Doyle Hall, Omitron Inc.
Keywords: Satellite Constellations; Astronomy; Space Sustainability/Space Traffic Management (STM)
Abstract:
Several commercial organizations have recently launched or plan to launch constellations containing hundreds or even thousands of Earth-orbiting satellites. Such large constellations can adversely affect astronomical observations, especially wide-field imaging in the visible and near-IR spectral bands [1-3]. Several variables contribute to a constellations overall potential impact on ground-based optical astronomy. These can be divided into two broad classes: constellation parameters and observational system parameters. Constellation parameters include the total number of satellites, the magnitude and variability of the brightness of the individual satellites, as well as the constellations altitude and other orbital parameters. Observation system parameters include the modality (e.g., wide-field imaging, narrow-field imaging, spectroscopy, etc.), the observatory location, the time criticality of the measurements, the required exposure times, as well as the capability of the sensors to schedule and perform mitigations such as mid-exposure interruptions. A wide array of quantitative metrics have been developed to measure the impact of constellations on ground-based astronomy [1,2], including (but not limited to) the number of visible or illuminated constellation satellites above an observatory, their effective stellar magnitudes, their capacity and frequency of glinting in reflected sunlight, and their angular drift rates across sensor apertures and detector arrays. These quantities also can change significantly throughout astronomical twilight and nighttime periods, which increases the number of potential diagnostic metrics even further. This wide array of metrics reflects the multivariate nature of the task of analyzing potential light pollution from large satellite constellations.
Unfortunately, in the regulatory decision process to approve or grade new proposed constellations, such an overwhelmingly wide array of information can hinder or even prevent the decision making process. This study focuses on developing a single semi-empirical metric (or small set of metrics) designed to provide decision makers a summarized method of comparing the overall impact of different constellations, both current and proposed. For instance, the analysis formulates the statistically expected number of brighter-than-recommended satellites which summarizes the potential effect of a constellation on ground-based visible and near-IR observational modalities. This single metric incorporates the effects of constellation population, brightness, variability, altitude and other parameters. Specifically, it provides a measure of the average number of constellation satellites above a typical low-latitude observatory that are brighter than the currently recommended limit (as specified in [2]) and also within a user-selected angle of the zenith direction. For existing constellations, this metric is based on actual photometric brightness measurements, which are now available in a web-accessible database for many constellation satellites [4-6]. For proposed or planned constellations, a semi-empirical approach can be used, which estimates pre-launch satellite brightnesses by adjusting the observed brightnesses of existing analog satellites, scaling appropriately for differences in satellite sizes, orbital altitude, etc.
[1] O.P. Hainaut and A.P. Williams, Impact of Satellite Constellations on Astronomical Observations with ESO Telescopes in the Visible and Infrared domain, A&A, v.636, p.A121, Apr 2020.
[2] C. Walker et. al., Impact of Satellite Constellations on Optical Astronomy and Recommendations Towards Mitigations, SatCon-1 Workshop Report, NSF NOIRLab, Aug 2020.
[3] P. Seitzer, Large Constellations of LEO Satellites and Astronomy, The 2020 Technical AMOS Conference, Sep 2020.
[4] S. Karpov, et. al., Photometric Calibration of a Wide-Field Sky Survey Data from Mini-MegaTORTORA, Astronomical Notes, Special Issue: 15th INTEGRAL/BART Workshop, v.339, Jun 2018.
[5] A. Malama, The Brightness of OneWeb Satellites, arXiv 2012.05100, Dec 2020.
[6] A. Malama, The Brightness of VisorSat-Design Starlink Satellites, arXiv 2101.00375, Jan 2021.
Date of Conference: September 14-17, 2021
Track: Dynamic Tasking