The current generation of Starlink satellites is already above the 7th magnitude, so it no longer saturates the CCD. [1] Of course, darkening them further would always be good.
https://www.lsst.org/content/lsst-statement-regarding-increa... ("Vera C. Rubin Observatory – Impact of Satellite Constellations")
> Darkening satellites to 7th magnitude would simplify removal of some artifacts in LSST images, but there is no guarantee most of the satellites will be limited in brightness to fainter than 7th magnitude.
I'm curious if they were indeed able to implement the artifact removal or if it remains challenging even then.
The 7th magnitude limit just minimizes the streak signal cross-talk through the rest of the camera. It also means the satellites are invisible to the naked eye.
https://www.lsst.org/content/lsst-statement-regarding-increa...
TLDR: the telescope's field of view means that it will be nearly impossible for them to find a "clear" patch of sky, the brightness off satellites saturates the CCD, which in turn causes crosstalk during readout of the CCDs, and even just masking the primary streak is difficult. I'm sure there are optics issues as well from such bright objects, in the field of view and not.
> During the nominal 30-second visit to a sky patch, satellites in 400-600km LEO orbits typically move about 15 degrees across the sky (about four times the diameter of Rubin Observatory’s field of view), and are visible a few hours after sunset and before sunrise. With 400,000 satellites orbiting Earth, tens of thousands of satellites would be visible above the horizon and it would be difficult to find a circle of 9.6 square degrees anywhere on the sky that does not contain satellite streaks. Simulations of the LSST observing cadence and the full SpaceX satellite constellation show that as many as 30% of all LSST images would contain at least one Starlink satellite trail. With the planned constellations of 400,000 satellites at 400-600 km, all images in twilight will contain streaks. The OneWeb constellation at 1200 km will be visible all night long in Chilean summer. Measurements of the brightness of the current LEO satellites in their final orbits indicate that these trails would cause residual artifacts in the reduced data. If these LEO satellites can be darkened to 7th magnitude, then a new instrument signature removal algorithm can remove some of the residual artifacts. This is challenging due to apparent non-linear crosstalk between the 16 channels on each of the 189 CCDs, the cause of which is still under study. The bright main satellite trail would still be present, potentially creating bogus alerts and systematics at low surface brightness. Masking of these trails is not 100% perfect. This is a challenge for science data analysis, adding potentially significant effort.