BlueWalker 3’s Unprecedented Impact on Night Sky Observations

Tracks in the night sky left by BlueWalker 3 over the Observatorio Astronomico Nacional, San Pedro Martir, Mexico, on November 12, 2022. The gaps in the path are caused by the gaps between the exposures that are stacked to form this image. Credit: I. Plauchu-Frayn

The new Nature paper contains the results of a 130-day international monitoring campaign.

Scientists, including astronomers at the International Astronomical Union Center for the Protection of Dark and Quiet Skies from Satellite Interference (IAU CPS), have published a paper. Nature Assesses comprehensive impact Blue Walker 3 Astronomical Satellite. These new results complement the initial observations since launch Initial understanding The paper details how the satellite’s brightness changes over time and the visibility of the jettisoned hardware. As companies intend to deploy more commercial satellites in the coming years, this paper highlights the need for pre-launch impact assessments.

„Interference from satellites has become a growing problem in astronomy over the past few years,” commented first author Sangeeta Nandakumar of the Universidad de Atacama Planetarias Instituto de Astronomia y Ciencias Planetarias in Chile.

AST Spacemobile BlueWalker 3 satellite

A recent study of the BlueWalker 3 satellite’s impact on astronomy underscores concerns about brightness and radio interference, prompting calls for pre-launch assessments and safety measures as commercial satellite deployments increase. Credit: AST SpaceMobile

Preliminary observations and findings

BlueWalker 3 was launched into low Earth orbit on September 10, 2022 AST Spacemobile As a prototype for a planned constellation of over a hundred similar satellites for use in mobile communications. Observations made shortly after launch showed the satellite to be one of the brightest objects in the sky. However, to better understand its impact on astronomy, NSF’s co-hosted CPS NOIRLab And this SCAO, launched an international surveillance campaign. As part of this initiative, professional and amateur observations were contributed from around the world, from Chile, the US, Mexico, Aurora New Zealand, the Netherlands and Morocco.

Newly released data show a sudden increase in BlueWalker 3’s brightness around day 130, which coincides with full exposure of the antenna array, and fluctuations in subsequent weeks.[1] The paper also reveals the relationship between the brightness that varies after unfolding and other factors, such as the satellite’s height above the horizon and the angle between the observer, the satellite, and the Sun. A subset of observations was also used to calculate the trajectory of the satellite over time. By comparing the predicted trajectory with the collected observations, the authors were able to evaluate Accuracy Note how it decreases over time as a result of these projections and factors such as atmospheric drag.

The BlueWalker 3 satellite was 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 reaching 0.4 magnitude – is displayed here as it travels across the galaxy. Background. By comparison, two fainter satellites can be seen in the scenes; Starlink-4781 (in front of BlueWalker) and Starlink-4016 (simultaneous and slightly behind BlueWalker in some frames) Credit: Delft Technical University/M. Longbrook

Satellite components and ground-based challenges

Additionally, the launch adapter attached to BlueWalker 3 was disconnected from the satellite. This component reached magnitude 5.5, exceeding the maximum brightness recommendations set by the International Astronomical Union to avoid adverse effects of satellites on optical astronomy. It remained unregistered in the public register for four days. As such hardware items drift for longer periods of time, incomplete data on their orbits presents further challenges for ground-based observations that try to avoid them.

„These results demonstrate a continuing trend toward larger, brighter commercial satellites, which is particularly concerning given plans to launch more in the coming years,” says study co-author Siegfried Eggl from CPS and the Department of Aerospace Engineering. University of Illinois at Urbana-Champaign (UIUC) „While these satellites can play a role in improving communications, it is imperative that their disruptions to scientific observations be minimized. This can be achieved by continued cooperation in mitigation efforts or, if that is not successful, by requiring pre-launch impact assessments as part of future launch authorization processes.”

The grounds where Blue Walker 3 was filmed

An 8 meter x 8 meter image of the BlueWalker 3 satellite as seen from the ground. Credit: M. Tzukran

Considering radio frequency interference

„Besides the effect on visible observations, BlueWalker 3 may also interfere with radio astronomy because it transmits at radio frequencies close to the frequencies observed by radio telescopes,” says Federico de Vruno, associate director of the IAU CPS. „A new feature of BlueWalker 3 is that it uses frequencies normally used by terrestrial transmitters,” he adds. Although some telescopes are located within designated radio-quiet zones, restrictions to protect these areas currently only apply to terrestrial transmitters, so they are not necessarily shielded from satellite transmission. More research is therefore needed to develop strategies to protect existing and future telescopes from the many satellites planned for launch over the next decade.

Balancing progress with safety

„The astronomy community understands the need for greater connectivity and improvements in Internet access, especially for rural and underserved communities. However, that progress must be balanced against the negative impact that bright satellites can have on the night sky. This is a global issue as satellites recognized by any country are visible in the night sky around the world, an international Highlighting the importance of coordination,” says study co-author Jeremy Dreglon-Reid of Atacama Chile, CLEOsat and CPS.

Observations of BlueWalker 3 will continue, with astronomers planning to monitor its thermal emissions later this year. Astronomers continue to debate this topic IAU Symposium: Astronomy and Satellite Constellations: Ways Ahead In October.

For more information on this research, see Massive satellite that outshines all but the brightest stars.


  1. The data shows brightness changing from an apparent magnitude of 6 (before exposure) to an apparent magnitude of 0.4 over 130 days.

Note: Sangeeta Nandakumar, Siegfried Egg, Jeremy Dreglon-Reid, Christian Adam, Jasmine Anderson-Baldwin, Michael D. Bannister, Adam Battle, Zuhair Benkeltoon, Jennifer Campbell, J. William Damke, Ilse Bluchu Frain, Mourad Kachoi, Peter F. Gillen, Aziz Etahar Kayoach, Harrison R. Grants, Marco Langbrook, Nicholas Rattenbury, Vishnu Reddy, Ryan Ridden-Harper, Brad Young, Edward VanDan, Alanta-. , Constance E. Walker, John C. Parentine, Piero Benvenuti, Federico Di Vruno, Mike W. Beale, Meredith L. Ravels, Cees Baza, Catherine Flores-Quintana, Pablo Garcia, Sam Kim, Penelope Longa-Otarola, Maria Romero-Colmenares, Pedro Sanhusa, Giorgio Chiringo, and Mario Soto, 2 October 2023, Nature.
DOI: 10.1038/s41586-023-06672-7

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