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The POLAR Investigation of the Sun (POLARIS) mission uses a combination of a gravity assist and solar sail propulsion to place a spacecraft in a 0.48 AU circular orbit around the Sun with an inclination of 75• with respect to solar equator. This challenging orbit is made possible by the challenging development of solar sail propulsion. This first extended view of the highlatitude regions of the Sun will enable crucial observations not possible from the ecliptic viewpoint or from Solar Orbiter. While Solar Orbiter would give the first glimpse of the high latitude magnetic field and flows to probe the solar dynamo, it does not have sufficient viewing of the polar regions to achieve POLARIS's primary objective: determining the relation between the magnetism and dynamics of the Sun's polar regions and the solar cycle.

b O 3 = {er, et, e h } is an orthogonal right-handed polar coordinate frame. er points always along the sun-spacecraft line, e h is the orbit plane normal (pointing along the spacecraft's orbital angular momentum vector), and et completes the right-handed coordinate system (er × et = e h). c See e.g. Ref. 3 pp. 38-39. d Note that one cos α results from the projection of the sail area onto er, whereas the other cos α results from the projection of the two SRP force components onto n.