There is a high traffic density not only on highways and federal roads in urban areas. Near-Earth space is also congested and, in some areas, overcrowded. It is packed with active satellites as well space debris – and this density is growing at a rapid pace. Just like on the road, this situation involves increasing risks. Collisions can destroy satellites and compromise infrastructure that is important to society. For this reason, it is crucial to detect, monitor and track space objects: If the orbiting objects are always in view, countermeasures can be initiated in time if danger is imminent, for instance evasive maneuvers for satellites. Space Situational Awareness, SSA in short – i.e. the detection, identification and position determination of space objects – is a research topic that is becoming increasingly important, both in the European as well as in the international context. This research field is gaining importance for military purposes as well. For example, there has been an increase in suspicious maneuvers with spy satellites approaching other satellites or even docking onto them. New space powers like India and China are testing anti-satellite missiles to exhibit their capabilities. US President Trump recently established the Space Force as a separate military branch due to the increasing threat in and from space. And France has announced plans for the development of space-based laser weapons for defense purposes.

GESTRA and TIRA: Hand in Hand

The radar systems that Fraunhofer FHR's Business Unit Space researches and develops are ideal for the monitoring, observation, and identification of objects in near-Earth space. In this respect, the two radar systems TIRA and GESTRA complement each other perfectly. The radar system GESTRA currently being developed for the DLR Space Administration allows for the continuous monitoring of large areas of space – it is capable of simultaneously determining the orbital data of a large number of objects. For example, GESTRA also makes it possible to determine the height of the objects as well as their inclination – the degrees between the Earth's equator and the orbit. Another special feature: GESTRA combines phased array antennas, mechanical mobility of the radar units in three axes, and the mobility of the entire system. Thus, GESTRA can be deployed at any given site and allows for the creation of a radar system network for space surveillance.

If, however, one wants to capture a certain satellite or any other space object in more detail, the system of choice is TIRA. TIRA is already in use and provides a significantly more accurate capturing and imaging of satellites – even delivering information about the satellite itself. For example, if a satellite is not working, TIRA can help find out if this might be due to a solar panel that failed to unfold correctly. The possibility of obtaining extremely sharp images of space objects with TIRA is unique in all of Europa – the system has already supported a multitude of missions.

To date, the focus of the Business Unit Space was on the described surveillance and tracking of space objects. Additional fields of work are set to be added in the future. On one hand, the plan is to complement Earth-based SSA sensors with a space-based radar. The radar system observing the space objects will then not be located on Earth, but on a satellite in orbit. On the other hand, the portfolio is to be expanded to include other research topics. Examples are active array antenna technologies for communications satellites, SAR (synthetic aperture radar) technology for Earth observation satellites and satellite-based microwave radiometers for climate and environmental research. Thus, in the future, the Business Unit Space will be even more diversified than now – this wealth of expertise of Fraunhofer FHR will then benefit other fields of space research as well.

Technical contributions from the business unit

GESTRA: Low earth orbit always »in sight«

Dipl.-Ing. Helmut Wilden

Retrieving space debris: The space observation radar TIRA can provide support

M. Sc. Nora Egli

Sharper ISAR images of satellites and other space objects

Dr.-Ing. Delphine Cerutti-Maori

Space debris under the spotlight: High- Precision orbit determination with TIRA

Dr. rer. nat. Jens Klare