Overview of the control strategies for the TMT alignment and phasing system

In this paper we present the current status of control algorithm development for the Thirty Meter Telescope (TMT) Alignment and Phasing System (APS).We discuss ways to address the main challenges inherent in the active control of extremely large segmented telescopes: high complexity of the control problem, disentangling the aberrations on the primary, secondary and tertiary mirrors, and the tight requirements for residual errors. We also present preliminary APS performance estimates derived from simulations. In particular, our simulations show that the tomographic aberration disentanglement is only marginally useful for TMT alignment.