Feasibility studies for the alignment of the Thirty Meter Telescope

The Alignment and Phasing System (APS) of the Thirty Meter Telescope (TMT) is an instrument that will be responsible for aligning the primary, secondary, and tertiary mirrors of TMT. The telescope and APS are modeled with a ray tracing simulation program. Various sets of initial conditions and alignment procedures are simulated, and results are compared to the image quality specifications for the telescope. A key factor in alignment quality is the rotation of the flat tertiary mirror (M3), which rotates to serve the science instruments. The procedures that use only APS measurements yield unacceptably large image diameters, while procedures that use measurements from APS and another WFS at a different location result in telescope alignments that produce acceptable image diameters at the 90% confidence level. These two-sensor procedures can separate M3 errors from errors on other mirrors better than APS-only procedures. However, APS-only procedures should be adequate for the restricted configurations of instruments available at first light. In general, APS-only procedures should also be capable of maintaining the alignment produced initially by the more complex two-sensor procedures.