Analysis of In-Orbit Break-Up Models, Debris Cloud Evolution, and Short-term Collision Risk Assessment

Kurzfassung

The primary objective of this thesis is to assess the short-term collision risk between a debris cloud and operational spacecraft, with the aim of developing a prototype tool to enhance the operational safety of resident space objects. As space technology has advanced, the rate of spacecraft launches has steadily increased, leading to congestion in Earth’s orbital environment. This overpopulation increases the likelihood of in-orbit break-ups, which generate significant amounts of space debris and pose substantial risks to operational spacecraft. While active debris-removal techniques continue to evolve, studying debris dynamics is essential for evaluating collision risks. The increasing accumulation of space debris presents a particularly acute hazard in the immediate aftermath of a break-up event, where traditional risk assessment methods are inadequate due to the lack of comprehensive tracking data. Key break-up models, such as NASA’s Standard Break-up Model (SBM), are analysed in terms of their ability to describe fragments distributions by size, velocity, and area-to-mass ratio. The research also investigates debris cloud evolution, particularly in the initial phase post-break-up, where the dynamics of fragments is significantly affected by ejection velocities. Understanding the short-term dynamics of debris clouds is crucial for establishing the assumptions on which the collision risk assessment tool is based. The study confirms that Keplerian motion assumptions hold in the short-term phase. The tool, developed in Python, calculates collision probability using the multi-revolution Lambert’s problem and a mapping technique from position space at a given time into spread velocity space at the time of break-up, as each debris acquires an additional velocity from the break-up. A novel approach to handling uncertainty in the break-up epoch is also introduced. The findings demonstrate the effectiveness of this approach in providing timely assessments of collision risks, which is crucial for the safe operation of spacecraft. A novel approach to consider uncertainties on the break-up epoch is also presented. The results underscore the need for improved risk models to ensure space safety in the increasingly congested low-Earth orbit environment.