The staggering growth in Starlink collision avoidance maneuvers over the past six months is raising concerns about the long-term sustainability of satellite operations as thousands of new spacecraft are set to be launched into orbit over the next few years.
SpaceX‘S Stellar connection broadband satellites were forced to detour more than 25,000 times between Dec. 1, 2022 and May 31, 2023 to avoid potentially dangerous approaches to other spacecraft and orbital debris, according to a relationship SpaceX filed with the US Federal Communications Commission (FCC) on June 30. This is roughly double the number of avoidance maneuvers SpaceX reported in the previous six-month period from June to November 2022. Since the launch of the first Starlink spacecraft in 2019, SpaceX satellites have been forced to drift more than 50,000 times to avoid collisions.
The sharp increase in the number of maneuvers worries experts because it follows an exponential curve, leading to fears that the safety of operations in the orbital environment could soon get out of hand.
“Right now, the number of maneuvers is growing exponentially,” Hugh Lewis, a professor of astronautics at the University of Southampton in the UK and a leading expert on the impact of megaconstellations on orbital safety, told Space.com. “It’s doubled every six months, and the problem with exponential trends is that they get to very large numbers very quickly.”
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1 million maneuvers by 2028
Data collected by Lewis shows that, in the first half of 2021, Starlink satellites conducted 2,219 collision avoidance maneuvers. The number grew to 3,333 in the following six months to December 2021 and then doubled to 6,873 between December 2021 and June 2022. In the second half of 2022, SpaceX had to change the paths of its satellites 13,612 times to avoid potential collisions. In its latest report to the FCC, the company reported 25,299 collision avoidance maneuvers over the past six months, with each satellite moving an average of 12 times.
“Right now, every six months, the number of maneuvers that are done doubles,” Lewis said. “It’s increased by a factor of 10 in just two years, and if you project that, you’ll have 50,000 within the next six-month period, then 100,000 within the next, then 200,000 and so on.”
If the trend continues, by 2028 Starlink satellites will need to maneuver nearly a million times in six months to minimize the risk of orbital collisions. And Lewis doesn’t expect that growth to slow anytime soon. SpaceX has so far deployed about a third of its planned first-generation constellation of 12,000 spacecraft and has been launching more than 800 satellites annually at a steady pace, a trend that is expected to continue for the foreseeable future.
The first generation Starlink constellation is, however, only the beginning. The FCC has partially approved plans for the second generation Starlink constellation, which could consist of up to 30,000 satellites. And other players around the world, including Amazon with its Project Kuiper and China with Guowang, are scrambling to secure orbital slots with their respective regulators.
How to swerve on the highway every 10 meters
According to Joanne Wheeler, satellite regulations expert at Alden Legal and chair of the UK-based Satellite Finance Network, more than 1.7 million satellites have been registered with the International Telecommunication Union, the United Nations agency that oversees the use of radio frequencies by satellites. While not all of these plans are likely to come to fruition, the numbers involved are so high that experts like Lewis question whether order in orbit can be maintained.
“If we expect to have 100,000 active satellites by the end of this decade, then my suspicion is that the number of maneuvers all space operators collectively will be simply enormous,” Lewis said. “You’re doing maneuvers to mitigate high-risk events, but it’s like driving down the highway and swerving every 10 meters to avoid a collision. It’s probably not safe.”
There are currently about 10,500 satellites in orbit around our planet, of which 8,100 are operational, according to the European Space Agency. Things have only started to get so congested recently. For example, there were only about 2,300 active satellites circling the planet in 2019, according to Statesman. The main driver of the growth is Starlink, by far the largest satellite constellation ever assembled.
New satellites aren’t the only cause behind the growing need for orbital detours. The amount of space debris – defunct spacecraft, old rocket stages and various fragments – it also continues to grow, making it increasingly difficult for operators to keep their spacecraft safe.
SpaceX currently conducts an avoidance maneuver whenever orbital models show a greater than 1 in 100,000 chance of one of the Starlink satellites crossing the path of another object. That threshold is 10 times lower than the standard advocated by NASA and other international agencies.
Lewis, however, wonders if SpaceX will be able to maintain such a high standard as the number of “joining notices” continues to snowball. He adds that despite the company’s best efforts, the residual risk of a collision will also continue to increase.
Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and another often-heard cautious voice in the satellite mega-constellation debate, agrees with Lewis: “SpaceX is convinced it can handle the growing maneuvering load,” McDowell told Space.com in an email. “I’m not convinced that SpaceX has adequately accounted for non-statistical errors (the potential for independent, unpredictable failures that combine to give a bad result – a collision) – so I’m concerned that we’re operating on the edge of what’s safe. “
Starlink is based on an autonomous collision avoidance system that instructs satellites to maneuver based on models of the orbital trajectories of objects in space. These templates provide warnings several days in advance and may not always work properly. In addition, other factors, such as changes in the density of The earth’s atmosphere at high altitude caused by space weathermay affect the accuracy of these calculations.
“There is a concern about conjunctions occurring where no maneuvers are being made,” Lewis said. “You could argue that the probability [of a collision in these cases] is very low, but given their very large number, they represent a rather substantial risk. It’s like buying a lottery ticket. If you buy just one, you’re unlikely to win, but if you buy a million tickets, you stand a good chance.”
Lewis predicts that unless regulators limit the number of satellites in orbit, collisions will soon become a normal part of the space business. Such collisions would lead to a rapid growth in the amount of completely out of control pieces of space debris, which would lead to more and more collisions. The end point of this process could be the Kessler syndrome, a scenario predicted in the late 1970s by former NASA physicist Donald Kessler. Depicted in the 2013 Academy Award-winning film “Severity,” Kessler syndrome is an unstoppable cascade of collisions that could render parts of the orbital environment completely unusable.
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