Onboard wavelength calibration of the CubeSpec high-resolution spectrograph using a Fiber Fabry–Pérot Etalon

Abstract

CubeSpec is a 12U CubeSat mission designed to demonstrate high resolution spectroscopy from a compact platform, with launch readiness targeted for early 2027. Its cross dispersed echelle spectrograph requires an onboard calibration system that is very compact, mechanically robust, and sufficiently stable and precise to meet the mission’s spectral performance requirements. A fiber-based Fabry–Pérot (FFP) etalon provides an attractive solution due to its very small footprint and stable line spacing, though it demands careful thermal stabilization. CubeSpec employs a fiber-coupled LED continuum source to both illuminate the FFP etalon for wavelength calibration and to supply broadband light for order identification and flat-fielding. The light is injected into the spectrograph via optics mounted on the telescope’s secondary mirror. We describe here the design of the FFP calibration unit and its expected performance.