# Crowded Space: A Review on Radar Measurements for Space Debris Monitoring and Tracking
## 4 European Countries' Radar Measurements
\begin{table}
\begin{tabular}{c c c c c} \hline _Object ID_ & _Doppler (Hz)_ & _Altitude (km)_ & _Slant Range (km)_ & _RCS (m\({}^{2}\))_ \\ \hline
22565 (I) & n.a. & 853.6 & 1732 & 11.6 \\ \hline
22565 (II) & \(-\)5200 & 852.7 & 2836 & 11.6 \\ \hline
33320 (I) & 6200 & 628.7 & 3640 & 1.5 \\ \hline
33320(II) & 4600 & 629.3 & 1832 & 1.5 \\ \hline
32783 & 5200 & 629.4 & 2056 & 2.3 \\ \hline
13552 & n.a. & 523.7 & 1093 & 8.4 \\ \hline
16206 & 3400 & 984.8 & 2326 & 0.5 \\ \hline
38047 & 5200 & 460.7 & 1664 & 0.3 \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of the debris measurements by Bistatic Radar for LEO Tracking (BIRALET) in 2014. Figure 21: Example of an echo of an unknown object received by the Medicina-Evpatoria bistatic system in 2007 [46]. Reprinted from Memorie della Societa Astronomica Italiana Supplementi, Copyright 2008, with permission from SAIt. results from a late 2004 campaign are available in the literature. On that occasion, the pool of objects observable by the GRAVES system was around 2300, but only a small portion were effectively detected; these are shown in Figure 7 of [51] in terms of altitude of apogee and perigee as a function of the inclination [51]. A further notable experiment is the project Antenna Bistatic for Space Surveillance (ABISS), led by the ONERA group, involving an L-band bistatic radar with a transmitter located 100 km west of Paris and a receiver located in Paliseau, 30 km south of Paris [52; 53]. The transmitting antenna is a phased array of 49 elements arranged in a panel, with an average gain of about 24 dBi, capable of sending a CW signal with 300-W power. The receiving antenna is also a phased array, consisting of 64 elements, with an overall gain of about 32 dBi [52; 53]. The transmitting and receiving beams are electronically controlled by means of DBF. After March 2015, the ABISS radar was routinely used for several debris campaigns, during which around 500 objects with a diameter of more than 2 m were detected and tracked. More than 43% of the global detections were recognized as rocket debris. The summary of the campaigns' measurements is reported in Figure 22, showing object diameter vs. perigee in comparison with the Space-Track catalog (a public online catalog where registered users can access satellite and debris TLEs [54]). An interesting study that may lead to future developments within space debris radar measurements is the employment of passive radar transmission by means of Digital Audio Broadcasting (DAB) services. In [55; 56], the possibility of taking advantage of the reflected signal from DAB stations using a Low Frequency Array for Radio Astronomy (LOFAR) located in Borowiec (Poland) as a receiver is envisioned. Unfortunately, there are no noticeable reported debris radar measurements from other European countries. However, major contributions in this field will be certainly expected from the United Kingdom and Spain. For the UK, the Chilbolton Advanced Satellite Tracking Radar (CASTR), a monostatic 25 m dish steerable parabolic antenna working in S-band (3076.5 MHz) with 700 kW peak-power, is suitable for tracking of objects in LEO with RCS greater than 0.5 m\({}^{2}\) beyond 2100 km range [57]. Spain, on the other hand, can count on the radars of the Spanish Space Surveillance and Tracking (S3T): the Monostatic Space Surveillance Radar (MSSR), a close monostatic L-band radar located in Santorczak  
Figure 22: Object diameter vs. perigee for post march 2015 Antenna Bistatic for Space Surveillance (ABISS) debris measurements [53]. © 2012 IEEE. Reprinted with permission from Saillant, S. Exo-Mars spacecraft detection with European Space Surveillance bistatic radar. 2016 CIE International Conference on Radar, Guangzhou, China, 10–13 October 2016. (30 km from Madrid, Spain), which is able to detect large objects in the 200-1200 km range, and the new S3T Surveillance Radar (S3 TSR) [58].