No one likes to be photobombed, especially astrophotographers, by the ever-increasing number of satellites.
Once a satellite leaves its trails on your frame, it’s near impossible to remove it after stacking.
Fortunately, PixInsight and other astrophotography processing software can deal with removing the trails during stacking. Some manual methods include PixelMath and d2Seg (which draws a line segment between two x and y points). But, by far, the easiest is to let the application replace the satellite trail.
This can be done in Image Integration. It works best if you have 10 subframes or more. The process is Pixel Rejection, and the pull-down selection is Winsorized Sigma Clipping. When a sample value falls outside the acceptable range, Winsorization does not simply reject it but replaces it with the nearest valid neighbor in the sample. So, the pixels making up the satellite trail magically disappear.
The process works by creating an average of all the pixels in your subframes and compares each pixel. It continues by computing which pixels are brighter or darker than all the other frames and rejects them. Removing the offending trails, cosmic ray strikes, and other artifacts that don’t belong.
The ability of the software to work out these statistics is the power behind Image Integration.