Optical-to-NIR magnitude measurements of the Starlink LEO Darksat satellite and effectiveness of the darkening treatment

Abstract

Four observations of Starlink's LEO communication satellites, Darksat and STARLINK-1113, were conducted on two nights with two telescopes. The Chakana 0.6\,m telescope at the Ckoirama observatory (Chile) observed both satellites on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) using a Sloan r' and Sloan i' filter, respectively. The ESO VISTA 4.1\,m telescope with the VIRCAM instrument observed both satellites on 5\,Mar\,2020 (UTC) and 7\,Mar\,2020 (UTC) in the NIR J-band and Ks-band, respectively. The calibration, image processing, and analysis of the Darksat images give r\,$\approx$\,5.6\,mag, i\,$\approx$\,5.0\,mag, J\,$\approx$\,4.2\,mag, and Ks\,$\approx$\,4.0\,mag when scaled to a range of 550\,km (airmass $=1$) and corrected for the solar incidence and observer phase angles. In comparison, the STARLINK-1113 images give r\,$\approx$\,4.9\,mag, i\,$\approx$\,4.4\,mag, J\,$\approx$\,3.8\,mag, and Ks\,$\approx$\,3.6\,mag when corrected for range, solar incidence, and observer phase angles. The data and results presented in this work show that the special darkening coating used by Starlink for Darksat has darkened the Sloan r' magnitude by 50\,\%, Sloan i' magnitude by 42\,\%, NIR J magnitude by 32\,\%, and NIR Ks magnitude by 28\,\%. The results show that both satellites increase in reflective brightness with increasing wavelength and that the effectiveness of the darkening treatment is reduced at longer wavelengths. This shows that the mitigation strategies being developed by Starlink and other LEO satellite operators need to take into account other wavelengths, not just the optical. This work highlights the continued importance of obtaining multi-wavelength observations of many different LEO satellites in order to characterise their reflective properties and to aid the community in developing impact simulations and developing mitigation tools.

Accepted for publication in A&A, 10 pages, 10 figures, 3 tables

References in corpus (7)

• The 2.5 m Telescope of the Sloan Digital Sky Survey
• The Low Earth Orbit Satellite Population and Impacts of the SpaceX Starlink Constellation
• The VISTA ZYJHKs Photometric System: Calibration from 2MASS
• On the Impact of Satellite Constellations on Astronomical Observations with ESO telescopes in the Visible and Infrared Domains
• Mitigation of LEO Satellite Brightness and Trail Effects on the Rubin Observatory LSST
• First observations and magnitude measurement of Starlink's Darksat
• Concerns about ground based astronomical observations: quantifying satellites' constellations damages

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• A Report to ESO Council on the Impact of Satellite Constellations
• Characterizing the All-Sky Brightness of Satellite Mega-Constellations and the Impact on Astronomy Research
• Diffuse and specular brightness models applied to LEO satellites. Case study: The ONEWEB constellation