When the Sun rages and storms in Earth's direction, it changes our planet's atmosphere. The atmosphere puffs up, meaning satellites in Low-Earth Orbit (LEO) meet more resistance. This resistance creates orbital decay, dragging satellites to lower altitudes. One researcher says we can change the design of satellites to decrease their susceptibility.
There's no distinct line where Earth's atmosphere stops and space starts. The layers of the atmosphere are more tenuous with altitude, and even in LEO, satellites are passing through a very tenuous region of Earth's upper atmosphere. This creates drag and a tiny amount of orbital decay, which normally is not much of a concern.
But when the Sun unleashes a geomagnetic storm our way, energetic particles strike Earth's thermosphere, the second highest atmospheric layer, just below the exosphere. The thermosphere starts at about 80km altitude and can extend up to 700 km. It gets its name from the heat it absorbs from the Sun. During a solar storm, it warms even more and expands. Most satellites avoid the lower thermosphere because of drag and orbit higher, at least about 400 km. During a solar storm, that safe altitude becomes a little more problematic.
New research suggests that while predicting solar storms more accurately is part of the solution, different satellite designs can also help. It's titled "Geomagnetic Storms and Satellite Orbital Decay," and the lead author is Yoshita Baruah. Baruah is from the Department of Physical Sciences in the Indian Institute of Science Education and Research.
"A geomagnetic storm results in dissipation of energy from the solar wind into the atmosphere, leading to Joule heating and thermospheric expansion," Baruah writes. "This has serious consequences on Low Earth Orbit satellite lifetimes." In his paper, Baruah examines the impact of different types of geomagnetic storms on satellites. He also writes about satellite design and how that can mitigate the effects of the storms.
Different transient energetic events on the Sun create space weather that has different consequences for Earth. Solar flares, coronal mass ejections (CMEs), and solar energetic particles (SEPs) all affect the atmosphere differently. So do high speed streams which are emitted from coronal holes. These streams travel between 400 and 800 km/s, much faster than the solar wind, and form stream interaction regions (SIRs) and corotating interaction regions (CIRs).
The author examined data from the ESA's Swarm satellites, spacecraft that study Earth's magnetic field. In 2015, two storms struck. One was a more powerful storm caused by a CME.
This figure shows how a powerful CME-induced storm affected the Swarm C satellite in 2015. The top panel shows the Disturbance Storm Time, the second panel shows the thermospheric mass density, the third panel shows the orbital decay rate, and the bottom panels shows the total orbital decay. During this storm, the satellite decayed a total of 37 meters. Image Credit: Baruah et al. 2025.
The author also examined data from a more moderate solar storm from 2015 and how it affected the Swarm C satellite. It was triggered by a CIR.
This figure shows how a moderate, CIR-induced storm affected the Swarm C satellite. Though weaker than CME-induced storms, CIR-induced storms last longer. The satellite lost a total of 97.6 meters. Image Credit: Baruah et al. 2025.
"We thus conclude that, in case of geomagnetic storms of similar intensity, CIR induced storms can prove to be more detrimental to satellite orbital lifetimes than those induced by CMEs," the research paper states.
The authors also considered the ballistic co-efficient (BC) of satellites and how that contributed to storm-induced orbital decay. The BC is calculated with a formula based on a satellite's mass, drag, and the cross-section perpendicular to the direction of travel and expressed in kg/m². It describes how well a satellite will overcome atmospheric resistance. A satellite with a higher BC will suffer less drag, and one with a lower BC will have more drag and its orbit will decay more quickly.
The researchers modelled satellites to study how their design affected their BCs. "We first simulate the orbit of Swarm C during the geomagnetic storm of 20 September 2015 and validate it using observations," the author writes. "The estimated orbital decay of Swarm C at 455 km during the time period is 17.28 m, which is in good agreement with the observed orbital decay of 19.35 m."
Baruah also modelled how the ISS would be affected by the same storm. It has a much lower BOC and e determined that the ISS's orbit would've decayed by 54.44 meters. "The ballistic coefficient of Swarm C is 303.9 kg/m2 while that of an ISS-like satellite is 100 kg/m2 , which explains a higher orbital decay for the latter," the author explains.
The Swarm satellite weigh only 369 kg, while the ISS weighs about 450,000 kg. Swarm C's dimensions are 9.1 m × 1.5 m × 0.85 m, while the ISS measures 109 m by 73m.
There are many calls for better monitoring of geomagnetic storms so that we can predict them with some accuracy. Baruah adds his voice to those calls, while also emphasizing how different satellite designs can help limit the orbital decay they suffer.
"Our work highlights the importance of monitoring and predicting space weather, and assessing their impacts on space-based human technologies," Baruah writes. "Physical properties of satellites, namely the ballistic coefficient also have an impact on their orbital lifetimes," he concludes.
