Charged particles and neutral atoms exchange electrons in many space plasma venues. Soft X-rays are emitted when highly charged solar wind ions, such as C6+, O7+, and Fe13+, interact with Hydrogen and Helium atoms. Soft X-ray images can be a powerful technique to remotely probe the plasma and neutral density structures created when the solar wind interacts with planetary exospheres, such as those at the Earth, Moon, Mars, Venus, and comets. The recently selected ESA-China-NASA joint spacecraft mission, “Solar wind – Magnetosphere – Ionosphere Link Explorer (SMILE)” will have a soft X-ray imager on board and provide pictures of the Earth’s dayside system after its launch in 2021. In preparation of the satellite mission, several simulation studies have been conducted using a global magnetosphere – ionosphere MHD model. This talk introduces SMILE mission and some of the simulation studies.