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

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