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SpaceX launched a joint NASA-European environmental research satellite early Monday, the second in an ongoing billion-dollar project to measure long-term changes in sea level, a key indicator of climate change.
The first satellite, known as Sentinel-6 and named in honor of NASA climate researcher Michael Freilich, was launched in November 2020. The latest spacecraft, Sentinel-6B, was launched from California atop a Falcon 9 rocket at 12:21 a.m. EST.
SpaceX webcast
Both satellites are equipped with a sophisticated cloud-penetrating radar. By timing how long it takes beams to bounce back from the ocean 830 miles below, the Sentinel-6 satellites can track sea levels to an accuracy of about one inch while also measuring wave height and wind speeds.
The project builds on earlier missions dating back to the early 1990s that have provided an uninterrupted stream of sea level data.
That data indicates sea levels are slowly but surely rising, widely interpreted as evidence of global warming caused in large part by human industrial activity.
But in keeping with recent Trump administration policies aimed at scaling back climate research and the interpretation of such data, NASA did not directly refer to “climate change” or “global warming” in a Sentinel-6B pre-launch briefing Saturday.
In the press kit released by NASA for the first Sentinel 6 mission in 2020, the first item in a “need to know list” said the satellite would “provide information that will help researchers understand how climate change is reshaping Earth’s coastlines – and how fast this is happening.”
In the press kit for the Sentinel 6B mission launched Monday, NASA’s first “need to know” item said simply that “Sentinel-6B will contribute to a multi-decade dataset that is … key to helping improve public safety, city planning and protecting commercial and defense interests.”
Karen St. Germain, director of NASA’s Earth Science Division, did not directly mention climate change in the Saturday briefing, focusing instead on the practical importance of monitoring sea levels.
SpaceX 
“Sentinel 6B is the latest in a line of missions stretching over three decades, keeping an uninterrupted watch over our planet’s sea surface height, finding patterns and advancing our understanding of planet Earth,” she said.
She said the data provided by the Sentinel-6 satellites “underpins navigation, search and rescue and industries like commercial fishing and shipping. These measurements form the basis for U.S. flood predictions for coastal infrastructure, real estate, energy storage sites and other assets along our shoreline.”
The data, she continued, will help scientists “understand and predict coastal erosion and salt water encroachment into inland supplies of water that are used for agriculture, irrigation as well as municipal drinking water.”
Regardless of interpretation, the launch of Sentinel-6B went off without a hitch.
After blasting off from launch complex 4E at the Vandenberg Space Force Base, the Falcon 9 rocket’s first stage powered the vehicle out of the dense lower atmosphere, separated and flew itself back to a landing pad at the California launch site.
The upper stage then carried out two firings of its single engine before releasing the 2,600-pound Sentinel-6B into an 830-mile-high orbit tilted 66 degrees to the equator, the same orbit used by Sentinel-6A and earlier sea level-monitoring spacecraft.
Taking 112 minutes to complete one orbit, the solar-powered satellite will fly over locations between 66 degrees north and south latitude, covering 90 percent of the world’s oceans.
NASA 
Along with measuring sea levels, the new satellite also will monitor temperature and humidity in the lower atmosphere as well as the higher-altitude stratosphere using an instrument that measures atmospheric effects on signals broadcast by navigation satellites.
But the primary mission is monitoring Earth’s changing sea levels.
“The dynamic balance that persisted before the industrial revolution has been upset by the almost instantaneous combustion of huge reserves of carbon as our society has developed,” Craig Donlon, a European Space Agency project scientist, said before the first Sentinel-6 launch in 2020.
“We see evidence of this dramatic change in many different measurements … but they all point the same direction: the Earth is warming. And the greatest indicator of this Earth system imbalance is sea level rise.”
The Sentinel-6 satellites are the result of a collaboration between NASA, the European Space Agency, the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and the National Oceanic and Atmospheric Administration.
St. Germain said NASA’s share of the cost for both Sentinel-6 satellites came to about $500 million. The Europeans contributed a similar amount.
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