Astronomers and other stargazers have new cause for concern about light pollution following claims that Starlink's latest satellites which support phone services may appear five times brighter in the sky than existing ones.

A recently published study [PDF] by the International Astronomical Union (IAU) asserts that the Direct to Cell (DTC) satellites being lofted by SpaceX for its satellite biz average 4.9 times brighter than other Starlink Mini spacecraft.

In a best case scenario where brightness mitigation techniques are employed, the report estimates that DTC satellites will still be about 2.6 times as bright as the others, based upon the lower altitudes they operate at.

The research is authored by IAU's Centre for the Protection of Dark and Quiet Skies from Satellite Constellation Interference, which is such a mouthful that it is simply known as CPS.

As The Register reported last year, increasing levels of luminous pollution from various sources including reflections from low Earth orbit (LEO) satellites are already affecting the view of the night sky, which has a particular impact on astronomers trying to peer out at distant objects in the universe.

Starlink confirmed a successful test of its technology in January 2024, using the initial DTC satellites it put into orbit. Elon Musk's company plans to offer a service with T-Mobile US that will let subscribers make phone calls via satellite using unmodified handsets, in areas where there is no coverage by terrestrial cell towers.

As SpaceX noted in a webcast at the time, "we do expect these first six Starlink direct-to-cell satellites to be a bit brighter than previous Starlink V2 Minis."

According to the IAU report, Starlink followed up the successful tests with a request to the US Federal Communications Commission (FCC) for an amendment to its license that would allow it to operate 7,500 of the new units, orbiting at heights between 340 and 345 km.

These satellites will join the 7,500 existing Starlink units that operate at higher altitudes, and are slightly larger (125 m² versus 116 m²) due to the antenna needed for DTC communications.

However, the research notes that while the early Starlink DTC satellites appear to average 4.9 times brighter than existing ones, it does not know what brightness mitigation procedures were in place at the time observations were made.

In other words, it is possible that Starlink was not employing mitigation procedures at the time, and if applied them in future, these could limit light pollution from the orbiting hardware.

We have asked Starlink to comment.

The study also found these satellites spend a greater proportion of their time in the Earth's shadow than those operating at higher altitudes, which will offset some of their impact on astronomical observing.

Meanwhile, rival satellite operator AST SpaceMobile was this week granted an initial license for space-based operations from the FCC, giving approval for the launch of its first five BlueBird satellites that will also support phone and broadband services. Launch is scheduled for some time in September.

"This regulatory milestone is a significant step to targeting nationwide coverage from space of the continental United States on premium cellular spectrum," AST SpaceMobile President Scott Wisniewski said in a statement.

The BlueBird satellites are described by the company as "the largest-ever commercial communications arrays to be deployed in low Earth orbit", with their antenna alone said to be 64 m² in size to enable them to focus a radio beam with a smaller Earth surface footprint to limit interference with other services.

Last year, AST SpaceMobile's BlueWalker 3 satellite, a test vehicle for its satellite broadband service, was reported to be the brightest object visible in the night sky at times.

We asked AST SpaceMobile what mitigations it has in place to minimize light pollution from its satellites, and will update with any answers. ®

https://www.theregister.com//2024/08/07/low_orbit_satellites_for_phone/