Hello Aspirant,

To join ISRO after your B.Tech,  you will need to appear in the entrance exam conducted by them. Almost every year the vacancies are released by the organization usually in Feb-March.

But do keep in mind, this is not a rule which ISRO follows every year.  The details regarding admission and procedure will be mentioned on the job ad.

It has few eligibility criteria:

• Candidates should have completed either diploma or B.Tech with more than 60% (different for reserved candidates)
• Should be an Indian citizen
• Age should be between 21 to 30 years
• Candidates in final year can also apply (only if they can produce degree certificate at time of interview)
• GATE score is also given huge importance

Also, note:

For Aeronautical Engineers there is no direct selection process. But ISRO recruits ECE, ME, CSE students.

So you need to apply under ME and they ask your specialization, where you will find option for Aeronautical Engineering.

Hope this helps and All the best.