Let’s start with the good news: There is no danger to anyone on the ground from the flock of 40 SpaceX Starlink satellites that are currently plunging from orbit and heading for Earth, knocked from the sky by a geomagnetic storm originating from the sun. Atmospheric drag will easily incinerate the small, 260 kg (575 lb.) satellites before they reach the surface. As for the bad news? Well, the fact that there is currently a cluster of 40 SpaceX Starlink satellites plunging from orbit at all.
The doomed spacecraft were part of a payload of 49 Starlink satellites SpaceX launched into orbit on Feb. 3, intended to join the 1,925 other Starlinks—which aim to improve and provide global access to broadband service—already circling the planet in orbits that range from 540 km (335 mi) to 1,300 km (800 mi). As is common practice for SpaceX, all Starlinks are originally placed in a brief parking orbit just 209 km (130 mi) up so that they can be run through a systems check-out from the ground to make sure they are functioning properly. Any duds among them are simply left in that low orbit, where atmospheric drag quickly pulls them back out of the sky on an incinerating reentry.
But that plan assumes that the sun behaves, and on Jan. 29 it didn’t, releasing a storm of charged particles toward Earth known as a coronal mass ejection. Such solar storms usually present little danger to Earth, and the Space Weather Prediction Center, a division of the National Oceanic and Atmospheric Administration, rated the storm as a 2 on a 1 to 5 scale, a severity it calls “moderate.” The catch: the tidal wave of charged particles was expected to reach Earth on Feb. 2 or 3—or just as SpaceX was planning its Starlink launch.
The company went ahead with its plans nonetheless, saying nothing about the wisdom of not waiting out the storm, but instead merely announcing in a blog post, “On Thursday, February 3 at 1:13 p.m. EST, Falcon 9 launched 49 Starlink satellites to low Earth orbit from Launch Complex 39A (LC-39A) at Kennedy Space Center in Florida. Falcon 9’s second stage deployed the satellites into their intended orbit, with a perigee of approximately 210 kilometers above Earth, and each satellite achieved controlled flight.”
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But that anodyne announcement masked what is starting to look like a major blunder. When energy from a solar storm reaches Earth, it causes the atmosphere to expand slightly, meaning that satellites flying in what would normally be a safe, 209 km parking orbit are suddenly encountering a lot of air resistance that can pull them back to the ground. SpaceX was aware of the problem as soon as the 49 satellites reached space and attempted to ride out the storm, positioning the relatively flat-shaped spacecraft edge-forward, to minimize air resistance.
“The Starlink team commanded the satellites into a safe-mode where they would fly edge-on (like a sheet of paper) to minimize drag—to effectively ‘take cover from the storm,’” SpaceX posted.
But in this case physics has a bigger vote than SpaceX, and the safe-mode maneuver worked for only nine of the fleet of 49. The others were effectively clawed out of the sky and are already reentering the atmosphere or will begin to do so by the end of the week.
SpaceX applauded itself for handling the problem with minimal risk to other satellites or to people or property on the ground—while ignoring the question of whether it would have been wiser simply to postpone the launch for a week or so. “This unique situation demonstrates the great lengths the Starlink team has gone to ensure the system is on the leading edge of on-orbit debris mitigation,” the company wrote.
https://www.yahoo.com/news/solar-storm-knocks-40-spacex-173705826.html