Abstract: The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter far-infrared (30-100 µm) double-Fourier Michelson interferometer designed to fly on a high altitude scientific balloon. The project began in 2011, and the payload was declared ready for flight in September 2016. Due to bad weather, the first flight was postponed until June 2017; BETTII was successfully launched on June 8, 2017 for an engineering flight. Over the course of the one night flight, BETTII ac…