[Prunkton]

interesting, not a single word about satellites and how they are influencing the quality of their work. I would imagine the telescope is affected in particular of this problem by taking constant snapshots of huge areas in the night sky, but nope...

[NitpickLawyer]

Those are filtered in the data processing pipelines, before the data is exported. Streak-detection algorithms work very well, and they can mask known satellites from the data. It was, in fact, a key requirement of them being allowed to operate. VR is sensitive enough that it can sense the "secret" [1] national security sats, so they filter those early in the pipeline, and only issue alerts for things that are not satellites.

[1] - https://www.theatlantic.com/science/archive/2024/12/vera-rub...

[prpl]

They are not all filtered early nor are they necessarily missing from images. The data can be embargoed until orbits change effectively.

[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...

[Jach]

From the observatory itself: https://rubinobservatory.org/for-scientists/frequently-asked...

[WithinReason]

I'm glad it's not a huge issue:

"Simulations of the LSST observing cadence and 40,000 LEO satellites show that about 10% of all LSST images would contain at least one satellite trail"

"Satellites and debris dimmer than 6th to 7th visual magnitude still cause streaks and glints, but typically leave the rest of the pixels scientifically usable."

[thrownthatway]

It’s such a non-problem it’s not even worth mentioning.

The surface of the Earth is big. If you place 40,000 car sized objects on it in random places, you’d not be able to see then from low earth orbit.

That’s approximately how irrelevant they are in the sky.

[thombat]

This overlooks that the Rubin telescope has a relatively wide field of view and a thirty second exposure time, so LEO satellites do routinely appear in images. The size of the object isn't so important as its relative brightness, so while a car on the surface of the Earth is hard to locate from 400km above, a sunlit car 400km up in the night sky is visible to the naked eye.

[thrownthatway]

A sun lit satellite on the night side of the Earth.

You’re really starting to push the friendship.

[hgoel]

It's a problem in that it needs to be handled in data processing, it isn't a problem in that the impacts on science are not too bad compared to the benefits of those satellites.

[rigonkulous]

Its a non-problem, until it is a problem .. and, wouldn't you want to know in that case?

Especially[0] if we can blast the thing out of the sky, one of these days ..

[0] - https://c.tenor.com/o9t2JYNU4LYAAAAd/tenor.gif