Have any spacecraft been either launched or proposed which involve a survivable close encounter with the Sun? This would include solar observation missions as well as any missions designed to make a close pass as part of their trajectories en-route elsewhere, and by "close" I mean at least within the orbit of Mercury.
How close have spacecraft approached or have been proposed to approach, and how long were they / will they be within the most extreme thermal/radiation/etc. conditions that would be encountered? What features would be required / have been incorporated into any such spacecraft in order to survive those conditions?