HydroGNSS at Surrey Satellite Technology facilities

ESA’s HydroGNSS Scout mission, which will investigate hydrological climate variables from space, is seen here at Surrey Satellite Technology Ltd (SSTL) facilities during the Flight Acceptance Review in June 2025. This set of tests meant the mission is a step nearer to launch.

The Flight Acceptance Review marked a milestone in the preparations of the two small spacecraft before they can be transported to the launch site in the US. The review is the final step in confirming that the satellites meet all mission and safety requirements, and is a significant achievement for the project team.

Here, members of the HydroGNSS team are pictured with one of the satellites.

The mission will provide measurements on water-related indicators such as soil moisture, freeze–thaw state over permafrost, inundation and wetlands, and above-ground biomass, using a technique called Global Navigation Satellite System (GNSS) reflectometry.

The mission consists of two microsatellites, both of which carry a GNSS reflectometry instrument in an orbit of 500-600 km, 180 degrees apart.

HydroGNSS has been developed by Surrey Satellite Technology Ltd (SSTL) for ESA’s Scout framework, part of the agency’s FutureEO programme. This new family of small ‘scout’ satellites are developed within short timeframes and deliver science data, either by miniaturising existing space technologies or by demonstrating new observing techniques.

Launch is expected in Q4 this year on a Falcon 9 rocket.