ALMASat Attitude Control Hardware-In-The-Loop Simulations
- Paper number
IAC-06-C1.P.2.03
- Author
Prof. Paolo Tortora, University of Bologna, Italy
- Coauthor
Dr. Fabrizio Giulietti, University of Bologna, Italy
- Coauthor
Mr. Alberto Corbelli, University of Bologna, Italy
- Coauthor
Mr. Valentino Fabbri, University of Bologna, Italy
- Year
2006
- Abstract
ALMASat is the first educational microsatellite completely designed and manufactured in the aerospace laboratories of the University of Bologna, in Italy. Its bus, weighing about 12 kg, was designed in order to fulfil the requirements of a wide range of different payloads, in terms of available power, downlink data-rates, physical space and attainable pointing modes and accuracies. The attitude determination and control subsystem (ADCS), in particular, was conceived to provide the spacecraft with operational capabilities usually confined to larger spacecraft (belonging to the minisatellites or higher classes). ALMASat first prototype, to be inserted into orbit presumably by the end of 2006 using a DNEPR Launch Vehicle, will be three-axis stabilized in Earth-pointing mode. This nominal attitude will be first acquired and then maintained by making use of three orthogonal magnetic coils and a momentum wheel, whose axis will be kept aligned to the orbit normal. Attitude control laws required in each state of the whole attitude acquisition/maintenance sequence were entirely developed and tested in the Forlì labs of the University of Bologna. By making use of the Matlab/Simulink® development tool, orbital and attitude dynamics where simulated using realistic models. Furthermore, the attitude control hardware (H/W) was fully designed and manufactured in the academic environment. This development represented without doubt the most challenging step towards the in-orbit validation of the new spacecraft bus. Moreover, all components of the attitude control system represent single points of failures for the whole spacecraft. This rendered mandatory the full validation, by means of intensive ground testing, of both the flight software (S/W) and H/W. At this aim, two sets of Hardware-In-the-Loop (HIL) simulations were prepared and executed. In the first one, the attitude control laws were plugged in the microcontroller of the flight electronic board, and tested in conjunction with the spacecraft dynamical models represented by the Matlab/Simulink® environment. These simulations allowed the successful validation of the S/W conversion process, from the Simulink® environment to the IAR® C Compiler needed by the Atmel AVR Microcontrollers. Secondly, the momentum wheel, developed as part of the ALMASat program, was inserted in the simulation loop. In the beginning, its operational performance was tested making use only of a rotating platform (specifically designed to keep the rotational friction torque to a minimum). Afterwards, the momentum wheel was experimented in conjunction with the flight electronic board (for a further validation of the flight S/W) and the Simulink® environment (where now the momentum wheel simulation block was removed and replaced by the actual momentum wheel). The HIL simulations design methodology and the lessons learned by the whole ADCS design process are thoroughly described in this paper, along with a detailed analysis of the performance of the newly developed hardware.
- Abstract document
- Manuscript document
IAC-06-C1.P.2.03.pdf (🔒 authorized access only).
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