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upstart writes:

Now We Know How a Solar Storm Took Out a Fleet of Starlinks:

On March 23rd, sky observers marvelled at a gorgeous display of northern and southern lights. It was reminder that when our Sun gets active, it can spark a phenomenon called "space weather." Aurorae are among the most benign effects of this phenomenon.

At the other end of the space weather spectrum are solar storms that can knock out satellites. The folks at Starlink found that out the hard way in February 2022. On January 29th that year, the Sun belched out a class M 1.1 flare and related coronal mass ejection. Material from the Sun traveled out on the solar wind and arrived at Earth a few days later. On February 3, Starlink launched a group of 49 satellites to an altitude only 130 miles above Earth's surface. They didn't last long, and now solar physicists know why.

A group of researchers from NASA Goddard Space Flight Center and the Catholic University of America took a closer look at the specifics of that storm. Their analysis identified a mass of plasma that impacted our planet's magnetosphere. The actual event was a halo coronal mass ejection from an active region in the northeast quadrant of the Sun.

The material traveled out at around 690 kilometers per second as a shock-driving magnetic cloud. Think of it as a long ropy mass of material writhing its way through space. As it traveled, it expanded and at solar-facing satellites—including STEREO-A, which took a direct hit from it—made observations. Eventually, the cloud smacked into Earth's magnetosphere creating a geomagnetic storm.

One of the side effects of space weather that can affect satellites is warming in a region called the "thermosphere". That increased the density of the upper atmosphere over a short amount of time and caused it to swell up. A denser atmosphere causes a phenomenon called "atmospheric drag". Essentially, the thicker atmosphere slows down anything moving through. It also heats things up.

The atmosphere thickened enough that it affected the newly launched Starlink stations. They started to experience atmospheric drag, which caused them to deorbit and burn up on the way down. It was an expensive lesson in space weather and provided people on Earth with a great view of what happens when satellites fall back to Earth. It was also that could have been avoided if they'd delayed their launch to account for the ongoing threat.

[...] The loss of the Starlink satellites cost the company millions of dollars. The company elected to launch, even though the space weather community warned about the effects of a geomagnetic storm. For years now, solar physicists have been warning about the effects of space weather. Most satellite companies pay attention to reports from such places as the Space Weather Prediction Center. If they get enough warning ahead of time, they can take steps to protect their equipment. Astronauts on the ISS can take shelter until the storm passes. And, power companies and others can follow forecasts of such storms so they can take whatever action is needed in the event of a strong event.

Solar physicists continue to study these solar outbursts in hopes of coming up with a foolproof prediction system. At the moment, when something erupts from the Sun, we get notifications from a fleet of satellites. Those give us minutes to hours of "heads-up" time to prepare for the worst. NASA and other agencies continue to improve solar studies and prediction methods so that companies launching satellites to low-Earth orbit can take steps to protect their investments.

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