Scientists estimate there are 20,000 particles of space junk measuring up at over 10 cm (4 in) in diameter currently hurtling around the earth at an average velocity of 25,000 km/h (15,500 mph), threatening to damage or destroy orbiting satellites. To combat the problem, the German Government has granted the German Aerospace Center (DLR) €25 million to create a system to track space junk as it orbits the earth and the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) has been tasked with creating the new system's radar component. 
The Institute will build on experience working with its existing Tracking and Imaging Radar Systems (TIRA) but Dr. Andreas Brenner, who is deputy director at FHR, says the new (German Experimental Space Surveillance and Tracking Radar (GESTRA) system is far more sophisticated.
"TIRA collects high-definition images of individual objects using a mechanically controlled, movable antenna," says Brenner. "The novel feature of the new GESTRA system is that its antenna is electronically controlled, and can therefore be reoriented even faster because it has no heavy moving parts. Unlike TIRA, it is capable of observing a very large number of objects simultaneously while still supplying data of high accuracy and sensitivity." 
The GESTRA system will be made up of retractable transmitters and receivers consisting of phase array antennae, each of which is made up of multiple individual antenna elements, working at a frequency of 1.3 GHz. The array antennae are fitted with high-performance processors that pick up satellites and space debris in a number of different directions at once. This allows the system to cover a large portion of the sky, although GESTRA can also use a narrower beam to track individual objects. The transmitters and receivers are also fully retractable, allowing them to be easily transported inside their containers, which measure up at 4 x 4 x 16 meters (14 x 14 x 52 ft).
Researchers are hoping to use the system as an alarm, protecting satellites orbiting between 300 and 3000 km (186 to 1,861 mi) from earth, as well as watching for bits of debris that leave their orbit and enter our atmosphere. 
Fraunhofer is aiming to have the project completed in 2018, at which point it will be operated by remote control from the German Space Situational Awareness Center in Uedem. 
The GESTRA system is one of several potential solutions to the problem of space debris. In 2021, ESA is planning on using a harpoon to skewer large objects orbiting earth and prevent them from breaking into smaller clouds of debris, while DARPA's Space Surveillance Telescope is set to jump into action in 2016 – all in an attempt to ensure the orbits between 800 and 1000 km (497 and 621 miles) remain usable and passable for spacecraft and satellites alike. 
Souce: Fraunhofer