Planet Earth is surrounded by spacecraft carrying out important work to study our changing climate, deliver global communication and navigation services and help us answer important scientific questions – but some of their orbits are getting crowded and increasingly churning with deadly, fast-moving pieces of defunct satellites and rockets that threaten our future in space.
In 2002, the Inter-Agency Space Debris Coordination Committee (IADC), of which the European Space Agency (ESA) is a member, published their Space Debris Mitigation Guidelines. The measures described in the voluntary guidelines set out how to design, fly, and dispose of space missions in ways that prevent the creation of further debris.
They were a major step for the protection of our important orbits and have served as the baseline for mitigation policy at ESA and beyond, national legislation and technical standards for two decades.
Since 2016, ESA’s Space Debris Office has published an annual Space Environment Report to provide a transparent overview of global space activities and determine how well these and other international debris-reduction measures are improving the long-term sustainability of spaceflight.
Headline findings from the latest report indicate that:
* Earth’s orbital environment is a finite resource.
* More satellites were launched in 2023 than in any year before.
* The number and scale of commercial satellite constellations in certain low-Earth orbits continue to increase.
* Not enough satellites leave these heavily congested orbits at the end of their lives.
* Satellites that remain in their operational orbit at the end of their mission are at risk of fragmenting into dangerous clouds of debris that linger in orbit for many years.
* Active satellites must perform an increasing number of collision avoidance manoeuvres to dodge out of the way of other satellites and fragments of space debris.
* The adoption of space debris mitigation measures is slowly improving, but it is still not enough to stop the increase of the number and amount of space debris.
* Without further change, the collective behaviour of space-faring entities (private companies and national agencies) is unsustainable in the long term.
The amount of space debris in orbit continues to rise quickly. About 35 000 objects are now tracked by space surveillance networks. About 9 100 of these are active payloads, the other 26 000 are pieces of debris that are larger than 10cm in size.
However, the actual number of space debris objects larger than 1cm in size – large enough to be capable of causing catastrophic damage – is over 1-million.
In 2023, payload launch traffic was again the highest ever, with most satellites becoming part of large commercial communication constellations.
Within low-Earth orbit, there are preferential altitude ranges for communication constellations, which show a clear peak in satellite concentration as a result.
Two-thirds of all active satellites, over 6 000, are currently located between altitudes of 500km and 600km. This trend will continue as most newly launched satellites in 2023 were also heading to these orbits.
Any collision or explosion creating a large number of debris pieces would be catastrophic for all satellites sharing a busy orbit – as well as for all spacecraft having to pass through these orbits.
Across low-Earth orbits, the number of events triggering collision avoidance procedures is increasing, partly because of the growing traffic congestion, partly because of the increasing amount of debris.
Mitigation efforts on the rise
In absolute terms, the number of objects reentering Earth’s atmosphere in 2023 went down. This is mostly because of the reentry of debris caused by a specific anti-satellite missile test at the end of 2021 peaked in the previous year.
However, efforts to improve compliance with space debris mitigation guidelines to remove satellites at the end of their lifetime from important orbits have intensified. This has led to a rapid rise in the number of satellites reentering the atmosphere.
Both rocket bodies and payloads are reentering in greater numbers year-on-year. This can partly be contributed to increased efforts to follow debris mitigation guidelines.
Another factor this year, and one that will continue to play a role for the next few years, is the high level of solar activity caused by the peak in the current solar cycle. This period of intense space weather events can often cause increase atmospheric drag, which contributes to accelerated reentry times.
The number of rocket bodies returning in a controlled manner is a particular area of improvement. About 90% of rocket bodies in low-Earth orbits are now leaving valuable orbits in compliance with the applicable standards in 2023, with more than half reentering in a controlled manner.
Growing Challenge
Despite the improvement in mitigation efforts, a lack of compliance and remediation meant that 2023 still saw a net growth of the space debris population. If we extrapolate current trends into the future, as before, catastrophic collision numbers could rise significantly.
This could lead to ‘Kessler syndrome’, which could see certain orbits become unsafe and unusable over time as debris continues to collide and fragment, creating a cascading effect.
Future aspirations in space are turning towards the Moon and beyond. On top of keeping low-Earth orbits safe to pass through for human space explorers, keeping cislunar space – the region between Earth and the Moon – clean is becoming an area of increasing importance.
Without strong gravity and a thick atmosphere to gradually remove debris from orbit, it is crucial to apply the lessons learned and keep lunar orbits free of debris from the start.
The net growth of the space debris population makes clear what must be done if we want to continue using our space environment. There is a growing consensus that stricter space debris mitigation practices need to be implemented globally to keep space activities viable.
Getting a better view on the problem through space debris tracking and reporting is just the first step in resolving the space debris problem.
ESA has set itself the goal to significantly limit the production of debris in Earth and lunar orbits of all future missions, programmes and activities by 2030 through its Zero Debris Approach
Stricter debris mitigation guidelines are welcomed by many in the space sector and shows itself in the increasing wave of community-driven activities. In 2023, ESA facilitated the creation of the Zero Debris Charter by the Zero Debris community in Europe. The Charter has since been signed by 12 countries and over 100 commercial and non-commercial entities have signed or committed to sign as well.
ESA is now supporting the next step, the creation of a Zero Debris Technical Booklet, bringing together the many stakeholders in the space sector to crowd-source technical solutions to achieve the joint aspirations defined in the Zero Debris Charter.
Even if no new space debris is created, it would not be enough to prevent a runaway series of collisions and fragmentations. Littered orbits need to be cleaned up by attempting to safely reenter missions already in orbit and conduct active debris removal via missions such as ESA’s ClearSpace-1.
Where possible, ESA is attempting to deorbit satellites that were designed and built well before its current guidelines came into effect. The agency is putting greater efforts into removing missions such as Aeolus and Cluster from orbit in more sustainable ways than were first envisioned.