US approves test of orbiting mirror that could turn night into day

A California startup has received U.S. regulatory approval to test a satellite capable of reflecting sunlight onto Earth after sunset, advancing a concept that supporters say could transform industries ranging from agriculture to renewable energy but that critics warn could dramatically brighten the night sky.

On July 9, the U.S. Federal Communications Commission (FCC) authorised Reflect Orbital to deploy and operate Eärendil-1, an experimental satellite equipped with an 18-meter-wide reflective film designed to redirect sunlight onto selected areas of the planet, ZME Science writes.

The satellite will orbit about 625 kilometres above Earth and use a motorised thin-film reflector to aim sunlight at designated locations. According to Reflect Orbital, the illuminated area could cover at least five kilometres.

The spacecraft will capture sunlight while flying above Earth's dark side before sweeping the reflected light across the ground. Because a single satellite in low Earth orbit can provide only brief illumination, sustained lighting would require multiple satellites operating in succession.

Reflect Orbital says the technology could support search-and-rescue operations, illuminate disaster zones and remote construction sites, extend growing hours for crops and enable solar farms to generate electricity beyond sunset. The company plans to launch two satellites in 2026, expand to more than 5,000 by 2030 and ultimately deploy over 50,000 satellites by 2035. It says future constellations could vary brightness from moonlight to full daylight.

However, the proposal has sparked strong opposition from astronomers, who warn that a large constellation of orbiting mirrors could interfere with scientific observations and permanently alter the appearance of the night sky.

A modelling study by the European Southern Observatory estimated that a fleet of 50,000 Reflect Orbital satellites could render every exposure taken by wide-field telescopes such as the Vera C. Rubin Observatory unusable whenever the mirrors remained sunlit. The study also projected that such a constellation could make the overall night sky three to four times brighter, even if operators avoided directing beams near observatories.

“For optical astronomy, this is an existential threat, and we hope that the regulators will share that view,” Betty Kioko, an institutional affairs officer at the European Southern Observatory, said before the FCC's decision.

The FCC received more than 1,800 public comments on the proposal, including objections from astronomy organisations and dark-sky advocates. However, the agency said its authority is limited to satellite communications and radio frequencies.

Space-based mirrors have been tested before. In 1993, Russia's Znamya 2 experiment successfully reflected sunlight onto a roughly five-kilometre-wide area of Europe for several minutes. A larger follow-up mission in 1999 failed after the reflector became entangled during deployment.

Reflect Orbital has said its satellites will remain inactive unless specifically requested, avoid observatories and environmentally sensitive areas, and operate only with local authorisation.

“Every spot of light Reflect delivers will be requested, approved and contained,” the company said in May.

By Sabina Mammadli