# Telescopic Network of Zhulong for Orbit Determination and Prediction of Space Objects
## 3 Results  
After obtaining the OD and OP results, two forms of accuracy assessment can be conducted. One is called internal consistency, which calculates the differences between the determined orbits and the angle observation. The other is external consistency, which compares the differences between the determined orbits and external data, in this case, the CPF orbits. In this section, an analysis of the internal and external consistency of OD's angular measurements for selected space objects, along with the external consistency of OP, will be presented.  
The example in Figure 3 utilizes the residuals (differences between observations and orbital determinations) of OD for 41,240 space objects from 4 to 8 July 2023. The example includes two files of angular data from Telescope Stn 5001. One file was recorded at 14:00 UTC on the 4 th, and the other was recorded at 13:00 UTC on the 7 th, with a time interval of approximately 3 days. The standard deviation of the declination and right ascension differences over the 3 days was calculated to be 1.6.  
Figures 4-7 present the results of precise OD and OP for three space objects using angular data over some time, compared to reference orbits. The results include along-track, radial, and across-track errors and spatial distance differences. The horizontal axis in the figures describes the time in days, with 0 representing the start of the prediction period, negative values corresponding to OD, and positive values corresponding to OP. From the results in the figures, it can be seen that OD can be achieved within a time range of 3 days to 10 days. The comparison of the OD results with the reference orbits shows an error within 800 m. The OP error tends to increase exponentially with time, and this trend is related to many factors, such as the OD error and the force model error. During the OD and OP, the NRLMSISE-00 and JB2008 were utilized. As the orbital altitudes of the three space objects surpassed 1000 km, coupled with the sparsity of angular data, the utilization of both density models in conducting precise OD and OP resulted in similar error outcomes.  
Figure 3: Differences between OD results and angular data starting from 4 July 2023.  
Table 3 provides results of the precise OD and OP for the three space objects over three months. The table includes information for each example case, including internal consistency information that compares the OD results with the measured angular data  
Figure 4: Error of No. 1328 from 23 July 2023.  
Figure 5: Error of No. 46984 from 16 June 2023.  
Figure 6: Error of No. 41240 from 3 July 2023 (OD duration 6 days).  
Figure 7: Error of No. 41240 from 3 July 2023 (OD duration 10 days).  
and differences in the OD and one-day OP compared to the reference orbits. The \"No. of observation files\" in the table refers to the number of angular data files used in the OD process. Each angular data file contains a complete observation arc, with each case in the table having a data period of approximately 3 min. The results in the table show that at least two angular data files are required during the OD period. The internal consistency errors of OD are all within 3 arcseconds, but the external consistency errors corresponding to similar internal consistency errors vary greatly, with OD errors ranging from tens of meters to over two kilometers. The correlation coefficients of OD errors concerning OP error, the number of angular data files, and OD duration are 0.986, \(-\)0.44, and \(-\)0.36, respectively.