You’ve probably seen science fiction movies with catastrophic scenes of satellites falling to Earth, causing widespread panic and destruction. However, these depictions are a far cry from reality. The re-entry of satellites and space debris into the Earth’s atmosphere is a common and desirable phenomenon, closely monitored by space agencies all over the world, and the threat it poses to the population is utterly negligible. But what is space debris?

The space race has been evolving significantly, from the technological duel between Cold War rivals to our new era of democratizing access to space. Over the course of all these years, since the launch of Sputnik 1 in 1957, the Earth’s orbit has been filling up with thousands of satellites that play a crucial role in everyday human life, providing us with critical telecommunications, navigation, Earth observation, and meteorology services, among others. Every day, we unknowingly interact with more than 100 of the nearly 10,000 satellites that are currently operational.

The problem is when all these satellites reach the end of their useful life and start orbiting out of control. Some of them might explode or crash into others, filling outer space with fragments. We call these fragments “space debris.” It’s estimated that over 1,000,000 objects larger than 1 cm in size are orbiting Earth, and we’re only able to track the 35,000 largest ones.

The accumulation of orbital debris poses a tangible threat to future space operations, potentially leading to collisions and the cascade effect known as the Kessler Syndrome, where the density of objects in low Earth orbit is enough to trigger a chain reaction of collisions.

To address this challenge, significant efforts are being made on two fronts: mitigation and remediation.

Mitigation seeks to prevent the creation of further space debris, thus avoiding possible in-orbit collisions. This is achieved by constantly monitoring space debris and enabling the satellites to carry out and coordinate evasive maneuvers.

Remediation means actively removing space junk by carrying out controlled re-entries from low orbits or sending satellites in high orbits that are not being used into “graveyard orbits.” However, this isn’t done frequently (and was even less common in the past), and so most satellites keep orbiting uncontrolled in crowded orbits. In these cases, satellite “tow trucks” are used to collect and remove the debris in a controlled manner. However, the technology needed for this active cleaning of space is still being developed, and faces significant challenges.

Unfortunately, most space debris re-entries to Earth today are completely uncontrolled. Indeed, objects in low orbits (altitude of less than 1,000 km) will re-enter the atmosphere naturally after a few months or years. This is due to friction with the upper layers of the atmosphere, which causes the satellite to gradually spiral downwards.

In fact, every week an old satellite weighing over a ton (the size of a car) re-enters the atmosphere, and twice a year an old satellite weighing over five tons (the size of a bus) does the same.

However, the risk of space debris harming people on Earth upon re-entry is extremely low. It’s estimated that there is a 2% annual chance of such an event happening to any given person (out of the 8 billion of us on our planet). This translates into each of us having a one-in-a-billion chance of being hit by space debris in our lifetime, which is less likely than playing the lottery only twice and hitting the jackpot both times. This leads us to a key conclusion: the real problem with space debris isn’t here on Earth, but rather up in outer space. 

There have recently been two major re-entries: the European Space Agency’s (ESA) Heritage ERS-2 satellite, which hadn’t been operational since 2011, and that of a pallet of batteries discarded by the International Space Station (ISS) in 2021. Each of them weighed over two tons. Both re-entries, like many others, were monitored by space agencies all over the world, and there was no damage in either case, as the objects fell into the sea.

Managing space debris and protecting the orbital environment are of the utmost importance in order to ensure satellites’ continued benefits for humanity. We must keep working to make space a safe place and an accessible resource for future generations. This commitment to space sustainability highlights the need for global collaboration and constant innovation to preserve this vital shared resource.

Author: Alberto Águeda