Our planet is surrounded by spacecraft helping us study our changing climate, save lives following disasters, deliver global communication and navigation services and help us answer important scientific questions.

But these satellites are at risk. Accidental collisions between objects in space can produce huge clouds of fast-moving debris that can spread and damage additional satellites with cascading effect.

In this animation, find out how teams at ESA’s European Space Operations Centre in Darmstadt, Germany, take action to keep satellites safe after receiving an alert warning of a possible collision between an active satellite and a piece of space debris.

When the alert is raised, ESA experts determine the risk of a collision and plan a collision avoidance manoeuvre that can be used to get the satellite out of harm’s way if necessary.

Additional observations of the piece of space debris help the team better understand its path and the risk of collision. If that risk remains too high (typically 1 in 10 000), the planned manoeuvre is carried out to temporarily change the orbit of the satellite until the threat has passed.

Each manoeuvre comes at a price. They take skill and time to plan, cost precious fuel – shortening the lifetime of the mission – and often require instruments to be temporarily shut off, preventing them from collecting important data.

While most alerts do not end up requiring evasive action, the number of alerts is rapidly increasing. Hundreds are already issued every week. Several companies have begun to launch large constellations into low-Earth orbit to provide global internet access. They have great benefits, but could be a source of huge disruption if we do not change our behaviour.

In just a few years, our current methods for avoiding collisions in space will no longer be enough. To safeguard humankind’s continued access to space for future generations, ESA is developing technologies for an automated collision avoidance system.

Find out more about ESA’s Space Debris and Clean Space Offices, both part of the Space Safety Programme, and the Agency’s conference on space debris - the world’s largest on the topic - taking place in April 2021.