## 4 Conclusions  
This paper introduced the novel Italian BIRALET radar system for resident space objects monitoring and tracking. A detailed description of the receiver sensor was provided in the first part of the manuscript. The receiver system consists of the Sardinia Radio Telescope, a fully steerable wheel-and-track 64-m dish located in Sardinia (Italy), with its P-band mono-beam receiver. Compared to the early years when the telescope was used for space debris measurement campaign, the system  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \(\epsilon_{\textbf{p},OD}^{\textbf{50\%}}\) & \(\sigma_{\textbf{p},OD}^{\textbf{50\%}}\) & \(\epsilon_{\textbf{v},OD}^{\textbf{50\%}}\) & \(\sigma_{\textbf{v},OD}^{\textbf{50\%}}\) & \(\epsilon_{\textbf{p},free}^{\textbf{50\%}}\) & \(\sigma_{\textbf{p},free}^{\textbf{50\%}}\) & \(\epsilon_{\textbf{v},free}^{\textbf{50\%}}\) & \(\sigma_{\textbf{v},free}^{\textbf{50\%}}\) & \(\mathbf{I}_{\textbf{p}}^{\textbf{50\%}}\) & \(\mathbf{I}_{\textbf{p}}^{\textbf{50\%}}\) \\ (**km**) & (**km**) & (**km/s**) & (**km/s**) & (**km**) & (**km**) & (**km/s**) & (**km/s**) & & **(**km/s**) & \\ \hline
1.19e2 & 1.98e2 & 1.15e-1 & 1.91e-1 & 4.81e2 & 1.85e3 & 4.47e-1 & 1.83 & 1.09e-1 & 1.09e-1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Range-Doppler OD performance in terms of median (50% superscript) of the error in position and velocity (\(\varepsilon_{p}\) and \(\varepsilon_{v}\)) and standard deviation in position and velocity (\(\sigma_{p}\) and \(\sigma_{v}\)) obtained with (“_OD”_ subscript) and without (“_free_” subscript) OD refinement, and median of the \(I_{p}\) and \(I_{v}\) indexes. All quantities are referred to epoch 02 August 2019 00:00:00 UTC.  
Figure 6: Object NORAD ID 00730, error in position (**a**) and velocity (**b**) as a function of time without performing OD refinement (black line), with Doppler-only (green) and range-Doppler (blue) OD refinement. Squares and triangles represent the error before and after the UKF, respectively.  
has been recently upgraded with the development of a dedicated channel for space debris monitoring. In this way, the Sardinia Radio Telescope can work with high performances in a bi-static radar configuration, providing Doppler shift and SNR measurements.  
The second part of the paper was dedicated to the analysis of the orbital state estimates accuracy achievable with the sensor. The importance of the availability of possible range measurements was stressed: the combined used of Doppler and range measurement would grant both an increase in the state estimate accuracy and a reduction in the estimate uncertainty. For this reason, the most important future work will certainly be the upgrade of BIRALET to a ranging radar. The approach here presented will be tested in the future during real observation campaigns. In addition, the behavior of the sensor against the re-observation of uncatalogued objects will be investigated.  
[PERSON] performed the assembly and characterization of the space debris dedicated channel of the SRT. [PERSON] carried out the numerical simulations for assessing the performance of the new space debris channel. All authors prepared the article.  
This research received no external funding.  
The authors are grateful to the Italian Space Agency and to the National Institute for Astrophysics for the support to their research activity, and to [PERSON], for his precious suggestions.  
The authors declare no conflict of interest.