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Solar Orbiter (SolO) is a planned Sun-observing satellite, under development by the European Space Agency (ESA). The mission will be launched with an Atlas V from the Cape Canaveral AFS in Florida in October 2018. SolO is intended to perform detailed measurements of the inner heliosphere and nascent solar wind, and perform close observations of the polar regions of the Sun, which is difficult to do from Earth, both serving to answer the question 'How does the Sun create and control the heliosphere?'

The Solar Orbiter will make observations of the Sun from an eccentric orbit moving as close as ~60 solar radii (RS), or 0.284 astronomical units (AU), placing it inside Mercury's perihelion of 0.3075 AU and providing it with the closest ever views of the Sun.[4]
A comparison of the size of the Sun as seen from Earth (left, 1 AU) and from the Solar Orbiter spacecraft (0.284 AU,right)
This photo shows the Solar Orbiter structural thermal model shortly before leaving the Airbus Defence & Space facility in Stevenage, UK.

Scientific objectives

The spacecraft will make a close approach to the Sun every five months. Around closest approach Solar Orbiter will be positioned for several days over roughly the same region of the solar atmosphere like geostationary satellites are stationed over particular spots on the Earth's surface, so the spacecraft will seem to 'hover' for a while over the Sun. Solar Orbiter will therefore be able to watch magnetic activity building up in the atmosphere that can lead to powerful solar flare or eruptions.

Researchers will also have the chance to co-ordinate observations with NASA's planned Solar Probe Plus mission which will make in situ measurements in 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?

Payload

Observation packages of baseline mission definitions:[5]

Heliospheric in-situ instruments

Solar Wind Analyser (SWA): To measure solar wind properties and composition
Energetic Particle Detector (EPD): To measure suprathermal ions, electrons, neutral atoms, as well as energetic particles in the energy range from few keV/nuc to relativistic electrons and ions up to 100 MeV (protons) and 200 MeV/nuc (heavy ions)
Magnetometer (MAG): will provide detailed measurements of the magnetic field
Radio and Plasma Wave analyser (RPW): To measure magnetic and electric fields at high time resolution

Solar remote-sensing instruments

Polarimetric and Helioseismic Imager (PHI): To provide high-resolution and full-disk measurements of the photospheric magnetic field
EUV full-Sun and high-resolution Imager (EUI): To image various layers of the solar atmosphere
EUV spectral Imager (SPICE): To provide spactral imaging of solar disk and corona, characterize plasma properties at the Sun
Spectrometer/Telescope for Imaging X-rays (STIX): To provide imaging spectroscopy of thermal and non-thermal solar X-ray emission from 4 to 150 keV
Coronagraph (Metis): To provide simultaneous UV (121.6 nm), and polarized visible light imaging of the corona
Heliospheric Imager (SoloHI): To image quasi-steady and transient flows of the solar wind

Timeline and status

2012 April : €300M contract to build orbiter awarded to Astrium UK.[6]
2014 June : Solar shield completes 2 week bake test.[7]