BURSTThe European Space Agency’s upcoming FORUM mission is set to provide unique insights into Earth’s radiation budget, filling in a missing piece in the climate puzzle. The mission’s spectrometer will be the first space-based instrument to measure Earth’s outgoing radiation in the far-infrared part of the electromagnetic spectrum with unprecedented resolution and accuracy. New technologies were needed to make this possible – among these an on-ground calibration device developed by the National Metrology Institute of Germany PTB within a recent activity funded by ESA’s General Support Technology Programme. This device is used to calibrate FORUM’s onboard reference source and ensures the accurate operation of the spectrometer.