# The Effect of Space Objects on Ionospheric Observations: Perspective of SYISR
## 4 Assessment of the Effect of Constellation Satellites on SYISR Observations  
A larger constellation is supposed to cause big problems for the ISR ionospheric observations. To quantitatively assess the effect of the constellation satellite number on SYISR observations, we use SpaceX's StarLink as an example here. StarLink is a large satellite constellation that provides high-speed internet communication services. The first generation of StarLink consists of approximately 12,000 satellites. It started launching in mid-2019 and will finish in 2024. The second generation of StarLink is set to be accomplished in 2027, and the number of satellites will increase to 30,000 [6]. Thus, this constellation plan will add more than 40,000 satellites to orbit. It now consists of a total of 2481 satellites in orbit. The maximum and minimum orbit inclinations are 97.5\({}^{\circ}\) and 53\({}^{\circ}\), respectively. We used the latest two-line element (TLE) information of StarLink [28] to perform the assessment. We only considered the effective detection area of SYISR (18.3\({}^{\circ}\)N, 109.6\({}^{\circ}\)E), whose latitude is free from the orbit inclination limit of the StarLink satellites. The assessment results are shown in Figure 6. The left panel shows the number of StarLink satellites that pass through the SYISR detection region during Days 1-10, which increases from \(\sim\)9000 to \(\sim\)90,000, with 90% occurring at altitudes above 500 km. Thus, the pollution on SYISR measurements will be 10 times worse if the satellites increase by 10 times, especially at higher altitudes. We  
Figure 5: (**a**) Power profile (unit: dB) with weak space object pollution in the ionosphere observed at 10:43:53 on 16 April 2022. (**b**) Autocorrelation function (ACF) with the space object pollution. (**c**) Power spectrum with the space object pollution. (**d**) Electron density profile from the measurement with the space object pollution (blue). The red line is the adjacent electron density profile without space object pollution, which is shown as a reference. suggested the data were more easily disturbed above 500 km because the ionosphere echo was usually weaker above this altitude. The right panel shows the number of StarLink satellites that passed through the SYISR detection region over 10 days in 2019-2022. This number increased from \(\sim\)2000 to \(\sim\)9000, which implies dramatically increased pollution on SYISR measurements due to the increased number of satellites in orbit each year. As a reference, the launched StarLink satellites during each year are 55, 734, and 957 in 2019, 2020, and 2021, respectively [28]. When a space object passes through the SYISR's beam, the power of the reflected echo is decided by its radar cross section (RCS), which is related to the size of the object, and the range between the object and the radar receiver. As shown in Figure 5, if the space object is too small to be eliminated by the SO-CFAR algorithm, its pollution will remain in the ionospheric observations and result in unrealistic ionospheric parameters. We performed a simulation based on the radar equation to quantify this \"dangerous\" situation, as shown in Figure 7. The altitude range of the radar measurements is from 100 km to 1200 km. Considering that the ionosphere echo is a kind of random signal, the incoherent integration and special waveform, which make a balance of range resolution and signal power, are used in the ionosphere measurements. The RCS limitation of the space objects described there is calculated using incoherent integration and the according ionosphere detection signal parameters. Moreover, we set the false alarm possibility to avoid confusing the ionosphere echo with the space objects. An RCS smaller than 0.08 m\({}^{2}\) is difficult to remove with the integration of 320 pulses (\(\sim\)5 s) at altitudes above 600 km. According to the data published by CeleStack [28], approximately 7465 cataloged space objects, whose RCS are known in orbit, satisfy the condition.