A Franco-US satellite is due for launch on Friday for a landmark scientific mission to survey nearly all water on Earth's surface to help scientists investigate its impact on climate.
The Surface Water and Ocean Topography (SWOT) mission will monitor the levels of oceans, lakes and rivers, including in remote locations.
SpaceX delayed the liftoff from California of a Falcon 9 rocket from Thursday to Friday to allow more time to review the source of moisture in two of the launcher’s booster engines.
Run by NASA and France's space agency CNES, the satellite is the result of 30 years of cooperation in the field and a symbol of a strong partnership between France and the United States.
Paris and Washington pledged last month to reinforce their cooperation in space, particularly on exploration and climate, during a visit by French President Emmanuel Macron to NASA headquarters alongside US Vice President Kamala Harris.
"We are so very proud to work with France," Harris, who chairs the White House's National Space Council, said, noting how the two countries have partnered on space exploration for more than 60 years.
"In this time, we have made great strides and yet in so many ways we are beginning a new journey together," she said.
Improve climate modelling
NASA says SWOT will survey nearly all water on Earth's surface for the first time.
It will improve weather and climate modelling, the observation of coastal erosion and help track how fresh and saltwater bodies change over time.
The 2.2-tonne SWOT mission will be put into orbit from Vandenberg Space Force Base in California atop a SpaceX Falcon 9 rocket.
The satellite's primary payload is an innovative instrument to measure the height of water called KaRin, or Ka-band radar interferometer. Its two antennas, separated by a big boom, create paralleled swaths of data.
With an "optimal" orbit of 890 kilometres (about 550 miles) above Earth, SWOT will "take in all the components that affect water levels such as tides and the sun," Thierry Lafon, SWOT project leader at the CNES said.
It will monitor water levels, surface areas and quantities at more than 20 million lakes with shores of more than 250 metres. The entire length of rivers more than 100 metres wide will also be observed.
Water management, flood and drought prevention will be improved, scientists said.
"We're going to get ten times better resolution than with current technologies to measure sea-surface height and understand the ocean fronts and eddies that help shape climate," said NASA Earth Science Division Director Karen St. Germain.
"It's like looking at a car number plate from space when before we could only see a street," Lafon added.
High stakes
The stakes are high. While the impact of major ocean currents such as the Gulf Stream is known, more local flows and eddies covering dozens of kilometres remain more of a mystery.
But they too affect sea water surface temperatures and heat transfer as well as the absorption by the oceans of carbon dioxide from the atmosphere.
SWOT has an estimated three-year lifetime, although Lafon said "nothing precludes the mission to last five to eight years". It is set to become the first satellite to make a controlled re-entry into Earth's atmosphere, reducing the amount of space debris, in line with the French space operations act.
Nearly 80 percent of the 400 kilos of onboard fuel will be used to that end.
SWOT's predecessor, TOPEX/Poseidon, launched in 1992, was also a Franco-US joint venture that measured ocean surface to an accuracy of 4.2 centimetres.
It aided the forecast of the 1997-1998 El Nino weather phenomenon and improved understanding of ocean circulation and its effect on global climate.
(with wires)
