Orbit: Solar Probe Plus will be placed into an elliptical orbit around the sun. The size of the orbit will be decreased over nearly seven years using seven Venus flybys. Solar Probe Plus will orbit the sun 24 times, gradually “walking in” toward the sun with each pass. The closest points of each orbit come well within the path of Mercury— the closest planet to the sun. On the final three orbits, Solar Probe Plus will fly to within 3.7 million miles of the sun's surface. That is about seven times closer than the current record-holder, the Helios spacecraft.
Solar Probe Plus will be an extraordinary and historic mission, exploring what is arguably the last region of the solar system to be visited by a spacecraft: the sun’s atmosphere, the outer corona. Eventually approaching almost as close as 3.7 million miles above the sun’s surface, Solar Probe Plus will repeatedly sample the near-sun environment, revolutionizing our knowledge and understanding of coronal heating and of the origin and evolution of the solar wind. Moreover, by making direct, in-situ measurements of the region where some of the most hazardous solar energetic particles are energized, Solar Probe Plus will make a fundamental contribution to our ability to characterize and forecast the radiation environment in which future space explorers will work and live. The spacecraft has a large sun shield that will be built to withstand temperatures of 2,500° F, so that the instruments that lie in the shadow of the sun shield can remain at room temperature.