Summary
NASA and international partners launched Sentinel-6B from California to continue high-precision measurements of Earth’s sea level. The satellite will support coastal flood predictions, marine weather forecasting and shipping safety.
NASA and its international partners have launched Sentinel-6B, a satellite designed to continue precise measurements of Earth’s changing oceans and sea level.
The satellite lifted off aboard a SpaceX Falcon 9 from Launch Complex 4 East at Vandenberg Space Force Base in California at 9:21 p.m. PST on Nov. 16, 2025. About 90 minutes later, a ground station in northern Canada established contact with the spacecraft. NASA’s Jet Propulsion Laboratory said all systems were functioning normally at that stage.
Sentinel-6B will eventually become the reference satellite for global sea-level measurements, continuing the work of Sentinel-6 Michael Freilich, which launched in 2020.
A new reference satellite for sea-level measurements
The Sentinel-6 satellites are part of the Copernicus Sentinel-6/Jason-CS mission, a collaboration involving NASA, the European Space Agency, EUMETSAT, the U.S. National Oceanic and Atmospheric Administration and the European Union. France’s CNES contributed technical support.
The mission uses radar altimetry to measure the height of the ocean surface. In basic terms, a satellite sends radar signals toward the sea and calculates surface height from the returned signal. Repeated measurements allow scientists to monitor sea-level differences across regions and over time.
When Sentinel-6B reaches its operating altitude, it will fly about 30 seconds behind Sentinel-6 Michael Freilich. The two spacecraft will first collect overlapping observations so their measurements can be cross-calibrated. After that process, Sentinel-6 Michael Freilich will move into a different orbit and Sentinel-6B will take over as the official reference satellite.
Sentinel-6B is planned to orbit about 830 miles, or 1,336 kilometers, above Earth and circle the planet roughly 13 times a day. NASA says the satellite will measure about 90% of the world’s oceans, with measurements precise to fractions of an inch.
The reference role matters because data from other ocean-observing satellites can be compared with Sentinel-6B’s measurements. That common standard helps maintain consistency across a long-running record of sea-surface height observations, extending a series that has monitored the oceans since the early 1990s.
How the measurements support forecasts
Sea-level measurements have uses beyond tracking long-term changes in the oceans. The observations provide a basis for U.S. flood predictions, which help inform decisions involving coastal infrastructure, real estate, energy-storage sites and other assets near the shore.
Sentinel-6B will also collect information about wind speeds, wave heights, atmospheric temperature and humidity. These measurements can contribute to marine-weather forecasting, including forecasts of hurricanes, which can intensify over warmer water.
Ocean-surface height also contains information about the physical state of the sea. Water expands as it warms, so higher sea-surface regions can indicate warmer water. Large ocean currents can also stand higher than surrounding water because of their temperature and dynamics. Measurements of these patterns can help researchers study interactions between currents such as the Gulf Stream and nearby waves, where rougher seas can create hazards for ships.
NASA says the resulting data will support coastal communities, commercial shipping and fishing, national defense, and emergency preparedness and response. The mission is also expected to provide information useful for safer atmospheric reentry, including future crews returning from Artemis Moon missions.
JPL contributed three science instruments to each Sentinel-6 spacecraft: the Advanced Microwave Radiometer, the Global Navigation Satellite System–Radio Occultation instrument and a laser retroreflector array. NASA is also providing launch services, ground systems and data-processing support for parts of the mission.
Sentinel-6B’s launch begins the transition to the next reference spacecraft. Its full operational role will follow the planned orbit adjustment and cross-calibration with Sentinel-6 Michael Freilich.