In 1976, NASA’s Helios 2 spacecraft set the current distance record by orbiting the Sun with a closest approach of 43.4 million kilometers. Even though this is barely inside the orbit of Mercury, the intense heat close to the Sun has previously prevented any closer observation. The Goddard Space flight Center “Living with a Star Program” hopes to change this. In 2018, NASA’s Solar Probe Plus is expected to launch from Cape Canaveral and begin a six-year journey to its closest approach to the Sun. Using seven Venus flybys to bleed off orbital energy and fall closer to the Sun, the spacecraft will enter a highly elliptical orbit with a record setting distance of closest approach of 6 million kilometers.
At this distance, the Sun is 500 times brighter than at Earth. To protect the sensitive instruments, the probe will be protected with a 4.5 inch thick carbon composite heat shield and will be actively cooled with large radiator arrays.
Using the data collected at close range astronomers hope to learn about the energy flow on the surface of the Sun, why the solar corona is hotter than the surface of the sun, and what accelerates the solar wind. Historically, the Sun has only been observed from around the equator, because the orbit of the Earth and other planets in the Solar System is approximately in the plane of the Sun’s equator. Solar Probe Plus will use the Venus flybys to increase its orbital inclination and better observe the solar poles.