Future space missions, such as those involving formation flying of multiple satellites require high operational
autonomy mainly with the aim of reducing the operation costs and improving reactivity to sensed data. In particular,
stringent performance requirements envisaged precision formation flying cannot be achieved by currently
available technologies. One of the main challenges in achieving autonomy is the capability of fault management
without extensive involvement of ground station operators. This paper uses a second order nonlinear sliding
mode observer to detect actuator faults in the attitude control system of a satellite with four reaction wheels in
a tetrahedron configuration. A post-processing of residuals is required to isolate and reconstruct the faults in all
four reaction wheels. Furthermore, the control strategy needs to be reconfigured to recover faults. Simulation
results show that the proposed strategy can detect, isolate and reconstruct reaction wheel faults in the attitude
control system of a satellite.
This paper investigates the problem of fault tolerant cooperative control for UAV rendezvous problem in which
multiple UAVs are required to arrive at their designated target despite presence of a fault in the thruster of any
UAV. An integrated hierarchical scheme is proposed and developed that consists of a cooperative rendezvous
planning algorithm at the team level and a nonlinear fault detection and isolation (FDI) subsystem at individual
UAV's actuator/sensor level. Furthermore, a rendezvous re-planning strategy is developed that interfaces the
rendezvous planning algorithm with the low-level FDI. A nonlinear geometric approach is used for the FDI
subsystem that can detect and isolate faults in various UAV actuators including thrusters and control surfaces.
The developed scheme is implemented for a rendezvous scenario with three Aerosonde UAVs, a single target,
and presence of a priori known threats. Simulation results reveal the effectiveness of our proposed scheme
in fulfilling the rendezvous mission objective that is specified as a successful intercept of Aerosondes at their
designated target, despite the presence of severe loss of effectiveness in Aerosondes engine thrusters.