ISS Eclipse Determination

The document discusses the importance of determining sunlight exposure for satellites, particularly when designing space missions. It highlights the need to account for eclipses, where satellites may experience complete darkness, affecting thermal and power budgets. Using the International Space Station (ISS) as an example, it explains the concepts of umbra and penumbra in relation to sunlight and shadow. The author outlines how to calculate the ISS's orbit using Two-Line Elements (TLE) and the Julia package SatelliteToolbox.jl for orbit propagation. The document includes a function to determine sunlight exposure based on position vectors and the radii of the Earth and Sun. The sunlight function returns values from 0 to 1, indicating the percentage of sunlight received. A plot illustrates the ISS's sunlight exposure over a 24-hour period, showing that it receives sunlight approximately 62% of the time, with minimal time spent in the penumbra. The analysis suggests that while the ISS has a low orbit, other orbits may experience varying sunlight exposure depending on the time of year. Overall, the document combines astrodynamics concepts with practical coding examples to analyze satellite sunlight exposure.

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