The first satellites of a Chinese broadband constellation, known as Qianfan or “Thousand Sails,” are significantly brighter than their Western counterparts, creating new challenges for astronomers. A recent study, published on the arXiv preprint server on September 30, observed 18 Qianfan satellites launched in August. These satellites are the initial batch of a planned constellation that could eventually include over 14,000 satellites.
Brightness Concerns
The study found that the brightness of these satellites ranges from magnitude 8 when low in the sky to magnitude 4 when nearly overhead. This makes them visible to the naked eye at higher elevations, surpassing the magnitude 6 threshold for dark skies and the magnitude 7 limit recommended by professional astronomers to avoid interference with major ground-based observatories.
“Qianfan satellites are brighter than magnitude 6 except when observed at low elevations in the sky,” the astronomers noted. This brightness could adversely impact both professional and amateur astronomical activities unless mitigated.
Design and Impact
The study analyzed the satellites’ brightness changes with elevation, fitting a model where a large flat-panel antenna faces Earth and a solar array points away. This design matches limited public information about the spacecraft. Unlike SpaceX’s Starlink satellites, there is no evidence that Qianfan satellites use mirrors to reflect light away from Earth.
Astronomers affiliated with the International Astronomical Union’s Centre for the Protection of Dark and Quiet Skies from Satellite Constellation Interference (CPS) conducted the study to raise awareness and prompt design changes in future Qianfan satellites. They cited SpaceX’s modifications to Starlink satellites, which now approach the CPS’s magnitude 7 recommendation, as a precedent.
Response and Future Actions
It remains unclear how Shanghai Spacecom Satellite Technology, the developer of the Qianfan satellites, will respond to the study. CPS representatives have had limited contact with Chinese officials, primarily through United Nations meetings.
The Qianfan satellites are among the latest challenges for astronomers. For instance, AST SpaceMobile recently deployed a large phased array antenna on its BlueBird satellites, raising similar brightness concerns. Additionally, radio astronomers have reported interference from Starlink satellites, with unintended emissions from spacecraft electronics affecting observations.
“Humanity is clearly approaching an inflection point where we need to take action to preserve our sky as a window to explore the universe from Earth,” said Federico Di Vruno, spectrum manager of the Square Kilometer Array Observatory and co-director of CPS. He emphasized the need for satellite companies to minimize unintended radiation as part of their sustainable space policies.
