Hello Santosh

In India, you will have to start focusing on your career once you pass 10th grade. One should choose Physics, Chemistry and Mathematics as core subjects in 12th.

After you are done with 12th grade and you have gotten good grades, you need to focus on a good Bachelors degree from a recognized university. One could choose a course in Physics, Chemistry, Maths, Biology, or Aerospace Engineering.

To be able to get a post graduation degree and a doctorate, you need to do well in your undergraduate degree. Post graduation and doctorate will basically be specialization in your stream.

After you are done with graduation, you can sit for the exam, which is held by NASA for the recruitment of scientists and astronauts. Or in order to join ISRO one needs to clear the Joint Entrance Exam which is held by the IITs.

And in order to be a mission specialist, you will need 3 years of related and responsible experience.