HydroGNSS: ESA’s first Scout
HydroGNSS is ESA’s first Scout mission. Developed within ESA’s Earth Observation FutureEO programme, Scouts are small satellite missions that pave the way to innovative science in a quick and agile fashion, and complement ESA’s larger Earth Explorer research missions.
The new Scouts, which are inspired by the principles of New Space, are designed to deliver both innovative science and pioneering approaches to Earth observation. These small satellites deliver value-added science, either by miniaturising existing space technologies or by demonstrating new observing techniques.
Importantly, the overarching aim is to achieve all of this quickly and within a tight budget.
A mission is required to be completed within three years from kick-off to launch and under a budget of €35 million, covering the satellite and ground segment development, launch, and in-orbit commissioning.
Science data are provided by the industrial consortium as a service to both the scientific community and ESA.
HydroGNSS is the first of three Scout mission to be launched. The other two Scouts are NanoMagSat and Tango.
Four other candidate Scout missions (HIBIDIS, NAIAD, SIRIUS & Sova-S) are currently being studied.
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Scouting for water
The first Scout mission, HydroGNSS, is designed to advance our understanding of Earth’s hydrological cycle, deepening insight into natural processes and the impact of human activity on land and water systems.
The mission comprises two small satellites, each carrying a GNSS reflectometry instrument, flying in polar orbit at an altitude of 550 km and separated by 180 degrees.
Using signals reflected from Earth’s surface transmitted by the Galileo and GPS navigation constellations – a technique known as GNSS reflectometry – the satellites observe key climate variables, including soil moisture, wetlands and inundation, freeze–thaw dynamics in soil and permafrost, and above-ground biomass.
HydroGNSS has been developed by Surrey Satellite Technology Ltd.
The two satellites were launched on a SpaceX Falcon 9 on28 November 2025.
