Hello Aspirant,

Aerospace Engineering is not mandatory to join ISRO. If you want to do engineering after 12th and after want to join ISRO then you can pursue B.Tech/ B.E.  any of the following specialization-

• Mechanical Engineering
• Electronics Engineering
• Aerospace Engineering
• Computer Science Engineering
• Radio Engineering and other related courses.

If you don't get into IISC, IIT or NIT, after completing your B.Tech/B.E from any Institution/college  you can take the test that is conducted by ISRO. This test includes a written exam and a personal interview.

You can also join ISRO after your Post Graduation. If you don't want to do B.Tech/B.E. then you can pursue Bachelor's and Masters in Physics. After that also you will able to join ISRO.

Hope this information will help you.