The sun goes through an 11-year cycle of activity, with the number of sunspots, along with the frequency and severity of solar storms, rising and falling over that span. Each cycle is a little different, making it difficult for space scientists to forecast.
One difference about the current solar cycle, set to peak around the middle of the decade, is its intensity. “The sun is far exceeding the consensus forecast,” said Scott McIntosh, deputy director of the National Center for Atmospheric Research, during the Space Weather Enterprise Forum conference June 22. He estimated solar activity was about 50% higher than that forecast, which expected a relatively quiet cycle like recent ones.
Much of the concern about solar activity revolves around space weather events like solar flares that can damage satellites and disrupt the terrestrial power grid. However, solar activity also heats and expands the tenuous upper atmosphere. That brings up another difference about this solar cycle: there are more satellites in low Earth orbit than ever before that can be affected by that activity.
The increase in solar activity is already impacting some satellite operators. In a June 8 earnings call, Planet said that two of its SkySat imaging satellites would reenter earlier than expected, forcing the company to accelerate depreciation of those spacecraft and lowering its margins. It blamed the early demise of the satellites on increased atmospheric drag from solar activity.
“What’s going on is that the sun has really an abnormal amount of activity,” said Will Marshall, Planet’s chief executive, in that earnings call. “Basically, all LEO satellite operators are facing this challenge, and this accelerated the end-of-life of these two satellites.”
Other satellite operators have not discussed similar issues with their spacecraft. BlackSky asked the FCC in May for permission to operate two of its imaging satellites in lower orbits than originally planned, stating that the satellites were running out of propellant even though they had yet to reach the end of their planned three-year lives. The company did not disclose what caused the spacecraft to run low on fuel.
The best-known problem involving satellites and space weather took place in February 2022, when SpaceX lost most of a batch of Starlink satellites shortly after launch. A solar storm increased the density of the atmosphere where the satellites were placed in a parking orbit, and their electric propulsion systems could not overcome the increased drag. A total of 38 of the 49 satellites reentered within days.
SpaceX has avoided similar problems since then, but space scientists remain concerned about the effects on satellites in LEO from a major storm or simply the overall increase in activity and thus atmospheric density. Delores Knipp, a research professor at the University of Colorado Boulder, noted at the Space Weather Enterprise Forum that major storms disrupted the Defense Department’s satellite catalog five times between 1967 and 2003 — and there are far more objects being tracked now than even in 2003.
“It’s kind of an unnerving position right now,” she said. “It’s looking a little dicey.”
She called for more research into that region of the upper atmosphere, called the thermosphere. “Our ability right now to be able to say what’s going on in the low Earth orbit environment is pretty limited,” she said. “We really need to put resources there.”
That’s unlikely to help with the current solar cycle, which may reach its peak as soon as next year. Increased atmospheric drag could lead to earlier reentries of satellites, requiring companies to replace them sooner than expected. That can disrupt business plans as companies spend more money to replace satellites, even as they are striving to reduce costs and reach profitability in a market where it is harder to raise funding.
There is, though, one silver lining to this increase in solar activity and atmospheric drag, helping tackle another problem companies are facing. The same increased drag bringing down satellites also affects orbital debris.
This article originally appeared in the July 2023 issue of SpaceNews magazine.
