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SpaceX tells astronomers: Fine, we'll try to stop Starlink spoiling stargazing sessions

Agrees measures to prevent streaks of light across the night sky in time-lapse observations

SpaceX has entered into a coordination agreement with the US National Science Foundation (NSF) to attempt to mitigate some of the negative effects its Starlink satellite network is having on ground-based astronomy observations.

The NSF said this week that Musk's space company is to cooperate on mitigating the impact of the Starlink constellation on optical and infrared ground-based astronomical facilities "to the extent practicable."

This news follows the Federal Communications Commission (FCC) granting only partial approval for SpaceX to deploy its second-generation Starlink satellites at the start of December.

According to reports, the FCC gave permission for the company to launch 7,500 of the nearly 30,000 satellites it hopes to send aloft, while deferring consideration of the rest of the constellation and making a coordination agreement with the NSF a condition of the licence.

The problem with satellite constellations such as Starlink is that there are a lot of them, and they are positioned in low-Earth orbit a few hundred kilometers up, placing them much closer to the Earth's surface than satellites in geostationary orbits sitting at about 35,000 kilometers.

This can make them appear as prominent lights in the sky when they reflect sunlight, as we reported on several years ago, and can ruin time-lapse captures of the night sky with bright trails crossing the field of view as the satellites move along their orbits.

But it isn't just light pollution that has the scientists vexed – some of the frequency bands which the satellites use to transmit to Earth are adjacent to those used for radio astronomy observations, according to the NSF.

With this new coordination agreement, NSF and SpaceX continue to explore methods to "further protect ground-based astronomy," the pair said in a statement issued by the NSF.

These include mitigations SpaceX has developed for its second-generation satellites such as a dielectric mirror film, solar array changes, and new black paint that minimizes brightness and glints, as well as adopting best practices during flight operations.

SpaceX has also committed to work towards recommendations from NSF's NOIRLab, the American Astronomical Society's SATCON workshops and the International Astronomical Union's Dark and Quiet Skies best practices guidance.

These recommendations include further work to reduce the optical brightness of the satellites to seventh visual magnitude or fainter, which would make them invisible to the naked eye, and providing orbital information publicly that astronomers can use for scheduling observations around satellites.

SpaceX also agreed to perform an analysis on the impact that astronomical facility lasers – shone into the sky as artificial guide stars for adaptive optics – might have on its satellites. Following this, the Laser Clearinghouse removed the coordination requirements for these lasers, meaning they do not have to be shut off every time SpaceX satellites pass nearby.

On the radio astronomy side, SpaceX has committed to "avoiding main beam illumination" or not transmitting during observations at key radio astronomy facilities that would be impacted by the signal, the NSF said.

"We are setting the stage for a successful partnership between commercial and public endeavors that allows important science research to flourish alongside satellite communication," NSF Director Sethuraman Panchanathan said in a statement.

But SpaceNews reports that the agreement is effectively voluntary, and that beyond the FCC requirement for such an agreement in the Starlink Gen2 license, there is no law requiring satellite operators to mitigate any effects they may have on astronomy.

Starlink has of course been greeted as a potential way to provide internet services in areas that are poorly served by terrestrial networks or which are hard to reach. In December, the UK government was the latest to announce a trial of the technology to examine how satellite broadband could be used to deliver a high-speed connections to various "hard to reach" locations around the country such as mountaintops or islands.

However, the NSF points out that many radio astronomy observatories are sited in remote locations precisely because of this – to get away from as much of the electromagnetic clutter and interference as possible. For this reason, the National Radio Astronomy Observatory (NRAO) is undertaking a pilot program to test the impact of SpaceX user terminals in close proximity to observatories like the Very Large Array (VLA).

The NRAO will henceforth be the contact point for technical exchanges with SpaceX relating to radio astronomy issues, while NSF's NOIRLab serves as the key point of contact for optical and infrared issues. ®

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