Cryorad would fill an important gap in observations of the cryosphere through the direct measurement of low-frequency passive-microwave brightness temperatures using a novel broadband radiometer. From these novel measurements key parameters such as the temperature profile of ice shelves, sea-ice thickness and sea-surface salinity in cold waters can be determined to improve our understanding of key processes in the polar regions. The mission would complement the upcoming Copernicus CIMR, CRISTAL and ROSE-L missions.

ECO would measure the difference between incoming solar radiation and outgoing radiation, which defines Earth’s energy ‘imbalance’, and which fundamentally controls Earth’s climate system. It would be the first time that this imbalance has been measured directly and would help reveal the future trajectory of the climate decades earlier than relying on monitoring global temperature and sea-level rise, as is currently the case. The unique concept envisages a satellite constellation, each carrying four wide field-of-view radiometers to ensure unprecedented coverage, accuracy and stability.

Hydroterra+ would be placed in geostationary orbit, which is unusual for an Earth-science radar mission. From this fixed position above the equator, the satellite’s C-band synthetic aperture radar would deliver data twice a day over Europe, the Mediterranean and northern Africa to understand rapid processes tied to the water cycle and tectonic events in these regions.

Keystone would provide the first direct observations of atomic oxygen in the altitude range of 50–150 km using a unique combination of limb-sounding techniques. These measurements together with observations of composition, temperature and winds would allow scientists to study the processes that drive the variability and energy balance of the mesosphere-lower-thermosphere region of the atmosphere, also looking at the impact of solar cycles and space weather.