Chance Johnson, Defence R&D Canada; Lauchie Scott, Defence R&D Canada; Stefan Thorsteinson, Defence R&D Canada
Keywords: NEOSSat,?Mega-constellation, satellite brightness, photometric measurement, SpaceX, Starlink, OneWeb,?Planet Labs, Flock, Dove,?light curve
Abstract:
To complement ground-based efforts to photometrically characterize the increasing LEO population that uses constellation-style architectures, this paper presents space-based photometric measurements of the OneWeb and Flock LEO constellations and compares them to photometric measurements of the Starlink constellation. Starlink is used as a photometric reference due to the large number of its constellation members, its simple solar panel and bus geometry, and that it is known to be bright – making space-based observing opportunities more frequent. Space-based photometric reference measurements of Starlink were collected by Canadas Near Earth Object Surveillance Satellite (NEOSSat) during a six-month observing campaign in 2020.?NEOSSat characterized 247 Starlink satellites using short duration ( < 4 minute) optical observation tracklets totalling more than 1400 observations. It was shown that a repeatable space-based light curve of the Starlink constellation can be produced by aggregating short duration tracklets of individual constellation members. All measurements were range-normalized to 1000 km removing range-dependent variations in their photometry and to enable future comparisons with other LEO space objects. After these basic reductions, the Starlink satellites exhibit magnitudes spanning Mv 4 12, with an average brightness of Mv 6.9 ± 0.2. A repeatable light curve in phase angle forming a V-shape with a minimum brightness cusp of Mv 7.5 at 90° phase angle is produced. It is shown that this V-shaped photometric behaviour is due to both a Starlink satellites phase angle and the degree to which the Starlink reflects earthshine toward the space-based observer. In this paper, the observations of the original Starlink constellation are further complimented with an additional 675 observations of Starlinks with solar reflection minimizing visors. It is shown that from a space-based perspective there is no noticeable change in the photometry of these satellites over most phase angles. A further 1400 observations of the OneWeb satellite constellation was later collected. The OneWeb satellites exhibit magnitudes spanning Mv 3 - 10, with an average brightness of Mv 7.4 ± 0.2, roughly half a magnitude fainter than Starlink. As the OneWeb constellation is 400 km above NEOSSats orbit altitude the elevations of the observations vary from -15° up to 30° above NEOSSats local vertical direction. This paper analyses the variations in OneWeb brightness as a function of elevation with respect to the space-based observer. Finally, a small sample of photometric measurements on a nanosatellite constellation (Planet Labs Doves) were acquired and compared to the larger Starlink and OneWeb satellites. The small number of Flock measurements (32) does not enable a general comparison of their photometric behaviour to the Starlink and OneWeb satellites, but their detected, range-normalized brightness span Mv 6 to 11 with an average brightness of Mv 9.3 ± 1.7. Date of Conference: September 14-17, 2021
Track: Non-Resolved Object Characterization