I think you got me wrong.! I'm not asking you to do that.. What I meant is, in such a case, would the top 10 or top 20 universities suffice to be applied to.? Or do I need to include some moderately ranked univ too.?
see, the admission process in US is not like in india where you just need to qualify an entrance exam and depending on the rank you can choose whatever you like, irrespective of how familiar or experienced you are in that field.
In US you need to prove that you have the prerequisite necessary for succeeding in gradschool in a given field of study, for this you need good research background and good recos showing that you are capable. also you need to know that PGRE score is not treated absolute, ie an american getting 850 is not equivalent to an indian or chinese getting 850, since our system is basically a commit and vomit system
(and so many times i have been a victim of it). so u need >900 to get into a decent school . For top 10 and even 20 you need to have a really strong background like publications or talks etc (see through 2009 profiles to get an idea)
you have to go through the dept websites of all the universities, i mean may be not the programs in alaska or north dakota or like (this is where the profiles 2009 comes in) , where they have research opportunities in your field of interest, see through their courses so you can understand what sort of grad exposure is given to your field, go through the prof's CV to know how good he is i mean his publications and sorts and also his age, if he is about to retire then you can just count him out, a large no of profs doing research in your field will be a +ve point for your admission. now as you did something in space physics , may be you can search google for US university depts of physics having that research.
you have to devote yourself for the cause..
Make sure to get atleast 22/30 in your speaking section of TOEFl iBT, it will help you to get TA position without having to take SPEAK.