Speaker
Description
The THEMIS approach allows modelling consumed space capacity. In the probability-based approach, environmental impact from all major objects (spacecraft, rocket bodies and derelicts) is aggregated. This gives a single value for the consumed space capacity. It can be evaluated for the current space environment and future predictions. Different scenarios or individual events like fragmentations can be evaluated to compare their consumed capacity. This approach cannot yet find an upper limit of the available capacity. Providing only one singular value also makes it difficult to evaluate the effect on individual objects. The evaluation of impacts of tens of thousands of objects is also computationally expensive. Finally, only the direct impact of a fragmentation is evaluated in THEMIS. Fragmentations caused by previous fragmentations are not counted when estimating the environmental impact. This work aims at improving the THEMIS model in these areas to improve interpretability of results, computational speed, modelling accuracy and, eventually, find an upper limit for Capacity.
To improve the interpretability of results, the effect term of the THEMIS space debris index is changed from a single value, average for the entire orbital region, to provide a vector giving the effect for every populated orbital bin ($\vec{EI}$). From this the probability of an impact on individual satellites or their expected number of collision avoidance manoeuvres (CAM) can be derived. This can help set an upper limit based on the maximum acceptable loss rate of satellites or maximum feasible CAM rates. While the current THEMIS approach evaluates the environmental impact for individual satellites, using representative objects like it is already done for the effect term can speed up computation. For each altitude and inclination bin, an average object is defined through mass, area and CAM capabilities. This allows the definition of a Matrix describing the effect of the fragmentation of a representative object on each other representative object $\textbf{e}$. Extracting also collision probabilities for the average objects from MASTER ($\vec{p_c}$) allows a fully matrix-based evaluation of the consumed capacity via:
$\vec{EI} = \textbf{e}\cdot\vec{p_c}$
Finally, to capture the effect of secondary, induced fragmentations, an expression is found using the Matrix of expected number of catastrophic collisions caused by the fragmentation of a representative object $\textbf{E}$:
$\vec{EI} = \textbf{e} \cdot (\textbf{I} - \textbf{E})^{-1} \cdot \vec{p_c}$
This formulation allows to find the point where each fragmentation would cause more than one secondary fragmentation leading to unmitigated growth. Some preliminary results of this approach are presented. This work is performed as part of the ESA Contract No. 4000145375/24/D/BL funded by the ESA safety office.
| Which section would you like to submit your abstract to? | Session 6: “How to measure the space capacity?” |
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