**4.2 Failure levels**

According to the impact of the failure on the satellite operation, the failure is categorized as follows:


According to the possible impact on components, functions, and systems, FDIR is designed for five failure levels from levels 0 to 4, according to the different sub-systems that each failure belongs to, including measurement and control FDIR, avionics FDIR, and power supply and distribution FDIR as illustrated in **Figure 3**. The larger the number, the higher the fault level, and vice versa.


**Figure 3.** *Schematic diagram of satellites in orbit during their lifetime.*
