Waste causes problems not only on Earth, but also in space. A research team from the Lucerne University of Applied Sciences and Arts is currently developing a space debris detector. This can autonomously control satellites that are to clean up space in the future.Above our heads, there is a huge mess: In low-Earth orbits - about 800 km above the Earth - there are currently around 5,500 active and defective satellites orbiting. In addition, there are countless pieces of debris, discarded rocket engines and tools that have slipped out of astronauts’ hands.
The celestial garbage is dangerousIn space, even tiny particles turn into destructive projectiles at high speeds. The manned International Space Station (ISS) already regularly has to dodge pieces of scrap metal. The trajectories of satellites also have to be adjusted frequently because of the debris.
According to estimates by the European Space Agency (ESA), there are currently almost one million objects larger than one centimeter circulating in space. Experts fear that the very existence of space travel is at stake if space debris is not removed within a reasonable time. ESA has therefore launched the "ClearSpace-1" mission. With this project, it wants to develop a probe that can track the junk, clamp around it and bring it down in a controlled manner so that it burns up in the Earth’s atmosphere without causing any damage.
Tinkering in Horw for space cleanupThe Lucerne University of Applied Sciences and Arts is also contributing to the development of this so-called hunter satellite. A five-person research team led by Jürgen Wassner and Klaus Zahn is currently working on a detector that is capable of reliably detecting space debris and autonomously steering the hunter satellite in the direction of a piece of debris.
"With the help of a computer simulation, we are trying to find out, among other things, how many images a camera installed on the hunter satellite needs to create per second in order for it to reliably detect an object and dock with it safely," explains Klaus Zahn, an expert in computer vision and machine learning.
The search for the optimal frame rate is done for good reason: The processor attached to the camera needs memory and power to process the data for each image. However, there is little power in space - a few small solar panels mounted on the fighter satellite will have to suffice. The processor shouldn’t be too heavy, either, because that makes it easier to transport it into space. This is where Jürgen Wassner comes in: as an expert in embedded computing and system design, he specializes in developing the most efficient algorithms possible, i.e. calculation rules, for such mini-computers.
Realistic dry run in virtual space"We’re working with simulations, since we can’t just fly into space briefly to test our cameras or the controls of a satellite in the field," Wassner explains. The team has selected the "Sentinel-6" satellite as the first sample scrap part to be disposed of by the hunter satellite in the model study. This still functions perfectly in reality and has the task of measuring the rise in sea level. Wassner: "For us, Sentinel was a good visual object primarily because the 3D model data were available from this satellite." Of course, Sentinel-6 will also have to be disposed of one day in the distant future, Wassner says with a twinkle in his eye; but at the moment, the primary goal is to develop a system that can be applied to various pieces of shot. And there are many of them: "There are now entire catalogs of shot parts. Space agencies keep meticulous records to keep track of tricky objects."
The research team has already fully incorporated the data from Sentinel 6 into the simulation; as well as the camera’s capabilities, assumptions about the hunter satellite’s control mechanisms, or the appearance of Earth from the satellite’s perspective.
The visual impression of this virtual world is amazing: With just a few mouse clicks, Jürgen Wassner demonstrates how the hunter satellite moves ever closer to Sentinel-6. In the background, the Earth moves through the image as a small, blue-white-brown sphere. It’s as if you’re looking through the camera’s eye.
Training for artificial intelligence"Until the end of May, we will now intensively test the simulation and run through realistic scenarios to train and further improve the algorithms," Wassner explains. A few examples: Sentinel-6 rotates on its own axis. How can the hunter satellite still dock safely without colliding? How high is the energy consumption of the mini-computer at different frame rates of the camera? How do temperatures in space affect its performance? In addition, the hunter satellite must always align its solar panels optimally with the sun to ensure the system’s power supply. Does that work? And what happens if a panel fails?
Cooperation with the University of TokyoIn February 2023, Wassner and Zahn will travel to Tokyo to discuss the next phase of this research project with Shinichi Kimura of Tokyo University of Science. "Shinichi Kimura has excellent laboratories where conditions in space can be recreated," explains Jürgen Wassner. "Together with him, we would like to build and test a prototype camera and processor."
Flying high thanks to a lot of experienceFor Zahn and Wassner, this is the first research project to take them into the vastness of space. They have Matteo Madi, a member of the management board of the Zurich-based company Sirin Orbital Systems AG, to thank for this assignment. This company is active in the fields of space and systems engineering and has already carried out various projects for ESA. Klaus Zahn: "Matteo Madi asked us if we would be interested in working on this exciting project. We were happy to accept this challenge."
The two researchers can draw on their many years of experience in the field of intelligent sensors and networks. For example, they have developed automated systems for counting and classifying vehicles in flowing traffic; as well as intelligent controls for street lamps that only light up when someone passes by, or a technology for reliable data transmission via aircraft power distribution networks. So now they’re going even higher, focusing on a field of work nearly 800 kilometers above sea level.