SMILE is in orbit, ready to photograph Earth's magnetic shield

On 19 May at 11:52 Beijing time, a Vega-C rocket lifted off from the European spaceport at Kourou in French Guiana carrying a satellite that two continents have spent most of a decade building together. SMILE, short for Solar wind Magnetosphere Ionosphere Link Explorer and nicknamed the ‘smiling satellite’ in Chinese, is the first space-science mission undertaken as a full-scale collaboration between the Chinese Academy of Sciences and the European Space Agency. It is now on its way to a scientific orbit, where it will spend three years doing something no previous satellite has done: photographing Earth’s magnetic shield as a whole.

The science is about a boundary we all live inside and never notice. The solar wind, a stream of charged particles from the Sun, constantly hits Earth’s magnetic field, which deflects most of it. The region where the two interact, the magnetosphere, is what protects the planet from the worst of the solar wind, and the behaviour of that boundary determines everything from auroras to the storms that can knock out satellites and power grids. Understanding it has always been hard because previous missions could only sample it at points, a handful of satellites measuring one location each. SMILE will instead image the whole interaction region at once, the difference between reading a weather forecast station by station and seeing the storm on a map.

The payload split reflects the partnership’s design. The European side built the spacecraft’s payload module and its soft X-ray imager, the first X-ray camera ever flown in space for this purpose, which will observe the magnetopause, the outer edge of the magnetic bubble, against the faint X-ray glow of the solar wind. The Chinese side built the satellite platform, the ground support and three of the four instruments: an ultraviolet auroral imager, a low-energy ion analyser and a magnetometer. Europe provided the rocket and the launch site; China provided the platform and the mission operations. Two space powers that have historically done very little of this kind of work together have, on this mission, divided the work down the middle.

The engineering context matters. This is the closing mission of the second phase of China’s space-science programme, a set of missions selected and run explicitly for science rather than demonstration, and it is simultaneously a statement by both agencies that full-scale cooperation is possible at a time when space collaboration between China and the West is otherwise rare. The mission was proposed two decades ago as a concept, survived years of negotiation over instruments, interfaces and data sharing, and was delayed, as so many joint missions are, by scheduling and politics. The science data will be shared openly with researchers worldwide, which is itself a small statement about how space science is supposed to work.

What comes next is a slow approach. SMILE will take roughly 42 days of orbital manoeuvres to reach its final orbit, a highly elongated one that keeps it in view of the dayside magnetosphere, then spend two months in testing before the three-year observation phase begins. The first images will not be the dramatic ones; auroral images arrive first, and the soft X-ray maps of the magnetopause will take longer to calibrate. The payoff, if the mission works, is a new way of watching space weather form in real time, with implications for the forecasts that satellite operators and power grid managers increasingly depend on.

The quiet significance of SMILE is that it treats the two most expensive habits in space science, cooperation and imaging, as worth the effort. Space physics has spent fifty years describing the magnetosphere from inside it; this mission is the first attempt to step outside and look. The scientists who built the instruments are already pointing at the same question the satellite will answer: whether the whole, seen at once, behaves the way the parts suggested. If it does, a lot of forecasting improves; if it does not, that will be even more interesting.