Fault-Tolerant Station-Keeping on Libration Point Orbits

This paper extends a linear quadratic regulator-based control scheme for station-keeping on libration point orbits to enable continued tracking in the event of thruster failure. In the first instance it is shown that by using an extended state observer the fault (as well as disturbances) can be measured and compensated for at each sampling period using continuous thrust. It is proved that this control yields asymptotic tracking to a small bounded region around the desired reference orbit in the presence of these uncertainties. In addition, it is demonstrated that by combining this method with a sliding mode or an adaptive control, asymptotic tracking can be achieved. An advantage of this method is that the required gain for asymptotic tracking of the sliding mode component is much smaller than traditional methods; the gain magnitude is required to be larger than the magnitude of the disturbance estimation error rather than the magnitude of the disturbance. A comparison of the controllers performance against an linear quadratic regulator control scheme is undertaken in an application to low-thrust station-keeping on a halo orbit in the Earth– Moon–spacecraft system in the presence of disturbances and various thruster faults.