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Astronomy and Space Domain Awareness are limited by the size of available telescope optics, which in turn is related to the cost of exquisitely ground and polished primary mirrors. This creates the cost-size scaling “law” of optics: as the primary mirror gets larger, the cost grows polynomially, limiting mass manufacturing and proliferation. It is possible that liquid mirrors (LMs) may present a solution. When rotated at a constant angular velocity, fluid surfaces take the form of a light-focusing paraboloid with good optical quality. LMs therefore have the potential to break the cost-size scaling law and enable large-diameter optical surfaces. However, fundamental limitations remain. Traditional LMs can only point straight upward (to zenith) and are, therefore, limited in the imagery they can gather. Since the surface is a liquid, any out-of-plane movement disrupts the surface, causing spilling and rendering the imaging surface useless. Rotating machinery also adds complexity and are not scalable to very large mirror sizes. To address these limitations and enable low-cost, very-large-aperture telescopes, DARPA has launched its Zenith program. Zenith will investigate alternate LM designs and develop modeling tools, materials, surface shape controls, and structures to eliminate these limitations. The goal is to demonstrate a 2-m diameter liquid mirror telescope system (LMT) and a 1-m diameter segmented LM that require no liquid motion (rotation) to operate. Achieving Zenith goals will require unique approaches to maintaining good optical quality of a liquid surface in real time during slew and while tilted from the zenith axis. Software and simulation tools specific to liquid mirror performance modeling will be released to the astronomical community as an open-source repository at the conclusion of Phase I of the Zenith program.
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