There are thousands of artificial satellites orbiting Earth, carrying out tasks from navigation to enabling communications to wildfire monitoring. What happens when a satellite reaches the end of its life, though?
There are two main ways old satellites are disposed of: they’re brought back to Earth, or they’re sent further away. We’re going to take a look at those disposal methods here.
Satellites falling to Earth
Old satellites can’t just be left in orbit, because leaving defunct satellites in place could obstruct the path of operational satellites later on, and satellites left unmaintained in low orbits will eventually come back down to Earth. By kicking a satellite into a controlled descent when it reaches the end of its life, satellite teams reduce the number of obstacles in space and ensure there won’t be an uncontrolled descent later.
It’s possible to push a satellite into descent by operating its thrusters from Earth. In orbit, a satellite doesn’t need to use thrusters; it’s kept moving by gravity. Essentially, an object in orbit is constantly falling towards the planet, while moving forward at such a speed that it will never actually reach the planet’s surface. However, it’s usual for a satellite to have some means of propulsion, which can help when placing it in orbit or making small adjustments.
When a satellite is reaching the end of its life, the satellite team on ground level can use its thrusters to slow it down. As the satellite is no longer travelling fast enough to go past the curve of the planet before being pulled down to the surface, gravity takes over and the satellite falls to Earth.
Smaller satellites will burn up in the atmosphere as they descend. The speed of the satellite meeting the resistance of the air creates friction and therefore heat. The satellite breaks into pieces, and these pieces will often burn away before they can reach the ground.
Occasionally, you might get the opportunity to see a burning satellite; they can appear in the form of a distant fireball streaking across the night sky. They’re no cause for concern, but they can be slightly alarming for people who don’t know what they’re looking at. The European Space Agency (ESA) has shared remarkable footage of the Jules Verne cargo delivery spacecraft burning on re-entry in 2008.
Some satellites are designed to stay intact through their descent and land safely on Earth, even if they’re unmanned. For example, what if, while it’s in space, a research satellite gathers material that will need to be tested on Earth? What if a satellite is launched with the goal of seeing how space radiation or low gravity will affect its cargo? In cases like this, if the satellite is destroyed on descent, the material it carries will be lost before research can be carried out.
However, most satellites are designed under the assumption that they’ll spend their entire working lives in space. By the time they return to Earth, they’ve done everything they needed to do, so it’s not a problem if they burn up in the atmosphere. In fact, in some ways it’s beneficial, as it reduces the amount of debris that falls to Earth.
What is the spacecraft cemetery?
A satellite won’t always burn up completely as it descends. Parts of larger satellites might survive the fall to the Earth’s surface.
These pieces of debris might cause damage if they landed in inhabited areas, so satellite descents are carefully calculated. When satellite teams plunge a satellite back into the atmosphere, they’re often aiming for a specific location: the spacecraft cemetery.
This is located at Point Nemo, also known as the oceanic pole of inaccessibility: the point in the ocean that’s furthest from land and therefore hardest to reach. It lies in the South Pacific Ocean, between New Zealand and Chile, over 2,600 km from solid ground. Because Point Nemo is so remote, it was chosen as a place to land decommissioned satellites without the risk of hitting inhabited areas or ships.
For context, the International Space Station orbits at about 420 km from Earth. If you travelled 2,600 km, you could go to the ISS and back three times.
The spacecraft cemetery already houses the remains of hundreds of satellites and is likely to see many more. According to BBC News, over 260 spacecraft had been crashed at Point Nemo as of 2017.
What is a graveyard orbit?
The higher a satellite is, the more fuel it takes to slow it down enough to fall out of orbit. This means it’s difficult to bring high-altitude satellites back down to Earth when they reach the end of their life.
For satellites in very high orbits, such as geosynchronous (GSO) satellites, disposal isn’t a matter of preventing a later natural descent. In lower orbits, satellites experience small amounts of air drag, slowing them down; this is why low Earth orbit satellites can’t keep orbiting indefinitely without maintenance. GSO satellites are well above the atmosphere and don’t encounter this drag.
However, it’s still best not to leave high-altitude satellites in place when they’re no longer useful, as they might obstruct other satellites. This is a particular concern with geostationary (GEO) satellites, which need to follow the equator at a specific height. Theoretically, if GEO satellites kept being added but were never removed, the GEO orbital path would eventually be too full to add new satellites.
Therefore, satellites in high orbits are sometimes sent into a graveyard orbit, as this uses less fuel than bringing them back down to Earth. A graveyard orbit is an orbit a few hundred kilometres above the GEO/GSO orbital altitude of 35,786 km. Satellites in a graveyard orbit are well above any operational artificial Earth satellites, so they won’t currently cause any obstruction.
However, leaving satellites in orbit after the end of their lives contributes to the problem of space debris, which we’ll talk about in more detail in a later article. The more material there is orbiting Earth, the greater the risk of issues like obstruction and collision. Although graveyard orbits are out of the way of active satellites, the satellites accumulating in them may eventually cause problems for other space missions.
Can satellites be recycled?
These methods are clever ways of ensuring that satellites don’t cause problems after reaching the end of their lives. However, there’s room for improvement.
If satellites burn away, land in inaccessible areas or are pushed further out into space, the materials can’t be reused. Because of this, organisations are researching methods of satellite disposal that could allow satellite materials to be recycled.
Part of the problem is that it’s difficult to either retrieve materials from space or recycle them in space without using large quantities of resources. If the act of recycling uses more resources than it would save, attempting to recycle satellite parts would ultimately just result in a greater loss of resources.
Because of this, it’s important to research more efficient ways of recycling materials that have been sent into space. ESA has been looking into the potential for in-orbit satellite recycling, and you can read about their efforts here.
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