Satellites orbiting the Earth move at many miles per second ̵
So far, only four such collisions have occurred in space history – most of the space debris comes from explosions of leftover fuel tanks or batteries – but they are likely to become more common.
"We want to understand what happens when two satellites collide," explains ESA 's structural engineer Tiziana Cardone, who oversees the project.
"So far many assumptions have been made about how the very high collision energy would dissipate, but we do not have a solid understanding of the physics involved
" We want to be able to visualize in detail how the satellites are broken and how many debris are produced to improve the quality of our models and forecasts. " The total energy is orders of magnitude higher than the space-typical building technology that focuses on sustaining the force of the launch." This is a really unknown area, "adds
"We need to understand this because we are currently working on expensive demolition strategies based on our understanding of debris," explains Holger Krag of ESA's Space Debris Office, "We project the development of the debris environment up to 200 Years ahead.
Of the four known clashes, only one of them took place as we had expected, with both satellites crashing catastrophically and creating debris clouds. The others were very different, so something is missing in our picture.
"By executing many different collision variants, we hope to understand what happened in the actual collisions to substantiate our modeling."
Two different types of software simulations are performed: at the German Fraunhofer Institute for Short-Term Dynamics and at a consortium led by the Center for Studies and Activities for Space at the University of Padua, Italy.
The first approach is based on a sophisticated method Numerical method for simulating the deformation and fragmentation processes in a collision. The colliding objects are modeled with realistic structural and mechanical properties represented by a "finite element mesh".
These elements are converted into discrete particles as satellite fragments. This allows the simulation of the structural response of the satellites to the collision as well as the generation of the fragment cloud and its temporal evolution.
The second approach treats the spacecraft as consisting of larger elements, such as fuel tanks or solar systems connected to physical connections. When the energy transfer of the collision takes place, these connections are disconnected and the elements are fragmented. A library of past simulations and empirical data is used to show how these elements fragment under the force of impact.
The two types of simulation, working at the material and component level, should give new insights into the underlying physics of collisions, but have begun to mimic the effects of a single piece of debris – the type of collision that will be simulated can physically be used in terrestrial laboratories.
Once these simulations double the observed reality, they are used to reproduce the total impact of satellites on a 500 kg scale.
The first known collision took place in 1991, when Kosmos was hit in Russia in 1934 by a piece of Cosmos 926. In 1996, the French satellite Cerise was hit by a fragment of an Ariane 4 rocket. In 2005, a US upper school was hit by a third-tier fragment of a Chinese missile. In 2009, an iridium satellite collided with the Russian Cosmos-2251.
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