SpaceX has launched the EarthCARE climate research satellite for ESA and JAXA

by William Graham

The joint European-Japanese EarthCARE satellite has begun its mission to improve our understanding of Earth’s climate Tuesday, with a launch atop a SpaceX Falcon 9 rocket. Liftoff from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California happened at 3:20 PM Pacific Time (22:20 UTC).

The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) is a joint project between the European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA), and the sixth Earth Explorer mission to be launched as part of ESA’s Living Planet Programme. The satellite, which has also been named Hakuryu — or White Dragon — by JAXA, carries four instruments that will study clouds and aerosols — fine particles and liquid droplets suspended in Earth’s atmosphere — and how these affect the planet’s climate.

By bringing a suite of different instruments together on one satellite, EarthCARE will be able to take different types of measurements that will complement each other, allowing scientists to build a better understanding of how clouds and atmospheric aerosols interact with solar radiation and how this affects the planet’s radiation balance – the difference between the energy that the Earth gains from the Sun and what it radiates into space.

Scientists have known for a long time that clouds have an impact on Earth’s radiation balance, both in terms of reflecting sunlight back into space and in absorbing heat that would otherwise have been radiated into space. The height and structure of the cloud, its water content, and the presence of different types of aerosol can alter the way in which it interacts with this system. By building a complete picture of the internal structure of clouds, EarthCARE will help to refine models used to predict changes in Earth’s climate.

The 2,200 kg EarthCARE satellite was developed by a multi-national consortium, with Airbus Defence and Space serving as its prime contractor. Power for the mission will be generated by a single deployable solar array, which is 11 m in length. The satellite is expected to operate for at least three years in a circular Sun-synchronous orbit at an altitude of 393 km and at an inclination of 97 degrees.

Development of the satellite began in 2008, with the signing of a contract between ESA and Astrium Satellites, which became part of Airbus in 2013. The four instruments were built separately before being shipped for integration with the rest of the spacecraft. Testing was carried out at the European Space Research and Technology Centre in the Netherlands, before final checkouts at Airbus’s facility in Friedrichshafen, Germany. In March 2024, the satellite was shipped to the launch site.

EarthCARE’s four instruments consist of an atmospheric LIDAR (ATLID), a cloud profiling radar (CPR), a multispectral imager (MSI), and a broadband radiometer (BBR). Atmospheric LIDAR (light detection and ranging) is used to measure the altitudes of cloud tops and aerosols. The instrument uses a laser, which emits 26-nanosecond ultraviolet pulses at a wavelength of 355 nm, and a 62 cm telescope as a receiver. Pulses from the laser will be transmitted into the atmosphere, where they will be scattered by particles and water molecules. Some of this will be reflected back towards the receiver, with the round-trip time used to calculate the altitude at which scattering occurred. Comparing the wavelength of the scattered light to the emitted light will also help to determine the type of scattering that occurred and, therefore, infer the type of particle that caused it to be scattered.

The ATLID instrument aboard EarthCARE was built by Airbus and has a mass of about 500 kg.

CPR will allow EarthCARE to penetrate clouds, collecting data on their vertical structure. This instrument is a major part of JAXA’s contribution to the mission and was built by Japan’s NEC Corporation. CPR will use millimeter-wave Doppler radar, broadcasting 3.3 microsecond pulses at a frequency of 94 gigahertz into the atmosphere. Signals that are scattered back are received using the instrument’s 2.5 m antenna. As well as allowing the internal structure of the clouds to be determined, studying how the signal has been Doppler-shifted will also enable measurements of the vertical motion of the cloud and elements of its structure.

Constructed by Thales, in the UK, BBR consists of three telescopes measuring the flux of radiation detected from the Earth. One of its telescopes points in the nadir direction — that is, directly downwards towards the Earth — while the others will target points along the satellite’s track that are ahead of and behind its current position. This allows observations of the same point to be made from three different angles as the satellite moves along its orbit.

Each telescope has a single mirror and a linear sensor. A rotating chopper drum alternates the telescope’s view between unfiltered light, a filter that only lets in short-wave radiation, and a constant-temperature surface to help maintain calibration.

The short-wave filter restricts BBR’s measurements to only radiation from the Sun that has been reflected by the Earth. Subtracting this value from the total reading without the filter will allow the amount of long-wave radiation emitted by the Earth itself to be calculated. These readings are important for monitoring the planet’s radiation balance.

MSI is an imaging system consisting of two individual cameras with a common electrical and control segment, developed by Surrey Satellite Technology Ltd in the UK. A thermal infrared camera operates in three different wavelength channels, while a second camera produces images in visible, near-infrared, and two short-wave infrared channels. Observations using MSI underpin the data from EarthCARE’s other instruments by providing context to the data collected by ATLID and CPR and spectral data to help calibrate BBR’s measurements. MSI has a resolution of up to 500 m, covering a 150 km swath of the Earth’s surface.

The EarthCARE satellite, pictured being removed from its shipping container after arrival at Vandenberg. (Credit: ESA)

EarthCARE will be launched by SpaceX aboard a Falcon 9 rocket, a two-stage vehicle consisting of a reusable booster and an expendable second stage. The launch will take place from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California.

The booster that was used for the EarthCARE mission is B1081.7, which made its seventh flight with this launch. B1081 first flew on Aug. 26, 2023, carrying Dragon Endurance on the Crew-7 mission to the International Space Station, following this up with the CRS-29 Cargo Dragon mission in November. After launching a group of Starlink satellites in December, its fourth launch carried NASA’s PACE satellite to orbit in February. B1081 was next used for the Transporter-10 rideshare launch in March, which marked its first launch from Vandenberg, before its most recent mission, another Starlink launch, on April 7.

ESA had originally selected the Soyuz rocket to deploy EarthCARE, with the launch to have been conducted by Arianespace from the Centre Spatial Guyanais in Kourou, French Guiana. Following Russia’s 2022 invasion of Ukraine, Arianespace’s partnership with Russia to carry out Soyuz launches ended, and the launch was moved to the new Vega-C rocket. This was then changed again in 2023 to Falcon 9, a decision which was made both because of delays following Vega-C’s failed launch in December 2022, and modifications that would have been required to its payload fairing to accommodate the EarthCARE satellite.

Falcon 9 flew a return-to-launch-site (RTLS) profile, with the first stage successfully coming back to land at Landing Zone 4 (LZ-4) close to the launch pad after completing its role in Tuesday’s mission. The ability to recover and reuse the first stage has contributed greatly to Falcon 9’s success: since its maiden flight in June 2010, it has already established itself as one of the most-flown rockets ever built. By some metrics, EarthCARE will mark the 350th flight or mission of the Falcon 9 and Falcon Heavy family: the former if 2020’s suborbital Crew Dragon In-Flight Abort (IFA) test is included in the count; and the latter if the 2016 Amos 6 mission, which saw the rocket explode on the launch pad during preparations for a static-fire test two days before the scheduled launch, is included instead.

Despite its high flight rate, Falcon 9 has also proven itself one of the most reliable rockets in service. Aside from Amos 6, it has only suffered one in-flight failure and one additional partial failure to date, and has made 320 consecutive successful launches since Amos 6 across the Falcon 9 and Falcon Heavy vehicles — the latter using two additional boosters burning in parallel with the first stage to enable it to launch heavier payloads into higher orbits.

Render of Falcon 9’s second stage and EarthCARE, at fairing separation. (Credit: ESA/P. Carril)

For Tuesday’s mission, the single-core Falcon 9 will be sufficient to place EarthCARE into its planned Sun-synchronous orbit, with enough performance left over to enable the booster’s return to the launch site. Falcon 9 uses RP-1 kerosene propellant with liquid oxygen (LOX) as the oxidizer. Propellant and LOX loading takes place during the final 35 minutes of the countdown, with the first stage’s nine Merlin-1D engines igniting about three seconds before the planned liftoff time, or T0. After lifting off, Falcon will fly a southerly course downrange.

The first stage will power the ascent for about two and a half minutes before shutting down, separating, and beginning its flight back to LZ-4. The second stage will light its Merlin Vacuum engine — a version of the Merlin optimized for use in space — to continue the mission. Shortly afterward, the payload fairing will separate from around EarthCARE at the nose of the rocket. The second stage will burn for a little over six minutes to reach EarthCARE’s planned orbit, with spacecraft separation coming around ten minutes after liftoff.

Once separated from the Falcon 9, EarthCARE will need to deploy its solar array and other key systems and begin on-orbit testing and commissioning before it can enter service.

(Lead image: Falcon 9 B1081-7 time-lapse image of the EarthCARE launch from Vandenberg Space Force Base. Credit: Pauline Acalin for NSF)

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