Which spacecraft was the first to orbit the Sun's poles?

The first spacecraft to orbit over the Sun’s poles was Ulysses. This joint NASA–European Space Agency probe was designed to study the Sun from high heliographic latitudes, rather than remaining close to the planets’ nearly flat orbital plane.

Ulysses launched aboard Space Shuttle Discovery on October 6, 1990. Reaching the polar regions directly would have required an enormous change in heliocentric inclination, so mission planners used a gravity assist at Jupiter in February 1992. Jupiter’s gravity redirected the spacecraft into an orbit inclined by roughly 80 degrees to the ecliptic, carrying it over the Sun’s north and south poles.

The spacecraft made major latitude scans in 1994–1995, 2000–2001, and 2007–2008. Its observations showed that the solar wind and magnetic field behave differently at high latitudes and revealed that the Sun’s polar magnetic field was weaker than earlier measurements suggested. Ulysses was powered by a radioisotope generator because sunlight was too weak for practical solar panels during its distant, high-inclination journey.