Is it normal to feel like I bought my way into graduate school after being rejected and then accepted when I was awarded an external fellowship? I initially got rejected by the two schools I applied to (horrible pGRE scores, lackluster GRE scores, and only did research at my undergraduate institute), but then I got an NSF fellowship, and was almost immediately accepted by both schools.

I feel a little hurt by the whole acceptance process. I feel like I was essentially told: "you are not good enough to pursue space physics in our program, but because you have money we will let you in". 

Question: In this situation, is it normal to feel like you essentially bought your way into graduate school? Or that people will always look at you as not good enough?
From what I've heard the NSF fellowship is not an easy one to get, and having one seems to carry some sort of prestige. Sure, the program may have accepted you on the ground that they don't have to pay you, but the fact that you have an NSF fellowship may have changed the admission committee's perception of your ability, which could be what tipped the balance in your favour. No matter what, there is no point in dwelling on the past. What matters is how you perform in the program now, not how you got in. Don't be the college freshman who keeps talking about his high school athletic achievement; truth be told, nobody cares.

As for your lack of passion for the subject, I want to point out that passion usually does not precede mastery of a subject. Rather, people usually develop passion after they become good at something. So I don't really think lacking passion at this point is a deal breaker. I'm sure astrophysics is large enough for you to find something that you are good at and can develop a passion for. Of course, if you can't see yourself doing research, teaching, or anything science-related in the future, you might want to rethink about your decision to go to graduate school in the first place.