Space-based infrastructures have become major assets for our economy and “space” has become part of our daily life. Meanwhile, the growing space debris population jeopardizes the use of space. The risk of a spacecraft colliding with debris depends on three factors:
- Debris density in a particular orbit region,
- Spacecraft cross section,
- Relative velocity of the objects.
However, the precise calculation of the collision risk of a given spacecraft over a certain period of time is a lot more complicated than it looks at first sight. Today, tracking the orbits of space debris is limited to larger pieces which represent only a small fraction of the entire debris population. As orbit determination for space debris is subject to inaccuracies, collision projections are a matter of probability calculus. As some debris experts say: You can only be 100% certain about a collision, once it has happened.
The most densely populated orbit regions are low Earth orbits and geostationary orbits. Today, satellites in low Earth orbit receive dozens of so called conjunction warnings every year. Only a few warnings will lead operators to initiate actual avoidance maneuvers. Avoidance maneuvers consume propellant and, hence, reduce a satellite’s lifetime. Defunct and uncontrolled spacecraft are a potentially dangerous source of space debris. Every collision creates even more new debris. In a worst case scenario, a cascade of collision events and a quickly growing number of debris pieces could render space utilization as we know it impossible. Luckily, such a situation can be avoided if we take the necessary steps. The risk from space debris can be managed. Reducing the creation of new debris by removing defunct and uncontrolled spacecraft is a major step towards a sustainable space environment for future generations.