Modeling the Optical Impact of the Second-generation Starlink Satellite Constellation

Abstract The optical impact of Starlink is of great concern and the Gen1 network is well studied. However, understanding of the planned second-generation (Gen2) constellation containing almost 30,000 satellites with two thirds in very low Earth orbit (VLEO) below 450 km is developing. This work models Gen2 orbital parameters and considers line-of-sight visibility and spacecraft illumination in relation to terrestrial latitude and investigates changes through the day/night transition period. At peak latitudes there will be over 1200 satellites illuminated above the naked-eye horizon that persist long into the local winter night. At higher latitudes in summer spacecraft may then remain illuminated during darkness hours without interruption. For optical astronomy around 90% will be below the observational horizon, still leaving up to 120 in the field of view. Of those illuminated at nightfall, traditional LEO satellites dominate and persist for longer. This is demonstrated at latitudes representing major observatories where VLEO satellites are fully eclipsed 30 minutes after astronomical dusk, but higher layers continue to restrict observations. Broader literature suggests that at nightfall the lower spacecraft may be brighter if larger, but will be out of focus and rapidly transit detectors before quickly eclipsing and so the impact may be further reduced. This work develops understanding of the Starlink Gen2 network and suggests that operators deploying satellites further below the recommend 600 km altitude limit will continue to reduce the impacts on terrestrial optical astronomy; however, that benefit must be considered against the wider environmental impacts throughout the lifecycle to make informed decisions on sustainability metrics.