Obstruction Angle Measurement to Improve Star Sensor Availability Based on LAPAN-A3 Experience

Abstract

It is widely known that star sensor is the most accurate attitude sensor. Nevertheless, despite the good accuracy, star sensor becomes vulnerable when facing bright objects such as sun, earth, and moon. Event when not face directly, due to stray light from sun, earth or moon, star sensor reading can be obstructed. Based on LAPAN-A3 flight experience, this research studied availability of its star sensor due to stray light from sun and earth. From star sensor availability profile, the angle between sun or earth to star sensor when its availability decreased, later stated as obstruction angle, can be measured. The measured obstruction angle will be used for recommendations to improve star sensor availability for the next generation satellite. To achieve the objective, telemetry data from January 1st, 2017 until May 25th, 2019 are observed. The result shows that the obstruction of the star sensor occurred when sun angle 68° or earth angle 95°. Star sensor of LAPAN-A3 is located 60° from the Y+ axis to the Z-axis, this configuration will lead to 38% of time star sensor availability less than 0.95. The next LAPAN's satellite, LAPAN-A4, is designed has the same orbit as LAPAN-A3, hence based on this research it is recommended that the star sensor is located between 5° to 50° from the Y+ axis to the Z- axis to avoids obstruction from sun and earth. To accommodate off-nadir maneuver, the best configuration for star sensor is 27.5° from Y+ axis to Z- axis that will give roll ability up to 22.5° before obstruction occurs.