Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a planned joint venture mission between the European Space Agency and the Chinese Academy of Sciences. SMILE will image for the first time the magnetosphere of the Sun in soft X-rays and UV during up to 40 hours per orbit, improving the understanding of the dynamic interaction between the solar wind and Earth's magnetosphere. The prime science questions of the SMILE mission are: "What are the fundamental modes of the dayside solar wind/magnetosphere interaction? What defines the substorm cycle? How do coronal mass ejection-driven storms arise and what is their relationship to substorms?" As of September 2025, SMILE is expected to launch in 2026.

The mission will observe the solar wind interaction with the magnetosphere with its X-ray and ultraviolet cameras (SXI and UVI), gathering simultaneous images and videos of the dayside magnetopause (where Earth's magnetosphere meets the solar wind), the polar cusps (a region in each hemisphere where particles from the solar wind have direct access to Earth's ionosphere), and the auroral oval (the region around each geomagnetic pole where auroras most often occur). SMILE will also gather simultaneously in situ measurements with its two other instruments making up its payload – an ion analyser (LIA) and a magnetometer (MAG). These instruments will monitor the ions in the solar wind, magnetosheath and magnetosphere while detecting changes in the local DC magnetic field.

SMILE must reach a high enough altitude to view the outside edge of Earth's magnetopause and at the same time obtain good spatial resolution of the auroral oval. The chosen orbit is therefore highly elliptical and highly inclined (70 or 98 degrees depending on the launcher), and takes SMILE a third of the way to the Moon at apogee (an altitude of 121 182 km, i.e. 19 Earth radii or R_E).

This type of orbit enables SMILE to spend much of its time (about 80%, equivalent to nine months of the year) at high altitude, allowing the spacecraft to collect continuous observations for the first time during more than 40h. This orbit also limits the time spent in the high-radiation Van Allen belts, and in the two toroidal belts. SMILE will be injected into a low Earth orbit by a Vega-C launch vehicle from Kourou, French Guiana, and its propulsion module will bring the spacecraft to the nominal orbit with perigee altitude of around 5000 km.

The SMILE spacecraft consists of a platform provided by the Chinese Academy of Sciences (CAS) attached below a payload module provided by ESA. The CAS platform is composed of a propulsion and a service module, together with the two detectors (or heads) of the ion instrument. The payload module hosts 3 of the 4 scientific instruments and an X-band communications system. It was built by Airbus. The SMILE ground segment comprises the Chinese Academy of Sciences (CAS) ground segment and the European Space Agency (ESA) ground segment, which collaborate closely on this mission. The Ground Support System (GSS) and the Science and Application System (SAS) are two important components of the CAS ground segment. The SAS is tasked with fostering collaboration between CAS and ESA, designing effective frameworks to coordinate scientists in planning SMILE science operations.

Key instruments on board the spacecraft include:

Several working groups have been set up to help preparing the SMILE mission including

SMILE in-situ science working group is established to support the SMILE Team in ensuring that the mission science objectives are achieved and optimized, and in adding value to SMILE science. The in-situ SWG activity is centred on optimizing the design, the operations, calibrations planning, identifying the science objectives and opportunities of the in situ instrument package, including conjunctions with other magnetospheric space missions.