Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRGESTRA detection algorithm proves itself in operational use
The German Experimental Space Surveillance and Tracking Radar (GESTRA) represents a state-of-the-art radar system in Germany that significantly contributes to European Space Situational Awareness. Developed at the Fraunhofer Institute for High-Frequency Physics and Radar Technology (FHR) on behalf of the German Aerospace Agency (DLR), GESTRA enables reliable detection and tracking of satellites and space debris in low earth orbit. To enable the detection of very small objects, a dedicated detection method was developed that combines coherent and incoherent integration. Given the steadily increasing number of satellite constellations and the rise in orbital debris, this system represents a key technology for the safety and sustainability of space operations.
Research at the Interface of Theory and Practice
At Fraunhofer FHR, an interdisciplinary team is working on further developing the detection algorithm. One of the project staff members at Fraunhofer FHR is Simon Kollecker, who has been part of the GESTRA team for three years. His role lies at the intersection of signal processing and software development, aiming to transfer complex algorithms to the real radar system and ensure its performance in operational use. Kollecker describes his work as follows: "Our task is to implement the signal processing in a way that fully utilizes the system's capabilities. The goal is to increase the sensitivity of GESTRA through an optimized data processing so that we can reliably detect as many objects as possible – from space debris to operational satellites – and have their orbits determined by the German SSA Centre."
Radar Technology as the Core of the System
GESTRA is based on a phased-array radar that emits radar pulses and analyzes their echoes. This allows for the determination of range, speed, and trajectory of objects in orbit. Obvious advantages over optical telescopes lie in its independence from time of day and weather conditions. This enables continuous monitoring of the heavily trafficked low earth orbit (LEO), where both operational satellites and the majority of space debris – tens of thousands of fragments – are located.
Incoherent and Coherent Integration
A central principle of signal processing involves correlating the received echo to the expected signal, thereby enabling the filtering out of even weak signals from small objects amidst the noise. To increase the likelihood of detection, the detection method of the GESTRA system is based on a two-stage signal processing approach: Incoherent integration sums the signal strengths over several radar pulses, thereby increasing the chance of capturing weak signals. This method is computationally efficient, but the signal-to-noise ratio (SNR) is limited. To still detect very weak targets, a low SNR threshold is initially chosen, resulting in some false detections.
Coherent integration not only considers the signal strengths, but also the phase information of the echo signals. If these are consistent over multiple pulses, the signal is amplified, allowing genuine objects to be reliably separated from noise signals. While this method is more computationally intensive, it significantly improves the signal-to-noise ratio. Thus, by combining both methods, as many signals as possible are initially captured at a low threshold and then precisely verified. This enables reliable detection of even relatively small objects, allowing them to be clearly distinguished from disturbances.
To enable near real-time application of these methods, a GPU-based high-performance computing cluster is installed in GESTRA. 128 Nvidia Tesla P100 GPUs, distributed across 16 nodes, process data in parallel. The results are compiled into so-called tracklets and transmitted to the DLR within the German SSA Center. The signal processing system has been operating extremely reliably within the last years and has proven its performance both in testing phases and in operational use.
European Dimension and Independence
GESTRA contributes to the European Space Surveillance Network (EU SST). Thus, the system not only supports collision avoidance and orbit tracking but also strengthens European autonomy in the realm of Space Situational Awareness. A central goal of the EU is to become less dependent in monitoring the space environment. With GESTRA, a cutting-edge system developed in Germany is available, which is integrated into the German and European security architecture.
In addition to the technical challenges, the societal relevance also plays an important role for the involved scientists, as Simon Kollecker emphasizes: "Scientific and economic activities in space are steadily increasing and gaining more importance for our daily lives. With our research at Fraunhofer FHR, we contribute to the sustainable and safe use of this space."
The GESTRA detection algorithm combines state-of-the-art radar technology, coherent signal processing, and GPU-based high-performance computing, providing accurate data on the space environment and operating reliably. Thus, GESTRA plays a significant role in protecting satellites, critical infrastructure, as well as future space missions. GESTRA is not only a tool for research but also an indispensable contribution to the safety of space operations – ultimately affecting our daily lives, which depend more than ever on satellites.
The funding for GESTRA is provided by the German Space Agency at DLR with federal resources under the contract No. 50LZ1401.