How Long Will Space Junk Take to Burn Up? Here's a Handy Chart

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If the Roman Empire had been able to launch a satellite in a relatively high Low Earth Orbit – say about 1,200 km (750 miles) in altitude – only now would that satellite be close to falling back to Earth. And if the dinosaurs had launched a satellite into the furthest geostationary orbit - 36,000 km (23,000 miles) or higher -- it might still be up there today.

While we've really only launched satellites since 1957, those examples show how long objects can stay in orbit. With the growing problem of accumulating space junk in Earth orbit, many experts have stressed for years that satellite operators must figure out how to responsibly dispose of derelict satellites at the end of their lives.

The European Space Agency (ESA) and the United Nations Office for Outer Space Affairs (UNOOSA) have collaborated for a new infographic to show how long it would take satellites at different altitudes to naturally fall back to Earth.

While the natural de-orbit process can be relatively fast for satellites flying at low altitudes -- taking less than 25 years -- for satellites launched into orbits tens of thousands of kilometers away, it can be thousands of years before they return.

Gravity has little effect on a satellite's return to Earth. The biggest factor in satellites decreasing their orbit is the amount of drag they encounter from Earth's atmosphere. A satellite can remain in the same orbit for a long period of time as the gravitational pull of the Earth provides a balance to the centrifugal force satellites experience in orbit. For satellites in orbit outside the atmosphere, there is no air resistance, and therefore, according to the law of inertia, the speed of the satellite is constant resulting in a stable orbit around the Earth for many years.

"If we look at our statistics, we have about 300 objects per year returning to Earth, burning up in the atmosphere," said Francesca Letizia, a space debris engineer at ESA, in a podcast on space debris. "Below 500 km, the effect of the atmosphere, the spacecraft can reenter within 25 years. At 800 km above Earth, it will take about 100-150 years to fall back to Earth."

Letizia said the biggest risk for old satellites that aren't currently operating is the risk they pose for exploding and creating more fragments, or for colliding with other satellites and either causing damage or destruction and also creating additional objects in Earth orbit.

In Depth: This is What Happens to Spacecraft When They Reenter Earth's Atmosphere

This means that as we launch satellites to space we must consider how they will be removed at the end of their lives, or else the area around Earth will be filled with old, defunct spacecraft at risk of collision, explosion, and the near-certain creation of vast amounts of space debris.

Further reading: ESA

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com