they just recently found a 3rd belt of radiation that exists
And? What were its properties that led to it being undiscovered until now? Could it be that it just wasn't intense enough to show up before? In which case, who cares?
i dont see how aluminum can shield radiation?
Well your lack of knowledge of the relevant physics is your problem, not ours. To begin with, do you understand that 'radiation' is not a single phenomenon but there are various types with different properties?
its said you need at least 2 feet of lead for protection
Said by whom regarding what kind of radiation of what intensity for what duration? The statement 'you need two feet of lead to protect against radiation' is meaningless.
but think of how difficult it would be to launch a massive lead space craft into orbit
Yes it would indeed, but since it wasn't necessary who cares how hard it would be?