The Scout mission ESP-MACCS focusses on understanding and quantifying atmospheric processes in the upper troposphere and in the stratosphere. In particular, it will make observations in tropical and sub-tropical latitudes to observe gases such as water vapour, carbon dioxide, methane, ozone and nitrous oxide as well as aerosols – all of which play a key role in the greenhouse effect and climate change. The mission comprises three 12-litre CubeSats, each carrying thermal infrared spectrometer, as well as a visible near-infrared hyperspectral solar disk imager as a secondary instrument.