Optical observations of an ultrabright constellation satellite

Abstract

Large constellations of bright artificial satellites in low Earth orbit pose significant challenges to ground-based astronomy [1]. Currently orbiting constellation satellites have visual brightnesses between apparent magnitudes 4 and 6, satellite operators, astronomers, and other users of the night sky are working on brightness mitigation strategies [2,3]. Here we report the outcome of an international optical observation campaign of a prototype constellation satellite, AST Space Mobile’s “BlueWalker 3”. BlueWalker 3 features a 64.3 m2 phased-array antenna, as well as a 10.0 m2 Launch Vehicle Adapter (LVA)1. The peak brightness of the satellite reached an apparent visual magnitude of 0.4. This made the new satellite one of the brightest objects in the night sky. With an apparent visual magnitude of 5.5, the LVA which jettisoned on 2022-11-10 (UT), for which an orbital ephemeris was not publicly released until four days later, was four times brighter than the current International Astronomical Union recommendation of magnitude 7 [2,5]. The expected build-out of constellations with tens of thousands of new, brighter objects will make active satellite tracking and avoidance strategies a necessity for ground-based telescopes. However, this requires a complete and highly accurate set of satellite orbits. For BlueWalker 3, we determine that at present these location predictions are only accurate to within 7.2 ± 3.1 arcmin. [1] See https://apps.fcc.gov/els/GetAtt.html?id=265584&x=