Yes, you can use GI Bill for grad school and generally is better for grad than undergrad because it reduces need based aid at private undergrad and their is no net difference in the cost.
I knew you weren’t eligible for NROTC, just being clear for other posters tha OCS makes GI Bill an option after 4 (?) years. If the Navy paid for undergrad, you have to fulfill initial commitment and then another four years to earn GI Bill.
I don’t know anything about NASA. I would check age limits there as well and understand that there is nothing wrong with pushing for a dream but understand odds might be similar to getting into Ivy, or less, due to the number of interested qualified candidates to positions available.