BlueBird 6 is Fainter than Block 1 Satellites

The night sky has long been a canvas for human curiosity, a place where the darkness reveals the distant workings of the universe. For centuries, astronomers have relied on the clarity of that darkness to capture faint light from stars and galaxies. However, the arrival of thousands of artificial satellites orbiting Earth has begun to alter this view. These machines, designed to beam internet signals or provide cellular coverage, reflect sunlight back to Earth, creating streaks of light that can cross telescope images and disrupt observations. The brightness of these objects is measured on a scale where lower numbers indicate greater luminosity, meaning a very bright star might have a low number while a faint one has a high number. When satellites are too bright, they can wash out the delicate details astronomers are trying to see, raising concerns about the future of ground-based astronomy and the aesthetic quality of the night sky.

A recent study by Anthony Mallama and Richard E. Cole investigates a specific new generation of these satellites, known as BlueBird Block 2, to see how they compare to the earlier models already in orbit. The researchers were particularly interested in a single satellite, BlueBird 6, which was launched in late 2025. This spacecraft is part of a constellation operated by AST SpaceMobile, designed to provide direct-to-cell services. The team gathered data from experienced visual observers using binoculars and the naked eye, as well as electronic measurements from a robotic observatory in Russia. By comparing the satellite's light to nearby stars, they could determine exactly how bright it appeared from Earth. The study focused on whether the new, larger satellite was indeed brighter than its predecessors, as its physical size would suggest, or if something else was happening.

The findings revealed a surprising twist. The new BlueBird 6 satellite is actually fainter than the older Block 1 satellites, despite being significantly larger. The researchers found that the average brightness of BlueBird 6 is about 0.55 magnitudes dimmer than the earlier models. This difference is consistent whether the satellite is viewed from its actual distance or adjusted to a standard distance of 1,000 kilometers. The result was unexpected because the new satellite's antenna panel is roughly three and a half times larger than the panels on the older spacecraft. Based on size alone, scientists had predicted the new satellite would be much brighter, perhaps by more than one magnitude. Instead, the new satellite is only about 17 percent as bright per unit of surface area as the older ones.

The paper notes that possible explanations for this dimming are discussed, including the presence of deployable elements intended to reduce glare. These structures intercept sunlight before it hits the main panel facing Earth and scatter it in a unique way. The researchers calculated that this design provides a significant improvement in brightness mitigation, making the new satellite far less luminous than its size would imply. However, the study also notes that even with this improvement, the satellite remains brighter than the limits recommended by the International Astronomical Union for protecting astronomical research. The average brightness of the new satellite exceeds the suggested safety limit by more than three magnitudes, meaning it is still bright enough to interfere with sensitive scientific instruments and is visible to the naked eye in dark skies.

Despite being brighter than the recommended limits, the overall impact of this constellation may be less severe than other groups of satellites currently in orbit. The Federal Communications Commission has authorized the launch of only 248 of these BlueBird satellites, a number far smaller than the thousands of spacecraft in other constellations like Starlink. While the new satellites are individually very bright, their lower total numbers mean they will not saturate the sky in the same way as larger groups. The researchers conclude that while the new design successfully reduces brightness relative to the satellite's size, the objects are still luminous enough to pose a challenge for astronomers. The study provides a clear picture of how these specific spacecraft behave in the sky, offering data that can help predict their appearance and guide future efforts to balance communication needs with the preservation of the night sky.