Blue Walker 3’s trajectory across the night sky, photographed from a backyard in Tucson, Arizona.
A. Block/IAU CPS
A prototype satellite for a proposed space-based mobile phone network is brighter than all but seven stars in the night sky. The satellite, or others like it, could force ground-based telescopes to track and avoid the satellite’s trajectory, or to extend observations to collect enough raw data.
In 2022, Texas-based company AST SpaceMobile launched the BlueWalker 3 satellite into orbit to test the feasibility of an integrated cellular network from space. Early observations of Blue Walker 3’s 64 square meter reflector antenna suggested it was brighter than most stars in the sky.
This was confirmed after a year of monitoring using telescopes in the United States, Chile, the Netherlands, and New Zealand. Siegfried Eggl Researchers at the International Astronomical Union in France found that Blue Walker 3 is even brighter than previously measured, with a brightness comparable to the brightest stars in the constellations Canis Major and Eridanus.
This poses a serious threat to ground-based astronomy, especially wide-angle surveys of the night sky such as those performed at the Vera C. Rubin Observatory in Chile, Eggle said. “If we have a large number of these very bright objects, I think if that risk is not mitigated, we could end up with massive data loss, if not damage to the detector.” he says.
Some of this could be avoided Even when telescopes employ track-and-avoid strategies, these methods can still fail due to the difficulty of tracking satellites. This could mean that the telescope would need to be stopped periodically while the satellite moves above the line of sight, potentially delaying observations and skewing the data set.
Eggl and his team also discovered that BlueWalker 3’s brightness fluctuated over time depending on its orientation and angle toward the sun. Because companies like AST SpaceMobile can control this angle, they play an important role in minimizing reflected light from satellites, Eggl says.
“We are working with NASA and specific astronomy working groups to develop advanced industrial solutions, including potential operational interventions,” an AST SpaceMobile spokesperson said in a statement. The company is also avoiding broadcasting in areas sensitive to radio astronomy and controlling the attitude of its satellites to minimize brightness for its next generation of satellites, which will number about 90, according to a spokesperson. It is said that they are developing an anti-reflection coating.
More observations are needed to fully understand the effects on astronomy, especially for longer wavelengths of light such as those in the radio band. Satellites like Blue Walker 3 are equipped with powerful radio transmitters that could cause even more damage to radio-based astronomy, Eggl said. “For optical light, these objects are as bright as stars in the sky, but for radio astronomy, they can be as bright as the sun,” he says.
says such a comprehensive observation campaign is essential. Aparna Venkatesan Because “the brightness of an individual satellite is a complex, time-varying function of its design, area, viewing angle, and altitude.”
“With the number of national and private space stakeholders rapidly increasing and more satellites being launched than ever before, we are not only exposed to light pollution and electromagnetic interference from a variety of individual satellites. “We also need to consider the overall impact of all the planned satellite constellations: low-Earth orbit,” she says.
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