Comment by NitpickLawyer

Right. I'm not sure if you're referring to LEO sats or "secret" sats here, but in any case you're correct that not all get removed. It's possible, depending on the particular orbit that a 30sec exposure wouldn't produce a long enough streak to get caught by the filters.

Anyway, here's what the oficial FAQ [1] says about the process, they are trying to remove them all, but not always succeeding.

> Streak detection is implemented in the Rubin data processing pipelines, and occurs in two main portions of the pipeline. First, pixels associated with detected streaks are identified in the image mask plane and excluded from contributing to the deep coadded images. Second, sources identified in regions associated with streaks or glint trains are flagged during image subtraction and not used to create new difference imaging objects. In addition, alerts are only sent for detected difference-image sources that do not coincide with known satellite sky locations.

> Signatures from satellites may appear in LSST data products despite the Rubin Data Management team’s best efforts. Difference imaging catalogs have some flag columns which are designed to indicate sources that may be affected by streaks or glints (e.g., look for columns with “streak” or “glint” in their name). The IAU CPS SatHub has developed NOIRLab-hosted tools that may be useful for scientists working with Rubin data products.

[1] - https://rubinobservatory.org/for-scientists/frequently-asked...