The European Space Agency (ESA) and the United Nations Space Agency (UNOOSA) have teamed up for a new infographic to show how long it will take satellites at different altitudes to fall back naturally to Earth.
Although the natural de-orbit process can be relatively fast for satellites flying at low altitudes – lasting less than 25 years – for satellites orbiting tens of thousands of kilometers away, it can take thousands of years before they return.
Gravity has little effect on the return of a satellite to Earth. The biggest factor in satellites that reduce their orbit is the amount of resistance they encounter from the Earth’s atmosphere. A satellite can stay in the same orbit for a long time, as the Earth’s gravity provides a balance to the centrifugal force that satellites experience in an orbit. For satellites in an orbit outside the atmosphere there is no air resistance, and according to the law of inertia, the velocity of the satellite is constant and has had a stable orbit around the earth for years.
“If we look at our statistics, there are about 300 objects a year that return to Earth, burning up in the atmosphere,” Francesca Letizia, a space department engineer at ESA, said in a podcast on space debris. “Below 500 km, the effect of the atmosphere, the spacecraft can re-enter within 25 years. At 800 km above the earth it will take about 100-150 years to fall back on the earth. ”
Letizia said that the biggest risk for old satellites that are currently not working is the risk of exploding and creating more fragments, or of colliding with other satellites and of causing or destroying damage and of including additional objects in to create the Earth.
In depth: this is what happens to spacecraft as they re-enter the Earth’s atmosphere
This means that when we send satellites into space, we must consider how they will be removed at the end of their lives, otherwise the area around the earth will be filled with old, dilapidated spacecraft with the risk of collision, explosion and the almost certainly creating large amounts of space debris.
Further reading: ESA