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The high-performance LQG tip and tilt controller implemented on the SPHERE AO system relies on a stochastic disturbance model of the combined effects of atmospheric turbulence, vibrations and windshake. Model parameters are periodically re-identified from AO telemetry and the controller is re-tuned accordingly. This modus operandi involves frequent updates of the controller while keeping the AO loop engaged. Because LQG is implemented in so-called state-space form, control switching is performed by simply loading new matrices and resetting the controller state (or a part of it) to zero. This results in possibly large transient bumps in both the control and residual phase trajectories. In a previous contribution, we proposed to mitigate these bumps by resetting the controller state to an appropriate non-zero value, which could be computed recursively by an additional RTC device called the control switching adapter. In this contribution, we introduce an improved implementation of the adapter with reduced computational complexity, and we evaluate its performance using SPHERE on-sky data. The results confirm that the adapter, when properly tuned, is indeed capable of effectively mitigating the amplitude of the bumps.

Bumpless SPHERE LQG tip/tilt control with the control switching adaptor