Hi Arijit!

For getting into Indian Space Reasearch Organization (ISRO), you can undergo Entrance Exams provided you have the required marks! Getting in ISRO, you must have Physics, Chemistry and Maths as the main subjects. First is JEE Advance, you must have 75% aggregate in 12th for appearing in JEE Advance, and then join Indian Institute of Space and Technology (IIST). Second, Kishore Vaigyanik Protsahan Yojana (KVPY), where you must have 60% aggregate in 12th. There are many National and State Entrance Exams to join India Institute of Science Education and Research (IISER) and this will be the third option!

Hope this is helpful!

All the best!