SpaceX’s attempt to reduce the reflectivity of Starlink satellites is working, but not to the extent that astronomers need.
Starlink satellites with an anti-reflective coating are half as bright as the standard version, he says Research published in The Astrophysical Journal. It’s an improvement, but still not good enough, said the team, led by astronomer Takashi Horiuchi of the National Astronomical Observatory in Japan. This one ‘DarkSatsAs they are called, they also continue to cause problems at other wavelengths of light.
The first batch of 60 Starlink satellites, launched in May 2019, raised concerns that large satellite constellations in low Earth orbit would interfere with astronomical observations. Indeed, this turned out to be the case, with Starlink satellites providing long-exposure photos of nearby galaxies and Come eat, for example. Astronomers, be aware of the problem described several ways the SpaceX satellites can confuse scientific research, including the operation of the upcoming Vera C. Rubin Observatory in Chile.
The first batch of Starlink satellites in orbit is brighter than 99% of objects in low Earth orbit. This is a big concern given Elon Musk’s desire to launch more than 12,000 Starlink satellites and possibly as many as 42,000. Starlink’s goal is to provide broadband internet to customers all over the world.
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Discouraging, remarks made by the SpaceX CEO in March 2020 seemed inconsistent with emerging reality, in which Musk claimed that Starlink “will have no impact on astronomical discoveries, zero.” However, he also said encouragingly that SpaceX would “take corrective action if it is above zero”. The company responded by deploying some DarkSats, in which Starlink satellites were given a darker coating to reduce albedo or reflectivity. These DarkSats, known as the Starlink-1130 version, are included in a series of satellites launched by SpaceX on January 7, 2020. The new study focused on evaluate the effectiveness of that dark coating.
To do this, Horiuchi and colleagues observed the satellites using the Murikabushi telescope at the Ishigakijima Astronomical Observatory. The team observed the DarkSats together with the original version, known as Starlink-1113, at multiple wavelengths of light. This telescope empowers scientists make simultaneous observations in the green, red and near infrared bands. The team also compared the brightness of the reflective objects to reference stars. In total, the team conducted four different observations from April to June 2020.
The scientists found that “DarkSat’s albedo is about half that of STARLINK-1113,” as they wrote in their paper. That’s quite an improvement on the visual spectrum, but still not great. In addition, there are problems persist at other wavelengths.
“The darkening paint on DarkSat certainly halves the reflection of sunlight compared to the regular Starlink satellites, but [the constellation’s] negative impact on astronomical observations persists, ”Horiuchi told Physics World. He said the softening effect is “good in the UV / optical region” of the spectrum, but “the black coating increases the surface temperature of DarkSat and affects intermediate infrared senses.”
A third version of Starlink should be even weaker. They are called ‘VisorSats’ and have a sun visor that ‘dims the satellites as soon as they reach their operational height’, according to to Sky and Telescope. SpaceX launched a number of 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 exhibit increased surface temperatures.
Horiuchi told Physics Globally, SpaceX should seriously consider raising the height of the Starlink constellation to further reduce the brightness of these objects. Star links are currently flipping heights reaching 340 miles (547 km). Compare that to OneWeb, a competitor to SpaceX, whose satellite constellation will orbit every 750 miles (1,200 km), and as a result will be significantly darker.
In January 2020, Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics and an expert on satellites, gave told I say “SpaceX is doing its best to fix the problem in good faith” and believes the company “can make the satellites fainter than what the naked eye can see.”
For the sake of astronomers around the world, I hope he is right on both counts.