Earlier this year, the Earth was hit by the most intense geomagnetic storms in twenty years. The most obvious consequences of the storm were the beautiful displays of aurora in the northern and southern hemispheres at unusual latitudes. In the following days, the internet was ablaze with these images.
But the storm also had more insidious consequences for the world’s rapidly growing population of satellites. Physicists have long known that these storms can fry circuits, interrupt communication and change the trajectories of objects in low earth orbit. So an important question is how these satellites fared during and after the storm.
Storm Damage
Now we get an answer thanks to the work of William Parker and Richard Linares at the Massachusetts Institute of Technology in Cambridge, who have studied the impact of the storm on the entire catalogue of satellites in low earth orbit and beyond. They say the storm seriously disrupted the ability to predict collisions in orbit for several days, which significantly increased the risk for all those operating in low Earth orbit.
Astronomers have long observed the 11-year solar cycle during which the number of sunspots, solar flares and coronal mass ejections rise and fall. In 2024 and 2025, the Sun will be near the peak of this cycle, so physicists are expecting a sharp increase in the number and intensity of solar storms reaching our shores.
Between 7-11 May this year, exactly that happened. Various solar observatories spotted five different coronal mass ejections heading our way. These are giant clouds of plasma that are emitted from the Sun’s surface and maintain their own powerful magnetic fields.
If these plasma clouds hit Earth, the plasma heats the upper atmosphere, causing it to expand and increase the drag for satellites in low earth orbit. The magnetic field can induce currents that fry circuits or disrupt communications in orbit and on Earth.
That could be particularly serious if it were to involve safety critical infrastructure such as satellite navigation systems. One way this can happen is if the storm influences the structure of the ionosphere and changes the path for transmissions between navigation satellites and the ground, thereby reducing the accuracy of timing signals.
In the event, solar scientists sent out warnings as soon as they observed the storms heading towards us and which usually take about three days to arrive. That gave satellite operators time to prepare a little in advance.
However, Parker and Linares say that after the initial warning, the forecasts were poor. They significantly underpredicted the geomagnetic intensity leading up to the storm and then overpredicted it in the days after. “The reality is that forecasting geomagnetic activity is very difficult,” they admit.
The researchers then attempted to gauge the changes the storm wreaked in the upper atmosphere. They say the density of the upper atmosphere at an altitude of 400 kilometers increased by a factor of 6 compared to 12 hours earlier.
This significantly increased the drag on satellites at this altitude. They give the example of the Kanopus-V 3, a Russian Earth observation satellite launched in 2018, that is tracked by the US NORAD air defense system. Before the storm, this satellite’s orbit was decaying at a rate of 38 meters per day, but this increased by a factor of four during the storm.
Many modern satellites operate automatic station-keeping systems that maintain their orbit in real time, particularly Elon Musk’s Starlink satellites which number in the thousands. Parker and Linares say these satellites maneuvered en masse during the storm to counter the effects of extra drag.
Astronaut Risk
All this unplanned movement created a significant safety risk. The orbits of all low Earth objects are constantly monitored to predict potential collisions — or conjunctions, as astronomers call them — so that satellites can move out of the way.
But throughout the storm and for several days afterwards, these calculations were next to impossible because of the rapidly changing orbits. “These challenges call into question the capabilities of the existing conjunction assessment procedures during geomagnetic storm conditions,” they say.
That will be a concern to space operators and particularly the astronauts aboard the International Space Station. This has had to move on various occasions to avoid potential collisions and so relies on these kinds of predictions.
The problem is set to become more acute because the number of objects in orbit is increasing significantly with the advent of satellite communication constellations, like Starlink and OneWeb.
There is one benefit of geomagnetic storms, however. Parker and Linares point out that the increased drag helps to remove space debris from low Earth orbit at a faster rate than usual. “Debris is notoriously difficult to remove, so a strong solar cycle with strong geomagnetic storms is one of the best things for helping to maintain a long-term operable environment,” they say.
That’s interesting work that highlights the need to better prepare for geomagnetic storms, particularly with regards to collision avoidance. With more storms expected during the peak of the solar cycle over the next year or so, this issue is set to become more acute.
Ref: Satellite Drag Analysis During the May 2024 Geomagnetic Storm : arxiv.org/abs/2406.08617
