HP3-RAD: A compact radiometer design with on-site calibration for in-situ exploration

Abstract

Many processes on planetary bodies are driven by their respective surface energy balance, and while planetary climate is influenced by the dynamics of the atmospheric boundary layer, surface radiation drives the Yarkovksy and YORB effects on small airless bodies. In addition, insolation governs cometary activity and drives the dust cycle on Mars. The radiative flux received and emitted at the surface of solar system bodies is thus a fundamental quantity, which is driven by the reception of solar radiation in the visible wavelength band, while re-radiation primarily occurs in the thermal infrared. Knowledge of the relevant radiative fluxes enables studies of thermo-physical surface properties, and radiometers to measure surface brightness temperatures have been payloads on many missions. The HP3-RAD is part of the Heat Flow and Physical Properties Package (HP3) on the InSight mission to Mars. It is a light-weight thermal infrared radiometer with compact design. HP3-RAD measures radiative flux in 3 spectral bands using thermopile detectors. The 120 g device includes integrated front-end electronics as well as a deployable cover that protects the sensors from dust contamination during landing. In addition, the cover is simultaneously used as a calibration target. The instrument concept as well as its implementation will be described, and special emphasis will be put on technological challenges encountered during instrument development. Potential future improvements of the design will be discussed.