# Recent Advances of the BIRALET System about Space Debris Detection
###### Abstract  
Space debris is internationally recognized as a planetary threat. Efforts to enhance the worldwide radar monitoring networks have been intensified in the last years. Among the new radars employed for the observations, one of the most promising is the Bistatic Radar for Low Earth Orbit (LEO) Tracking (BIRALET), which employs the Sardinia Radio Telescope as a receiving segment. The Sardinia Radio Telescope (SRT) has recently been proven to be a reliable instrument for space debris monitoring and, for this purpose, over the years has undergone some substantial modifications in order to be able to rise to the status of a fully functional radar receiver. However, an extensive measurement campaign, in order to assess the real potential of the radar, has never been done before. In this paper, the authors present the first real space debris measurement campaign of the SRT, made between December 2018 and October 2019 using the new dedicated channel of the P-band receiver. A total of 27 objects were correctly detected during this campaign, characterized by a radar cross section (RCS) interval between 0.13 and 13.4 m\({}^{2}\) and a range interval between 459 and 1224 km. S 2021 17 March 2021 19 March 2021 1  
in the Italian and European space debris monitoring program and it has been gradually upgraded to make it more suitable for space debris observations [12]. As pointed out in both [11; 13], the first measurements performed in April 2014 were planned to assess the potential of the SRT as a receiver in a bistatic radar system for space debris monitoring. On that occasion, the observation schedule included a total of six pieces of debris, each one correctly spotted [11]. However, these first results, although encouraging, showed the shortcomings of the employed system, tied also to the inadequacy of the back-end (e.g., speed of the frequency sweep tied to the resolution bandwidth selected, poor processing capabilities, and missing information due to the sampling time), which was mainly used for the primary mission of the radiotelescope, i.e., radioastronomical observations [9; 14]. Because of these limitations, in a recent paper, the authors presented the design and realization of a new space debris dedicated channel for the SRT [12; 13]. The new channel is based on the introduction of a few filtering stages and a down-conversion section necessary to match the working frequency of the new back-end, based on the FPGA commercial board Red Pitaya (model STEMLab 125-14: [[https://www.redpitaya.com/f130/STEMlab-board](https://www.redpitaya.com/f130/STEMlab-board)]([https://www.redpitaya.com/f130/STEMlab-board](https://www.redpitaya.com/f130/STEMlab-board)), accessed on 19 March 2021). The channel has been tested taking advantage of the reentry of the Chinese space station Tiangong-1 on April 2018, in a joint operation with the BIRALES system, with the aim to retrieve the speed of the falling object from the Doppler measurements [13]. However, as the Tiangong-1 was characterized by an overall radar cross section (RCS) of about 20 m\({}^{2}\), that measurement cannot be considered a real testing ground for the capabilities of the new system. Moreover, the observation of the Tiangong-1 was focused on the calculation of the speed from the Doppler frequency of the space station. Therefore, a further set of observations has been scheduled, including objects with a rather wide interval in terms of RCS and range. Accounting for objects with different RCS and range is pivotal for an extensive campaign to assess the capabilities of a radar system. Small and far objects can give a hint on the sensitivity of the system, whereas large and near objects are useful for the calibration of the receiving chain, as the blinding of the receiver must be avoided. Despite the great distance between radar and debris, the reflected signal could be high enough to saturate the amplification stage of the receiving chain. In this paper, the most extensive space debris measurement campaign ever performed by the BIRALET system is presented.