If you had to estimate how many Starlink satellites burn up in Earth's atmosphere each day, what number would you suggest? This isn't a trick question; SpaceX is currently deorbiting approximately one or two satellites daily, and as their constellation expands, this number is expected to increase significantly. The implications of this trend for our planet remain uncertain, according to renowned astrophysicist and space tracker Jonathan McDowell from Harvard University.
In a recent discussion with the science news site EarthSky, McDowell highlighted the staggering volume of Starlink satellites re-entering the atmosphere. He estimates that once the combined total of low Earth orbit constellations, including Starlink, reaches about 30,000 satellites, roughly five satellites could re-enter the atmosphere daily, assuming an average replacement cycle of around five years. This raises vital questions about the health of our planet and the potential onset of Kessler syndrome—a scenario where orbital debris collides, triggering a chain reaction that could render parts of Earth's orbit unusable.
While Starlink is not the predominant threat concerning the Kessler tipping point, McDowell acknowledges it remains a source of concern. He stated that active satellite maneuvers designed to prevent collisions are crucial in mitigating the risks associated with Kessler syndrome. However, the success of these maneuvers is uncertain, making this a significant concern for the future of space operations.
The current strategy for deorbiting Starlink satellites involves utilizing their thrusters to maneuver them into a low orbit, where they eventually experience atmospheric drag and burn up in what McDowell describes as an “uncontrolled but assisted reentry.” He emphasizes that a combination of intentional deorbiting and successful collision avoidance could help us avert the disastrous outcomes associated with Kessler syndrome.
Beyond the regular operations of Starlink, McDowell warns of the potential for freak accidents, such as solar storms or other significant radiation events that could incapacitate numerous satellites, resulting in increased space debris. He notes that if just one percent of the planned 30,000 Starlink satellites were to fail while in orbit, this could lead to 300 defunct satellites contributing to the debris problem, pushing low Earth orbit closer to a Kessler scenario.
McDowell points out that while Starlink's operations are worrisome, China's satellite initiatives pose an even larger threat. The orbital region most at risk of Kessler syndrome lies between 600 and 1,000 kilometers, which is already cluttered with remnants from old Soviet rocket stages. As more satellites are added to this region, the likelihood of a catastrophic event increases. Many of China's proposed constellations will operate in low Earth orbit at altitudes similar to Starlink, but some are planned for altitudes above 1,000 kilometers, where the risk of long-term debris accumulation is significant.
While the prospect of Kessler syndrome is alarming, McDowell raises another critical issue: the environmental impact of burning satellites upon reentry. The possibility of polluting our atmosphere with remnants from these satellites could be catastrophic. McDowell argues that if humanity fills the atmosphere with debris and adversely affects our climate, it could be more detrimental than simply reaching a Kessler syndrome scenario.
Research on the effects of increasing satellite reentries on our atmosphere is sparse, leaving a significant blind spot in our understanding. According to the US National Oceanic and Atmospheric Administration (NOAA), around 10 percent of aerosol particles in the stratosphere contain aluminum and other metals believed to originate from burned-up rockets and satellites. This percentage could rise to 50 percent as space launches and reentries continue to increase.
McDowell indicates that the current research findings are inconclusive, with opinions ranging from "this is too small to be a problem" to "we're already in trouble." This uncertainty is alarming, as there’s a growing possibility that we are inadvertently damaging the upper atmosphere. Various organizations are actively studying the consequences of regular satellite incineration, with concerns about potential climate change and other catastrophic impacts.
As SpaceX continues to expand its constellation, and other companies enter the low Earth orbit market, we must remain vigilant about the implications of increased satellite activity. The potential risks associated with satellite reentries and the looming threat of Kessler syndrome necessitate urgent attention from researchers and policymakers alike. If we fail to address these challenges, we may find ourselves facing dire consequences in the near future.
