# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
## 2 Characteristics and Performance of Some European SST Radars  
The feasibility study and design of the intended Romanian SST tracking radar included a survey and comparative analysis of the characteristics and performances of similar installations. The sensor function of the EU SST capability consists of a network of sensors to survey and track space objects in all the orbital regimes (LEO, MEO, HEO, and GEO). The network includes (2021 status) 11 operational radar sensors of the member states of the SST Consortium, three for discovery and surveillance (GRAVES, S3 TSR, and BIRALES) and eight radar sensors that also have tracking capabilities (TIRA; SATAM1, 2, and 3; GESTRA; BIRALET; and MFDR-MR and LR) [8]. The characteristics and performances of some radar sensors in the EU SST network are summarized below:  
* The GRAVES radar (Grand Reseau Adapte a la Veille Spatiale) is a bistatic radar operating in the VHF band with transmitters located near Dijon and receivers located near Apt, France, operated by the French air force. GRAVES concerns itself with active satellites as a priority, carries out continuous surveys, and is able to acquire simultaneous observation data (angles, Doppler shifts, and Doppler rates) for several objects to an altitude of maximum 1000 km, equivalent to a range of more than 2500 km [9]. * The S3 TSR radar (Spanish Space Surveillance and Tracking Surveillance Radar) is a ground-based radar in close monostatic configuration operating at the L band from 1215 to 1400 MHz and capable of providing automatic surveillance and tracking of space objects in LEO from 200 km to 2000 km of orbit height above Earth. The design of S3 TSR allows for scalable evolution in size and capabilities by adding multiple Tx and Rx units. The sensor is fully operational since early 2019 and is providing high-accuracy orbital data of more than 2400 LEO objects included in the catalogue maintained by the Spanish Space Surveillance and Tracking Operation Centre (S3 TOC), which also generates autonomous conjunction analysis products [10; 11]. * The Italian radar sensor BIRALES (BIstatic RAdar for LEo Survey) is a UHF band (410 MHz) bistatic radar composed of a transmitter antenna situated in Cagliari, Sardinia, and a portion of the Northern Cross Radio Telescope operating as a receiving antenna situated in Medicina, Emilia-Romagna, at a 580 km distance. The transmitter is able to supply a maximum power of 10 kW and uses a 7 m fully steerable wheel-and-track parabolic antenna, with a maximum speed of 3 deg/s. The two installations operate for the space surveillance of debris in the LEO. The radar sensor initially operated in CW mode and performed only Doppler measurements. The system was upgraded to use pulse compression, which enables BIRALES to also perform range measurements [12; 13]. * The sensor BIRALET (BIstatic RAdar for LEo Tracking) is a bistatic radar configuration located in Sardinia, Italy. The transmitter is a 7 m fully steerable wheel-and-track parabolic antenna located north of Cagliari that transmits a continuous wave (CW) signal of 10 kW at 410 MHz. The receiving system is the Sardinia Radio Telescope (SRT), a 64 m fully steerable wheel-and-track parabolic antenna devoted mainly to radio astronomical observations located at approximately a 40 km distance from the transmitter operating in the frequency range from 0.3 to 116 GHz. The antenna Gainat 410 MHz is 46.6 dBi, and the efficiency at 410 MHz is 57.7%. During measurement campaigns, the BIRALET has been able to detect objects in orbit with radar cross-section (\(RCS\)), ranging from 0.13 to 13.4 m\({}^{2}\) in the range interval between 459 and 1224 km [14; 15]. New radar sensors will likely be added to the EU SST network, one of these being the ATLAS SST tracking radar, which has been developed since 2019 in Portugal. ATLAS is a new monostatic radar tracking sensor located at the Pampilhosa da Serra Space Observatory (ErPoB), Portugal. ATLAS uses a 9 m parabolic antenna with 46 dB of gain at 5 GHz and a 5 kW solid-state transmitter.