Sorry, with a 1.8 GPA you're not getting into colleges with good programs in anything, no matter what your ACT score is. A high ACT score tells colleges you're smart, but your GPA isn't considered passing by college standards and tells them you're lazy - no college will want to take you on. Your best bet is to start at community college. Do well there for a few years and you can transfer to a good school - but you have to get over your motivation problems first. You really can't do anything in astrophysics if you don't have a PhD in the field, and that requires a LOT of motivation, mostly coming from you - no adviser is going to push you through a PhD program, you have to do that on your own.
Start at community college, then try to transfer to a good state school - like Berkeley, UC Santa Cruz, UCLA, U Arizona, U Washington (Seattle), UMass Amherst, U Wisconsin, U Michigan, U Virginia, Ohio State, Purdue, Clemson, or Rutgers.
Start at community college, then try to transfer to a good state school - like Berkeley, UC Santa Cruz, UCLA, U Arizona, U Washington (Seattle), UMass Amherst, U Wisconsin, U Michigan, U Virginia, Ohio State, Purdue, Clemson, or Rutgers.