Priya, You have to start with science stream such as PCM or PCMB with any vocational subjects such as electronics, computer etc. Then you can write JEE Mains to get admission in IISc (India Institute of science), if you want to become scientist in any space related organization (ISRO). Or other way is to write ISAT entrance exam to join top space science related institute such as IIST, with this you can get into ISRO with ease. There is one other way if you are not able to clear jee mains exam, you can qualify ISRO recruitment exam conducted by ISRO itself after your undergraduation degree. To join NASA, candidate must be US citizen (native) or green card holder. There are very roles under ISRO and as per your undergraduation degree you can join. You can join CSE, EEE, ECE, Civil engg, , geo informatics, IT , chemical engg. course. You can also pursue Mtech in the above mentioned courses or can go for MSc related course or MBA degree.

Hope I answered your query, thankyou!