Design and feasibility study of a scalable liquid mirror

Enabling tilt and imaging-while-slewing for ground-based liquid mirror telescopes would allow for very large-scale, low-cost mirror solutions. To explore how to accomplish this, our team has taken a systems approach leveraging optical, manufacturing, material, and modeling expertise to address the key technical challenges of creating a stable liquid surface. These technical challenges include maintaining optical quality surface figures while slewing and tilting, creating high optical reflectance concomitantly with controllable liquids, characterizing large-scale deformable optics, and manufacturing and scalability of proposed designs to greater than 50 m configurations. In this paper, we present both a solution framework as well as preliminary modeling results to demonstrate mirror feasibility for a ferrofluid, magnetically-actuated approach. In parallel with the overall telescope liquid mirror design effort, we discuss nanomaterial synthesis techniques for reflective ferrofluid as well as manufacturing development of a magnetically permeable metallic paraboloid shell with surface wicking structure and electromagnetic control coil arrays. The forces from the coils and capillarity from the wick establish the requisite control and stability to deliver required wavefront performance and maintain fluid stability. We share our initial model and small-scale coupon test results for baseline ferrofluid, wicking structure, and actuation inputs to demonstrate feasibility. We also outline next steps for our optical and ferrofluid modeling and material synthesis for a prototype 50 cm mirror we anticipate building in the near future.