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• Modelling the Space Debris Environment.

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https://www.tu-braunschweig.de/ilr/forschung/raumfahrttechnik

Submitter

Luke Goater

A significant amount of the larger orbital objects is continuously tracked by sensors. The catalog of orbital data generated from these measurements includes about 16,300 objects. This orbital data is published and made available for analysis purposes. The cataloged objects, however, make up only a small fraction of the actual space debris population. The existence of smaller objects is known from sporadic measurement campaigns. But their orbits cannot be tracked. The number and the orbital distribution of small objects must be described by statistical models. These models must have the capability to reproduce the sporadically obtained measured data. Especially in the millimeter and centimeter range there are large uncertainties due to missing data. Currently there are about 700,000 man-made objects larger than one centimeter on all Earth orbits. The number of objects larger than one millimeter is estimated to be 200 million. The number of objects in the sub-millimeter range is several trillion. The most dangerous objects exist between one and ten centimeters in diameter. They are too small to be tracked and too big for protective measures. It is important to identify the main risk factors for the most important orbits. For these orbits it is useful to implement regulations on the mitigation of space debris. The highest spatial object density exists at altitudes near 900 km. (Only in the micrometer size range, the highest density is found near 1000 km.) This can be shown by simulations. Below 900 km, the orbital lifetime of objects decreases due to the atmospheric drag, leading to a reduction in spatial object density towards lower altitudes. Above 900 km altitude, space activities decrease so that less debris is produced here. Generally speaking, the collision risk increases with the spatial object density. So the highest risk of collision with debris exists on nearly polar orbits, especially sun-synchronous orbits near 900 km altitude. In polar or near polar orbits the probability for head on collisions is very high. In this case the collision velocity equals two times the orbital velocity resulting in extremely high kinetic energies.

The amount of debris has increased significantly in the recent past, due to further fragmentation events.

The occurrence of catastrophic collisions can be expected in regions where the highest spatial density of debris objects exists. The locations of future catastrophic collisions were calculated assuming a business-as-usual scenario and using an initial population from the ESA MASTER model. The highest concentration of orbital debris can be found in 900 km orbital altitude. At this altitude the highest probability of collision exists.