Reflect Orbital's Space Mirrors Would Be 40 Times Brighter Than the Full Moon, Study Finds

Each of the sun-reflecting mirrors planned by the US startup Reflect Orbital would appear 40 times brighter than the full moon to anyone standing within its beam, according to a new study led by Princeton University astrophysicist Gaspar Bakos. "You would not see any stars if you were in the beam," Bakos said. "It will be worse than big cities like London."

Reflect Orbital has received a US Federal Communications Commission (FCC) licence to launch a demonstration satellite called EARENDIL-1, carrying an 18-by-18-metre mirror into an orbit 600 kilometres above Earth, to test whether reflected sunlight can extend solar power plants' operating hours into the night or light disaster zones after dark. The company ultimately wants to fly 40,000 mirrors, each measuring 54 by 54 metres.

The study calculated that a single operational mirror would light up a beam 5.4 kilometres wide with sky glow as bright as after-sunset twilight, and that atmospheric scattering would leave the sky brighter than a full moon as far as 34 kilometres from the beam. Generating useful power would require at least 400 mirrors shining on one spot at once, the researchers found; that combined beam would be 10,000 times brighter than the full moon and produce sky glow visible from 80 kilometres away.

A Reflect Orbital spokesperson said the study relied on "inaccurate assumptions" and that most people would never see the light because most service locations would be remote construction or solar sites, with only satellites serving active locations switched on. The researchers said the company has not provided technical data to support those claims.