The European Space Agency, ESA, Solar Orbiter mission will study the Sun from a highly elliptical orbit getting as close as 0.28 AU or 42 million km from which it will use a suite of instruments to make high-latitude observations of the Sun and heliosphere, including the magnetic field, energetic particles, solar wind, and transient phenomena.

The Solar Orbiter primary science objectives are to study:

• 1. the drivers of the solar wind and the origin of the coronal magnetic field to determine how solar transients drive heliospheric variability
• 2. learn how solar eruptions produce the energetic particles that fill the heliosphere
• 3. how the solar dynamo works and drives connections between the Sun and the heliosphere

Solar Orbiter comprises a 2.5 m ⨯ 3.0 m ⨯ 2.5 m box-shaped bus with two solar panel wings spanning 18 m to supply power. Total launch mass is 1800 kg. There is a 4.4 m instrument boom and three 6.5 m antennas protruding from the spacecraft body. A carbon fiber composite, titanium layered solar shield covers one side of the spacecraft. The shield has apertures for various instruments. The spacecraft is 3-axis stabilized to keep the heat shield oriented towards the Sun. Telemetry is dual X-band through steerable medium and high-gain antennas. Low gain antennas are used in the launch and early orbit phase and are available for backup.

Solar Orbiter carries two types of instruments, in-situ instruments making direct measurements of the heliospheric environment, and remote sensing instruments, which view the Sun and heliosphere from a distance.

The in-situ instruments comprise:

• 1. Energetic Particle Detector, EPD
• 2. Magnetometer, MAG
• 3. Radio and Plasma Waves sensor, RPW
• 4. Solar Wind Plasma Analyser, SWA

The remote-sensing instruments comprise:

• 1. Extreme Ultraviolet Imager, EUI
• 2. Coronagraph, METIS
• 3. Polarimetric and Helioseismic Imager, PHI
• 4. Heliospheric Imager, SoloHI
• 5. Spectral Imaging of the Coronal Environment, SPICE
• 6. X-ray Spectrometer/Telescope, STIX

The total massm of the scientific payload is 209 kg.

Solar Orbiter launched from Cape Canaveral Air Force Station on 10 February 2020 at 04:03 UT or at 23:03 Eastern Standard Time, EST, on February 9th. The spacecraft launched on an Atlas 5-411 (AV-087) into a short Earth parking orbit followed by injection into an elliptical heliocentric orbit. The first perihelion will be in June 2020. The mission will use six gravity assist maneuvers during the 7-year nominal mission:

+---------------------------------+
| Flyby | Planet | Encounter Date |
|---------------------------------|
| 1 | Venus | 2020-12-26 |
| 2 | Venus | 2021-08-08 |
| 3 | Earth | 2021-11-26 |
| 4 | Venus | 2022-09-03 |
| 5 | Venus | 2025-02-18 |
| 6 | Venus | 2026-12-28 |
+---------------------------------+

The series of encounters will tilt the spacecraft orbit to an inclination of 25° and will yield an orbit with a perihelion of 0.28 AU, an aphelion of 0.91 AU, and a period of 168 days. Solar Orbiter will make fourteen perihelion passes during the nominal mission. If a three year extended mission is approved, Solar Orbiter will make three more Venus flybys that will bring the inclination to 33°.

+---------------------------------+
| Flyby | Planet | Encounter Date |
|---------------------------------|
| 7 | Venus | 2028-03-17 |
| 8 | Venus | 2029-06-10 |
| 9 | Venus | 2030-09-02 |
+---------------------------------+

The extended mission will involve an additional eight more perihelion passes.