The goal of the project is to develop precision alignment techniques that can be applied to the ELT Prefocal Station (PFS). The PFS is an optical sensing subsystem of the ELT that will be used as a reference for aligning of the ELT telescope optics; consequently it plays a key role in defining the optical interface with the Nasmyth platform science instruments. The PFS includes three sensor arms that perform imaging and wavefront sensing using the starlight from the telescope; these sensor arms rotate around the optical axis to follow the apparent sky rotation during telescope observations.

The PFS is required to be self-referencing, which means that it will implement all necessary internal measurements and diagnostics to assure that it is well-aligned, without using external calibration or on-sky measurements.

The work in this project includes:

1. developing the framework for converting metrology measurements into usable alignment corrections for the PFS via coordinate transformations;
2. performing laboratory experiments (using laser trackers and other optical alignment instruments) to determine the measurement techniques and associated errors; and
3. combining the experimental data into the measurement framework to provide a quantitative assessment of the alignment accuracy and the remaining errors.