There are more than 12,000 active satellites circling Earth at the moment, a growing figure that has nearly doubled in less than three years. This recent boom in the satellite industry has been a major headache for astronomers, with bright satellites appearing as streaks in telescope images of the universe and tarnishing views of the night skies.
A new paper reveals that satellite constellations are brighter than the recommended limits set forth by astronomers, with only one company adhering to the guidelines. The paper, appearing in the preprint server arXiv, compares the observed brightness magnitudes of satellite constellations in Earth orbit with brightness limits established by the International Astronomical Union’s (IAU) Center for the Protection of the Dark and Quiet Sky (CPS).
Nearly all the satellites were found to exceed the limit of +7 brightness magnitude, thereby interfering with observations of the cosmos. The brightest satellites belonged to Texas startup AST SpaceMobile, with its BlueWalker constellation exceeding a brightness magnitude of +2.
Saving our views of space
Due to more affordable access to space, the cost of launching satellites to orbit is at an all-time low. In response to the growing number of satellites, the IAU established its center in 2022 in an effort to ensure satellite constellations do not interfere with the study and enjoyment of the night skies.
Although there are no official regulations in place, the CPS established recommendations for maximum acceptable brightness for satellites orbiting below 341 miles (550 kilometers). The IAU established a maximum brightness of +7 magnitude for professional astronomy and below +6 magnitude as the aesthetic reference so it does not impact the public’s ability to stargaze without interference from satellites.
SpaceX’s Starlink constellation, which includes more than 8,000 satellites currently in orbit, is of major concern to astronomers due to its size and brightness levels. SpaceX has been working with the IAU and other astronomy groups to mitigate the effects of its satellites on astronomical observations after its satellites photobombed a number of telescope images. Early versions of Starlink satellites were at a brightness magnitude of around +3, but SpaceX’s modifications have decreased that number to +5 or +6.
The paper, however, does raise concern that although the Starlink Minis are four times larger than the new generation Starlinks, the Gen 2 Mini satellites orbit Earth at a lower altitude of 279 miles (450 kilometers). As a result, the mean apparent brightness of the newer Starlinks is greater despite the company’s mitigation efforts to decrease its satellite’s reflection.
The worst of the worst
SpaceX’s competitor, AST SpaceMobile, is the worst offender by far. The company’s BlueWalker satellites have an average apparent magnitude of +3.3, often outshining most objects in the night sky. The BlueWalker satellites boast an array that stretches across 693 square feet, the largest communications array ever deployed in low Earth orbit. AST SpaceMobile is seeking to build a constellation of 100 satellites.
While most companies violated the suggested guidelines, one company stuck to them. London-based OneWeb has 652 satellites in orbit with an average apparent magnitude of +7.85, meeting the adjusted limit considering their altitude of 745 miles (1,200 kilometers) above Earth’s surface.
The IAU’s center has only set forth suggestive guidelines so far, but it wants to expand its efforts to encourage governments and state officials to better regulate the booming industry. So far, the center’s calls have been largely ignored, suggesting regulations do need to be in place if we want to maintain our views of the skies.
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