Design and Implementation of a Thermopile-Based Earth Sensor

Abstract

In recent years, microsatellites have attracted great attention for their low cost, rapid development, and utilization capability. Demand for more requirements is increasing, and reliable attitude control is indispensable for secure operation. An Earth sensor is typically used to detect the direction of Earth’s center relative to the spacecraft’s attitude. Unlike Sun sensors, an Earth sensor can be functional even in the eclipse region in orbit, which enables a spacecraft to determine its attitude regardless of orbital position. The thermopile-based Earth sensor developed in this research is designed to have full sky coverage, i.e., it is operational independent of satellite attitude. Therefore, it can be used in safe-hold-mode operation. As a result of this research, an Earth sensor is realized by utilizing multiple thermopile sensors. The geocentric vector can be determined from the output voltages of thermopiles that are mounted on the entire satellite in a distributed manner and pointed in different directions. In order to establish a data processing algorithm, the output voltage and angle characteristics of the sensors were investigated analytically and experimentally. A numerical model of the sensor was developed, and its performance in orbit was evaluated in a software-based simulation and verification environment.