The unfolding of the BlueWalker 3’s giant flat-panel antenna array resulted in a satellite 40 times as bright, outshining most stars.
The prototype of a new constellation of very bright Earth-orbiting satellites, named BlueWalker 3, was launched on September 11th, and as of a few days ago, it has brightened considerably. The AST SpaceMobile company behind the launch plans to orbit at least 100 more satellites like BlueWalker 3 by the end of 2024.
Amateur astronomers are concerned that the constellation of satellites will detract from the beauty of the starry skies; for professional astronomers, the satellites will interfere with scientific observations of faint objects. This new constellation would add to the numerous spacecraft already crowding the heavens.
The BlueWalker 3 spacecraft is so large it had to be folded up to fit in its rocket before launch. The satellite was designed to unfold itself after ground controllers had completed on-orbit testing. When fully deployed, its giant flat-panel antenna array spans 64 square meters (689 square feet).
In response to the concerns of sky watchers, Sky & Telescope invited readers to record the brightness of BlueWalker 3 before and after unfolding. Characterization of satellite brightness provides information for observers wanting to avoid the brightest spacecraft. Brightness measurements also provide feedback to engineers in order to make satellites fainter.
Visual magnitudes recorded by backyard observers and CCD magnitudes obtained at professional observatories have already been used to study the brightness of the thousands of Starlink satellites launched by SpaceX since 2019. Visual findings are directly applicable to the appearance of satellites in the sky as seen by amateur astronomers and others who view the heavens. CCD magnitudes are generally filtered to isolate brightness at specific wavelengths, so they apply more directly to the impact of satellites on astronomical research.
Observers began sending me reports just a few days after BlueWalker 3 was launched. In addition to the magnitudes recorded by Sky & Telescope readers, I also collected data from the SeeSat email archive and other public sources of satellite information. Early results indicated that the satellite in its folded-up configuration was relatively faint, with magnitudes generally between 4 and 8, depending on the distance to the satellite as well as its illumination by the Sun.
Then, on the morning of November 11th, Scott Harrington in Arkansas and Paul Maley in Arizona reported that the satellite had suddenly become much brighter. They recorded magnitudes 1.5 and 1.0, respectively, as BlueWalker 3 passed overhead. These observations indicate that the flat-panel array had been deployed, reflecting much more sunlight. Scott and Paul added more observations to the database every morning through November 14th. Richard Cole processed much of the data during that time.
Deployment resulted in about a 4-magnitude change; that is, the satellite became 40 times brighter in the sky. This study confirmed that this satellite and the constellation of similar satellites to follow will pose problems for amateur and professional astronomers. The follow-on satellites, called BlueBirds, are expected to be even larger than BW3, so they will likely be brighter, too, unless AST SpaceMobile changes their design.