Foust forward | The sky is not falling (yet)

Two years ago, when astronomers gathered at the 234th Meeting of the American Astronomical Society (AAS) in St. Louis, one word was on the minds of many attendees: Starlink. A few weeks earlier, SpaceX had launched the first set of 60 Starlink satellites, and the unexpected appearance of the satellites in the twilight sky in the form of a necklace of shiny pearls has dismayed astronomers. With SpaceX planning to potentially launch tens of thousands of these satellites, astronomers have had visions – or, more precisely, nightmares – of a crumbling night sky.

At the 238th AAS meeting, held online in early June, the threat posed by Starlink did not seem as urgent among attendees as it was then, or at the next AAS meeting in January 2020. who devoted a special session on the subject. One reason may be that virtual meetings, even with chat rooms and Slack channels, can’t mimic hallway chats in in-person conferences where people share what they really think about these topics.

Another, however, is that astronomers have made strides in mitigating the threat through cooperation rather than confrontation. Meetings between astronomers and SpaceX have led to design changes to Starlink satellites, including the “VisorSat” design where a visor prevents sunlight from reaching reflective surfaces like antenna panels. SpaceX has launched around 1,000 VisorSat versions of Starlink.

These VisorSat versions of Starlink are considerably weaker than previous versions, said Richard Green of the University of Arizona in a public policy session at the AAS conference on June 9. The original Starlink satellites have a visual magnitude of about 5 once in their operational orbits. , while the VisorSats are at around 6.5, or a dimmer factor of four. This makes them invisible to the naked eye in all night skies except the darkest.

Green also praised the FCC’s approval of SpaceX’s license amendment that moves Starlink satellites originally intended for altitudes above 1,000 kilometers to the 550-kilometer orbits used by the rest of the constellation. “It’s good for us for visibility, because they are mostly visible at dusk and near the horizon, and not visible later,” he said. (SpaceX’s primary motivation for the orbit change involved reducing latency, not mitigating the impacts of satellites on astronomy.)

Astronomers, however, are yet to declare victory. They set a goal of reducing the brightness of the Starlink satellites to magnitude 7 to avoid the worst interference effects on sensitive instruments, such as those at the Vera Rubin Observatory under construction in Chile. “He hadn’t quite hit the seventh magnitude goal, but it’s a huge improvement,” Green said.

OneWeb’s satellites are even weaker, at an average magnitude of 7.85. The problem with these satellites is that they are in higher orbits, so they are visible longer every night, including all night in summer.

However, there are many other constellations that astronomers need to worry about. A workshop last year recommended that satellite constellations operate their satellites at altitudes no greater than 600 kilometers to minimize the duration of their visibility at night. However, several proposed systems, such as Telesat’s Lightspeed and the Viasat constellation, would operate at over 1,000 kilometers.

Green also raised concerns about AST SpaceMobile, a company that wants to operate hundreds of satellites with very large antennas in low earth orbit. “They’re going to be huge, if they’re built as planned, so they’re going to be extremely bright,” he warned. “There is a question of how they could meet the seventh magnitude requirement. “

Astronomers plan to continue their efforts with the existing and new constellations at a workshop in July, following one last year that developed technical recommendations for dimming the brightness of satellites. “This deals with how these technical recommendations can be implemented, both technically and through policy,” he said.

There is much more to be done, both in policy and in spacecraft engineering, but the progress astronomers have made with Starlink shows that there is a way to solve similar problems with other constellations. satellites through coordination and cooperation.


Jeff Foust writes on space policy, commercial space and related topics for SpaceNews. His Foust Forward column appears in every issue of the magazine. This column was published in the June 2021 issue.


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