SUN DIRECTION ESTIMATION USING COARSE SUN SENSOR MEASUREMENTS CONSIDERING THE EARTH`S ALBEDO INTERFERENCE ON NANOSATELLITES

Sun sensors are used in almost all satellite missions as they are used for thermal, power budget calculations or to determine the sun direction for covering sensitive sensors as well as to estimate the attitude of the satellite. However, Coarse Sun Sensors (CSS) can be influenced by the light reflected from Earth. Earth’s albedo interference can cause anomalous Sun sensor readings. The mathematical model of the Sun sensor can include diffuse and specular reflections from Earth which represents the perturbed Sun sensor measurements. The Earth’s albedo is treated as noise and not predicted in most of the studies. The sun direction can be mathematically modeled comprising the albedo coefficients. However, if only the average albedo coefficient for the active areas is assumed to be 0.30 which is the number for the entire Earth, the model can over-correct the CSS which would be an undesirable result. Therefore, the position of the satellite and Sun in addition to the other parameters, which might affect the albedo coefficients such as clouds, should be considered. In this study, we present the preliminary results of the sun direction estimation using CSS considering the Earth’s albedo. The albedo interference is assessed by determining the rate of the maximum and albedo voltage outputs of the CSS in a simulation environment of a nanosatellite with rotational motion at low altitudes around Earth.