Radar techniques for space situational awareness

Radar systems play an outstanding role for space observation. For an efficient space surveillance system at the current state of technology a twofold radar strategy is necessary: Only by means of phased array radar a complete hemispherical surveillance for known and unknown objects is possible. Nevertheless, such systems will have only a limited bandwidth and the position estimate will not be accurate enough to predict reliably probabilities for collisions with space debris. On the other hand, wide bandwidth - high power systems are able to image space objects via inverse synthetic aperture (ISAR) techniques and can estimate the target's position very accurately. Today such systems are efficiently based on mechanically steerable dish antennas - which on the other hand cannot survey the hemisphere because of their mechanical inertia. So, a phased array system has to survey the space and transfer the extracted information to a high bandwidth system capable to analyze the space object in detail. At Fraunhofer FHR an experts group investigates space observation techniques with radar for many years. The high performance radar system TIRA (Tracking and Imaging Radar)provides exact orbit determination and high-resolved ISAR images. Besides this, FHR is also active in the phased array part - a receiving system with digital beamforming is currently built up for a demonstrator of a future ESA European Space Situational Awareness System.