SpaceX Uses Sentinel-6 Satellite To Explore The Ocean

On November 21, SpaceX’s Falcon 9 rocket was launched from SLC-4E at Vandenberg Air Force Base in California, with the latest Sentinel-6 Earth remote sensing satellite. After completing the allotted time, the first stage of the rocket gently returned to the cosmodrome.

Sentinel-6 (Jason-CS) is part of Copernicus, the European Commission’s program for global, continuous, autonomous, high-quality, and wide-range monitoring of the Earth’s surface.

Roughly speaking, this is a space altimeter jointly developed by specialists from Europe (ESA, CNES, EUMETSAT) and the USA (NASA, NOAA). It is based on the legacy of the Eurosatellites Sentinel-3 (first launched in 2016) and CryoSat-2 (in 2010), US-French TOPEX / Poseidon (1992-2005), Jason-1 (2002-2013), Jason- 2 (2008-2019), and Jason-3 (launched in 2016).

Sentinel-6 is not one, but two identical satellites: Sentinel-6A Michael Freilich and Sentinel-6B, which were designed and assembled by a consortium of 58 companies operated by Airbus Defense and Space (FRG). The second is scheduled to launch in 2025. The first device is named after Dr. Michael Frailich (1954-2020), ex-director of NASA’s Earth Science Department.

“The earth is changing, and this satellite will help us better understand how this is happening. Changing earth processes affect sea levels around the world, but the impact on local communities is very different. International cooperation is critical to both understanding these changes and informing coastal communities around the world,” said Karen Saint-Germain, director of NASA’s Earth Science Division.

Mission goal

On average, the sea level rose 3.2 mm from 1993 to 2018, but there are regional differences in this trend. Using satellite data, scientists have confirmed that the average sea level rise is now twice as fast as it was at the beginning of the century.

Thanks to this project, humanity will gain new knowledge and clarify already known data on the role of the ocean in climate change. There will be a clearer understanding of how technogenic activities affect the “health” of the World Ocean.

Sentinel-6 will continue to measure ocean topography (including rivers and lakes) with the highest accuracy until at least 2030, something that has been done continuously since 1992.

The size of a small pickup truck, Michael Freilich’s Sentinel-6 will expand on a nearly 30-year, continuous set of sea level data collected from the ongoing collaboration of American and European satellites. The satellite’s mission will improve weather forecasts and provide detailed information on large-scale ocean currents to support shipping along coastlines.

These programs will help to track the formation of hurricanes (in dynamics, the wave height and wind speed are measured) and predict, in near real-time, the direction where storms may go. This is critical for the adaptation and assistance of coastal areas and small islands.

Equipment

The key payload of the vehicle, its “heart”, is the POSEIDON-4 altimeter, which scans the surface with a synthetic aperture radar. The design is adapted to alternate between SAR and LRM modes.

NASA Satellite ‒ Advanced Microwave Radiometer AMR-C. Water vapor in the atmosphere affects the rate at which the radar pulses travel, and hence the estimate of sea-surface height. AMR-C takes this pair into account to correct measurements.

Weight of Sentinel-6A ‒ 1191 kg (including 230 kg of fuel), dimensions ‒ 2.35 × 4.17 × 5.13 m. Power consumption ~ 891 W, power supply ‒ two Li-ion batteries 108 Ah each from solar panels with a minimum wattage of 850W at end of life (approximately 5.5 years). Data transfer ‒ 1200 Gbps / day, onboard storage ‒ 496 Gbps at the beginning of the mission. The orbit of the vehicle is low near-earth, polar, not sun-synchronous, altitude ‒ 1336 km with an inclination of 66°. It allows mapping 95% of the ice-free ocean every 10 days.

The USA also supplied a device for studying the atmosphere using the GPS radio eclipse method: Sentinel-6 will receive a signal from a GPS satellite, which passes tangentially through the atmosphere and is refracted along the way; the amount of refraction depends on the temperature and the concentration of water vapor. Due to this, the states of the atmosphere in the field of measurements can be found almost instantly.

The device also carries a French civilian system DORIS receiver and a set of LRA laser retroreflectors ‒ for determining the orbit and positioning with centimeter precision.

Sentinel-6 will be able to measure sea-level change with an accuracy of less than 1 cm, enabling scientists to plot the ongoing effects of global warming over long periods of time. And this, according to scientists, is an excellent indicator.

“This satellite is so good that we built it twice,” said project scientist Josh Willis of NASA’s Jet Propulsion Laboratory. He said that in 5 years, his successor, Sentinel-6B, would be launched into space.

“This is a huge deal for us climatologists because it means that we can look at the oceans for as long as 10 years continuously. And this is the first time we’ve been able to build two satellites in a row so that we can launch them back to back and capture a lot more information than we have been able to so far,” said Willis.

Even before the launch of an ultra-precise satellite, scientists were able to draw disturbing conclusions about sea-level rise. Josh Willis said that if in the 90s sea level rose by about 2 mm per year, now this figure has doubled. The reason for this is the greenhouse effect, 90% of the heat from which is absorbed by the ocean. Among the reasons for the rise in sea level, scientists cite such problems as the increase in the space of water molecules due to heating and the melting of glaciers.

Along with measuring sea level on the planet, the new satellite will also track temperature and humidity in the lower atmosphere, as well as in the stratosphere at higher altitudes, using an instrument that measures atmospheric effects on signals transmitted by navigation satellites. But the main mission is to monitor sea levels in 90% of the world’s oceans.

“The dynamic equilibrium that prevailed before the Industrial Revolution was upset by the almost instantaneous burning of huge reserves of carbon as our society evolved. We see evidence of this dramatic change in many different ways, but they all point to one thing: the Earth is warming up. And the most important indicator of this imbalance in the earth’s ecosystem is rising sea levels,” said Craig Donlon, project scientist for the European Space Agency.

You can see in detail how the satellite works in this ESA video: