Humans routinely send spacecraft into orbit to ensure services on the ground and to explore other planets. This extraordinary ability comes with a great responsibility: our space activity risks contaminating the space surrounding the Earth, but also other planets and moons that have potential for past or present life.

Space benefits humanity by making many of our activities on Earth possible: telecommunication, weather forecasting, geolocation through the global navigation satellite system used for ground, maritime and air traffic, as well as remote sensing for monitoring the health of our planet. At the same time, scientific missions increase our knowledge of our solar system, while enabling the development of new technologies, science and space exploration.

However, increased space activity comes at a cost, both in terms of fuel consumption for spacecraft and space debris produced. This debris is in the form of spacecraft abandoned at the end of its operational life, or remainders of space missions and upper stages of launchers, along with all the fragments resulting from collisions and explosions in orbit.

The very existence of the more than 900,000 pieces of debris larger than 1 centimetre in size – large enough to damage operational satellites due to their high orbital speed – poses a serious threat to the sustainability of space activities. The amount of space debris has been rising exponentially, according to the European Space Agency (ESA).

An environmental problem

Interestingly, the growth in space debris has followed a similar trend to many other environmental stressors such as carbon dioxide, ocean acidification, tropical forest loss and terrestrial biosphere degradation. Indeed, all these issues have several aspects in common. Given their global nature, the solutions require strong international cooperation for defining mitigation measures. Indicators of this problem that are relevant, accepted, credible, easy to monitor and robust against manipulation and errors must be agreed upon internationally.

The space debris problem also compels us to use radar and visual telescopes to determine the orbit of space debris, and to develop mathematical and numerical approaches to model their evolution in space and time, as well as tools for collision-avoidance and end-of-life manoeuvres. Many uncertainties must be taken into account in the predictions, such as the Earth’s atmosphere and its interaction with the solar activity, the physical characteristics of uncooperative objects, and untraceable fragments, which make it impossible to achieve a perfect prediction of the debris’ orbit and evolution.