Shaping a gallium alloy and an ionic liquid into spherical mirrors for future liquid-based telescopes - Experimental setup and demonstration in parabolic flights

Space telescopes play a key role in the exploration of our universe, from imaging planets to gathering spectra of distant stars. To date, all space telescopes are manufactured on Earth and launched into orbit, with their size constrained by the diameter of the launcher's payload fairing. This approach sets a hard limit on the telescope light collection ability, which determines its resolution and contrast. The Fluidic Telescope (FLUTE) project proposes to overcome launch constraints through the in-space creation of large liquid mirrors by utilizing interfacial physics under microgravity conditions. We present the design of experiments for the creation and measurement of spherical liquid mirrors under microgravity and their successful execution in parabolic flights. We describe the design of the mechanical apparatus and experimental methods used to pin, constrain, and control liquid gallium alloy and ionic liquid, as well as the optical technique used to reconstruct their surfaces in situ using Shack-Hartmann wavefront sensing. The results validate our experimental approach and show that the surfaces obtained under microgravity are indeed spherical, as expected from theory, though parabolic flight conditions prohibit optical-grade liquid surfaces. This set of experiments is a key milestone in maturing the FLUTE approach toward future extremely large liquid space telescopes.