SpaceX’s attempt to reduce the reflectivity of Starlink satellites works, but not at the level required by astronomers.
Starlink satellites with an anti-glare coating are half as bright as the standard version, according to research published in The Astrophysical Journal. It’s an improvement, but it’s still not good enough, according to the team, led by astronomer Takashi Horiuchi of the National Astronomical Observatory in Japan. These “DarkSats“As they are told, it continues to cause problems at other wavelengths of light.
Launched in May 2019, the initial batch of 60 Starlink satellites caused concern that large constellations of satellites in low Earth orbit would interfere with astronomical observations. And indeed, that seemed to be the case, with Starlink satellites photobombingexposure photos of nearby galaxies and comets, e.g. Be alert to the problem, astronomers described different ways in which SpaceX satellites could mix scientific research, including process of the future Vera C. Rubin Observatory in Chile.
The first batch of orbiting Starlink satellites is brighter than 99% of objects in Earth’s low orbit. This is a huge concern, given Elon Musk’s desire to launch more than 12,000 Starlink satellites and possibly up to 42,000. Starlink’s goal is to provide broadband internet to customers around the world.
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Discouraging, comments made by CEO SpaceX in March 2020 seemed inconsistent with the emerging reality, in which Musk argued that Starlink “will have no impact on astronomical, zero discoveries.” Encouragingly, however, he also said that SpaceX “will take corrective action if it is above zero.” The company responded by implementing DarkSats, in which Starlink satellites were given darker coverage to reduce albedo or reflectivity. These DarkSats, known as the Starlink-1130 version, were included in a batch of satellites launched by SpaceX on January 7, 2020. The new study targeted evaluate the effectiveness of that dark coating.
To do this, Horiuchi and his colleagues observed satellites using the Murikabushi Telescope at the Ishigakijima Astronomical Observatory.. The team observed DarkSats together with the original version, known as Starlink-1113, at several wavelengths of light. This telescope allows scientists make simultaneous observations in the green, red, and near-infrared bands. The team also compared the brightness of the reflecting objects with the reference stars. In total, the team made four different observations from April to June 2020.
The scientists found that “the albedo of DarkSat is about half that of STARLINK-1113,” as they wrote in their paper. This is a decent improvement in the visual spectrum, but it’s still not great. Moreover, problems persists at other wavelengths.
“The dark paint on DarkSat certainly halves the reflection of sunlight compared to regular Starlink satellites, but [the constellation’s] the negative impact on astronomical observations still remains “, Horiuchi said Physics World. He said the attenuation effect is “good in the UV / optical region” of the spectrum, but “the black coating increases the temperature of the DarkSat surface and affects intermediate infrared observations.”
A third version of Starlink should be even weaker. Called “VisorSats”, they have a sunshade that “will dim the satellites once they reach their operational altitude.” according to Sky and Telescope. SpaceX released some VisorSats last year, but the extent to which their albedo is reduced compared to the original version is not yet known or whether these versions will have high surface temperatures.
Horiuchi said in Physics The world in which SpaceX should seriously consider raising the altitude of the constellation Starlink to further reduce the brightness of these objects. Starlinks currently orbit at Elevation reaching 547 km. Compare it to OneWeb, a SpaceX competitor whose the constellation of the satellite it will orbit 1,200 km (750 miles) and, as a result, be much darker.
In January 2020, Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics and a satellite expert, said I that “SpaceX is making a good faith effort to fix the problem” and that he believes that the company “can make satellites weaker than the naked eye can see.”
For the sake of astronomers around the world, I hope he’s right on both sides.