A NASA spacecraft set to launch in 2015 will come eight times closer to the Sun than any previous probe, operating within the star's scorching outer atmosphere, or corona. The $750 million Solar Probe will study the birthplace of the solar wind. During its expected seven-year lifetime, Solar Probe will make seven gravity slingshots around Venus, each time getting closer to the Sun. At its closest approach, it will orbit the Sun from within the outer part of the corona, at a distance of between 8 and 10 solar radii from the centre of the Sun. That is much closer than the previous record holder, the Helios spacecraft, which came within 67 solar radii of the star in the 1970s.Scientists hope the probe will help solve two enduring solar mysteries: Why is the Sun's outer atmosphere, or corona, so much hotter than its visible surface, which lies beneath it? And what accelerates the solar wind, a stream of charged particles from the Sun, to supersonic speeds? Heat shield: The idea of studying the Sun at close range was first proposed by the US National Academy of Science in 1958. But scientists have only recently been able to design heat shields for such a spacecraft within NASA's tight budgetary guidelines. The mini-bus sized Solar Probe will be protected from the Sun's fierce radiation by a disc-shaped, carbon-composite heat shield that will be 2.
The probe is 7 meters in diameter and about 15 centimeters thick. The heat shield technology is based on that used in Messenger, a NASA spacecraft that completed its first flyby of Mercury in January and that was also designed by engineers at APL. The side of the shield facing the Sun will heat up to 1400 °Celsius (2600 °F), while the instrument-carrying payload behind the shield will remain at room temperature.