hi,

ISRO is the prominent space research organization in India and also in world. however mostly astrophysics, space science related research and development works done here. however you may join isro by studying in engineering field or bachelor of science course in physics field. after completing b.sc physics you have to  do m.sc or m.sc+ phd, Isro has recruitment for scientific officer post where you may apply after completing masters.

another option is b.tech , ISRO hires graduate engineer or scientist B post for electrical, civil, mechanical, computer science, electronics and communication stream degree holders.  so from these mentioned stream b.tech pass candidates has scope to join Isro after clearing the recruitment exam and interview.

another good option is studying aerospace engineering from Indian institute of space science. Student get campus placement opportunity to join Isro.

so you must study science in 10+2 course and prepare for entrance exams like JEEMAIN, jee advance.

hope it would help.