Brightness evolution of LEO Starlink mega-constellation satellites from 2021 to 2023: A multi-year ground-based photometric study

Abstract We report a multi-epoch V-band campaign (2021–2023) with uniform processing and a common 550 km normalisation across Starlink generations. Median magnitudes (68% confidence intervals; N in brackets) are: v1.0: 5.365,[5.084,5.553] (34), Gen-2: 6.012,[5.801,6.173] (6), v1.5: 6.106,[6.065,6.154] (164), VisorSat: 6.618,[6.403,6.804] (54), DarkSat: 8.431,[5.916,10.947] (2). This yields the ordering v1.0 < Gen-2 ≲ v1.5 < VisorSat ≪ DarkSat, i.e. mitigation-era designs are typically fainter than the original v1.0. The Gen-2–v1.5 difference is small (0.094,mag) and Gen-2 has limited coverage (N = 6), so the trend is not strictly monotonic. We use an open, Python-based processing pipeline built on astropy for standard image calibration (bias, dark and flat-field correction), astrometric and photometric calibration against Gaia DR3, and derivation of the viewing geometry (solar phase angle, range, elongation and airmass). Satellite tracks are identified from TLE-based ephemerides, matched to the detections, and then used to measure a brightness value for each track in a reproducible way. At a common height, the medians are 5.37 (v1.0), 6.01 (Gen-2), 6.11 (v1.5), 6.62 (VisorSat) and 8.43 (DarkSat; N = 2), which are ∼0.4–1.6 mag brighter (numerically smaller) than the target of V ≈ 7. Thus, mitigation shows clear progress but does not yet meet the IAU CPS/SATCON goal of V ≥ 7 at ∼550 km. These benchmarks can guide future satellite designs, survey planning and avoidance strategies, with the main uncertainties arising from the very small samples for DarkSat and Gen-2.