Tzu-Wei Fang will always remember February 3, 2022. It was a Thursday just after Groundhog Day, and Fang, a physicist born in Taiwan, was analyzing satellite images of a cloud of charged particles that had erupted from the sun. The incoming cloud was a coronal mass ejection, or CME—essentially a massive burst of magnetized plasma from the sun’s upper atmosphere. It looked like dozens of similar CMEs that hit Earth every year, usually making their presence known mostly through mesmerizing polar light displays. 

“The CME wasn’t significant at all,” says Fang, who had been analyzing the incoming data from her office at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado.

But five days later, Fang learned that the CME was not as innocuous as it had seemed. Just as the cloud of plasma was making its way to the planet, a SpaceX Falcon 9 rocket was blasting off from a launchpad at the Kennedy Space Center in Florida with 49 new Starlink satellites in its nose cone. 

The CME heated the tenuous gases in Earth’s upper atmosphere, causing it to swell, pushing the lower, denser layers upward. When the satellites were released from their rocket, they struggled against an unexpectedly thick medium. With thrusters too weak to push them to a higher, safer orbit, 38 of them spiraled back to Earth. 

Scientists had long known that solar activity can change the density of the upper atmosphere, so the fact that this happened wasn’t a surprise. But the Starlink incident highlighted a big gap in capability: researchers lacked the ability to precisely predict the sorts of density changes that a given amount of solar activity would produce. And they did not have a good way to transfer those changes to predictions about how satellite trajectories would be affected.

The need to improve predictions was growing more urgent. A new solar cycle had just begun picking up strength after a prolonged quiet period, and the sun was spouting many more solar flares and CMEs than it had in years. At the same time, the number of satellites orbiting the planet had grown sevenfold since the last solar maximum. Researchers understood that a powerful solar storm could make conditions in near-Earth space so unpredictable that it would be impossible to tell whether objects were on a collision course. And that was a worry. One head-on crash between two large spacecraft can create thousands of out-of-control debris fragments that ...