solar pass at 17° inclination, increasing to 33° during a proposed mission extension phase, bringing even more of the polar regions into direct view. Scientific objectives The spacecraft makes a close approach to the Sun every six months. The closest approach will be positioned to allow a repeated study of the same region of the solar atmosphere. Solar Orbiter will be able to observe the magnetic activity building up in the atmosphere that can lead to powerful solar flares or eruptions. Researchers will also have the chance to coordinate observations with NASA's Parker Solar Probe mission (2018-2025) which is performing measurements of the Sun's extended corona. The objective of the mission is to perform close-up, high-resolution studies of the Sun and its inner heliosphere. The new understanding will help answer these questions: How and where do the solar wind plasma and magnetic field originate in the corona? How do solar transients drive heliospheric variability? How do solar eruptions produce energetic particle radiation that fills the heliosphere? How does the solar dynamo work and drive connections between the Sun and the heliosphere? Instruments The science payload is composed of 10 instruments: Heliospheric in-situ instruments (4) SWA – Solar Wind Plasma Analyser (United Kingdom): Consists of a suite of sensors that measures the ion and electron bulk properties (including density, velocity, and temperature) of the solar wind, thereby characterizing the solar wind between 0.28 and 1.4 au from the Sun. In addition to determining the bulk properties of the wind, SWA provides measurements of solar wind ion composition for key elements (e.g. the C, N, O group and Fe, Si or Mg) EPD – Energetic Particle Detector (Spain): Measures the composition, timing and distribution functions of suprathermal and energetic particles. Scientific topics to be addressed include the sources, acceleration mechanisms, and transport processes of these particles MAG – Magnetometer (United Kingdom): Provides in situ measurements of the heliospheric magnetic field (up to 64Hz) with high precision. This will facilitate detailed studies into the way the Sun's magnetic field links into space and evolves over the solar cycle; how particles are accelerated and propagate around the Solar System, including to the Earth; how the corona and solar wind are heated and accelerated RPW – Radio and Plasma Waves (France): Unique amongst the Solar Orbiter instruments, RPW makes both in situ and remote-sensing measurements. RPW measures magnetic and electric fields at high time resolution