André Moitinho de Almeida: from the unsustainability of space debris to the glow of the Milky Way

Imagine “a highway with an uncontrolled crowd of trucks, balls and millions of bullets flying”. This is not just an exercise in creativity: it is what happens in Earth’s orbit. Operational satellites orbit among “enormous amounts of space debris” and “other smaller uncontrolled objects” in a scenario that André Moitinho de Almeida describes as a “Wild West resulting from decades” of “unregulated” space use and exploration.  

The long-term sustainability of space activities is a familiar theme to the astrophysicist. Between 2011 and 2020, he was part of the working group that engaged in “Long-term Sustainability in Space Activity” at COPUOS (United Nations Committee for the Peaceful Use of Outer Space). That work resulted in 21 guidelines that, in 2019, the organization would eventually adopt for long-term sustainability in space activities. But we will get to that in a moment.  

Before looking at the disorderly dance of debris in Earth’s orbit, André Moitinho de Almeida was fascinated by the Milky Way, which still illuminates his path. Nothing like starting at the beginning of things. “My interest in Astrophysics comes from a young age. I was about five years old when I received two books: one about the night sky and the other about space exploration, which impressed me a lot. I read them countless times,” he recalls.  

Then, he saw his thoughts consumed by the “immensity and variety of things in space”. For a kid in 1972, “everything seemed possible”: “In less than four years, we had gone to the Moon six times.” “On the other hand, Portugal was a very backward country, very different from what it is today. To be an astronomer or an astronaut, which for a child seemed the same thing, was unattainable”, he says.  

He thought of Electronic Engineering as a safe option to follow his academic studies, but the “publication by Gradiva of extraordinaire and captivating books on Physics and Astrophysics” changed his mind. So he studied Physics and, in his Master’s, he focused his thesis on Astronomy. Another “unexpected turn”.  

The fascination with star clusters 

Today a professor at the Faculty of Sciences of the University of Lisbon (FCUL) and a researcher at CENTRA (Centre for Astrophysics and Gravitation), André Moitinho de Almeida is also a specialist in the study of the Milky Way. And his interest arose precisely during his Master’s degree, with the study of star clusters”, which the astrophysicist considers “very interesting”: “Most star formation occurs in clusters, which end up functioning as the fundamental building blocks of galaxies. On a larger scale, galaxies can, in turn, be considered the fundamental building blocks of the Universe, so understanding how they form and evolve is one of the central questions of astrophysics.” 

Throughout his PhD and career, André Moitinho de Almeida says he and his collaborators have identified and characterized “thousands of star clusters,” intending to obtain a map and model “the structure and evolution of the Milky Way”. In 2006, he threw himself into “a great adventure” that allowed him to see it “in super-resolution: the European Space Agency’s Gaia mission, “dedicated to creating a dynamic 3D map of the Milky Way to study the structure and evolution of our galaxy”, in which he plays the role of national coordinator. The biggest function, he points out, is “to make things happen” – even amid “unforeseen events, lack of people, lack of funds, and other storms”.  

A real danger 

What has also created difficulties in astronomical observation through terrestrial telescopes are the satellite mega-constellations already mentioned by André Moitinho de Almeida. “Besides the trail they leave behind, making part of the observations useless, their brightness can be big enough to damage the detectors,” explains the astrophysicist, who is also the president of the Portuguese Astronomical Society. 

“There are currently around 5,700 operational satellites orbiting the Earth, of which more than a third already belong to the first stages of implementation of these mega-constellations. The best known, Space-X, is already licensed by the US regulator to fly 12,000 and is licensing 30,000. A fraction of them will break down, increasing the proliferation of space debris. These numbers and this kind of growth are unsustainable and could prevent fair access to Space by other countries,” he warns.  

Rescuing the idea of a Wild West of trucks, balls, and bullets, one can understand the real risk of “a chain reaction of collisions with fragments” leading to “successive fragmentations and collisions” – the Kessler syndrome – which can “make low orbits unusable for years”. But is there any real danger for the Earth’s population? “There is also the risk of an uncontrolled re-entry of objects that don’t disintegrate in the atmosphere, possibly hitting people or property,” he replies.  

Nevertheless, we are witnessing “an evolution in the perception of the issue of space sustainability, accompanied by concrete measures and policies”. But one cannot talk about the sustainability of space exploration without first looking at the larger issue of things: the sustainability of human activity itself, based on a model “that depends on growth with resources that we borrow from the future”. The issue is not new, nor are the concerns – and “the same thing happens in space exploration, for the same basic reasons”.