SMILE mission fuelled ahead of launch: European-Chinese satellite sets out to investigate the Sun’s influence on Earth
The European-Chinese scientific mission SMILE has entered one of the most sensitive phases of preparation for liftoff after the spacecraft’s fuelling with fuel and oxidiser was completed on 20 March 2026 in French Guiana. This opened the way for the planned launch on the Vega-C rocket on 9 April 2026 from Europe’s Spaceport in Kourou, and the entire project is now moving from its multi-year development and testing stage into the final stretch before the start of the operational mission in orbit.
SMILE, fully named Solar wind Magnetosphere Ionosphere Link Explorer, is a joint mission of the European Space Agency and the Chinese Academy of Sciences. It is a project which, according to the plans of the scientific teams involved, should provide the most comprehensive insight so far into how Earth’s magnetic environment reacts to the solar wind, a stream of charged particles that constantly arrives from the Sun. Precisely because of this goal, SMILE is regarded in expert circles as one of the more important current missions for understanding space weather, a concept that is becoming increasingly relevant not only for astrophysics but also for the protection of satellites, communication systems, power grids and future human missions in space.
Why fuelling is such an important step
Fuelling a satellite in the space industry is not a routine technical procedure, but one of the most delicate operations of the entire launch campaign. In the case of the SMILE mission, according to ESA data, the spacecraft has four tanks, each with a capacity of 380 litres, and it is fuelled with hydrazine and oxidiser. Beneath the solar panels, those tanks create the recognisable, widened lower part of the structure. The total mass of the spacecraft is about 2,300 kilograms, of which as much as 1,580 kilograms is propulsion fuel needed for the satellite to reach its working orbit after separation from the rocket.
That alone already shows how great an energy demand is envisaged for this mission. SMILE, namely, will not remain in the simple low orbit into which the Vega-C rocket will place it. On the contrary, after the initial insertion into a circular orbit about 700 kilometres above Earth’s surface, the spacecraft must gradually change trajectory through a series of precisely planned manoeuvres. ESA states that during the first 25 days, 11 firings of the main engine will be performed, during which about 90 percent of the total fuel will be consumed. The main engine develops a thrust of 490 newtons, and precisely those manoeuvres will be crucial for transforming the orbit from the initial, relatively low and stable path into a highly elongated scientific orbit.
Because of the dangers involved in working with hydrazine, only a small number of specially trained experts remain in the fuelling hall during the operation. They wear SCAPE suits, an acronym for Self-Contained Atmospheric Protective Ensemble. Those suits resemble astronaut equipment, but they serve to protect against extremely toxic and explosive fuel. According to ESA’s explanations, exposure to hydrazine can cause serious damage to the brain, blood, lungs and skin, which is why strictly controlled safety protocols are applied during the procedure, from the preparation of connections and equipment to the final pressure stabilisation of the system.
An orbit that was not chosen by chance
The special feature of the SMILE mission lies not only in its instruments, but also in its orbital geometry. After a series of manoeuvres, the satellite should reach an altitude of about 121,000 kilometres above the North Pole, and then descend to approximately 5,000 kilometres above the South Pole, with one orbit lasting about two days. Such a highly inclined and elliptical trajectory was not chosen for spectacle, but because it enables scientists to view key regions where the solar wind affects Earth’s magnetosphere.
Earth is constantly exposed to streams of charged particles and occasional stronger eruptive ejections of material from the Sun. Most of that impact is absorbed by the magnetosphere, a vast magnetic shield that deflects or stops a large portion of the particles before they reach the atmosphere and the surface. The problem is that the processes at the boundary between the solar wind and Earth’s magnetic field are difficult to observe as a unified whole. Previous missions have mostly recorded local processes or individual events, whereas SMILE, according to ESA, aims to provide a global picture and connect multiple levels of the same phenomenon: from changes at the very boundary of the magnetosphere to the aurora and changes in the upper layers of the atmosphere.
That is precisely why the spacecraft must go far enough away to be able to “see” the sunward-facing edge of Earth’s magnetic shield. From a great distance above the North Pole it will be able to image regions such as the bow shock, the magnetopause and the polar cusps, while during its approach to the southern hemisphere it will focus on transmitting data to ground stations. According to official information, the bulk of the scientific data should be sent via the Antarctic O'Higgins station, operated by the German DLR, and the Sanya station in China.
What SMILE will actually measure and image
The mission carries four scientific instruments, and their combination is one of the reasons why the project is considered technologically and scientifically ambitious. Two instruments are intended for remote imaging, and two for measurements directly around the spacecraft itself. The Soft X-ray Imager, or SXI, is a wide-field X-ray instrument that should for the first time make it possible to observe Earth’s magnetosphere in the soft X-ray range. The Ultraviolet aurora imager, UVI, will image the aurora in the ultraviolet part of the spectrum. Alongside them operate the MAG magnetometer and the LIA light ion analyser, which will record particles and magnetic fields in the space through which the spacecraft passes.
According to ESA data, it is precisely the combination of these instruments that will make possible what was not previously achievable: simultaneously tracking the broad picture and local measurements. The X-ray images should show where and how the solar wind strikes the boundary of Earth’s magnetic shield, while the ultraviolet images of the aurora will reveal how changes in the space environment are reflected in the polar regions. Scientists especially value the fact that SMILE will be able to observe the aurora continuously for up to 45 hours, which ESA highlights as the first such observation of its kind.
The very principle on which the X-ray observation is based is also interesting. Instead of “looking at” solid objects like a conventional telescope, SXI relies on the process of charge exchange between solar wind particles and neutral atoms in Earth’s geocorona. That process creates X-ray radiation that can be imaged, so researchers reconstruct from those data the position and behaviour of the magnetosphere’s boundaries. In other words, SMILE will not only register the consequences of solar activity, but will provide a visual and physical map of where, when and in what way the solar wind changes Earth’s surroundings.
Scientific and operational goal: better understanding space weather
In recent years, space weather has increasingly moved from narrowly scientific circles into broader public and institutional interest. The reason is simple: solar eruptions and disturbances in the solar wind can affect the operation of satellites, navigation systems, radio links, electrical grids and astronaut safety. The more technologically connected modern societies become, the greater their vulnerability to such disturbances.
SMILE will not be a meteorological satellite in the usual sense, nor will it serve for the operational issuance of real-time warnings. Still, according to ESA, the data from this mission should help fill one of the major gaps in understanding the Sun-Earth system. The mission aims to clarify three fundamental questions: what exactly happens where the solar wind meets Earth’s magnetic shield, what causes sudden magnetic disturbances on Earth’s night side, and how to recognise earlier the conditions that lead to dangerous geomagnetic storms.
Such data are important both for basic science and for practical applications. If space weather models become more precise, satellite operators and power-system operators can assess risks earlier, and future crewed missions can gain better protection against radiation exposure. That is why ESA emphasises in its materials that SMILE is not just another research mission, but also an investment in the safety of the technologies on which the modern world increasingly depends.
European-Chinese cooperation in a sensitive international context
SMILE is also an interesting example of international scientific cooperation. According to official mission descriptions, ESA provides the rocket, the payload module, one of the instruments and part of the mission operations, while the Chinese Academy of Sciences provides the spacecraft platform, three instruments, and spacecraft and science-operations management. More than 250 European and Chinese scientists are participating in the project, and ESA states that this is the first mission that Europe and China have jointly selected, designed, implemented, launched and operated.
That is important on both a symbolic and a practical level. At a time when many international technological projects are burdened by geopolitical tensions, space missions remain one of the rare areas in which scientific cooperation can outlast political differences. At the same time, such projects require a clear division of responsibilities, complex coordination of standards, and multi-year alignment of teams, suppliers and operational centres. SMILE is therefore also a test of the ability of major institutions to jointly carry out a long-term, technically demanding and financially sensitive programme.
On the European side, the project gains additional weight from the fact that the launch is taking place on the Vega-C rocket, Europe’s light launcher, which in recent years has been going through a demanding period of rebuilding confidence after earlier problems in the programme. For ESA, the SMILE mission is therefore important not only scientifically but also in the context of European autonomy of access to space. The successful launch of a high-value scientific mission on a European launcher would be an important signal of the reliability of the entire system.
What follows after launch
If the launch on 9 April proceeds according to plan, the work for the teams on Earth will only then enter a particularly demanding operational phase. After separation from the rocket’s upper stage, the opening of the solar panels and the verification of the basic subsystems will follow, and then a series of propulsion manoeuvres by which SMILE will gradually move into its final scientific orbit. Precisely the first month after launch is crucial because the bulk of the fuel will then be consumed and it will be confirmed whether all key systems are ready for long-term operation.
Once it reaches the planned orbit, according to ESA, the spacecraft should have enough remaining fuel to maintain the orbit for several more years, while the nominal mission lifetime is three years. That means that a successful early phase determines not only the start of operations, but also the project’s overall scientific reach. The more stably and precisely the transition to the operational orbit is carried out, the more time will remain for collecting measurements that could redefine understanding of the relationship between solar activity and Earth’s space environment.
In that sense, fuelling is not merely a technical detail from the final stage of preparations, but a moment that sums up the entire logic of the mission. Pumped into the tanks were not only hydrazine and oxidiser, but also years of development, international coordination and scientific expectations. If everything proceeds according to the current schedule, on 9 April a spacecraft will lift off from French Guiana whose goal is to record one of the most important, and still insufficiently explained, links in our planetary environment: the one between the solar wind, Earth’s magnetic shield and phenomena from space that can directly affect technology and life on Earth.
Sources:- European Space Agency (ESA) – official SMILE mission page with basic information on the launch, instruments and mission objectives (link)- ESA – “Smile fuelled for launch” announcement on the completion of spacecraft fuelling on 20 March 2026, the amount of fuel, orbital manoeuvres and safety procedures (link)- ESA – “Smile launch kit” with confirmation of the planned launch on 9 April 2026 and an overview of the roles of ESA and the Chinese Academy of Sciences in the mission (link)- ESA – “Smile factsheet” with data on the orbit, spacecraft mass, scientific objectives, instruments and expected mission duration (link)- ESA COSMOS – overview of SMILE’s instruments, including SXI, UVI, LIA and MAG and their scientific purpose (link)
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