Integration of an attitude control and power management subsystem for a modular satellite

In the recently years, nanosatellite are playing a more and more important role in our scientific research and many university are designing their own nanosatellite. This trend began in 1999, when California Polytechnic State University (Cal Poly) and Stanford University developed the CubeSat specifications to help universities worldwide to perform space science and exploration. Several companies have built CubeSats, including large-satellite-maker Boeing. However, the majority of development comes from academia, with a mixed record of successfully orbited CubeSats and failed missions.
Politecnico di Torino has also developed its own satellite which is called PiCPoT (Piccolo Cubo del Politecnico di Torino). The main goals of PiCPoT is to test commercial components (COTS) in space and collect data in the space environment. It contains several on-board cameras and telemetry system transmitting on either a 437MHz (9600 FSK AX.25) or 2440MHz (10Kbps GFSK, +/-125KHz deviation) link. PiCPoT was launched aboard on 26 July 2006. Unfortunately, according to mission control officials, the engines of the Dnepr rocket shut down 86 seconds into its flight. The rocket crashed down and all satellites on board were destroyed.
After that, Politecnico di Torino starts to design another nanosatellite which is the evolution of PiCPoT. The new project named Aramis and it proposed a new modular architecture. The advantages of this architecture are the following. Firstly, better reusability through modularity. Secondly, overcome the limited CubeSat size (practically limited to 10×10×30 cm3).
Aramis consist of two main parts. One is power management subsystem and another one is telecommunication subsystem. The main work of this thesis is to implement the attitude control system which is part of power management subsystem. In order to implement a precise attitude control system, the key point is to design a good motor control system.
To design the proper motor control system, this work made the following studies:
1. Analyze different kinds of motors and compare the difference between them. According to the requirements of project Aramis, choose the proper motor type. After that, a motor control system simulation was carried out to find out the details of working procedure. Then, explore two kinds of design strategies and figure out which one is fit for project Aramis.
2. Realize the motor control system in hardware level. To meet the requirements of project Aramis, the following functions have to be designed. Firstly, for the limitation of power bus, a voltage regulator is necessary. Secondly, in order to ensure the motor works in a safe state, the function of current measurement has to be implemented. Thirdly, to handle the speed of motor rotation, a speed control loop is designed. After this, the whole motor control system design is complete, and the system can be built.
3. Implement the motor control system in software level. Since the motor control system is controlled by the MSP430 microcontroller, it is required to study the architecture and functional units of MSP430. According to the needs of project Aramis, the details of timer and ADC12 are introduced. The basic operation data flow for motor control is finally described.