With ESA’s Space19+ Ministerial Council meeting set for November, a new satellite mission called TRUTHS will be added to the list of missions to be financed in the Earth Observation Earth Watch programme. The TRUTHS mission aims to establish an SI-traceable space-based climate and calibration observing system to improve confidence in climate-change forecasts – a kind of ‘standards laboratory in space’. It would carry a hyperspectral imager to provide benchmark measurements of both incoming solar radiation and outgoing reflected radiation with an unprecedented accuracy. These benchmark measurements would improve our ability to estimate radiative imbalance underlying climate change and, importantly, in a shorter time than is currently possible. Reference datasets from TRUTHS would also serve to calibrate other satellite sensors, such as those carried on the Copernicus missions.