White light interferometry: a method for coarse phasing segmented telescopes without dedicated hardware

Current approaches for phasing of segmented space telescopes have required complex dedicated optics and mechanisms, such as Dispersed Hartmann sensors or grisms. These methods do not scale well as the number of segments increases. The broadband phasing approach used at the Keck Observatory does scale well and can work on space telescopes without the need for any additional hardware. We show that this method implemented as white light interferometry (WLI), using a standard imaging detector and filters, has a capture range limited only by the range of the segment actuators and can easily phase the mirrors to within the capture range of single wavelength phasing methods. An analysis of the Keck broadband phasing performance is presented and used to develop a formula for implementation of WLI on other segmented telescopes. As an example, a WLI implementation for the NASA Habitable Worlds Observatory telescope is developed and demonstrated via detailed wave-optics simulations. The implementation, performance and limitations of the proposed WLI method are discussed in detail in the paper.