UK Scout climate mission HydroGNSS begins water cycle mapping from orbit

by Sophie Jenkins
London, UK (SPX) Nov 28, 2025

The UK has placed the twin HydroGNSS satellites into orbit to measure how water moves through the Earth system using signals from existing navigation satellites. The mission was launched on 28 November on a SpaceX rocket as the first Earth observation Scout mission for the European Space Agency, led by the UK with Surrey Satellite Technology Ltd in Guildford as prime contractor and supported by 26 million pounds from the UK Space Agency. The small-satellite mission is designed to deliver climate-relevant measurements at relatively low cost while building on UK industrial capability in satellite engineering and climate monitoring.

HydroGNSS will provide data on soil moisture, surface water extent, freeze or thaw state of land, and vegetation cover, all of which are key indicators in the global water cycle and in assessing climate change impacts. The measurements are intended to support weather and seasonal forecasting, flood and drought risk assessment, and planning for agriculture and land management. The satellites will also complement existing missions such as ESA's SMOS and Biomass and NASA's SMAP by adding additional coverage and revisit times using a different measurement technique.

The spacecraft employ GNSS Reflectometry, which records navigation signals after they reflect from the Earth's surface to infer geophysical properties. Because this technique does not rely on an onboard transmitter and can operate through cloud and over dark surfaces, HydroGNSS can collect frequent observations over land and ocean under a wide range of conditions. The two satellites fly in low Earth orbit with separation in longitude to increase temporal coverage of target regions.

Space Minister Liz Lloyd said: "The launch of HydroGNSS is yet another success story for British space innovation. Backed with government funding, this UK-built satellite will play an invaluable role up in space, helping tackle some of the most pressing environmental challenges we face on Earth.

"As we build the UK's space capabilities, groundbreaking missions like HydroGNSS demonstrate that Britain is at the forefront of space technology that delivers real-world impact for people and our planet."

Andrew Cawthorne, Managing Director, Surrey Satellite Technology Ltd, said: "It's a proud moment to see both HydroGNSS satellites successfully launched and sending back their first signals from orbit.

"This mission is a fantastic example of how the UK, working through ESA and with support from the UK Space Agency, is delivering world-class climate science from space. HydroGNSS represents SSTL's 75th and 76th satellites, launched in our 40th anniversary year, and showcases the strength and innovation of the UK's space industry at the heart of Europe's environmental monitoring efforts."

The satellites will deliver frequent, global measurements that feed into climate models and help researchers analyse the dynamics of the water cycle. The resulting data will be used to assess the impact of climate change on ecosystems, to inform agricultural planning, and to support disaster response in regions affected by droughts, floods, and other extreme weather events.

Paul Clements, Director of Operations at the Environment Agency, said: "Climate change means more frequent and severe environmental incidents across the UK. Now more than ever, we must harness cutting-edge technology to develop the tools we need to protect communities from flooding and other hazards.

"The launch of this new mission is a compelling example of how British leadership and expertise in space delivers real, tangible benefits to the public. The enhanced data it provides will significantly strengthen our flood forecasting and warning capabilities, enabling a more effective operational response to safeguard lives, property, and infrastructure."

HydroGNSS complements ESA's SMOS and Biomass missions and NASA's SMAP mission as part of a wider international effort to monitor and mitigate environmental impacts. By focusing on high-value science with small satellite platforms, the mission shows how this class of spacecraft can contribute to monitoring key climate variables and supporting policy and operational decision-making.

Simonetta Cheli, Director of Earth Observation Programmes at ESA, said: "As the first of ESA's Scout missions to launch, HydroGNSS marks an important milestone for this new family of rapid, low-cost Earth observation missions. It serves as a reminder of the maturity of the Earth observation sector in the UK and we extend our thanks to the mission's prime contractor, SSTL.

"The launch also represents a key step in the evolution of our FutureEO programme, where the Scouts embody a fast, agile, innovative and cost-efficient approach - complementing our larger Earth Explorer missions. We now look forward to seeing how HydroGNSS will employ GNSS reflectometry to deliver valuable insights into key hydrological variables that shape Earth's water cycle."

The mission also coincides with changes in UK civil space governance and investment. The UK Space Agency is scheduled to be integrated into the Department for Science, Innovation and Technology from April 2026, and the UK has agreed a 1.7 billion pound package for ESA programmes, taking total planned ESA investment to 2.8 billion pounds over the next decade.