The Bright BlueWalker 3 Satellite Threatens Astronomy

BlueWalker 3 is the prototype for a new constellation of communication satellites. Astronomers were concerned even before it was launched, because its large size foretold a bright new source of light pollution. The spacecraft was folded up inside its launch vehicle and placed into orbit in September 2022. After on-orbit tests were completed, it unfurled into a 64-square-meter (689-square-foot) flat panel, making it the largest communication array ever flown.

Sky & Telescope readers found that the fully deployed BlueWalker 3 routinely brightens to 1st magnitude when it is high in the sky. Additional observations and analysis revealed temporary fadings (shown in the light curve below), which were attributed to tilting of the satellite relative to the Sun to boost solar power. During these times, only the dark side of the array was visible to observers on the ground. This implies that the satellite’s brightness can be limited by the operator.

Meanwhile, in the commercial arena, BlueWalker 3 made headlines last month when AST SpaceMobile and AT&T completed the first 5G connection by satellite, using an unmodified smartphone. The call was placed from a wireless dead zone in Maui, Hawai‘i, to Madrid, Spain. This success indicates motivation for companies to launch similar satellites in order to provide worldwide network coverage.

Now, a study published in Nature reports on a research campaign organized by the International Astronomical Union’s Centre for the Protection of Dark and Quiet Skies from Satellite Constellation Interference (IAU CPS). Observers from five continents contributed magnitudes that characterized the spacecraft’s visible brightness over time.

Sangeetha Nandakumar (University of Atacama, Chile) and her coauthors point out that astronomers and some in the aerospace industry are working together to limit satellite luminosity to acceptable levels. They cite the successful brightness mitigation practices employed on Starlink’s VisorSat and Generation 2 Mini satellites. However, the unmitigated brightness of BlueWalker 3 is an example of what the scientists cite as a “trend toward the launch of increasingly large and brighter satellites.”

Siegfried Eggl (University of Illinois, Urbana-Champaign), a coauthor of the Nature study, emphasizes the importance of amateur astronomers in this endeavor. “Not only did they flag BlueWalker 3 soon after launch as an object that could be particularly bright, they also contributed timely and accurate data after it unfolded,” he says.

“Amateurs also first discovered the changes in brightness likely due to a change in the satellite's attitude,” he adds, referring to the satellite’s tilt relative to the Sun. “This is why the IAU CPS works closely with amateur associations and professional astronomers in their observation campaigns. Together we provide valuable feedback for space industry partners regarding the actual brightness of their satellites on orbit.”

Recently, the U.S. Federal Communication Commission began requiring satellite operators to coordinate with the National Science Foundation in order limit the impact of their spaceraft on astronomy, as reported by spacenews.com. These rules should also apply to the constellation of BlueBird satellites that will follow BlueWalker 3. Proper orientation of the follow-on spacecraft could render them much fainter than the prototype.