When I went through Brinstar, I somehow missed the Charge Beam. I've gotten to Kraid, but I can go back only so far (There's a room, I can't remember which one, where there's a ledge you have to get to that's too high to reach, and I can only get to there). Can someone tell me...
1)If it is, in fact, possible to get the Charge Beam going back from Kraid, and
2)If not, will I be able to get it later?

The only way to get back to the region of Brinstar that contains the charge beam is to get the ice beam. The ice beam can't be obtained without the help of an item that's deep within Norfair.

You will gradually lose health in about 90% of Norfair unless you have the varia suit, which is the prize for defeating Kraid.

Unless you save your game at the second save station in Tourian, you can always backtrack to get any items you've missed.