Science

ISRO has centralized recruitment system in order to hire young engineers as research scientist (RA) and other various ways to hire highly skilled experienced scientists from the scientific community across the globe. ISRO doesn't go hiring spree like most of the so called Indian IT giant nor it simply fills the positions by hiring some X number of engineers each year like other PSU's does, they only hire bright and the most talented graduates that to when they really need more manpower. This is perhaps a good step to prevent unnecessary expenditure on human resources, something that Air India should have done a decade before. Their preliminary exam is as good as GATE, in fact when I appeared in one of their exams couple of years before I found it more challenging than GATE itself. Instead of focusing only on space and astronomy I would suggest you to find your interest and work towards getting better and better in that field no matter if its electronics/computer science or mechanical as far as its related to science and you have Engineering degree in hand you are eligible for their exam, now in order to become their RA you really must be excellent with your desired set of skills with respect to your area of interest. ISRO has got something for everyone right from electronics engineer to geologist, so first find your interest and work towards that.