UK-led HydroGNSS launches as ESA’s first Scout mission

If you teach geography or physics, this is a moment to bring into class. On 28 November 2025, two small UK‑led satellites called HydroGNSS rode a SpaceX Falcon 9 from Vandenberg into orbit, becoming the first of the European Space Agency’s rapid‑turnaround Scout missions to fly. Their task is clear: listen for signs of water across Earth.

Built in Guildford by Surrey Satellite Technology Ltd and supported with £26 million from the UK Space Agency, HydroGNSS showcases the UK’s small‑satellite strengths. SSTL reports both spacecraft separated cleanly on SpaceX’s Transporter‑15 ride and began returning first signals a few hours later, marking the company’s 75th and 76th satellites in its 40th year.

What will these satellites measure? Soil moisture, areas where water is pooling or flooding, whether land is frozen or thawing, and how much vegetation is above ground. Those readings support weather forecasts, flood warnings and decisions on planting, grazing and irrigation. ESA frames this as a sharper picture of how water moves through our world in a warming climate.

Here’s the simple idea you can share with students. Navigation satellites such as GPS and Galileo constantly transmit L‑band radio signals. HydroGNSS carries two antennas: one listens to the direct signal from space, the other listens for the same signal after it has bounced off Earth’s surface. By comparing the two, scientists infer how wet or rough that surface is. Because L‑band radio passes through cloud and light vegetation, observations continue even in stormy conditions.

Coverage matters when rivers rise or soils dry out. With two satellites flying half an orbit apart, HydroGNSS aims to revisit most places every three to four days, fast enough to track changes after big weather events. Each pass produces a delay‑Doppler map - a pattern of the reflected signal that researchers convert into the numbers you’ll later see on maps and dashboards.

HydroGNSS joins, rather than replaces, the larger Earth‑observation workhorses. It works alongside ESA’s SMOS mission, which maps soil moisture and ocean salinity, and NASA’s SMAP mission, which delivers global soil‑moisture and freeze–thaw data. Using these missions together helps fill gaps and cross‑check results that feed into models and operational services.

There’s a wider policy story here. HydroGNSS is part of ESA’s FutureEO line for fast, value‑for‑money science missions. Just before launch, the UK confirmed a £1.7 billion package for ESA programmes, which takes its expected support to about £2.8 billion over the next decade - money that comes back to British labs and firms as contracts and skills.

Keep an eye on how UK space is organised too. The government plans to fold the UK Space Agency into the Department for Science, Innovation and Technology as a single civil space unit on 1 April 2026, with officials promising simpler decision‑making and clearer ministerial oversight of strategy, policy and delivery.

What does this mean on the ground? The Environment Agency says fresher, more frequent moisture and inundation data should strengthen flood forecasting and warnings - the kind of practical upgrade communities notice when rivers rise and roads close. That is why launches like this matter beyond the space sector.

If you run a classroom, you can model the principle with a torch, a foil‑lined tray and a card. Shine the torch to create a ‘direct’ beam, tilt the tray to send a reflection onto the card, then change the angle or gently ripple the foil to see how the brightness and shape shift. That changing pattern is the basic idea behind HydroGNSS, only using radio waves and careful maths.

Media‑literacy moment: today’s news started with a government press release. We cross‑checked those claims with ESA mission pages and SSTL’s engineering update to confirm the date, the launch vehicle, the twin‑satellite design and the first‑signals milestone. You can repeat that source‑checking exercise with your students.

What comes next is commissioning and calibration, then routine data flowing to forecasters and researchers. When the first maps arrive, we’ll translate them for classrooms - turning those radio echoes into stories about soaked fields, dry soils and safer flood response. That’s where space and school meet.