Forecasters were briefing the Federal Emergency Management Agency on May 9 as part of the 2024 Space Weather Tabletop Exercise when they learned a real solar storm was coming. Powerful solar flares and a series of coronal mass ejections (CMEs) were headed for Earth.

“I’m briefing FEMA Region 8 [in Denver] about real-time space weather in the middle of this exercise,” said Shawn Dahl, a forecaster at the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center in Boulder, Colorado. “My counterpart was doing the same at the national level over in the Washington, D.C. area.”

The biggest solar storm in more than two decades struck Earth on May 10 and 11.

“We saw expansion of the atmosphere and an increase in charged particles reaching the Earth,” said Rebecca Bishop, Aerospace Corp. principal scientist and a member of the U.S. Space Weather Advisory Group. “Environmentally, it was very exciting.”

The aurora borealis was visible as far south as Florida, a rarity for the light show triggered by the interaction of solar particles and Earth’s magnetic field. The storm’s impact on technology is harder to gauge.

Planes were rerouted to prevent interference with high-frequency radios. There were widespread reports of malfunctioning GPS receivers. Power grid managers saw enhanced amps on high-voltage transmission lines. And satellites in low-Earth orbit experienced increased drag, potentially shortening their lifespan.

Still, most space-based and terrestrial infrastructure survived the storm relatively unscathed.

“It certainly could have been a lot worse,” Dahl said. “It shows the work that’s been done over at least the last 10 years, preparing people for the fact that storms like this were going to happen.” Plus, the storm wasn’t as powerful as some forecasters feared.


While the May 10-11 event was designated G5, the highest geomagnetic storm rating, it was far less powerful than the 1859 Carrington Event. Researchers continuing to study the recent storm think the 1859 Carrington Event, a G5 storm that caused widespread electrical outages, “was likely five to 10 times stronger than what we experienced,” Dahl said.

Both storms were designated G5 because “the upper end of the geomagnetic storm scale is condensed,” said Ian Cohen, Johns Hopkins Applied Physics Laboratory deputy chief scientist for the Space Exploration Sector. “We don’t have a category above G5 right now that would capture the difference between a big one and what I’ll call a weak G5.”

NOAA is leading discussions on potentially revising that scale. It’s one of the many activities prompted by the Halloween storms of October 2003, which struck with little warning, disrupting communications and damaging satellites.

“From the Obama administration through the Trump administration on into the Biden administration, space weather has continued to be a forefront,” Dahl said.

Resulting legislation and executive orders sought to mitigate the impact of space weather on the terrestrial economy. In 2016, President Obama directed federal agencies to come up with plans to prepare the nation for space weather events.

In 2020, Congress stepped in with the Promoting Research and Observations of Space Weather to Improve the Forecasting of Tomorrow (PROSWIFT) Act, which called for a coordinated federal response. It directed NOAA, for instance, to improve space weather forecasts by bolstering its own observations and evaluating commercial data.

Over the last decade, the National Weather Service Space Weather Prediction Center has worked closely with state, city and county emergency managers to help them understand the threat posed by space weather.

Power grid managers also receive alerts when G3, G4 or G5 activity is expected. Prior to the May storm, the Space Weather Prediction Center took the unusual step of holding a conference call with North American power grid reliability coordinators.

“This was the first time I’m aware of that we talked to the power grid in advance,” Dahl said. “I provided details about what we were expecting and said that the next call would be when we see the CME arrive 1 million miles from Earth. At that point, we’re able to tell how quickly it might arrive.”


Satellite operators closely track space weather forecasts, too. Planet paused imaging for its SkySat and SuperDove Earth-observation constellations for about 24 hours from May 10 to 11. Iridium halted autonomous maneuvers.

“We have learned through the decades how to mitigate the impact,” said Daniel Bock, Morpheus Space CEO and co-founder.

Payloads may be turned off or put on standby. Operators can turn satellites to better protect sensitive instruments. With a few days warning, operators also can raise satellite orbits to lessen the impact of drag, Bock said.

What’s more, satellite components are better able to withstand energetic protons.

In the 2003 storm, Iridium’s first-generation communications satellites “were dropping, the clocks were going crazy, and I was like, ‘What the hell was going on?’” said Christopher Jones, who led Iridium’s flight dynamics team.

During the recent storm, “I expected some of the same, so I might have freaked out the younger generation here a little bit,” said Jones, now Iridium vice president of network operations.

Instead, the Iridium Next satellites experienced significant drag but no other issues. Satellites in one of Iridium’s six orbital planes dropped 30 meters during the storm. With normal drag, the satellite altitudes decrease roughly five meters per day. Thanks to onboard propulsion, Iridium quickly returned its satellites to their intended slots when the storm died down.

“We know we’re going to see a bunch of drag,” Jones said. “But we also know that drag is going to go back to normal within a couple of days.”

Enhanced atmospheric drag may shorten the operational lifespan of satellites without thrusters. The two cubesats that make up Low-Latitude Ionosphere/Thermosphere Enhancements in Density, a NASA mission focused on atmospheric density, dropped from an altitude of 412 kilometers before the storm to about 400 kilometers.

What does that mean for the lifespans of the cubesats that were expected to reenter Earth’s atmosphere in December prior to the May event? Three days after the storm, models predicted the LLITED cubesats would reenter in September. Two weeks later, the anticipated reentry date was in late November.

“The key takeaway is that our models are not very good,” said Bishop, LLITED principal investigator.


Additional observation of solar activity would improve models.

“Think about terrestrial weather. We have all these satellites and ground stations,” Bishop said. “We get these very detailed maps of frontal systems. We don’t have that sort of infrastructure to monitor space weather or predict it.”

Space weather experts are eager for CME imagery that will be gathered by the Compact Coronagraph on the Geostationary Observation Environmental Satellite-U, the NOAA weather satellite launched (CONFIRM) on June 25. “For the first time, we will have continuous observations of the sun’s fainter outer atmosphere, creating the equivalent of a total solar eclipse every 30 minutes,” Elsayed Taalat, NOAA Office of Space Weather director, said June 24 during a GOES-U pre-launch briefing. “The coronagraph working in tandem with the magnetometers, Solar Ultraviolet Imagers and Extreme Ultraviolet and X-Ray Irradiance Sensors aboard GOES-U and GOES-18, in the GOES West position, will strengthen NOAA’s ability to predict space weather.”

Forecasters also obtain coronal imagery from the Large Angle and Spectrometric Coronagraph on the European Space Agency-NASA Solar and Heliospheric Observatory. SOHO, in orbit since 1995, is well beyond its lifespan. “We need a modern, higher-fidelity instrument,” Dahl said.

NASA’s Deep Space Climate Observatory, launched in 2015, and the Advanced Composition Explorer, launched in 2017, track solar activity from Earth-sun Lagrange point 1. The next observatory, Space Weather Follow-On Lagrange 1, is slated for launch in 2025.

While it’s critical to continue watching the sun from L1 — approximately 1.6 million kilometers from Earth — and geostationary orbit, space weather researchers want additional views.

“One of the problems that we have right now is that we have line-of-sight observation,” Cohen said. “We can see the CME coming off the sun, but then we don’t get any additional information until it gets 99 percent of the way to Earth at L1.”

Forecasting when CMEs will reach Earth is like trying to determine the speed of someone running straight toward you with a flashlight. It would be much easier if you could observe the activity from the side.

If instruments observed the sun from one or more locations off the sun-Earth line, “you could get updates of how a CME is moving through space, whether it’s slowing down,” Cohen said. “In particular, we’d like to get additional assets at L4 and L5.”

This article first appeared in the July 2024 issue of SpaceNews Magazine.

Debra Werner is a correspondent for SpaceNews based in San Francisco. Debra earned a bachelor’s degree in communications from the University of California, Berkeley, and a master’s degree in Journalism from Northwestern University. She...