Twinkle, Twinkle, Giant Satellite: The Dazzling Dilemma in Our Skies

BlueWalker 3 Satellite

Bright satellites, notably BlueWalker 3, are impacting night sky observations, a research study reveals. The increasing number of these satellites presents new challenges for astronomers. The authors emphasize the importance of finding solutions and encouraging cooperative efforts between the space industry and the astronomical community. Credit: AST SpaceMobile

Highlighting the conflict between bright satellites and astronomy, a recenty study shows satellites like BlueWalker 3 affecting night sky observations.

The ability to have access to the Internet or use a mobile phone anywhere in the world is taken more and more for granted, but the brightness of Internet and telecommunications satellites that enable global communications networks could pose problems for ground-based astronomy. University of Illinois Urbana-Champaign aerospace engineer Siegfried Eggl coordinated an international study confirming recently deployed satellites are as bright as stars seen by the unaided eye.

“From our observations, we learned that AST Space Mobile’s BlueWalker 3—a constellation prototype satellite featuring a roughly 700 square-foot phased-array antenna—reached a peak brightness of magnitude 0.4, making it one of the brightest objects in the night sky,” Eggl said. “Although this is record-breaking, the satellite itself is not our only concern. The untracked Launch Vehicle Adapter had an apparent visual magnitude of 5.5, which is also brighter than the International Astronomical Union recommendation of magnitude 7.”

BlueWalker 3 Measured Brightness

Measured brightness from nine passes of BlueWalker 3 as observed from Steward Observatory. The colored dots correspond to measurements of the optical brightness of the BlueWalker 3 satellite. At its peak BlueWalker 3 reached 0.4 magnitudes, which made it one of the brightest objects in the night sky. Credit: UIUC

For comparison, the brightness of the stars we can see with an unaided eye is between minus 1 and 6 magnitude, minus 1 being the brightest. Sirius, the brightest star, is minus 1. Planets like Venus can sometimes be a bit brighter–closer to minus 4, but the faintest stars we can see are roughly magnitude 6.

The BlueWalker 3 satellite captured on April 3, 2023. The optical brightness of the 8 meter x 8 meter satellite — one of the brightest objects in the night sky having reached a peak brightness of magnitude 0.4 — is exhibited here as it travels across the starry backdrop. For comparison, two fainter satellites can also be seen in the footage; Starlink-4781 (in front of BlueWalker) and Starlink-4016 (paralell and slightly behind BlueWalker in a few frames). Credit: Delft Technical University/M. Langbroek

“One might think if there are bright stars, a few more bright satellites won’t make a difference. But several companies plan to launch constellations,” Eggl said. “For example, Starlink already has permission to launch thousands of satellites, but they’ll probably get their full request of tens of thousands granted eventually.

“And that’s just one constellation of satellites. Europe and China want their own constellations and so does Russia. Just those in the United States being negotiated with the FCC amount to 400,000 satellites being launched in the near future. There are only 1,000 stars you can see with the unaided eye. Adding 400,000 bright satellites that move could completely change the night sky.”

Starlink Satellites Pass Over Carson National Forest

Starlink satellites pass overhead near Carson National Forest, New Mexico, photographed soon after launch. Credit: M. Lewinsky

Eggl is a member of the International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference, IAU.

“BlueWalker 3 is so bright that most of the big telescopes such as the Rubin Observatory believe it could obliterate large parts of exposures,” Eggl said. “They already have to avoid observing Mars and Venus for the same reason, but we know where the planets are so we can dodge them. We cannot accurately predict where all the satellites will be years in advance. Just accepting recurring data loss in multi-billion-dollar observatories is not an option either.”

He said although satellites won’t necessarily damage the telescope’s CCDs, or charge-coupled devices, they will still cause data loss from the streaks. Extremely bright satellites could ruin the entire field of view, like trying to stargaze when someone periodically shines a flashlight into your eyes.

Eggl said several solutions to the problem are being explored in collaboration with the Laboratory for Advanced Space Systems at Illinois and satellite operators such as SpaceX.

“Starlink is looking at making their satellites’ surfaces darker, which absorbs more and reflects less visible sunlight. But the absorption generates heat. The satellites then have to emit infrared light which means observations in optical wavelengths don’t have as large of a problem, but infrared observations might. And heat is one of the biggest engineering problems that we have in space. So, painting everything black comes with repercussions,” he said.

Trail Left by BlueWalker 3 Over Observatorio Astronomico Nacional

The bright streaks drawing an arc across the night sky are caused by the satellite BlueWalker 3. Credit: I. Plauchu-Frayn

Another idea from SpaceX is to make satellites’ solar panels more reflective with dielectric mirrors. The mirrors allow the satellites to change the direction of the reflection so that it’s not pointing directly at the Earth.

“If SpaceX can make the solar panels point in a different direction to avoid glints, or use these mirror tricks, they might solve a lot of the problems we have with the optical flaring of Starlink satellites,” Eggl said. “With other providers, it’s not quite as easy. AST has gigantic satellites, with hundreds of square feet of electronic phased arrays, that they need to communicate with cell phones on the ground. If they made satellites smaller more of their radio signals would leak out through so-called ‘side lobes’ potentially affecting radio astronomy sites.

Eggl said AST also prefers to keep the satellite pointed toward the surface of the Earth to achieve maximum efficiency. Starlink solutions may not easily translate to AST satellites and new mitigation strategies are needed.

“We are trying to work with the space industry, where possible,” he said. “We want to solve this together so it’s a collaborative effort that everybody can sign onto because that’s the fastest route to get things done.”

For more on this research:

Reference: “The high optical brightness of the BlueWalker 3 satellite” by Sangeetha Nandakumar, Siegfried Eggl, Jeremy Tregloan-Reed, Christian Adam, Jasmine Anderson-Baldwin, Michele T. Bannister, Adam Battle, Zouhair Benkhaldoun, Tanner Campbell, J. P. Colque, Guillermo Damke, Ilse Plauchu Frayn, Mourad Ghachoui, Pedro F. Guillen, Aziz Ettahar Kaeouach, Harrison R. Krantz, Marco Langbroek, Nicholas Rattenbury, Vishnu Reddy, Ryan Ridden-Harper, Brad Young, Eduardo Unda-Sanzana, Alan M. Watson, Constance E. Walker, John C. Barentine, Piero Benvenuti, Federico Di Vruno, Mike W. Peel, Meredith L. Rawls, Cees Bassa, Catalina Flores-Quintana, Pablo García, Sam Kim, Penélope Longa-Peña, Edgar Ortiz, Ángel Otarola, María Romero-Colmenares, Pedro Sanhueza, Giorgio Siringo and Mario Soto, 2 October 2023, Nature.
DOI: 10.1038/s41586-023-06672-7

Ph.D. student Nandakumar analyzed the data for this first international study to be published from the center. Nandakumar works with Jeremy Tregloan-Reed at the Universidad de Atacama in Chile.

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