ESA GNC Conference Papers Repository
Design and Development of ITU pSAT II: On Orbit Demonstration of a High-Precision ADCS for Nanosatellites
ITU pSAT II is the second student satellite project from ITU FAA Controls and Avionics Laboratory, which aims to design and on-orbit demonstrate a standardized bus and a novel ADCS for pico and nano sized satellites (1-10 kg) with multi objective applications. Main aim of this project is to demonstrate specific challenges and solutions for ADCS design for nanosatellites, which require a high precision, fault tolerant and reconfigurable control system. ITU pSAT II is scheduled for launch on 2012 Q3. In this paper, we review the ITU pSAT II design including the ADCS and the software/hardware in the loop test system of ITU pSAT II. ADCS of ITU pSAT II consists of three distinct hardware layers integrating sensors, actuators, and ADCS computer over the CAN bus. The sensor layer embeds a set of low-cost inertial and magnetic sensors, sun sensors, a GPS receiver and an in-house developed multifunctional camera/star-tracker. The actuator layer includes a redundant assembly of reaction wheels, magnetic torquer coils and an experimental set of ?PPTs(micro pulse-plasma thrusters). Embedded within the ADCS Computer is a filter which allows the asynchronous fusion of filtered sensor data with outputs from the orbit and attitude propagation algorithms. Propagation algorithms simulate the spacecrafts dynamical response (including effects of disturbances, and uncertainties in sensor and actuator models) and compare it with actual sensor data to improve accuracy of determination of spacecrafts attitude and orbit position. These filtered and fused state data is fed to a faulttolerant and reconfigurable control layer. The control layer is divided into different operation modes and associated control strategies depending not only on the actual spacecraft operation mode (such as de-tumbling or high-precision attitude control for image capturing) but also depending on the health-status of the individual sensors and the actuators. This paper presents development stages of ADCS of ITU pSAT II, focusing on estimation and control algorithms and hardware implementation suited for high precision attitude control for small satellites, and development of a testbed which simulates spacecraft dynamics and space environment. Specifically, we present a software and a hardware in the loop system, which integrates components of the ADCS with an in lab developed air bearing table to simulate attitude dynamics and Helmholtz Coil system to emulate earth's magnetic field. Overall architecture is suitable for testing under number of possible hardware failure scenarios and control modes, and compensates re-design process of the system, such as improving reliability of algorithms and re-selection of hardware components.