Thirty Meter Telescope Alignment and Phasing System risk reduction studies and experiments

The Alignment and Phasing System (APS) of the Thirty Meter Telescope (TMT) will use Shack-Hartmann-type measurements to determine the relative alignment and shapes of the segments of the primary mirror (M1). These measurements are required to be made with minimal errors in order for M1 to act as a diffraction-limited mirror. As TMT commissioning time will be limited, full performance must also be achieved as quickly as possible. From the earliest stages of the design, the TMT APS team has therefore emphasized work that ensures that APS will work as well and as close to out of the box as possible and reduces the associated risks. We describe efforts on algorithm and software development, analytical studies and simulations, on-sky and laboratory experiments, and prototyping. We explain how they have affected the design of the APS hardware and software and why we are confident that this critical subsystem of TMT will achieve its goals.