That there is a problem of rubbish left on the streets, at least in some big cities, is well known to many of us, who are often forced to change sidewalks to get around piles of rubbish. That there is a problem of garbage in the sky around the Earth, however, is something little known.
From Sputnik 1 in 1957 to today, thousands of satellites have been launched, some of which – following explosions or collisions – have generated a multitude of fragments, large and small, which orbit around our planet at different altitudes: bolts, flakes of paint, powders, rocket stages.
To these are added objects lost during space missions: an astronaut’s glove, a camera, a pair of pliers. Today it is estimated that around the Earth there are 36,500 objects larger than 10 centimeters, one million between 1 and 10 centimeters in size, 330 million between 1 millimeter and 1 centimeter. Due to their high speed, impact with space debris can cause significant damage to operational satellites.
In the 1970s, a NASA consultant, US astrophysicist Donald J. Kessler, predicted that debris will increase to the point that the Earth will be enveloped in a blanket of debris that will prevent space activities for many future generations.
It’s an apocalyptic scenario, but certainly not unrealistic if rules are not adopted to determine how to dispose of satellites at the end of their operational life. It is equally crucial to develop appropriate mitigation strategies to minimize the damage that can be caused by space debris, possibly by moving it to safe regions, such as so-called graveyard orbits.
Therefore, the study of the trajectories of space debris is of great importance for the protection of our planet. The European research project Stardust Reloaded deals with this topic, born with the aim of exploring the exploitation of asteroids and making the use of space sustainable.
Together with researchers Giuseppe Pucacco and Tudor Vartolomei, I studied a mathematical method for associating groups of space debris with the satellites that generated them. In other words, the explosion of a satellite produces fragments which, over time, are scattered in space. It therefore becomes difficult to understand from which object they come. Here mathematics comes into play through the theory of perturbations, already used in the eighteenth century to study the orbits of the planets.
This theory allows us to calculate mathematical quantities, called “proper elements”, which remain unchanged over time. It is as if each fragment were associated with a fingerprint, its own element, a quantity that takes on the same value at the moment of the explosion, after months or even years.
The calculation of the proper elements can be an effective tool to reconnect the debris to the satellite that generated them, thus allowing to trace the object that caused the increase in space junk, the “responsible”. Let’s hope it happens as little as possible but, if needed, we’ll know who to ask to clean up the space!