Reflect Orbital wants to use giant mirrors in space to direct sunlight onto Earth after sunset, but new research suggests the technology could dramatically brighten the night sky far beyond the areas it intends to illuminate. The California company plans to launch its first demonstration satellite, Eärendil-1, later this year, tells MIT Technology Review (full article available to subscribers).
Eärendil-1 will deploy an 18-by-18-meter reflective surface in low Earth orbit. It is a precursor to a proposed constellation of roughly 50,000 larger mirrors. Reflect Orbital envisions using reflected sunlight to extend solar-energy generation and provide illumination when natural sunlight is unavailable.
The concern is that reflected sunlight will not remain confined to its intended target. Researchers modeled how light from the mirrors would scatter through molecules and aerosols in Earth’s atmosphere and reflect from the ground. Their calculations suggest that a single future 54-meter mirror could appear about four magnitudes brighter than the full moon to someone inside its beam.
The resulting diffuse glow could make the sky resemble twilight shortly after sunset, washing out even bright stars. At 14 kilometers from the illuminated area, much of the sky could still be brighter than a moonlit sky. Effects could remain noticeable more than 30 kilometers away. If hundreds of mirrors illuminated one location simultaneously, the glow could extend considerably farther.
Such widespread illumination could create serious problems for professional and amateur astronomy while altering naturally dark environments.
Reflect Orbital disputes aspects of the research. CEO Ben Nowack says the study relies on inaccurate assumptions and that the company’s safeguards account for atmospheric scattering and include exclusion zones. Lead researcher Miroslav Kocifaj argues that the company has not released enough technical data to independently evaluate those claims.
The debate highlights a larger question surrounding commercial space development: whether delivering sunlight on demand is worth fundamentally changing darkness on Earth.
