SpaceX’s Direct-to-Cell Starlink Satellites Are 5 Times Brighter Than Before, Worrying Astronomers

SpaceX has been launching batches of Starlink satellites designed to operate like cellphone towers in space, beaming connectivity directly from low Earth orbit. The new satellites are adding to the company’s ever-growing constellation, which has been disrupting observations of the cosmos, and may even be brighter than their regular counterparts.

A recent study found that direct-to-cell (DTC) Starlink satellites are five times brighter than the rest of the broadband constellation, raising concerns about increased interference with astronomical observations. SpaceX wants to launch thousands of these DTC satellites to low Earth orbit, which have been appearing as streaks in telescopic images of the night sky.

SpaceX launched its first group of DTC Starlinks in January, using one of the six satellites to send a text message to a cellphone on Earth. The Federal Communications Commission (FCC) gave SpaceX a temporary license to test the new satellite technology over a duration of six months using 2,000 test devices and 840 satellites. In March, SpaceX requested an amendment to its license, hoping to operate up to 7,500 DTC satellites in orbit. The Starlink satellite services will begin with text messages, while voice and data coverage are meant to follow, possibly in 2025. SpaceX has partnered with T-Mobile, which has invited global providers, with Rogers in Canada, KDDI in Japan, Optus in Australia, One NZ in New Zealand, and Salt in Switzerland opting in.

That’s great news for people living in remote areas with generally bad connectivity, but not so much for astronomers wanting to capture clear views of the skies to help us learn more about our universe and spot incoming asteroids.

The DTC satellites, according to the study, may appear brighter due to their lower altitude. Regular Starlink satellites orbit at an altitude of 340 miles (550 kilometers) above Earth’s surface, while their DTC equipped counterparts orbit at a much closer distance of 217 miles (350 kilometers).

The researchers behind the study, available on the preprint platform arxiv, measured the visibility of the first six DTC satellites launched by SpaceX to estimate their brightness. Although the DTC satellites are measured to be 4.9 times brighter than regular Starlinks, researchers estimate they would be only 2.6 times brighter if they were at the same altitude.

Their closer proximity to Earth, however, may not be all bad. “The new satellites are much lower than the classical ones…that makes them brighter,” Olivier Hainaut, an astronomer at the European Southern Observatory, told Gizmodo in an email. “But also it means that their apparent motion is much faster. This means that the trails they leave on our cameras is more diluted (the “motion blur” is much stronger).”

For large telescopes, satellites in lower orbits appear wider, or out of focus, which further dilutes their light. That effect compensates for the additional brightening caused by their lower orbit, according to Hainaut. The DTC satellites also travel faster than the regular Starlinks and spend more time hidden in Earth’s shadow due to their lower orbit, making them less visible and potentially reducing their interference with telescopes, according to the study.

SpaceX has been working on dimming its Starlink satellites, hoping to mitigate its constellation’s effects on astronomical observations of the universe. The first Starlink satellites were visible to the unaided eye and saturated the lenses of telescopes pointed in their direction. However, SpaceX has been working with the International Astronomical Union, and its Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference, in addition to other astronomers at various institutions. As a result, the company has changed the orientation of the satellites and their solar panels, and installed visors to reduce their brightness.

The new study does note that the measurements of the DTC satellites were taken before SpaceX had a chance to apply the brightness-mitigating efforts. “When in operation, Starlink adjust the orientation of the body of the satellite and of its solar panels to minimize their brightness,” Hainaut said. “It is actually neat: with a small change to the panel orientation, they can hide the panel behind the bus of the satellite, or make sure that we see the back side of the panel (which is not illuminated) rather than the illuminated side.”

It’s not just SpaceX seeking to launch these types of satellites. AST SpaceMobile and Virginia-based Lynk Global are also working to develop space-based cellular broadband networks directly accessible by cell phones. AST launched its prototype satellite in September 2022 (on board SpaceX’s own Falcon 9 rocket), which succeeded at making the first 5G phone call to a Samsung Galaxy S22 using AT&T spectrum. The BlueWalker 3 has a massive antenna array that stretches across 693-square-feet (64-square-meters), the largest ever deployed in Earth orbit. Once it unfurled its antenna, the satellite became one of the brightest objects in the night sky and caused concern among astronomers that it could interfere with observations of the surrounding universe.

SpaceX has been in communication with the astronomy community, but it’s not clear whether other companies will follow suit. The growing threat of satellites surrounding our planet is becoming more real as the space industry continues to grow, altering our views of the night sky as we know it

“Satellites are annoying for astronomers…[we] would prefer pristine night sky without light pollution,” Hainaut said. “Needless to say, we realize this is not realistic nor desirable.”