It launched an advanced joint European-Japanese satellite to measure how clouds affect the climate.
Some low level clouds are known to cool the planet, others at high altitude will act as a blanket.
The Earthcare mission will use laser and radar to probe the atmosphere to see exactly where the balance is.
This is one of the big uncertainties in the computer models used to predict how the climate will respond to rising levels of greenhouse gases.
“Many of our models suggest that cloud cover will decrease in the future, and that means clouds will reflect less sunlight back into space, more will be absorbed at the surface, and that will act as an amplifier of the warming we would get from carbon dioxide,” Dr Robin Hogan of the European Center for Medium-Range Weather Forecasts told BBC News.
The 2.3-ton satellite was launched from California on a SpaceX rocket.
The project is led by the European Space Agency (ESA), which describes it as the organization’s most complex Earth observation effort to date.
Of course, the technical challenge of making the tools work as intended is enormous. It takes a full 20 years from mission approval to launch.
Earthcare will orbit the Earth at an altitude of about 400 km (250 miles).
In fact, there are a total of four instruments that will work in unison to get the information climate scientists are looking for.
The simplest is an imager, a camera that will take pictures of the scene passing beneath the spacecraft to give context to the measurements made by the other three instruments.
Earthcare’s European UV laser will see thin, high clouds and cloud tops below. It will also detect the tiny particles and droplets (aerosols) in the atmosphere that influence the formation and behavior of clouds.
Japan’s radar will look at the clouds to determine how much water they carry and how it precipitates as rain, hail and snow.
And a radiometer will sense how much of the energy falling on Earth from the Sun is reflected or radiated back into space.
“The balance between this outgoing total amount of radiation and the amount coming in from the Sun is what fundamentally drives our climate,” said Dr Helen Brindley of the UK’s National Center for Earth Observation.
“If we change that balance, for example by increasing greenhouse gas concentrations, we reduce the amount of energy going out compared to what’s coming in, and we warm the climate.”
Beyond the long-term climate outlook, Earthcare data will be used here and now to improve weather forecasts. For example, how a storm develops will be influenced by the initial state of its clouds, as observed by satellite days earlier.
The original scientific concept for Earthcare was presented by Prof. Anthony Illingworth of the University of Reading and colleagues in 1993.
He said it was a dream come true to see the satellite finally fly: “It has been a long and challenging journey with an amazing team of dedicated scientists and engineers from the UK and abroad. Together we have created something truly remarkable that will change the way we understand our planet.”
One of the key technical struggles was the space laser, or lidar.
Developer Airbus-France had a torrid time arriving at a design that would work reliably in the vacuum of space. A fundamental reconfiguration of the instrument was required, which not only caused delays but also greatly increased the final cost of the mission, which today is estimated at around €850 million (£725 million).
“These are not missions that you put in place to be cheap and quick, to solve small problems; this is complicated. The reason Earthcare has taken so long is because we want the gold standard,” said Dr Beth Greenaway, head of Earth observation at the British Space Agency.
Earthcare won’t have to collect its data for long. Flying at 400km means it will feel the drag of the residual atmosphere at that altitude. This will work to pull the satellite down.
“There is fuel for three years with a reserve of another year. Mainly its lifetime is limited by its low orbit and the drag there,” said ESA’s Dr Michael Eisinger.
Industrial development of Earthcare is led by Airbus-Germany, with the main chassis or structure of the spacecraft built in the UK. The UK also supplied the radiometer from Thales Alenia Space UK and the imager from Surrey Satellite Technology Ltd. GMV-UK prepared the ground systems that will process all the data.
The Japanese Space Agency (Jaxa), due to its strong interest in the mission, will follow its usual practice of giving the spacecraft a nickname – “Hakuryu” or “White Dragon”.
In Japanese mythology, dragons are ancient and divine creatures that rule the water and fly in the sky. This year, 2024, also happens to be the Japanese year of the Dragon, known as “tatsu-doshi”.
There is also a connection in the appearance of the satellite, which is covered in white insulation and has a long, trailing tail-like solar panel.
“Earthcare, like a dragon rising into space, will become an entity that predicts the future for us,” said Jaxa project manager Eiichi Tomita.