International satellite launches to extend measurements of sea level rise

A Falcon 9 rocket lifts off from Vandenberg Air Force Base with the Sentinel-6 Michael Freilich oceanography satellite. Credit: SpaceX

A European-built satellite with the unusual shape of a house launched into orbit Saturday aboard a SpaceX Falcon 9 rocket from California’s Central Coast, carrying a sophisticated radar altimeter to measure rising sea levels on our home planet.

The Sentinel-6 Michael Freilich observation satellite lifted off at 9:17:08 a.m. PST (12:17:08 p.m. EST; 1717:08 GMT) Saturday from Space Launch Complex 4-East at Vandenberg Air Force Base around 140 miles (225 kilometers) northwest of Los Angeles.

Flying toward the south-southeast, the 229-foot-tall (70-meter) Falcon 9 rocket hauled the satellite into orbit on SpaceX’s first mission from the West Coast launch site since June 2019.

Less than two-and-a-half minutes into the flight, the Falcon 9’s first stage booster detached and fired cold gas thrusters to flip around and fly tail first. A boost-back burn and entry burn by a subset of the rocket’s Merlin engines guided the Falcon 9 booster back toward Vandenberg.

The supersonic return maneuvers culminated in a landing burn by the rocket’s center engine. Four landing legs unfurled just before touchdown as the 15-story booster settled to a bullseye landing at SpaceX’s rocket recovery facility at Vandenberg Air Force Base about eight-and-a-half minutes after liftoff.

The successful landing marked the third time SpaceX has returned a Falcon 9 booster to the onshore landing site at Vandenberg, and the 66th recovery of a Falcon booster overall.

Here’s a replay of the Falcon 9 rocket’s launch from SLC-4E at Vandenberg Air Force Base, California, with the Sentinel-6 Michael Freilich oceanography satellite.

Continuing coverage:

— Spaceflight Now (@SpaceflightNow)

The rocket’s upper stage continued firing its single Merlin to reach a parking orbit around Earth, then reignited the engine for about 10 seconds to circularize its orbit before separation of the Sentinel-6 Michael Freilich satellite around 58 minutes after launch.

Live video from the Falcon 9’s upper stage showed the 2,628-pound (1,192-kilogram) spacecraft flying free of the rocket over the Indian Ocean.

The Sentinel-6 Michael Freilich satellite was built by Airbus in Germany and is the size of a small pickup truck. Sentinel-6 Michael Freilich carries a radar altimeter, a microwave radiometer, and instruments to precisely locate the satellite in orbit. Working together, the instruments will track changes in sea level down to a few centimeters.

The mission is a partnership between NASA, the European Space Agency, Eumetsat, and NOAA. The European Commission — the EU’s executive arm — and the French space agency CNES also provided support to the mission.

The Sentinel-6 Michael Freilich satellite is named for the former head of NASA’s Earth science division, who died of cancer earlier this year.

“Congratulations to everyone that made today’s launch of the Sentinel-6 Michael Freilich satellite possible!” NASA Administrator Jim Bridenstine tweeted. “A fitting tribute to an incredible trailblazer in Earth science.”

Ground teams at the European Space Operations Center in Germany received the first signals from the new oceanography satellite about an hour-and-a-half after liftoff, while the spacecraft sailed over a ground station in Alaska. Controllers confirmed the satellite extended its power-generating solar panels, and the spacecraft appeared to be in good shape in a first-look health assessment.

Initial data showed the Falcon 9 rocket placed the satellite into an orbit very close to the mission’s target altitude of 830 miles (1,336 kilometers). The launcher aimed to inject the spacecraft in an orbit inclined about 66 degrees to the equator, the same orbital plane where a predecessor oceanography satellite named Jason 3 flies.

Falcon 9 has landed! The brand new booster that launched the Sentinel-6 Michael Freilich oceanography satellite has returned to a bullseye landing on California’s Central Coast.

This marks the third landing of a Falcon 9 booster at Vandenberg.

— Spaceflight Now (@SpaceflightNow)

Rising sea levels are one consequence of climate change. Data from previous satellites show the rate of sea level rise is accelerating, according to mission scientists.

Sentinel-6 Michael Freilich is the next in a series of oceanography missions tracking sea level rise, beginning with the U.S.-French Topex/Poseidon mission that launched in 1992. The Jason 1, Jason 2, and Jason 3 satellites followed Topex/Poseidon, and an identical satellite to Sentinel-6 Michael Freilich named Sentinel-6B is planned for launch in 2025 to further extend the data record of sea level rise.

The Topex/Poseidon and Jason satellites have charted about 3.5 inches (9 centimeters) of global sea level rise over the last 30 years, said Remko Scharroo, Sentinel-6 project scientist at Eumetsat.

The cost of the two Sentinel-6 missions is roughly $1 billion, and was evenly divided between the U.S. and European partner agencies, according to Thomas Zurbuchen, head of NASA’s science mission directorate.

“It’s the satellite so nice we built it twice,” said Josh Willis, Sentinel-6 project scientist at NASA’s Jet Propulsion Laboratory.

“The record of global sea level rise actually goes back to the early ’90s,” Willis said. “What’s interesting about it is that you can see the rate of rise is actually increasing. In the ’90s, sea level was rising at about 2 millimeters per year. In the 2000s, it was more like 3 millimeters per year, and now it’s more like 4 or close to 5 millimeters per year. So we’re watching the rate of sea level rise increase right before our very eyes, and it’s satellites like this that allow us to do it.”

Artist’s concept of the Sentinel-6 Michael Freilich satellite. Credit: ESA/ATG medialab

Craig Donlon, Sentinel-6 mission scientist at ESA, said rising sea levels “threaten major cities with increased flooding, including New York, London, Amsterdam, Tokyo, and more. It’s estimated that about 2 to 3 million more people are exposed for every 1 millimeter rise in sea level.”

Sentinel-6 Michael Freilich is the eighth satellite to launch for the European Copernicus constellation, a fleet of orbiting sentinels observing Earth’s land surfaces, oceans, ice sheets, and atmosphere with radar, optical, microwave, altimetry, and spectral instruments. The European Commission manages the Copernicus program, with ESA providing technical expertise and coordinating development of the Sentinel satellites.

A primary goal of the Copernicus satellites is to collect data on Earth’s changing climate. The fleet is the most capable satellite program focused on Earth observation. Data from the Sentinel satellites are distributed worldwide free of charge.

“We see evidence of this dramatic change in many different measurements and events around the world, but they all point in the same direction — the Earth is warming,” Donlon said in a pre-launch news conference. “And the greatest indicator of this Earth system imbalance is sea level rise. That’s because it integrates the total impact of global warming. That’s dominated by the ice sheets melting, the thermal expansion of the sea water, and changes in terrestrial water storage.”

The Sentinel-6 Michael Freilich spacecraft carries a European dual-frequency Poseidon 4 radar altimeter that transmits signals toward the ocean surface more than 800 miles below the satellite. A receiver measures the time it takes for the signal to bounce off the ocean and return to the satellite.

A microwave radiometer provided by NASA measures atmospheric properties that can introduce minuscule effects on the travel time of the radar altimeter signal, allowing scientists to correct for the perturbations and obtain a more precise measurement of sea level.

Sentinel-6 Michael Freilich also carries instruments to help determine its exact location using GPS navigation signals, Doppler measurements, and laser tracking.

This chart illustrates the sea level rise observed by satellites since the early 1990s. Credit: NASA

The satellite will also measure wave height and derive wind speed estimates by observing the roughness of the ocean surface. It will cover about 95 percent of the world’s oceans every 10 days.

The unusual house-like shape of the spacecraft itself is also an important factor in its performance. Engineers designed it for simplicity, and its lack of articulating solar array wings and other structures “makes for a very stable satellite design, which is really important for a satellite altimeter mission,” Donlon said.

Sentinel-6 Michael Freilich will take its measurements with higher resolution than earlier satellites looking at sea level rise. That means the new satellite will be able to better see how rising sea levels are impacting coastlines.

Eumetsat will take over regular operations of Sentinel-6 Michael Freilich for its planned five-and-a-half year mission after it completes a three-day activation timeline.

Ground teams will maneuver Sentinel-6 Michael Freilich into position flying about 140 miles, or 230 kilometers, behind the Jason 3 satellite — which launched in 2016 — for about a year’s worth of cross-calibration to ensure the new spacecraft provides the same reliable data as its predecessor.

Sentinel-6B will replace Sentinel-6 Michael Freilich after it launches in 2025, extending the sea level rise data record through at least 2030.

SpaceX tentatively plans to reuse first stage that flew with the Sentinel-6 Michael Freilich mission Saturday on the company’s next launch of a NASA spacecraft from Vandenberg next July, NASA launch director Tim Dunn said in a recent interview with Spaceflight Now.

On that flight, a Falcon 9 rocket will launch NASA’s Double Asteroid Redirection Test, or DART, mission from Vandenberg. It will mark the first time a NASA science mission has launched on a previously-flown Falcon 9 booster.

DART is scheduled for launch in a window opening July 2021, allowing the probe to reach its asteroid target in late 2022. DART will intentionally crash into a tiny moonlet orbiting asteroid Didymos to test out deflection techniques that scientists could use to move an asteroid off a collision course with Earth.

Dunn said NASA’s Launch Services Program, which manages launch procurement and preparations for NASA science missions, has approved the rocket reuse plan for the DART mission, pending post-flight inspections and refurbishment on the booster after the Sentinel-6 Michael Freilich mission.

NASA has already approved launches of SpaceX’s Dragon space station cargo ships on previously-flown Falcon 9 boosters, and the agency earlier this year agreed to launch Crew Dragon astronaut missions on reused rockets beginning with the next SpaceX crew flight in March 2021.

One caveat to the booster’s future is its possible use as a backup for the SpaceX Crew-2 mission in March. Kathy Lueders, head of NASA’s human spaceflight directorate, said last week that the Falcon 9 first stage from the Sentinel-6 Michael Freilich mission could be a backup for the Crew-2 launch if problems arise with the primary rocket assigned to astronaut mission.

NASA and SpaceX have agreed to use the same booster for the Crew-2 launch that sent the Crew-1 mission toward the International Space Station on Nov. 15. That stage landed on a SpaceX drone ship in the Atlantic Ocean and returned to Cape Canaveral on Thursday with a lean after it apparently slid across the deck of the vessel in high winds or rough seas.

The booster otherwise appeared to be in good shape, and SpaceX offloaded the rocket from the drone ship for transport to a hangar at Cape Canaveral for inspection and refurbishment.

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