Here's a graph of the PSP distance from the sun in solar radii: https://space.stackexchange.com/questions/17562/how-does-the-parker-solar-probes-heat-shield-pro

Here's a graph of the PSP distance from the sun in solar radii: https://space.stackexchange.com/questions/17562/how-does-the-parker-solar-probes-heat-shield-protect-it-from-dust-near-the-sun https://space.stackexchange.com/questions/17562/how-does-the... The corona can be expected to be out to ~12 solar radii, which suggests about a day of really severe conditions. (The data pass is 30 hours, which suggests that's about right.) That's why it needs to be a really good head shield. It's smallest orbit has a period of 88 days.