Dark SpaceX satellites may still disrupt astronomy, new research suggests


Launch of SpaceX Starlink satellites on November 24, 2020.

Launch of SpaceX Starlink satellites on November 24, 2020.
The image: SpaceX

SpaceX’s attempt to reduce the reflectivity of Starlink satellites is working, but not to the degree required by astronomers.

According to the StarLink satellite standard version with an anti-reflective coating is half as bright, The research Published in The Astrophysical Journal. This is an improvement, but still not enough, according to the team, led by astronomer Takashi Horuchi from the National Astronomical Observatory in Japan. these “Darksat, “As they are called, continues to cause problems in other wavelengths of light as well.

Launched in May 2019, an initial batch of 60 Starlink satellites raised concerns that large satellite constellations in low Earth or orbit Will interfere with astronomical observations. And in fact, it appeared as if Starlink satellites had been photobombing for a long time –Exposure shots Galaxies nearby And Comet, for example. Problem-conscious, astronomer Described Different ways in which SpaceX satellites can involve scientific research, including operation The upcoming Vera C in Chile. Rubin Observatory.

The first group to orbit StarLink satellites is brighter than 99% of objects in low Earth orbit. This is a big concern, Elon Musk wishes to launch 12,000 Starlink satellites And possibly as many as 42,000. Starlink aims to provide broadband internet to customers around the world.

Discouraged, notes It seemed incompatible with the emerging reality created by the CEO of SpaceX in March 2020, with Musk claiming that Starlink “would not cause any effect in astronomical discoveries, zero.” However, enthusiastically, he also stated that SpaceX would “take corrective action if it is above zero.” The company has responded by deploying some DarkSat, in which Starlink satellites were given a darker coating to reduce albedo, or reflectivity. These darksets, known as the Starlink-1130 version, were included in a batch of satellites launched by SpaceX on January 7, 2020. Evaluate the effectiveness of that dark coating.

To do this, Horichi and colleagues observed satellites using the Murikabushi telescope at the Ishigkijima Astronomical Observatory. Team Overview of DarkSat Together The original version, known as Starlink-1113, At several wavelengths of light. This telescope allows scientists Observe simultaneously in green, red and near-infrared bands. The team also compared the brightness of reflective objects to refer to the stars. In total, the team made four separate 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 still not great. What’s more, problems Persists at other wavelengths.

“Darker colors on DarkSat certainly reduce the reflection of sunlight compared to normal Starlink satellites, but [the constellation’s] The negative impact on astronomical observations still persists, “Horuchi told Physics world. He said the spectrum’s quenching effect is “good in the UV / optical region”, but “the black coating increases the surface temperature of the darksat and affects the intermediate infrared observations.”

The third version of Starlink is also considered retarded. Called “VisorSats”, they have a sun visor that “satellites will dim once their operational height is reached”. accordingly For the sky and binoculars. SpaceX launched a few Vizoratas last year, but the degree of their albedo lowering compared to the original version is still not known, or if these versions will display elevated surface temperatures.

Horichi told Physics WorldX SpaceX should seriously consider lifting the height of the Starlink constellations to reduce the brightness of these objects. Starlinks currently revolves Heights Reaching 340 mi (547 km). Compare this to OneWeb, a SpaceX competitor whose Satellite constellation Would orbit 750 miles (1,200 km), and would result in a much deeper run.

Back in January 2020, Jonathan McDowell, an astronomer and expert on satellites at the Harvard-Smithsonian Center for Astrophysics, told I think “SpaceX is making a good-faith effort to fix the problem,” and he believes the company can “faint satellites that can see the naked eye.”

For astronomers around the world, I hope he is correct in both respects.

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