Brightness evolution of LEO Starlink mega-constellation satellites from 2021 to 2023: a multiyear ground-based photometric study

Abstract

We report a multi-epoch V-band campaign (2021-2023) with uniform processing and a common 550 km normalization across Starlink generations. Median magnitudes (68 percent 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 v 1 . 0 < Gen-2 less than or similar to v 1 . 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 similar to 0.4-1.6 mag brighter (numerically smaller) than the target of V approximate to 7 . Thus, mitigation shows clear progress but does not yet meet the IAU CPS/SATCON goal of V >= 7 at similar to 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.