Oct. 29, 2021: Imagine waking up to this headline: “Half of Earth’s Satellites Lost!” Impossible?  It actually happened on an October day in 2003.

Turn back the clock 18 years. Solar Cycle 23 was winding down, and space weather forecasters were talking about how quiet things would soon become when, suddenly, the sun unleashed two of the strongest solar flares of the Space Age. The first, an X17-category blast on Oct. 28, 2003, hurled this CME directly toward Earth:

Traveling 2125 km/s (almost 5 million mph), the cloud slammed into Earth’s magnetic field only 19 hours later, sparking an extreme (G5) geomagnetic storm. The storm had barely begun when the sun erupted again. An X10-flare on Oct. 29th created another CME traveling almost as fast, 1948 km/s. It also arrived in 19 hours. The one-two punch kept the geomagnetic storms going for almost three full days–Oct. 29, 30, and 31, 2003.

Researchers named them “the Halloween Storms.” Modern accounts of the event tend to focus on auroras. Northern Lights descended as far south as Georgia, California, New Mexico, Arizona, Texas, and Oklahoma: photo gallery.

But auroras were just the tip of the iceberg. High energy particles accelerated by the CMEs rifled toward Earth, peppering our planet’s atmosphere with protons and electrons. Onboard the International Space Station, astronauts took shelter in the hardened Zvezda service module. Hundreds of miles below, airline pilots were changing course. Almost every flight over Earth’s poles detoured to lower latitudes to avoid radiation, costing as much as $100,000 per flight. Many Earth-orbiting satellites experienced data outages, reboots and even unwanted thruster firings. Some operators simply gave up and turned their instruments off. Goddard’s Space Science Mission Operations Team estimates that 59% of NASA’s Earth and space science satellites were affected in one way or another.

There’s a dawning awareness that something else important happened, too. Many of Earth’s satellites were “lost.”

In a 2020 paper entitled “Flying Through Uncertainty,” a team of researchers led by Thomas Berger at the University of Colorado’s Space Weather Technology, Research, and Education Center report some little-known recollections from USAF satellite operators. During the Halloween storms, they recalled, “the majority of [low Earth orbiting] satellites were temporarily lost, requiring several days of around-the-clock work to reestablish [their positions].”

Satellites often go course during geomagnetic storms, but this was extreme.

“The Halloween storms pumped an extra 3 Terrawatts of power into Earth’s upper atmosphere¹,” explains Martin Mlynczak, principal investigator of NASA’s SABER spacecraft, which measured the energy dump. “We didn’t feel it down on the planet’s surface, but it was a big event for Earth orbiting satellites. The extra power puffed up the atmosphere, sharply increasing aerodynamic drag.”

Simulations show that even moderate geomagnetic storms can shift the expected position of a satellite by 10 km or more. The Halloween storms created far larger uncertainties with the potential for collisions. United States Space Surveillance Network radars and telescopes worked urgently to find everything again.

Not knowing where satellites are is a problem mainly because of collisions. There are thousands of objects in Earth orbit ranging from billion-dollar active satellites to worthless nuts and bolts. Satellites are routinely maneuvered to avoid predicted collisions–but you can’t avoid a collision when you don’t know where you are.

“Fortunately, the Halloween storm did not cause any major collisions that we know of,” write Berger and his co-authors. “But if a geomagnetic storm on the level of the 2003 event were to occur today, the situation could be very different. Most satellite operators today have never experienced anything like the Halloween 2003 storm, and there are now (in 2020) more than 1,700 operational satellites and at least 19,400 pieces of debris larger than 10 cm in low Earth orbit.”

A number of countries and corporations are planning mega-constellations (Starlink is the most famous), which could ultimately swell the satellite population to 65,000 or more. Losing track of satellites in such a congested environment could theoretically trigger a cascade of collisions, rendering low Earth orbit unusable for years following an extreme geomagnetic storm.

Now that’s scary.

End notes:

1. Martin Mlynczak provides some context:”While 3 Terawatts sounds like a lot of power (and it is!), averaged over the area of the Earth it is 6 milliwatts per square meter. The global average outgoing infrared radiation from the entire planet and atmosphere below 100 km is 240 watts per square meter.”
2. For more information about the Halloween Storms, check out this excellent summary from NOAA.