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Francesco Sanfedino

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 SHORT BIOGRAPHY

Francesco Sanfedino was born in Mesagne (ITALY). He graduated in Aerospace Engineering at Politecnico di Torino in 2012. He took part of a double degree program with Politecnico di Torino and the Institut Supérieur de l’Aéronautique et de l’Espace (ISAE) in Toulouse with specialization in Automatic Control and Space Systems. He received his Master of Science in Aerospace Engineering with the thesis “Evolution of Eurostar E3000 AOCS” in 2015. He accomplished a Research Master in Automatic Control, Signal and Images Treatment with the Ecole Normale Supérieure (ENS) of Cachan in 2015. He started his PhD entitled “Experimental Validation of High Accuracy Pointing System” with the European Space Agency (ESA), ISAE and Airbus DS in a Networking/Partnering Initiative (NPI) in March 2016. His research areas include : structural dynamic modeling, micro-vibration analysis, guidance and control, system identification, Space systems.

 RESEARCH INTERESTS

Control of flexible structures

  • Dynamic modelling, Multi-body dynamics
  • Robust control
  • Experimental validations

Experimental Identification

  • Characterization of sensors and actuators
  • Model validation

Robust control of micro-vibrations

  • Modelling of micro-vibration sources
  • LOS robust stabilization
  • Experimental validations

 PhD SUMMARY

The micro-vibrations are the most detrimental problem for the high accuracy pointing performances of the future Science and Earth observation Space missions. Reaction wheels are generally the main source of micro-vibrations. Also other components, such as solar Array Drive Mechanism (SADM), antenna stepper motors, antenna trimming mechanism or chemical thrusters, can have a huge impact.

The degradations of the pointing performances are induced by the interaction between the excitation frequency of the perturbation source and the structural flexible modes of the spacecraft. These perturbations are generally of harmonic nature, i.e. they generate simultaneously several sinusoidal forces and/or torques with frequencies proportional to the fundamental frequency (e.g. the wheel rate).
There exist many ways to counteract the micro-vibrations but they are often impractical or present huge drawbacks : adapt the SADM rate profiles to avoid the excitation of structural modes (drawback : uncertainties on spacecraft modes), switch off the wheels during the mission phase (drawback : loss of the AOCS spacecraft control), etc. Passive isolators collocated with the source of micro-vibrations can efficiently filter the perturbations at high frequencies (typically > 100 Hz), but they introduce supplementary flexible modes in the middle frequencies (typically between 1 Hz and 100 Hz).
Active control solutions can then provide the suited level of micro-vibrations mitigation. The common practice is to employ a Cold Gas Micro Propulsion system that, however, involves considerable costs and weight.
The goal of the thesis is to propose an alternative active control system by meeting both the desired high pointing performances and the cost- mass/volume constraints.
The research activities have been driven towards both theoretical modelling of the micro-vibrations sources and validation of a robust control system for micro-vibrations on an experimental bench (in ESTEC AOCS/GNC laboratories). From the theoretical point of view the dynamics of the spacecraft and the sources of perturbations have been described thanks to new contributions to the Two-Input Two-Output Port Theory.
The same perturbations have then been used to feed the experimental bench for their active robust control : a system of piezoelectric Fast Steering Mirrors (FSM) coupled with high-bandwidth sensors has been conceived and validated in order to achieve the desired performances up to 100 Hz.

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