Climate change effects on the Earth’s water cycle and the availability of water on our planet are the missions of the first European Space Agency Scout mission.
Launched from Vandenberg SFB, the twin HydroGNSS smallsats were launched on November 28, 2025, as a payload within a SpaceX Falcon 9 rocket as a member of the Transporter-15 rideshare flight.
Surrey Satellite Technology Ltd. (SSTL), this missions prime, has received signals from the satellites, indicating that both of them are safely in their assigned orbits.around Earth.
A technique—GNSS reflectometry—finds these satellites, which orbit the Earth with 180 degrees of separation, capturing L-band signals from navigation systems, such as GPS and Galileo, and then transmit L-band microwave signals that change when reflected off the Earth’s surface. These signals are then compared with the signals received from the navigation satellite and uncover the valuable information about water cycle properties and more. These systems gather high-quality data and capture more detailed and definitive data from ground-based GPS-reflection sites, more accurately than has previously been available.
In order to accomplish these tasks, each of the HydroGNSS smallsats carry a zenith and nadir antenna that comprise a delay doppler mapping receiver. The received signals are processed into delay Doppler maps.
Simonetta Cheli, the ESA’s Director of Earth Observation Programs, said, “HydroGNSS marks an important milestone for this new family of rapid, low-cost, Earth observation missions, and we extend our thanks to the missions prime, SSTL. We look forward to seeing how HydroGNSS will employ reflectometry to deliver valuable insights into key, hydrological variables that shape Earth’s water cycle.”