Observations conducted by the Murikabushi Telescope of Ishigakijima Astronomical Observatory confirmed that dark coating can reduce satellite reflectivity by half. There are concerns that numerous artificial satellites in orbit could impair astronomical observations, but these findings may help alleviate such conditions.
Today's growing demand for space-based services has spawned a wave of satellite constellation projects which operate numerous artificial satellites in orbit. Since these satellites can shine by reflecting sunlight, the astronomy community has raised concerns about their potential impact on astronomical observations.
In January 2020, SpaceX launched "DarkSat," an experimental satellite with an anti-reflective coating, and asked astronomers to assess how much this coating can reduce the satellite reflectivity. Brightness measurements of artificial satellites have already been conducted, but until now, there was no verification that a dark coating actually achieves the expected reflectivity reduction.
The Murikabushi Telescope of Ishigakijima Astronomical Observatory can observe celestial objects simultaneously in three different wavelengths (colors). Comparing multicolor data obtained under the same conditions provides more accurate insight into how much the coating can reduce the satellite brightness.
Observations conducted from April to June 2020 revealed for the first time in the world that artificial satellites, whether coated or not, are more visible at longer wavelengths, and that the black coating can halve the level of surface reflectivity of satellites. Such surface treatment is expected to reduce the negative impacts on astronomical observations. Further measures will continue to be implemented to pave the way for peaceful coexistence between space industries and astronomy.
Quelle: SD
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Simultaneous Multicolor Observations of Starlink's Darksat by the Murikabushi Telescope with MITSuME
Abstract
In this paper, we present the SDSS g'-, the Cousins Rc-, and Ic-band magnitudes and associated colors of Starlink's STARLINK-1113 (one of the standard Starlink satellites) and 1130 (Darksat) with a darkening treatment to its surface. Using the 105 cm Murikabushi telescope/MITSuME, simultaneous multicolor observations for the above satellites were conducted four times: on 2020 April 10 and May 18 (for Darksat), and 2020 June 11 (for Darksat and STARLINK-1113). We found that (1) the SDSS g'-band apparent magnitudes of Darksat (6.95 ± 0.11–7.65 ± 0.11 mag) are comparable to or brighter than that of STARLINK-1113 (7.69 ± 0.16 mag), (2) the shorter the observed wavelength is, the fainter the satellite magnitudes tend to become, (3) the reflected flux by STARLINK-1113 is extremely (>1.0 mag) redder than that of Darksat, (4) there is no clear correlation between the solar phase angle and orbital altitude-scaled magnitude, and (5) by flux model fitting of the satellite trails with the blackbody radiation, it is found that the albedo of Darksat is about half that of STARLINK-1113. In particular, result (1) is inconsistent with previous studies. However, considering both solar and observer phase angles and atmospheric extinction, the brightness of STARLINK-1113 can be drastically reduced in the SDSS g' and the Cousins Rc band. Simultaneous multicolor–multispot observations of more than three colors would give us more detailed information regarding the impact of low-Earth-orbit satellite constellations.
