ISS Eclipse Determination

The webpage discusses the importance of determining sunlight exposure for satellites, particularly in the context of mission design. It highlights how satellites, such as the International Space Station (ISS), experience periods of complete darkness due to eclipses, impacting their thermal and power budgets. The document explains the concepts of umbra and penumbra, using diagrams to illustrate how satellites in different orbits experience varying sunlight conditions. A focus is placed on the ISS's low orbit, which minimizes time spent in the penumbra. The author details the process of calculating sunlight exposure using Two-Line Element (TLE) data and the Julia programming language, employing the SatelliteToolbox.jl package for orbit propagation. A function named "sunlight" is defined to compute the fraction of sunlight received at any moment, returning values from 0 (complete darkness) to 1 (full sunlight). Results from the function are visualized in a plot, showing that the ISS receives sunlight approximately 62% of the time, with minimal time in the penumbra. The analysis suggests that while the ISS consistently receives sunlight, variations in sunlight exposure could occur in other orbital types due to seasonal changes. Overall, the document provides a technical overview of eclipse determination and sunlight calculations for satellites.

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