Hi

After 10 std take up science. In 11 and 12 std of science you will be introduced about classical physics, modern physics etc which will help you in future. Parallely prepare for JEE Main and Advanced. Their are several study material available online. 

Apply for JEE Main and Advanced and try to get good score. Try to get above 95 percentile. By that you will have a good oppurtunity to get into NITs or IITs.

ISRO mosty hire Mechanical, Electronics, Computer graduate Engineers.

So according to your interest take up undergraduate course in top Engineering colleges in India.

Your preference order should be like this 

1. IIT

2. NIT

3. Top privite university.

Once you get into engineering, during your first 3 years build up your foundation. Your foundation should be good for later entrance test.

ISRO organises its own entrance test everyyear. Start preparing for those exams. You can start from 3 rd year of your engineering.

After you clear their entrance test you will have to go through interview.

If you clear their interview you are hired as a Junior Engineer/ Scientist