The First Mission to Our Nearest Star, the Sun
Solar Probe Plus will be a historic mission, flying into the Sun's atmosphere (or corona), for the first time. Coming closer to the Sun than any previous spacecraft, Solar Probe Plus will employ a combination of in situ measurements and imaging to achieve the mission's primary scientific goal: to understand how the Sun's corona is heated and how the solar wind is accelerated. Solar Probe Plus will revolutionize our knowledge of the physics of the origin and evolution of the solar wind.
Although the Solar Probe Plus science objectives remain the same as those established for Solar Probe 2005, the new mission design differs dramatically from the 2005 design (as well as from all previous Solar Probe mission designs since the 1970s). The 2005 and earlier missions involved one or two flybys of the Sun at a perihelion distance of 4 RS by a spacecraft placed into a solar polar orbit by means of a Jupiter gravity assist. In contrast, Solar Probe Plus remains nearly in the ecliptic plane and makes many near-Sun passes at increasingly lower perihelia.
The baseline mission provides for 24 perihelion passes inside 0.16 AU (35 RS), with 19 passes occurring within 20 RS of the Sun. The first near-Sun pass occurs 3 months after launch, at a
heliocentric distance of 35 RS. Over the next several years successive Venus gravity assist (VGA) maneuvers gradually lower the perihelia to ~9.5 RS, by far the closest any spacecraft has ever come to the Sun. The spacecraft completes it nominal mission with three passes, separated by 88 days, at this distance.