Thanks for the general info ... have we found any caves on or in the moon?? And the reference, just skimmed it but it appears to be written at a high and thorough level.

But I wasn't clear about my real question: is there a shield planned for the Orion spacecraft to keep astronauts alive during a sufficiently bad solar event on a trip to or from the moon? As I recall the lunar orbiting space station was going to be unmanned but I was wrong or they've changed their minds: https://www.nasa.gov/gateway So they've got to be thinking about this problem, and as the reference notes we'll need for example adequate space weather surveillance which I note we've been emplacing as of late.

I've never checked it out like running the numbers but I've heard for a long time Apollo was timed for a low part of the solar cycle and one reason Nixon cut it short was because delays put those canceled missions into the active part of the cycle.