Scientists and agency officials preparing for next month’s launch describe the Sentinel-6B mission as a simple but indispensable act of continuity for climate monitoring. Sentinel-6 Michael Freilich, launched in November 2020 as a joint mission of NASA, NOAA, ESA, EUMETSAT and France’s CNES, was designed for a five-to-six year lifetime; its successor, an almost identical satellite designated Sentinel-6B, is slated to lift off from Vandenberg Space Force Base this November with operations expected to begin in early 2026 after the normal checkout and calibration period.

“The overlapping operations will allow us to ensure data continuity down to millimeter-level accuracy,” a NASA spokesperson said, underscoring why the twin-satellite arrangement matters. The Sentinel-6 series continues a multidecade record of precise ocean topography that began with TOPEX/Poseidon in the early 1990s and has been critical for quantifying the rate of global sea-level rise driven by melting ice and thermal expansion.

Sentinel-6B carries the same core instruments as its predecessor — a high-precision radar altimeter (Poseidon-4), a microwave radiometer to correct for the wet troposphere, precise orbit-determination systems including GNSS receivers, a Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system and laser retroreflectors. These instruments together measure the height of the sea surface relative to Earth’s center with remarkable accuracy, allowing scientists to detect long-term trends and short-term variability such as storm surge and El Niño-driven shifts.

“We rely on these satellites to separate natural variability from long-term trends,” said Josh Willis, a sea-level scientist at NASA’s Jet Propulsion Laboratory, noting that simultaneous observations from two healthy, interleaved platforms are the best insurance against gaps or unrecognized drifts in the record. During the planned handover period, the two spacecraft will fly concurrently and cross-calibrate, a process that helps identify and correct subtle biases that could otherwise masquerade as climate signals.

The data produced by Sentinel-6 missions are publicly available and feed everything from global climate assessments to operational services that warn coastal communities of flooding risk. That information also informs insurance models, port operations and national adaptation planning. “It’s not just a physics exercise,” said a spokesperson for NOAA. “These measurements translate directly into actionable intelligence for people living on coasts and for governments making long-term investments.”

The technical simplicity of launching a near-identical replacement belies the broader geopolitical and ethical stakes. As sea levels climb, low-lying nations and vulnerable communities face existential threats; accurate, continuous measurements help quantify those risks and hold policymakers accountable. The Sentinel-6 program — a transatlantic partnership — also illustrates how international cooperation in Earth observation can serve a common public good.

With a current target in November and a Falcon 9 expected to deliver the spacecraft to low Earth orbit from Vandenberg, mission teams are urging observers and researchers to watch for official launch timing updates. If all goes to plan, the twin satellites will keep the world's ocean-altimetry record seamless through the next decade, preserving an essential dataset for climate science and the societies that increasingly depend on it.