The vagaries of the Sun, whose activity will continue to increase until 2025, represent a real threat for certain satellites.
For a few months now, the space weather has been particularly tumultuous. According to the ESA, it is even so bad that it has a considerable impact on certain satellites, which simply begin to drop out of their orbits. And according to the agency, the situation will probably get worse in the short and medium term.
Normally, all objects in low Earth orbit tend to lose altitude over time. This is a consequence of friction with the few air particles still present in the very upper atmosphere. This is a well-known phenomenon (we speak of orbit decline) to which engineers know how to respond without too many problems. Very briefly, all you have to do is give a little boost to a specific point in the orbit to rectify it.
However, the agency spotted a strange dynamic on its SWARM swarm: some of the machines began to dive at a worrying speed. In recent years, satellites have been “sinking” at around 2 km per year. But between December 2021 and April 2022, this rate has largely increased; compared to one year, this now corresponds to a loss of altitude of 20km per year, according to the project manager interviewed by Space.com.
The solar wind, a plague for satellites
And you don’t have to look far to identify the origin of this phenomenon; the culprit is none other than our Sun itself. Indeed, the latter regularly emits streams of charged particles (we speak of plasma) in favor of solar flares. And the resulting solar wind also plays a very important role in the dynamics of satellites in Earth orbit.
Interactions between the Earth’s magnetic field and these particles can disrupt the atmosphere. The precise details of the phenomenon remain quite mysterious. But the researchers were able to observe empirically that the lower, denser layers of the atmosphere tended to rise temporarily once bombarded with plasma.
This results in an increase in the resistance to movement of the satellite, much like a cyclist riding with an increasingly powerful headwind. Result: it loses speed and, by extension, altitude. It is this phenomenon which is at the origin of the dizzying fall of ESA’s SWARM. During intense solar storms, they can sometimes fall too quickly for researchers to have time to correct their course.
The activity of the Sun is increasing visibly
It is no coincidence that this dynamic has accelerated in recent months. In effect, the intensity of this solar wind directly depends on magnetic field activity of the star. It is estimated by counting the number of sunspots.
This activity varies according to an 11-year cycle. And the current cycle just started quite recently. Officially, the Sun entered this new phase in December 2019. And since then, we have seen a very rapid increase the number of sunspots and associated geomagnetic storms.
The latter have already had some perceptible effects on Earth; we remember, for example, the few radio blackouts recorded during the Easter weekend (see our article). But above all, this means that satellites in very low orbit have much more difficult to maintain a viable trajectory in these conditions.
And unfortunately, this situation seems set to last. Indeed, we are only at the beginning of this 25th solar cycle (they are counted since 1755). And yet, it has already turned out to be much more intense than the researchers had anticipated.
If we look at the graph detailing these predictions, we can see that the number of sunspots today is almost at the expected level at the peak of cycle activity – while it is not supposed to occur before 2025…
The risk of a dramatic event
The other problem is that this increasing activity significantly increases the likelihood that Earth will experience a major geomagnetic storm. In this case, the main risk is no longer even the fall of the satellites; it is the survival of on-board electronics that is called into question.
Indeed, a particularly intense solar flare could easily fry a large part of the world’s electricity infrastructure (see our article). And since they evolve at the border – or completely outside – of the magnetosphere which protects the Earth, these satellites would then find themselves particularly exposed. With all that this implies for terrestrial communication networks.
A worrying situation in the midst of the space race
Engineers are therefore warned: they will have to make significant efforts to ensure the survival of their devices in low orbit. And no question of taking this warning from the Sun lightly, especially since the timing is far from ideal.
It has not escaped anyone, we are currently at the beginning of a new space race. And it’s not just SpaceX’s massive rockets that are making progress; the amount of satellites is also increasing at an exponential rate. However, among them, we find a whole bunch of cubesats, satellites perfectly adapted to this new commercial philosophy of space; they are ridiculously small, inexpensive, and only carry the bare minimum.
For this reason, many of them have chosen to switch entirely from propellant. These satellites are therefore small high-tech boxes that are placed in orbit, then left to fend for themselves. They are unable to correct their own orbit if they deviate.
So far, these craft have been able to benefit from favorable space weather; the start of this new space rush has indeed coincided with a very quiet period in terms of solar activity. But the closer we get to the 2025 peak, the more complicated the situation will become, especially for cubesats without thrusters.
Could the industry have been complacent and underestimated the impact of the sun? The future will tell. But even if this dynamic is worrying, its impact must also be qualified. This situation only concerns devices in very low orbit which evolve at the border of the Earth’s atmosphere, around 150km. More distant machines, such as SpaceX’s Starlinks, which are parked at an altitude of 550 km, should therefore escape it.
But as the situation settles down, there is still good news in this story. Because it is not only the satellites in operation that are influenced by the solar winds. This is also the case of the innumerable debris that pollute the Earth’s orbit.
In concrete terms, these solar storms therefore contribute to clean the orbit. And this is excellent news, knowing that the accumulation of this waste is among the most significant threats to the conquest of space on a large scale.