SpaceX’s effort to reduce the reflection of Starlink satellites does not work, but not to the extent that astronomers need.
Starlink satellites with an antireflective layer are half as bright as the standard version research published in The Astrophysical Journal. According to the team led by astronomer Takashi Horiuchi of the National Astronomical Observatory in Japan, this is an improvement, but still not good enough. This “DarkSats, ”As they are called, also continue to cause problems at other wavelengths of light.
The initial group of 60 Starlink satellites, launched in May 2019, has raised concerns about large satellite constellations orbiting in low Earth would interfere with astronomical observations. And that seems to be the case, with Starlink satellites bombing for a long timeexposure shots of nearby galaxies and comet, for example. Warn about the problem, astronomers describe various ways in which SpaceX satellites can confuse scientific research, including the operation of the upcoming Vera C. Rubin Observatory in Chile.
The first group to orbit Starlink satellites is brighter than 99% of the objects in a low-Earth orbit. This is very worrying, 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 around the world.
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Discouraging, comment made by SpaceX’s CEO in March 2020, seems illegitimate with the emerging reality, in which Musk claims that Starlink ‘will cause no impact on astronomical discoveries, zero.’ Encouragingly, however, he also said that SpaceX “will take corrective action if it is above zero.” The company responded by using a pair of DarkSats, in which Starlink satellites were given a darker layer to reduce albedo or reflection. This DarkSats, known as the Starlink 1130 version, was incorporated into a number of satellites launched by SpaceX on January 7, 2020. The new study aimed to evaluate the effectiveness of that dark layer.
To do this, Horiuchi and colleagues observed the satellites using the Murikabushi telescope at the Ishigakijima Astronomical Observatory.. The team observed the DarkSats with the original version, known as Starlink-1113, at various wavelengths of light. With this telescope, scientists can make simultaneous observations in the green, red and near-infrared bands. The team also compared the brightness of the reflective objects with reference stars. The team made a total of 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. It’s a decent improvement in the visual spectrum, but still not good. What’s more, problems continue at other wavelengths.
‘The darkening paint on DarkSat certainly halves reflection of sunlight compared to ordinary Starlink satellites, but [the constellation’s] negative impact on astronomical observations remains, ”Horiuchi tell Physics World. He said the mitigating effect was ‘good in the UV / optical range’ of the spectrum, but ‘the black layer increases the surface temperature of DarkSat and affects intermediate infrared observations.’
A third version of Starlink is supposed to be even duller. They are called ‘VisorSats’ and have a sunscreen that will dim the satellites as soon as they reach their altitude. according to to Sky and Telescope. SpaceX introduced some VisorSats last year, but the extent to which their albedo is reduced compared to the original version is not yet known, and whether the versions have increased surface temperatures.
Horiuchi told Physics World that SpaceX should seriously consider raising the height of the Starlink constellation to further reduce the brightness of these objects. Star links are currently spinning heights 547 km reach. Compare that to OneWeb, a competitor of SpaceX, whose satellite constellation will orbit 1,200 km (11 km) and consequently be significantly darker.
Back in January 2020, Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics and a satellite expert, tell me that ‘SpaceX is trying in good faith to solve the problem’, and that he believes the company ‘can get the satellites fainter than the naked eye can see.’
For the sake of astronomers around the world, I hope he is right on both counts.