GigaBIT: design and analysis of a diffraction-limited balloon-borne telescope

Abstract

Balloon-borne systems are excellent platforms for astronomy observations, as they avoid major atmospheric distortions that hinder ground-based telescopes, while being significantly cheaper than space-based missions. Following the success of the Super-pressure Balloon-borne Imaging Telescope (SuperBIT) experiment, the University of Toronto, Princeton University, and StarSpec Technologies are collaborating on the development and flight implementation of the Gigapixel Balloon-borne Imaging Telescope (GigaBIT), a custom wide-field, diffraction-limited telescope and stabilization platform. GigaBIT houses a three-mirror anastigmat (TMA) telescope with a 1.2 m diameter primary mirror. The telescope is being developed in collaboration with Optiques Fullum and is scheduled for a test flight in 2027. It is designed to reach sub-0.15 arcsecond resolution over a 0.1 square degree field of view, while housing 14 selectable filters spanning near ultraviolet to visible wavelengths. Balloon-borne astronomy poses a unique combination of challenges that are not typically experienced by ground-based or space-based telescopes, including harsh thermal environments, significant gravity-induced deformations over a wide elevation range, mechanical vibrations, and disturbances caused by stratospheric winds at float altitude. These effects are further magnified for GigaBIT’s metre-class optics, requiring careful integration of optical, thermomechanical, and alignment considerations to achieve diffraction-limited performance. This paper presents the design of the GigaBIT telescope, including optical design and performance, thermomechanical modelling and optimization, and system-level alignment strategy in the context of the telescope’s wavefront error budget. We discuss detailed optical tolerancing and manufacturing strategies, the design of a tunable radiative thermal environment to minimize thermally driven wavefront error, the lightweighting and mechanical optimization of the primary mirror, and a multi-stage alignment strategy for ground integration and in-flight phases. We also highlight design strategies that are specific to balloon platforms, with the aim of informing future high-fidelity stratospheric astronomy missions.