GESTRA (German Experimental Space Surveillance and Tracking Radar)
The researchers at Fraunhofer FHR (Fraunhofer Institute for High Frequency Physics and Radar Techniques) in Wachtberg, Germany, are currently developing an innovative radar system on behalf of the Space Administration of the German Aerospace Center (DLR). On completion, the system will allow 24/7 observation of near-Earth space. When put into operation at the German Aerospace Center in mid-2019, GESTRA will supply space object-related data that was previously not available – a milestone in space observation in Germany. 1)
Due to its many years of experience in the area of space observation with radar, Fraunhofer FHR is a renowned expert in this field. With its radar system TIRA (Tracking and Imaging Radar), the institute offers capabilities that are not available anywhere else in the world. At the beginning of April, Fraunhofer FHR provided the last images of the Chinese space station Tiangong-1. These images went around the world. The scientists are, however, working hard to extend these capabilities. With the new radar system GESTRA (German Experimental Space Surveillance and Tracking Radar), round-the-clock observation of active satellites and space debris will be possible for the first time in Germany. This will pave the way for the creation of an orbital data catalog which will be instrumental in preventing collisions.
Radar warns of space debris
The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space debris resulting, for example, from burned-out rocket stages and fragments of exploded space objects. These are gradually transforming the orbit into a junkyard. Approximately 20,000 objects with a minimum diameter of ten centimeters are presently orbiting the Earth at an average speed of 25,000 kilometers per hour. Added to this are 700,000 smaller objects with a diameter greater than one centimeter. Due to their enormous speed, these small debris particles can also damage or destroy active satellites.
Collisions between space debris and satellites can be prevented by means of evasive maneuvers. Maneuvers of this kind are, however, time consuming and tie up valuable resources and are therefore only required by operators when the satellite is in real danger. Comprehensive cataloging of the space objects and high-precision orbit determination of the potential collision objects are essential to assess this risk. Radar systems can carry out both of these tasks.
GESTRA: Wide-range space surveillance with leading-edge technology
Seamless and continuous space surveillance can only be achieved with phased array radars. The electronically controlled array antennas are capable of conducting large-scale space surveillance in near-Earth space around the clock. The new space surveillance radar GESTRA, which is currently being developed by Fraunhofer FHR for the Space Administration of the German Aerospace Center (DLR), is equipped with an electronically steerable antenna which is able to scan large areas of the sky within milliseconds due to the integration of the latest semiconductor technology. The sensor consists of a transmit and receive module, each of which is integrated into an 18 m x 4 m x 4 m shelter. Due to its compact design, GESTRA is a mobile system which can be transported to any required location.
When put into operation for the German Space Situational Awareness Center of the German Armed Forces in 2019, wide-range surveillance of the debris population in near-Earth space (orbital heights of 300 km to 3,000 km) will be possible from German territory for the first time. GESTRA will then operate continuously to create a catalog of the debris in near-Earth space. This new data basis will have a great influence on the further development and operation of the space infrastructure of Germany and Europe.
GESTRA: LEO (Low Earth Orbit) always »in sight«
In order to monitor low Earth orbit and know which objects are moving around there, a phased array radar with high beam agility is required. Fraunhofer FHR is building such a radar for the Federal Ministry of Economics. In September 2020, the partially mobile space surveillance radar GESTRA will be handed over to the German Aerospace Center (DLR). 2)
What is flying around in LEO (Low Earth Orbit) and where? This question is not only an interesting in itself, it is also relevant for our daily lives. LEO is where the satellites travel along their orbits, providing us with information – whether for navigation systems, for critical infrastructures such as communications, stock markets etc. And this is also where significant amounts of space debris are flying around – representing an increasing danger to satellites. NASA has created a catalog – the Master Catalog - to be able to warn satellite operators in time when a piece of debris is getting dangerously close to a satellite. This catalog contains most of the flying objects in LEO. When it comes to US satellites, however, most of them cannot be found in the lists due to tactical reasons. Therefore, Germany would like to free itself from this dependency. This requires two different radar systems: One that tracks and images individual space objects – this is done by the space observation system TIRA at Fraunhofer FHR and another one that fulfills the surveillance function, i.e. that detects the different objects in a large section of space. This can only be achieved by a phased array radar with a high range and beam agility that has not been available in Germany until now.
Figure 1: Phased array antenna of the GESTRA transmitter and receiver (image credit: Farunhofer FHR / Philipp Wolter)
Core Competence: Fast Space Surveillance
The Federal Ministry of Economics therefore commissioned the Fraunhofer FHR to set up such a phased array radar: from the conception and the design phase to the operational system. The design involves a quasi-monostatic system consisting of separate transmitting and receiving subsystems. The phased array antennas are each set up with a 3-axis positioner: This makes it possible to first set the surveillance area mechanically and then scan this area electronically within milliseconds. In the process, the radar beams form a type of fence that can be likened to windshield wipers. Every object that is large enough and passes through the fence will be detected. GESTRA's unique feature: It is partially mobile, meaning that it can be set at any location. In addition, it is able to very accurately determine the position of objects.
September 2020: Handover to the DLR
By now, the GESTRA system is about 90% complete. Next up will be the series acceptance of the components from Fraunhofer FHR, particularly the electronics in the transmitting and receiving antennas. In May 2020, GESTRA is to be brought to the military training area Schmidtenhöhe near Koblenz to be connected to the existing infrastructure on site. System checks for the German Aerospace Center (DLR) as the project management owner on the contract side will then follow. In September 2020, GESTRA will be handed over to the DLR as well as the Space Situational Awareness Center. The Space Situational Awareness Center will use the new radar system to create a German master catalog. If there is more interest in a specific object, it will in turn task Fraunhofer FHR with the tracking and imaging of this object using TIRA.
Since GESTRA is to be operated in Uedem in North Rhine-Westphalia – i.e. remotely – it has to be possible to check the system's »health« anytime. That is why the 34-member GESTRA team installed over 2000 sensors that can be monitored via a remote control. When all sensors give the »green« light, GESTRA can be started. The sensors also monitor the different functions during operation.
In the long run, interconnecting multiple GESTRA systems will make sense: Because if the radars are set up 300 kilometers apart from each other, they will see the objects from different angles, allowing for a more significantly accurate position determination than when using only a single radar. This is precisely the possibility provided by GESTRA's partial mobility.
GESTRA development status
• October 13 2020: After five years of development and construction, the first German space radar with transmitter and receiver units has been installed at Schmidtenhöhe near Koblenz. 3)
- Close cooperation between the DLR Space Administration, the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) and the GSSAC (German Space Situational Awareness Centre).
- GESTRA data will also be used to improve security in low-Earth orbit at the European level.
- Focus: Space, Space security, space situational awareness, protection of space-based infrastructure.
Activity in space continues to increase. Several thousand satellites, spacecraft and other objects orbit Earth at altitudes of between 300 and 3000 km. In addition to the inactive satellites and upper stages of rockets that are left behind here after missions, there are hundreds of thousands of smaller pieces of debris. Satellites and other space infrastructure such as the ISS (International Space Station) need to be continuously monitored to avoid collisions. Active objects can engage in evasive maneuvers, while inactive space debris such as disfunctional satellite parts, or the remains of rockets, pose a threat. 4)
The German Experimental Space Surveillance and Tracking Radar (GESTRA) system can monitor objects in low-Earth orbit around the clock. The complex radar system is unique in its design. Consisting of transmit and receive systems that are housed in two separate containers, it can be transported to different locations. The antenna consists of 256 individual, electronically controlled transmit/receive modules.
On 13 October 2020, GESTRA was inaugurated at its operating location on the premises of the German Bundeswehr at Schmidtenhöhe near Koblenz. "From here, the experimental radar will make a decisive contribution to securing our satellites in low-Earth orbit," says Walther Pelzer, German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Executive Board Member and Head of the DLR Space Administration. "GESTRA consists of transmitter and a receiver units, both of which are installed here. With these, we can detect objects in low-Earth orbit and measure their orbital parameters. From here, the measurement data are sent to the German Space Situational Awareness Centre (GSSAC) in Uedem. A comprehensive catalogue will be produced there that will inform us about the situation in space and any possible dangers. When GESTRA enters operation, most likely at the beginning of 2021 following the completion of all the necessary testing, Germany will begin receiving independent data for the creation of its own catalogue of objects in low-Earth orbit for the first time."
GESTRA is Germany's first space radar system. It was developed and constructed over five years by the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) in Wachtberg, near Bonn, on behalf of the DLR Space Administration and with funding from the Federal Ministry for Economic Affairs and Energy (BMWi). In recent months, GESTRA was installed at its operating location at Schmidtenhöhe near Koblenz. The data from the German experimental radar are processed at GSSAC in Uedem, which is jointly operated by the DLR Space Administration and the German Air Force, Lower Rhine. Last year, on 27 November 2019, GESTRA received its first signals from objects in Earth orbit during tests at FHR in Wachtberg. Operation of GESTRA is financed by the German Federal Ministry of Defence (BMVg).
Figure 2: Handover of GESTRA to DLR (image credit: DLR)
"Satellites have long been indispensable for governments, the economy and society, with the key words being navigation and communications services and Earth observation data," says Thomas Jarzombek, a Member of the German Federal Parliament and Federal Government Coordinator of German Aerospace Policy. "We are currently experiencing an almost exponential growth in the use of space. According to the latest figures, more than 3000 active satellites are currently orbiting Earth. In the future this number will increase significantly."
Figure 3: Aerial view of the two GESTRA units at Schmidtenhöhe (image credit: Fraunhofer FHR, Jens Fiege)
As a result, space situational awareness is becoming increasingly important for the protection and sustainability of space activities. "We need to know exactly where the satellites and tens of thousands of space debris objects are, at any given time, in order to prevent catastrophic collisions," adds Jarzombek.
At the European level, GESTRA is also involved in the European Space Surveillance and Tracking (EUSST) project. Here, Germany has the task of processing the measurement data from the sensors that contribute towards EUSST to create a European orbit data catalogue. Due to the high velocities involved, a satellite can be completely destroyed by a collision in orbit. The resulting debris increases the risk of chain reactions and further collisions. In 2009, a severe collision between the American satellite, Iridium 33, and the inactive Russian satellite, Cosmos 2251, generated more than 3000 measurable pieces of space debris. Many of them still pose a threat to satellites today, which are regularly forced to engage in evasive maneuvers as a result.
• November 29 2019: A new era in space observation has begun. The German Experimental Space Surveillance and Tracking Radar (GESTRA) system, which has been developed and constructed by the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) on behalf of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration, received its first signals reflected by objects in space on 27 November 2019. 5)
- In addition to the use of the latest electronic components, what makes GESTRA particularly special is its transmission and reception technology. The complex radar system employs 256 individual, electronically controlled antennas. The phase-controlled antennas (phased array technology) operate digitally and their performance is currently unsurpassed worldwide. The digital control system allows the beam direction to be changed within a few milliseconds and the radar signal to be transmitted so that it is highly focused in the direction of an object. The resulting return signal is then accurately recorded by the receiving system.
- In addition, the antenna array can be rotated in any direction using a mechanical steering system. This enables space to be monitored flexibly, in all directions. Each antenna element has its own water-cooling system, ensuring particularly high radar performance, while also increasing the sensitivity of the system. This means that GESTRA is not only highly dynamic when it comes to the observation of objects in space, but also extremely sensitive.
- The transmitter and receiver systems are housed in two separate containers, enabling them to be transported to different locations. This combination of mobility and digital technology makes GESTRA unique. The system is currently at the FHR site in Wachtberg and will be transported to its ultimate destination, at Schmidtenhöhe near Koblenz, after it undergoes its final tests. "With GESTRA, one of the world's most modern radar systems for space observation will soon be available to the German Space Situational Awareness Centre (GSSAC) in Uedem," says Thomas Eversberg, GESTRA Project Manager at the DLR Space Administration.
- At GSSAC, DLR's civilian staff are working with members of the German Air Force to integrate GESTRA, which is operated jointly by the DLR Space Administration and the Air Force. The radar observations will be used at GSSAC to create a catalogue of objects in Earth orbit. GSSAC needs such a catalogue in order to protect national space assets from collisions with other objects in space.
- Once GESTRA has been commissioned, GSSAC will be responsible for controlling the system. All of the data from the experimental radar will be collected there. The orbits of objects in space will be determined and this information will be made available to users at universities and research institutions in Germany. In addition to the creation of a German orbital data catalogue, GESTRA will also be involved in the European Space Surveillance and Tracking (EUSST) project. Germany has the task of processing the measurement data from the sensors that contribute towards EUSST, including GESTRA, to create a European orbit data catalogue. Simulations have shown that the technology employed by GESTRA can play a major role in the European sensor architecture.
- This new technology successfully demonstrated its capabilities in recently conducted tests. "We are proud that we have succeeded in working with our colleagues and suppliers to build such a complex system and have now managed to survey some objects in space," says FHR Project Manager Helmut Wilden. DLR, FHR and a number of subcontractors can be proud of their successful collaboration to create this unique, state-of-the-art system. In the near future, GESTRA will make a significant contribution to space security at national, European and international levels.
Figure 4: Photo of the GESTRA receiver (image credit: FHR)
Figure 5: Photo of the GESTRA antenna (image credit: FHR)
Figure 6: GESTRA monitoring and control room (image credit: FHR)
Space debris as a threat
Several thousand satellites, spacecraft and other objects are travelling in Earth orbit. However, this region also contains hundreds of thousands of pieces of space debris. In total, this amounts to approximately 8000 tonnes of material. The majority of the debris – approximately 75 percent – is at altitudes of between 200 and 2000 kilometres, referred to as 'low-Earth orbit' (LEO). There is therefore a high risk of collisions with space infrastructure. The International Space Station (ISS), which is orbiting Earth at an altitude of approximately 400 km, is affected by this. A constant supply of reliable data on the situation in space is required in order to prevent collisions. This has created the need for radar systems such as GESTRA.
GESTRA was developed by the Fraunhofer Institute for High Frequency Physics and Radar Technology (FHR). Finance was provided by the DLR Space Administration using funds from the German Federal Ministry of Economic Affairs and Energy (BMWi). In the future, the radar system will be operated by the German Space Situational Awareness Centre in Uedem, which is financed by the BMWi and the German Federal Ministry of Defence (BMVg). The BMVg will fund the operation of GESTRA.
GSSAC (German Space Situational Awareness Centre)
The Federal Government's Space Strategy: 6)
• Space based systems are becoming ever more important for the civil and military security in Germany and Europe
• The threat to major infrastructure in outer space is increasing
• Ensuring our security must in future also include the protection of these infrastructures
Use of Outer Space for Civil and Military Security
• use synergies of civil and military space research
• strengthen the inter-ministerial coordination
• avoid duplication and make best use of resources
• ensure full functional capability of space systems and access to the use of outer space
Figure 7: German Space Situational Awareness Centre — “User Network”(image credit: DLR)
Figure 8: Building-up the Space Situational Awareness Centre (image credit: DLR)
Overview of the GSSAC mission configuration
• German Experimental Space Surveillance and Tracking Radar (GESTRA) 7)
• The Space Surveillance and Tracking Support Framework of the European Union (EU-SST)
Concept for a Space Surveillance System (2008): Creation of a national capability to provide and assess the space situation
Strategy for Space of the Federal Government (2010):
• Joint efforts to ensure the security and protection of space infrastructure
• Establishment of national competence for recording and assessing the space situation
Agreement between German Ministry of Defence (BMVg) & German Ministry for Economic Affairs and Energy (BMWi)
• Joint realization (of the project) “GSSAC" between German Air Force and DLR Space Administration
• The central contact point of Federal Government regarding Space Situational Awareness towards third parties is GSSAC
Figure 9: The setup of GSSAC (image credit: DLR)
Figure 10: Mission of GSSAC (image credit: DLR)
Figure 11: GESTRA concept for interacting radars (image credit: DLR)
The current implementation has radars in two shelters.
GESTRA parameters and configuration
• Monostatic L-band System with dislocated Transmitter and Receiver Shelter
• Project start 2014, deployed 2019
• Detection & Tracking of objects in LEO
• Basis for future operational space surveillance activities
• Separate transmitter and receiver each in its own shelter
• Transmitter: uniformly filled array
• Frequency: 1280 – 1380 MHz (L-band)
• Bandwidth: 100 MHz
• Transmitted power (Peak): 256 kW
• Transmitted power (Mean): 64 kW
• WLAN/LAN: Connection between both shelter elements and between the GSSAC and the receiver.
• Dimensions of the Shelter: 18.5 m x 4 m x 4 m
• Mass of the Shelter (incl. systems): 90 tons
• Dimensions of the radiation dome: 5 m diameter, 5 m height
• Antenna mounted on a scissors lift
Figure 12: General layout of a radar in a shelter (image credit: DLR)
Antenna frontend on 3D-Positioner
• Aperture contains 256 transmitting elements
• 3D-Positioner with highest precision
• Ad hoc provision of 340 kW by 256 UltraCaps
• High capacity to limit the drop of transmitted power during the radar pulse.
Figure 13: Antenna frontend on 3D-Positioner (image credit: DLR)
The Space Surveillance and Tracking Support Framework of the European Union (EU-SST)
EU-SST in the EU Space Strategy
Ensuring the protection and resilience of critical European space by:
- Improving performance and geographical coverage of sensors
- Evolving depth & breadth of services
- Fostering synergies between civil and defence actors
- Reinforcing EU autonomous access and utilization of space
1) ”GESTRA – New space surveillance capabilities in Germany,” Fraunhofer Press Release, 10 April 2018, URL: https://www.fhr.fraunhofer.de/en/press-media/press-releases
2) ”GESTRA: Low earth orbit always »in sight«,” Fraunhofer FHR, 2020, URL: https://www.fhr.fraunhofer.de/en/businessunits/space/gestra-low-earth-orbit-always-in-sight-jb2019.html
Improved safety in Space – GESTRA space radar
ready to begin operations,” DLR News, 13
October 2020, URL: https://www.dlr.de/content/en/articles/news/2020
Gerald Braun, ”Improved safety in Space – GESTRA space
radar ready to begin operations,” DLR News, 14 October 2020, URL:
5) ”GESTRA space radar passes its first test,” DLR, 29 November 2019, URL: https://www.dlr.de/content/en/articles/news/2019/04/20191129_latest-radar-technology.html
6) GSSAC current status & perspective, UNOOSA, Vienna, 16 February 2011, URL: http://www.unoosa.org/pdf/pres/stsc2011/tech-41.pdf
Braun, ”German Space Situational Awareness Centre (GSSAC): Status
& Perspective,” JS Forum, 10 March 2018, URL: http://www.jsforum.or.jp/stableuse/2018
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).