• To become a scientist at ISRO one first needs to have opted Math and Physics as his subjects at 10+2 level and have a thorough basic knowledge of these subjects.
• Getting admission in IIST (Indian Institute of Space Science and Technology) can be the easiest ticket to get absorbed in ISRO as a scientist/engineer.
• ISRO often picks up graduates and post-graduate engineers from IITs, NITs and other reputed government and private institutions. So it is better to have a degree in a course that is more likely to be shortlisted for the consideration of such jobs such as B.Tech in Aerospace Engineering, Mechanical Engineering, Radio Engineering, and Engineering Physics. There is sometimes a requirement of electronic engineers and developers as well. There are sometimes vacancies for Civil Engineers as well.
• After completing B.Tech from any college, an examination namely ICRB (centralized Recruitment Bangalore) is conducted by ISRO and individuals are tested as per their respective branches of engineering and after clearing the interview, one can get appointed as a scientist or an engineer at ISRO. Candidates must have a minimum aggregate percentage of 65% and above in B.tech in their respective relevant streams.
• After the completion of M.Tech or D. in trades such as Geoinformatics, Remote Sensing, Instrumentation, applied Mathematics, Geophysics, Geography or any other equivalent degree in the field of Physics or Mathematics one can apply directly for the job of a scientist at ISRO. The selection consists of written exam and Interview and after clearing these sages scientist/Engineer position can be obtained in ISRO.
• One can get selected as the junior research fellow in ISRO; by this, they can get to research as scientists and engineers. The screening process for the selection of Scientist in such an organization is very tough and requires the best of knowledge, wits and a very presentable and calm attitude.

Hello, 

You can either join as SC, that is, Scientist Engineer or join via the ICRB recruitment. Engineering will be a preferable course for this. 

You can also join by doing

P.hd (Astro physics).

P.hd (Geophysics).

P.hd (Metaphysics), preferably from IIST. 

Good luck!