# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
## 3 Cheia Space Surveillance and Tracking Radar Design Overview  
Romania, represented by the Romanian Space Agency (ROSA), is a member of the EU SST consortium and has a significant contribution to the European SST system. ROSA operates the national SST Operational Centre that coordinates the contribution of the Romanian sensors within the consortium. The sensor network currently includes several optical telescopes that have already provided timely and valuable data to the EU SST. ROSA has coordinated and participated in efforts to add a Romanian radar sensor to the consortium's assets [17]. The choice of adding a tracking radar sensor to the Romanian network for SST took into consideration its ability to operate in almost all weather conditions, day and night, without sensitivity to atmospheric or light pollution. The data output provided by a tracking radar include the target's position in polar coordinates (range and angles), as well as its radial velocity for a certain segment of its course, improving the information accuracy about its trajectory. As the majority of space debris around Earth is present in the LEO, this domain represents the priority interest for SST data collection activity. For this reason, the design project for the Romanian tracking radar sensor stated the requirement that the range of acquiring and tracking of targets should cover the LEO domain, i.e., 200-2000 km. The task of developing a Romanian tracking radar sensor for SST applications was carried out by a consortium led by the local company RARTEL, a Romanian-Italian joint venture specialized in satellite services and applications [18]. A preliminary study funded by the ESA (entiled SSA for Romania) presented an inventory of existing facilities and infrastructure with associated technical know-how available at Romanian entities and capable to be integrated in international SSA, especially in SST activities. The survey also pointed to the possibility to develop the first Romanian radar sensor for SST data collection by reusing the parabolic C-band antennas available at the National Satellite Communication Center in Cheia, Prahova County [17]. A subsequent project also financed by the ESA (contract SSA CHEIA PHASE 1) resulted in a study detailing the retrofit of the Cheia antennas (two former satellite telecommunication antennas with diameters of 32 m) to a space surveillance tracking radar system [19]. Phase 1 activities included: a review of the current technical condition of the antennas and of the associated devices and support infrastructure; an analysis of necessary changes and refitting that should be carried out in order to obtain a functional SST radar; and evaluation of options and the decision on the future antenna configuration as a monostatic or quasi-monostatic radar system by using either one or two antennas. The detailed original design of the tracking radar was developed with block diagrams, costs, schedule, and risks up to the level of the preliminary design review. The implementation of the design and the actual development of a working tracking radar for SST is being carried out by RARTEL in the framework of a third contract financed by the ESA as a Cheia Retrofit Phase II activity. Radar Site Antennas Opportunities and Constraints  
The Cheia Satellite Communication Center in Prahova County, Romania, comprises two decommissioned 32 m diameter parabolic antennas originally installed in 1976 and 1979, respectively, positioned at latitude 45\({}^{\circ}\)27\({}^{\prime}\)24\({}^{\prime\prime}\) N and longitude 25\({}^{\circ}\)56\({}^{\prime}\)48\({}^{\prime\prime}\) E at a 900 m altitude (Figure 3). The antennas baseline is 80 m, and each antenna is mounted on top of its own support building. The most important parameters of the antennas are presented in Table 1[19]:  
One of the main reasons for pursuing this radar development opportunity was the possibility to reuse the two decommissioned antennas and retrofit them to a SST radar.