Purpose
The population of Earth-orbiting satellites is dramatically increasing with the advent of commercial satellite constellations that form global consumer communication networks. The impact of these satellite constellations on astronomy and the night sky depends strongly on the brightness of their constituent satellites, which is a complex function of time, attitude, orbital position, and wavelength.
In the optical, when observed well after sunset or before sunrise, satellites can reflect enough sunlight to be visible to the unaided eye. However, the impact extends out to longer wavelengths, with thermal emission at infrared wavelengths, and licensed and spurious emission at microwave and radio wavelengths.
Accurately predicting the location and brightness of a satellite for an observer or instrument on Earth is extremely difficult, and empirical observations are necessary to help build models of reflectivity and emission. The necessary preparations to observe satellites in order to constrain their brightness have significant overlap with the tools needed to avoid or model satellite contamination in astronomical observations. For more details, please see the Algorithms Working Group Report.
Of course, the impacts of hugely increased numbers of bright low-Earth orbit (LEO) satellites (LEOsats) are not limited to professional astronomical observers. There are a variety of different human traditions of astronomical observations and their uses, and humans have long relied on outer space to facilitate their life in the Earth system. This epistemic relationality extends beyond astronomy and can range from more traditional forms of navigation to current uses of satellite data to monitor climate change. All of these ways of knowing, importantly, can be impeded if the LEO is overwhelmed with light pollution and/ or space debris. For more details, please see the Community Engagement Working Group Report.
The SATCON1 workshop studied the situation one year ago, in mid-2020, with a focus on mid-latitude observatories utilized by North America-based astronomers working at optical and near-infrared (NIR) wavelengths. The two main findings were that lower-altitude (below 600 km) satellites are strongly preferred, and that various mitigations can help but not fully avoid the impacts of satellite trails on science from present and future astronomy facilities. The published report following SATCON1 (Walker et al., 2020a; hereinafter the SATCON1 Report) further detailed 10 recommendations, three of which were
