Since 1989, astrophysicist Jonathan McDowell has tracked every human-made object in space. McDowell’s meticulously maintained catalog, updated every few weeks, is more comprehensive and detailed than that of most governments.

From his front-row seat, he has watched with growing alarm as private companies launched dozens, then hundreds, then thousands of satellites over the last decade. So when McDowell heard that a space company called Reflect Orbital plans to launch a satellite to reflect the sun’s light onto the night side of Earth, he heaved a deep sigh.

“It’s an insane project,” says McDowell, who retired from Harvard this year and is now an honorary professor at Durham University in England. “There’s a failure to understand that darkness is a good thing.”

Reflect Orbital, based near Los Angeles, hopes its satellite and others like it some day offer “sunlight on demand,” illuminating disaster areas for search and rescue efforts, lighting up nighttime events and festivals and allowing solar farms to run all hours of the day. “We believe that exploring how new technologies can help the world forgo fossil fuels is a responsible application of the scientific process,” Christopher Buscombe, a spokesperson for Reflect Orbital, wrote in an email to Science News. “We will continue to work closely with scientific partners who share this belief.”

But many space observers and dark sky enthusiasts are in an uproar. The consequences to astronomy could be catastrophic, they say, and the reflected light could threaten human health and safety and disrupt wildlife. In March, the American Astronomical Society petitioned the Federal Communications Commission to deny Reflect Orbital’s request to operate the test satellite. When the FCC granted approval in July, nonprofit organizations including DarkSky International asked the agency to reverse its decision.

The response to Reflect Orbital reflects growing concerns about the crowding of space more generally. The number of active satellites orbiting Earth has ballooned from 2,000 in 2018 to over 16,000 today, McDowell says. Many more are expected to launch in the years ahead.

This traffic jam, along with the proliferation of space junk from dead satellites and discarded rocket stages, has space scientists worried about collisions that could wipe out GPS navigation and other essential tools. The satellites are also a problem for astronomers, interrupting observations by leaving streaks on telescope images.