Cellular Starlink Satellites Light Up the Night Sky a Bit Too Much

Don’t be surprised if you spot SpaceX’s cellular Starlink technology lighting up the night sky: A new study finds that the company’s “direct to cell” satellites are nearly five times brighter than a regular Starlink satellite. 

A team of scientists published a paper examining SpaceX’s new direct-to-cell Starlink satellites, which the company began launching in January. Although there are only about 100 of these satellites in orbit, they already stand out from the rest of the Starlink constellation for their ability to reflect sunlight. 

The study finds the direct-to-cell satellites average about 4.9 times more in brightness when measuring all the Starlink satellites at a common distance. That surprised the research team since the new satellites haven't massively increased in size at the same rate, according to Anthony Mallama, one of the paper's authors.

Although the exact size of a Starlink satellites can vary depending on the generation, Mallama looked at past comments Elon Musk made describing the direct-to-cell technology to arrive at an estimate. "Since they are only about 10% larger than (a regular V2 Mini Starlink) internet satellite, the difference must be attributed to the orientation of their chassis and solar panels," he told PCMag in an email.

The findings are also surprising because SpaceX has been developing ways to prevent Starlink satellites from reflecting sunlight as they orbit the Earth, which can occur during the early hours after dusk and before dawn. It covered the satellites with a “dielectric mirror film” to scatter the incoming light and reposition the satellites' solar cell arrays away from the sun.  

The efforts are part of SpaceX’s commitment to preventing the Starlink satellites from interfering with astronomy — which has become a hot topic among scientists and even at the United Nations. But for now, it looks like the new direct-to-cell Starlink satellites are orbiting the Earth without some of the measures in place. 

“On June 12, SpaceX explained to me that they had not yet turned on post-launch brightness mitigation for the DTCs because the spacecraft were still being tested,” said Mallama, who also represents a group under the International Astronomical Union dedicated to protecting the night skies from satellite interference. 

SpaceX didn’t respond to a request for comment. But for the past several months, the company has been testing the cellular Starlink system across the US before a commercial launch slated for this fall. The technology promises to help mobile carriers serve users in cellular dead zones with text messages, voice, and data. But astronomers are worried that Starlink and other next-generation satellite constellations could end up photo-bombing their observations and polluting the night sky with light. In SpaceX's case, the company has requested the Federal Communications Commission allow it to launch up to 7,500 direct-to-cell satellites. The current Starlink constellation numbers at over 6,200.  

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Mallama’s team also noted that even if SpaceX does roll out the mitigations across future direct-to-cell satellites, the brightness problem might get worse. That’s because SpaceX has proposed lowering the orbits of thousands of Starlink satellites—including the cellular ones—by 200 kilometers, bringing them closer to Earth. Even in a best case scenario, the DTC satellites will be about “2.6 times as bright as the others based upon their lower altitudes,” the study estimates. 

“Despite the increased luminosity of low altitude satellites, there is one benefit to optical astronomy,” Mallama added. “They spend more time eclipsed by the Earth’s shadow than those at higher altitudes. The spacecraft are then invisible.”

Scientists are also concerned about SpaceX’s cellular Starlink satellites disrupting radio astronomy due to the increase in radio signals. But for now, the FCC has yet to grant SpaceX a commercial license to operate the cellular Starlink system in the US. Mallama said the observations taken for the study were conducted from January 18 through May 31 of this year.