A satellite in low Earth orbit alternates between sunlight, when its panels generate power, and eclipse, when Earth's shadow blocks the sun entirely and every system must draw from the battery instead. This simulator lets you set the orbit's eclipse fraction, the spacecraft's continuous power draw, the battery capacity and the solar array's power rating, then watch the battery's charge level cycle up and down across several consecutive orbits. A well-matched battery and array settle into a stable repeating cycle; an undersized battery empties mid-eclipse and trips a power failure; an undersized array can't fully recharge the battery in the sunlit window it gets, so the peak charge visibly sinks a little further every orbit until the system fails anyway.