BlueWalker 3 Satellite Brightness Characterized and Modeled

The BlueWalker 3 (BW3) satellite was folded into a compact object when launched on 2022 September 11. The spacecraft's apparent visual magnitude initially ranged from about 4 to 8. Observations on November 11 revealed that the brightness increased by 4 magnitudes which indicated that the spacecraft had deployed into a large flat-panel shape. The satellite then faded by several magnitudes in December before returning to its full luminosity; this was followed by additional faint periods in 2023 February and March. We discuss the probable cause of the dimming phenomena and identify a geometrical circumstance where the satellite is abnormally bright. The luminosity of BW3 can be represented with a brightness model which is based on the satellite shape and orientation as well as a reflection function having Lambertian and pseudo-specular components. Apparent magnitudes are most frequently between 2.0 and 3.0. When BW3 is near zenith the magnitude is about 1.4.