The prototype satellite launched by AST SpaceMobile a year ago is sometimes one of the brightest objects in the night sky, raising new concerns about its impact on astronomy. In the extended copy of the article to be published in the journal Nature On October 2, astronomers documented months-long observations of BlueWalker 3, a spacecraft launched into low-Earth orbit by AST SpaceMobile in September 2022. The spacecraft then deployed a 64 square meter antenna to maintain direct communication with the device.

The paper analyzes observations made by astronomers around the world in the months following the spacecraft’s launch. Shortly after the spacecraft deployed this antenna in November 2022, the spacecraft’s brightness increased from magnitude 6 to magnitude 0.4, which is the limit visible to the naked eye in dark places. This made the satellite one of the brightest objects in the night sky, similar in brightness to the stars Procyon and Achernar.

The spacecraft then darkened, possibly due to a change in orientation, and then brightened again, returning to magnitude 0.4 in April 2023. According to astronomers, the brightness of a satellite is a function of several factors, including the satellite’s height above the horizon, its distance from an observer on the ground, and the phase angle of the Sun.

“These results show a continuing trend toward larger and brighter commercial satellites, making plans to launch many more of them particularly concerning in the coming years,” said Siegfried Eggle of the University of Illinois at Urbana-Champaign, one of the authors. Statement published by the International Astronomical Union Center for Protecting Dark and Quiet Skies from Satellite Constellation Interference (IAU CPS). This center studies the impact of satellite constellations on astronomy and methods to mitigate this impact.

In a statement to SpaceNews, an AST SpaceMobile representative did not directly mention the BlueWalker 3 brightness observations reported in the article. But the company said it was working with NASA and select astronomy working groups to develop industry-leading solutions, including possible operational interventions, to resolve these issues.

AST SpaceMobile said it was trying to reduce the brightness of its satellites through “inclined flight maneuvers” to minimize reflected sunlight from the ground. It also plans to add anti-reflective materials to future satellites.

The company also said its constellation would be much smaller than others in terms of the number of satellites, with only around 90 satellites needed “to provide significant global coverage.” OneWeb has more than 600 satellites in orbit, while SpaceX’s Starlink group is approaching 5,000 satellites in orbit.

However, these satellites are significantly fainter than BlueWalker 3. SpaceX is working with astronomers on how to reduce the brightness of Starlink satellites, and in January signed a coordination agreement with the National Science Foundation (NSF) to collaborate on ways to solve this problem. brightness problem. from the larger V2 satellites.

At the Sept. 19 Astronomy and Astrophysics Advisory Committee meeting, an NSF official said the agency had finalized similar coordination agreements with Amazon and OneWeb for its constellations and praised the Federal Communications Commission for introducing updated licensing requirements for smaller constellations. Iceye and Planet said that these companies also work in coordination with NSF.

However, NSF has not announced a coordination agreement with AST SpaceMobile. At this committee meeting, Connie Walker, co-director of the IAU CPS and an astronomer at NSF’s National Optical-Infrared Astronomy Research Laboratory, said that a paper on the BlueWalker 3 observations will soon be published in Nature and that its findings published. It was previously shared with AST SpaceMobile, but the content of the article was not mentioned.

Astronomers are also concerned about radio astronomy interference by the AST SpaceMobile spacecraft, which uses spectrum reserved for terrestrial communications. Federico Di Vruno, another co-director of the IAU CPS, said these frequencies are close to those used in radio astronomy, and that radio telescopes located in “radio-quiet zones” on Earth designed to avoid terrestrial interference may still be sensitive to radio telescopes. interference from satellites.

AST SpaceMobile said it would refrain from broadcasting from its satellites into or near the U.S. National Radio Quiet Zone in Virginia and West Virginia and “other locations in radio astronomy where appropriate or necessary, including those not officially recognized.” The company will also avoid radio-quiet regions for its gateway antennas.

Although possible optical and radio interference from satellite constellations worries astronomers, they also recognize that they will need to coexist with such systems.

“The astronomical community understands the need for greater connectivity and improved Internet access, especially for rural and underserved communities,” Jeremy Tregloan-Reid, co-author of the paper at Atacama University in Chile, told IAU CPS. said. . . “But this progress needs to be balanced against the negative impact that bright satellites can have on the night sky.” Source