Yeah, I've done that myself.

I've decided to take the MkII with a 28-300 telephoto and 2x extender instead of hauling that monster 600mm around. There should be enough light that the 2x won't be a limiting factor plus I can shoot video with it as well.

 

D3X and that big 'ol lens will go a lot farther than you think. I'd say bring it. Even if you are that far away, with 24MP, you can crop the hell out of it and it'll still be a decent picture.

 

Forget it. Go with your son and be in the moment together marveling at what man has accomplished. With the camera you're going to be glancing in and out of the viewfinder / preoccupied with dialing in the lens, etc. Besides, how many awesome photos have you seen of space shuttle launches? They're going to do the same thing for this one and it's probably going to come out better than any of your photos.

 

what ever you end up doing I can't wait to see