When the fuel tanks are full, the total weight of the stack will be around 2200 kg. The platform structure is made from an aluminium sandwich with carbon-fiber frames. It supports two deployable solar arrays with a combined area of 5.8 m² that supply a set of lithium-iron batteries with a total capacity of 60 Ah. A 490 N engine will bring the spacecraft to its operational orbit of 2 x 20 Earth radii (geocentric distance) and 70^o or 98^o inclination. Two star trackers and twelve 10-Newton thrusters are used for attitude control and two antennas will transmit telecommands and spacecraft housekeeping data to the ground station. A single 20-mm-thick, 1m-by-1m aluminium honeycomb sandwich plate forms the top cover of the platform and the base plate of the payload module.

The payload module carries three instruments — two imagers operating in the ultraviolet (UVI) and X-ray (SXI) wavelengths, and one in situ instrument (MAG) for measuring the solar-wind magnetic field. The UVI and SXI are mounted on the main platform, while the MAG’s two sensor heads will be positioned 80 cm apart along a deployable 3-m-long boom to reduce the influence of magnetic fields generated by the spacecraft. The fouth instrument will measure the solar wind ions (LIA) and its two sensors will be mounted on the platrform.

SMILE will be three-axis stabilised, so that the SXI and UVI can continuously point towards their magnetospheric and auroral targets. However, since this requires pointing close to the direction of Earth, a baffle is required to shield the CCDs of the SXI from unwanted light pollution, bringing the total SXI height to 95 cm. The science data collected by the four instruments will be transmitted from the payload module using an X-band antenna. SMILE is a joint mission between the European Space Agency (ESA), that will provide the payload module and the launcher, and the Chinese Academy of Science (CAS), that will provide the platform.