The watchful eye of the TIRA radar system
It looks like an oversized golf ball and is located on the edge of the Eifel: The Tracking and Imaging Radar TIRA is one of the most powerful radar systems for space observation in Europe. TIRA targets the sky above the clouds to track, map or find damage to all types of artificial satellites. It also detects small space debris.
In the Drachenfelser Ländchen in the Eifel region, one of the world's largest antenna domes is visible from afar (see "The TIRA space radar"). They are also called radomes – a neologism of radar and dome, with the latter referring to the dome of an observatory in astronomy. The golf ball-like radome with a diameter of 47.5 meters consists of 1330 different triangles that protect the sensitive interior from wind and weather: one of the most powerful European radar systems called Tracking and Imaging Radar (TIRA). A 34 meter parabolic antenna is hidden inside the sphere. The antenna can be rotated in azimuth at an angular rate of up to 24 degrees per second. A complete rotation therefore takes only 15 seconds, whereby 240 tons of mass have to be moved - that's a world record!
TIRA was built in the late 1960s and was initially developed as an early warning system for potential long-range missiles during the Cold War, for which it was never used. It turned out to be especially useful for observing space objects. The very high dynamics of the mechanical system result from the requirements of an early warning system in order to be able to track even very fast-flying long-range missiles safely and almost completely. Since it is not possible to tilt the antenna at the zenith of overflying objects - i.e. objects with a large elevation angle, the antenna is rotated at high speed by 180 degrees in the azimuth angle so that the object is picked up again immediately after the rotation and tracked further can be.
With the founding of the Research Institute for High Frequency Technology in 1957 - the forerunner of the Fraunhofer Institute for High Frequency Physics and Radar Technology FHR (Fraunhofer FHR for short)nbsp;- the resumption of radar research began in Germany. The first major project was the development and construction of TIRA. In the context of defense and security research, the system has been a constant for the observation of near-Earth space since the 1980s, so that since then satellites, space stations, space debris and aircraft have become the focus of the radar system. It didn't take long for completely new forms of space surveillance to be demonstrated in Europe with TIRA. The European Space Agency ESA soon became interested in the radar system. TIRA has been an integral part of ESA observations since the 1990s. The high dynamics of the system also allows objects that are flying close to the zenith and traveling at around 7.5 kilometers per second or 27,000 kilometers per hour to be tracked almost seamlessly. The technicians continuously developed the system further and adapted TIRA to constantly growing challenges. For example, they continually increased the radar bandwidth in order to better resolve objects. The distance resolution ∆r=c /(2 B) is inversely proportional to the bandwidth B (in Hertz) of the transmitted signal, which propagates at the speed of light c. The higher the bandwidth, the better the range resolution.
Furthermore, the drive was renewed in 2012 and a new antenna control was implemented. A year later, a new L-band transmitter was installed. After 46 years of operation, the complete radome was replaced for the first time in 2014 in order to be able to continue to protect the radar from the weather for future tasks. To do this, it was necessary to prevent the radar from being exposed to the weather for several months during this facelift. The solution: First, scaffolding was erected inside the old shell up to just in front of the parabolic mirror. After that, the new shell could be built step by step and finally, when the weather was nice, closed with an "old for new" cap exchange. The designers removed the remaining old radome outside the new shell piece by piece. At the end of this complex procedure, the "giant golf ball" shone in new splendor. This radome consists of randomly aligned aluminum struts with edge lengths between 2.1 and 4.5 meters. In this way, the struts form triangles of different sizes. This ensures that the struts do not cause any disruptive superimposition of the radar waves, which would impair performance. A membrane is used between the struts, which allows the radar waves to pass through undisturbed.
TIRA essentially consists of three components: on the one hand the mechanically high-precision and very mobile parabolic antenna, on the other hand a target tracking radar for highly precise tracking and orbit determination of space objects and an imaging radar for high-resolution imaging of space objects. The quality of the antenna surface is so high that even observations at radar frequencies of up to around 40 gigahertz would be possible.
The complete surveillance of the near space is reserved for other radar technologies, such as the phased array systems of the USA or GESTRA, the German Experimental Space Surveillance and Tracking Radar. Whenever you need to take a closer look to get detailed information, TIRA comes into its own.
