Overview: A Bold Idea Awakens Strong Reactions
A US startup, Reflect Orbital, proposes a radical way to extend solar power beyond daylight: a constellation of mirrors in orbit that would beam sunlight down to Earth, effectively delivering “sunlight on demand.” The plan centers on an 18-meter test satellite, Earendil-1, slated for launch in 2026, with an eventual fleet of roughly 4,000 satellites by 2030. While the promise could revolutionize solar farming, the concept has astronomers and light-pollution advocates rattled about potential impacts on the night sky, wildlife, and scientific observation.
How the Concept Would Work
The basic idea mirrors a familiar demonstration: reflecting sunlight from a mirror onto a surface to create a bright spot. Reflect Orbital envisions deploying flat mirrors on satellites at about 625 kilometers altitude, with planed mirrors as large as 54 meters across. When the Sun shines, these mirrors would redirect sunlight toward a designated patch of Earth to power solar farms after sunset or during cloudy periods.
However, the Sun is not a point source; it spans roughly half a degree in the sky. At orbital distances, even perfectly flat or curved mirrors cannot focus sunlight to a tiny, intense point. The reflected beam would spread, creating a bright, diffuse patch on the ground rather than a tight laser-like beam.
Calculations suggest that a single 54-meter satellite reflecting onto Earth from 625 kilometers up would illuminate an area at least 7 kilometers across. The resulting light intensity would be about 1/15,000th of the noonday Sun, still far brighter than the full Moon and easily visible to the naked eye in many conditions. The practical footprint, however, would depend on geometry, weather, and the precise timing of the reflection.
Tested Angles: Balloons, Mirrors, and Real-World Limits
In a demonstration video, the founder shows a 2.5-meter square mirror mounted on a hot air balloon directing light onto solar panels, achieving roughly 516 watts per square meter—about half of peak sunlight. Yet, space could demand a vastly larger reflector to reach meaningful power densities. Scaling a balloon experiment to space would require a mirror thousands of meters across, or dozens of satellites working in concert—raising questions about feasibility and cost.
Operational Realities and Limitations
Reflect Orbital’s public statements describe a target of around 200 watts per square meter, equating to roughly 20% of midday sunlight. To meet a single 20% threshold across a region would necessitate a massive fleet of satellites — possibly in the thousands or more. The orbital dynamics complicate timing: a satellite at 625 kilometers altitude travels about 7.5 kilometers per second, remaining within 1,000 kilometers of a target location for only a few minutes. Even with thousands of satellites, lasting illumination would be sporadic and weather-dependent.
In one interview, the company hinted at plans for a sun-synchronous constellation that would keep satellites in constant sunlight above the day-night terminator. The aim would be to produce illumination during adverse solar conditions, but this strategy would need extraordinary scale and coordination. Critics point out that even large fleets would illuminate far fewer locations at any given time than proponents claim, with cloudy conditions further reducing utility.
What It Means for Astronomy and Nightscapes
Astronomers warn that mirrored satellites could introduce pervasive light pollution, not just a single bright beacon. Unlike conventional satellites, the intention here is to create deliberate, directed illumination across the night sky. If even a portion of the fleet is operational, observers could see spots of sky brighter than the Moon or, in some cases, approaching daylight levels during beam events. The cumulative effect could hinder telescope work, disrupt astronomy education, and complicate long-term sky monitoring. Wildlife that relies on natural light cycles could also be affected by altered dawn/dusk cues and nocturnal behavior changes.
Reflect Orbital maintains that the beams would be brief, predictable, and targeted, with locations shared publicly to aid researchers. Yet the very premise raises concerns about unintended consequences—how to prevent accidental illumination of protected areas, observatories, or migratory pathways, and how to address light leakage from moving beams across the globe.
Regulatory and Ethical Considerations
Current space governance emphasizes debris mitigation, collision avoidance, and astronomical protection, but there is no clear precedent for deliberate night-time illumination. If such a system proceeds, it will require rigorous risk assessments, transparent operations, and independent oversight. Questions remain about long-term ecological impacts, potential glare hazards for pilots and drivers, and the treatment of night-sky heritage as a public good.
Outlook: Cautious Optimism or Cautionary Tale?
Reflect Orbital’s ambition to extend solar power into the night is provocative and technically audacious. Yet the practical hurdles—scale, cost, timing, and the unintended consequences for astronomy and ecosystems—are substantial. The project, if pursued, would be a litmus test for how far technology should push the boundaries of light in the night sky. For now, scientists urge a careful, evidence-based evaluation of the trade-offs, with strong emphasis on protecting the night sky we collectively depend upon.
By: Michael J. I. Brown, Associate Professor in Astronomy, Monash University, and Matthew Kenworthy, Associate Professor in Astronomy, Leiden University
