From Starlink To VisorSat: Cutting Satellite Brightness To Preserve Our Night Skies

By John Oncea, Editor

The use of anti-reflective coatings on satellites can significantly reduce light pollution, aiding astronomy while balancing space innovation.

The rapid expansion of satellite mega-constellations has revolutionized global communication. However, reflected sunlight from these satellites creates bright streaks that interfere with astronomical observations and diminish our view of the night sky. This phenomenon, known as satellite light pollution, threatens scientific research and the natural beauty of dark skies.

To address this issue, engineers and researchers are developing anti-reflective coatings to minimize the impact of satellites on astronomy while maintaining their operational efficiency.

Understanding The Challenge

Satellite mega-constellations are a large group of artificial satellites, typically numbering in the hundreds or thousands, working together as a system to provide specific functions including navigation, communications, and Earth observation. One such mega-constellation – SpaceX’s Starlink – has 7,135 satellites in low Earth orbit (LEO) as of March 28, 2025, and the company hopes to one day have six times as many comprise its mega-constellation, according to Space.com.

It’s the sheer number of satellites needed to create these mega-constellations that is worrying astronomers and researchers who fear that the bright, orbiting objects will interfere with observations of the universe, Space.com writes.

Starlink is just one of several notable satellite mega-constellations deployed or in development, joined by OneWeb, Amazon’s Project Kuiper, China’s Guowang, Telesat, ViaSat-3, Samsung, and Boeing. All of these mega-constellations have or are planned to have hundreds to as many as 42,000 satellites in LEO. Combined, the number of satellites orbiting Earth – currently numbering just over 11,800, according to Kongsberg, is going to explode.

Dr. Meredith Rawls, a stellar astronomer and software developer working as a research scientist with the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) group at the University of Washington, told Space.com about the impact satellite mega-constellations are having on ground-based astronomy. “The main thing is there are so many of them that are currently being launched and planned to be launched, and they reflect sunlight so they can be bright.”

These satellites, often designed with reflective surfaces to manage thermal loads, can reflect sunlight during twilight hours, creating visible trails that mar long-exposure astrophotographs and disrupt ground-based observations. For example, modeling suggests that light pollution could reduce the Vera Rubin Observatory's ability to detect stars by 7.5%, adding nearly $22 million in costs to its survey, reports Phys.org.

Rawls continues, saying, “The brightness surprised some of the satellite operators, they had not anticipated how bright their satellites were going to be. Astronomers were used to sometimes seeing satellites, but now it’s an order of magnitude more and they’re going to be showing up very commonly in observations from ground-based telescopes.”

Rawls and her fellow astronomers have expressed concerns that increasing numbers of bright satellites will not only pollute our night skies but also hinder critical research as the interference reduces the clarity of images and limits the available observation time.

The Embry-Riddle Aeronautical University added its concern, emphasizing the need for international cooperation to balance space innovation with dark sky preservation. Researchers advocate for policies that prioritize minimizing light pollution alongside technological advancements, not only to reduce light pollution but to protect Earth’s natural environment as “research has shown that light pollution can negatively impact human, animal, and plant health in many ways, such as disrupting circadian rhythms.”

SpaceX Responds To Calls For Improvements

The urgency to mitigate these effects has led to innovative solutions like anti-reflective coatings, something SpaceX has been working on for the past several years, according to PC Mag. Initially, the company experimented with “sun visors” to block sunlight reflections but abandoned this approach due to technical limitations such as increased atmospheric drag and interference with laser links. Instead, SpaceX shifted to using advanced materials:

1. Mirror Films: SpaceX developed a second-generation mirror film that scatters reflected sunlight away from Earth, reducing brightness by over ten times compared to earlier designs.
2. Darker Materials: First-generation Starlink satellites now feature dark red pigmentation on solar cells, while second-generation satellites use low-reflectivity black coatings on various components.
3. Solar Array Adjustments: Solar panels are angled away from the Sun during critical orbital phases to minimize reflections.

These measures have been praised by astronomy groups for their effectiveness in reducing brightness and fostering collaboration between industry and science. According to The Register, Piero Benvenuti, Director of the International Astronomical Union’s Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS), said of SpaceX’s efforts, “This is a real demonstration of corporate good citizenship, representing a significant investment of engineering resources in both hardware and operational modeling to reduce reflected sunlight hitting telescopes on the ground.

“SpaceX sharing their technical approaches, accepting trade-offs toward the goal of reducing brightness, offering to sell a darkening film to other operators at cost, and publishing accurate and timely state vectors all promote the spirit of cooperation that is the centerpiece of CPS goals for interacting with industry.”

Benvenuti went on to say IAU CPS “shares SpaceX’s hope that the described brightness mitigations for second-generation Starlink satellites can meet published brightness goals and shift many impacts into a regime where ground-based optical/near-IR astronomy data are significantly less compromised.”

The Promise Of Anti-Reflective Coatings

One promising strategy is the use of specialized anti-reflective coatings. These coatings work by reducing the surface reflectivity of satellite components, particularly in areas most visible from Earth. The concept is to absorb or scatter incident sunlight rather than reflect it directly back, thereby lowering the satellite’s apparent brightness.

The coatings are engineered to be effective in the visible spectrum while remaining transparent in other wavelengths essential for satellite operations. By selectively reducing visible light reflection, satellites can become less obtrusive in the night sky without compromising their thermal control or communication capabilities.

Anti-reflective coatings typically involve applying a thin, nanostructured layer on the satellite’s surface. The micro- or nano-scale features of the coating disrupt the path of incoming light, reducing specular reflection. The ideal coating has two key properties:

• Low reflectivity in the visible range: This minimizes the brightness seen by observers and telescopes.
• High transmission in the near infrared (NIR): Maintaining NIR reflectivity ensures that essential functions such as heat dissipation and sensor operations are not adversely affected.

This dual property is achieved through careful material selection and fabrication processes that control the coating’s refractive index and surface morphology.

Recent industry updates have demonstrated significant progress in this field. For example, SpaceX announced its latest generation of satellites – referred to as the VisorSat series – features an upgraded anti-reflective visor design. This innovation reportedly cuts the satellite’s brightness by up to 60%, a notable improvement over earlier iterations that used only dark coatings.

Similarly, researchers have developed coatings that reduce visible light reflection by nearly 50% while maintaining or even enhancing NIR reflectivity. This improvement not only benefits astronomical observations but also aids in the tracking of satellites via LiDAR systems, thereby enhancing space situational awareness.

These recent advancements indicate that the industry is actively working to balance the needs of commercial satellite operations with the imperative to protect our dark skies. While the primary goal of reducing light pollution is to aid astronomers, the benefits extend further.

Preserving dark skies is essential not only for scientific research but also for cultural, environmental, and health reasons. Many communities and Indigenous cultures rely on the night sky for traditional practices and as a source of inspiration.

Moreover, lower light pollution levels contribute to energy savings and reduce the ecological impacts on nocturnal wildlife. Migratory species, for example, are particularly sensitive to artificial light, and minimizing skyglow can help maintain natural behavioral patterns and ecosystems.

Challenges In Implementation

Despite the promising results, several challenges remain, starting with thermal management. One of the reasons satellites are built with reflective surfaces is to manage the extreme thermal conditions in space. Reducing reflectivity can lead to increased absorption of solar radiation, potentially raising the satellite’s temperature. Engineers must ensure that any anti-reflective coating is compatible with a satellite’s thermal design.

Durability in space is challenging as well. The harsh environment of space – characterized by radiation, micrometeoroid impacts, and temperature fluctuations – demands coatings that are not only effective but also durable over the satellite’s operational life.

Finally, incorporating advanced coatings can add complexity and cost to satellite manufacturing. As companies scale up their satellite constellations, maintaining affordability while integrating these technologies becomes a critical economic challenge.

Researchers and manufacturers are actively addressing these issues. For instance, the new VisorSat design incorporates materials that are engineered to withstand the rigors of space while minimizing visible reflection. Ongoing tests and real-world performance data from recent launches will be vital in refining these technologies further.

Future Directions

Looking ahead, continued collaboration among satellite operators, material scientists, and the astronomical community is essential. Some of the key future directions include:

• Enhanced Material Research: Further development of coatings that can achieve even lower reflectivity in the visible spectrum without compromising thermal control is a high priority.
• Regulatory Frameworks: International bodies and industry groups are beginning to consider guidelines that mandate the use of non-reflective or low-reflective materials on satellites. Such regulations could ensure a more balanced approach to space utilization.
• Integration with Satellite Design: Beyond retrofitting existing satellites, future satellite designs can incorporate anti-reflective materials from the outset, optimizing performance and cost-efficiency.
• Broader Applications: The same coating technologies have potential applications in other fields, such as enhancing the performance of optical sensors and reducing stray light in terrestrial observatories.

The proliferation of satellite constellations is a double-edged sword: while they promise to revolutionize global communications and connectivity, they also pose a significant challenge to preserving our dark skies. Recent technological advances in anti-reflective coatings offer a viable solution, cutting visible light reflection by up to 60% in new satellite models like SpaceX’s VisorSat series. These innovations not only benefit astronomers but also support environmental sustainability and cultural preservation.

However, to fully realize these benefits, ongoing research and collaborative efforts are necessary. Engineers must balance reflectivity reduction with thermal management, durability, and cost. As regulatory frameworks begin to emerge, industry stakeholders have the opportunity to set standards that protect both commercial interests and the natural night sky.

The development of advanced anti-reflective coatings represents a critical step toward a future where space can serve as both a conduit for global connectivity and a canvas for the wonder of the stars.