This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A U.S. startup has booked two Indian rocket launches to test a planned service no company has sold before: sunlight at night. California-based Reflect Orbital plans to place giant mirrors in low Earth orbit and use them to steer reflected sunlight onto selected locations on the ground.
The company wants to sell space-based illumination for a wide range of purposes, from keeping solar farms generating energy after sunset to search-and-rescue operations. Its first orbital demonstrator, Eärendil-1, will carry an 18-by-18-meter (59-by-59-foot) reflector. Using space mirrors to deliver useful illumination will require overcoming formidable engineering challenges.
But there's another pressing question: Who will decide where sunlight redirected from space is allowed to hit the ground? You might think a space mirror could illuminate a customer's solar farm or a rescue site while leaving everywhere else untouched. That's not quite how it works, because Earth's atmosphere doesn't respect sharp boundaries.
A peer-reviewed scientific study published last August modeled what happens when reflected sunlight passes through our atmosphere. Molecules and aerosols scatter some of the light beam across the surrounding sky. Light reaching the ground is reflected upward and then scattered again.
This means the light can affect a much wider area than intended. For a proposed future 54-meter (177-foot) mirror, the study's authors found that the resulting sky glow could remain substantial well beyond the target area. At 14 kilometers (8.7 miles) from the beam, it could be brighter than a full moon across most of the sky.
Even 34 kilometers (21 miles) away, the sky glow toward the beam could still be brighter than under a full moon. These are predictions from a model, not measurements from real space mirrors. Still, they expose the unresolved regulatory problem: The people affected may not have ordered the light.
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