TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio-Studies) is a a ‘standards laboratory in space’, setting the ‘gold standard’ reference for climate measurements. Carrying a cryogenic solar absolute radiometer and a hyperspectral imaging spectrometer as well as a novel onboard calibration system, TRUTHS is designed to make continuous measurements of incoming solar radiation and reflected radiation to evaluate Earth’s energy-in to energy-out ratio.