Smile factsheet

Name: Smile (Solar wind Magnetosphere Ionosphere Link Explorer)

Status: The mission’s Critical Design Review was successfully completed in 2023. Engineers are in the final stages of testing flight models of different parts of the spacecraft. The integration and testing of the entire spacecraft is planned to start towards the end of 2024.

Mission objectives: Smile will study Earth’s magnetic environment (its magnetosphere) on a global scale, building a more complete understanding of the Sun–Earth connection. It will do this by observing the flow of charged particles streaming out from the Sun into interplanetary space (the solar wind) and exploring how these interact with the space around our planet.

How is Smile unique?: Although numerous spacecraft observe the Sun and its effect on Earth's environment, these missions largely study localised processes and individual space weather events. Smile will be able to view the full Sun–Earth connection, filling a big gap in Solar System science.

Our understanding of the Sun–Earth connection has been limited by the financial and technical constraints of developing the multi-satellite missions needed to obtain a global perspective of Earth's environment. However, recent discoveries have shown that Earth's outer magnetosphere can be imaged another way, which will be utilised by Smile. The method is based on a process known as ‘solar wind charge exchange’ – a process detected through the X-ray light emitted when solar wind particles interact with neutral particles in Earth’s upper atmosphere. This technique has been successfully demonstrated by ESA’s XMM-Newton in recent years, and Smile will gather the X-ray data needed to apply it to Earth’s magnetic environment.

To complement this X-ray imaging, Smile will continuously image the auroras in ultraviolet, with the ability to observe non-stop for more than 40 hours for the first time ever. Such data have been missing since 2008 when NASA’s Polar mission stopped operations after its fuel was exhausted.

Furthermore, Smile marks the first time that ESA and China have jointly selected, designed, implemented, launched and operated a space mission.

Key question(s): Smile will address a key theme of ESA's Cosmic Vision 2015–2025: how does the Solar System work? Within this theme, Smile will specifically improve our understanding of space weather and solar storms – essential to protect both space-based technology and the lives of any humans in orbit around the Earth

More specifically, Smile will address three fundamental queries that remain unclear due to a lack of available data:

• What happens where the solar wind meets Earth’s magnetic shield?
• What causes magnetic glitches on the dark side of Earth?
• How can we predict the most dangerous space weather threats in advance?

Collaboration: Smile is a joint European–Chinese mission. ESA is responsible for the payload module (carrying the scientific instruments), the launch vehicle, one of the scientific instruments and part of the science operations. The Chinese Academy of Sciences (CAS) is responsible for three scientific instruments, the platform, and the mission and science operations.

Launch: Scheduled for launch in 2025 from Europe’s Spaceport in Kourou onboard a Vega-C rocket

Nominal mission lifetime: Three years to achieve its science goals

Orbit: Smile will be placed in a highly inclined, highly elliptical orbit around Earth

Development: Smile was selected from a pool of 13 potential missions that were proposed under a joint ESA-CAS call for mission concepts in 2015. The mission entered its study phase at the beginning of 2016 and has been in implementation since 2019, following adoption by ESA’s Science Programme Committee. During the implementation phase, the mission has been designed, developed and tested as a joint effort between ESA and CAS both in Europe and China.

Spacecraft: Smile is three-axis-stabilised, has one main 490-newton engine and weights 2.3 tons, including 1.6 tons of propellant to reach the scientific orbit after launch. The spacecraft has two deployable solar arrays. It carries two star trackers and twelve 10-newton thrusters for attitude control, and has two antennas to transmit telecommands, spacecraft housekeeping and science data to the ground station. In launch configuration, the payload module will be stacked atop the spacecraft platform and sit 3 m tall.

Instruments: Smile will make clear and quasi-continuous observations of key regions in near-Earth space with both remote-sensing and in situ instruments. The spacecraft will carry four instruments:

The UVI, SXI and MAG will be mounted on the payload module, with MAG’s sensors mounted 80 cm apart along a deployable 3-m-long boom. The two LIA sensors will be mounted on the main spacecraft platform. The four instruments together 

Legacy: Smile builds upon findings and studies by ESA satellites such as Cluster and XMM-Newton

Smile mission facts

Smile will gather up to 40 hours per orbit of continuous observations in soft X-rays and extreme ultraviolet wavelengths, including simultaneous images and videos.

When deployed, Smile’s solar arrays will have a combined area of 4.2 m².

Smile’s orbit will take it as far as 121 000 km from Earth above the North Pole (nearly one-third of the way to the Moon at most, and far enough from Earth to allow Smile to image the boundary of Earth’s magnetic field).

When the four 380-litre fuel tanks are full, the total weight of the platform-payload stack will be around 2300 kg.

The spacecraft assembly, integration and testing will take place at ESTEC, ESA’s technical heart in the Netherlands.

Smile will send down its science data mainly to a ground station located in O’Higgins, Antarctica, which is operated by the German Aerospace Center (DLR).