Hello Aspirant

After your 12th standard you should join a B.E/B.Tech in EEE or ECE. And maintaining good score in your study is must. After B.E/B.tech You need to apply for the exam conducted by ISRO and then from ISRO u can go to NASA, U cannot directly go to NASA.

NOTE : Doing Masters of degree preferably increase ur chances

Hope it helps

Thank you