David Galadí-Enríquez
Lecturer in the Department of Physics at the University of Cordoba
The work of Byers et al. raises a key issue of sustainability in the use of space: the uncontrolled proliferation of launches poses a risk to the Earth's population that cannot be ignored. The industrial age has shown that the survival of the planet and humanity requires responsible resource management. Circumterrestrial space has been managed in a pre-modern way, as if it were an infinite realm where everyone can operate at will. The authors argue that it is time to consider the Earth's orbit as a congested environment into which only artificial materials should be introduced on a sustainable basis.
The article discusses the risks of launch proliferation for human communities, concludes that these risks are not negligible and can be countered by existing technical solutions. They show that most of the consequences are borne by poor countries, i.e. that advanced countries are externalising the environmental impact of their launches. They propose an international political solution. The study is an excellent example of a technical astronautical problem with international economic, political and social implications. Fittingly, it is signed by specialists in political science, interdisciplinary studies, astrophysics and engineering.
Each time a satellite is launched, a portion of the launch rocket is left in orbit in the form of space debris that eventually falls back to Earth. Although most of these rocket bodies disintegrate as they brush against the layers of air, in a process called re-entry, fragments are often left behind that can cause damage to the ground, or even to aircraft in flight.
Using the actual orbital elements of rocket bodies abandoned in recent decades, and drawing on actual Earth population density data, the authors construct a robust model. Byers et al. conclude that the risks from uncontrolled re-entry are mostly the responsibility of the United States (71%), with the other three major space powers tied for second place: China, the European Space Agency and Russia (14-17% each). At the same time, they show that the risk is concentrated in the equatorial zones of the planet and mainly affects poor countries that have not participated in launches and do not benefit from them.
The study points out that there are sufficient means, without the need for new technologies, to ensure the safe re-entry of all rocket bodies. However, these measures cost money, and this is the only real difficulty in remedying the challenge. This is a collective action problem whose solutions should be adopted by all satellite-launching companies and countries at the same time, to avoid companies being disadvantaged by incorporating good environmental practices.
The study lists cases of successful collective action (to a greater or lesser extent), such as the treaty banning gases that affect the ozone layer, the imposition of double-hulled tankers or agreements against anti-personnel landmines. Curiously, they forget one case that concerns the aerospace industry: the obligation to park retired geostationary satellites in waste orbits where they do not saturate useful servicing positions.
The rampant increase in launches makes Byers et al's conclusions all the more pressing. Low Earth orbit remains a 'lawless city'. The congestion of satellites is jeopardising the observation of the sky, which has put the entire global astronomical community on the warpath. But alarms have also been raised in the aerospace industry itself by the increased danger of collisions in space, which could ruin low orbit as an economic resource for decades, if not centuries. The environmental effects of materials vaporised in the stratosphere during re-entries of both rocket bodies and end-of-life satellites are beginning to be assessed. Now Nature Astronomy publishes this study, which shows that the non-vaporised part of these objects also poses a risk that is both considerable in its magnitude and unfair because of its externalised cost.