Hey there

After completing 12th class you need to get admission in Indian Institute of space Science and technology which is the best way to get job in Indian space Research Organisation. If we talk about which course you should pursue, then you need to pursue Bachelor of Technology or bachelor of engineering and must have completed 65% atleast in the aggregate.

For more: https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/articles/isro-recruitment/amp&ved=2ahUKEwjHn7mC8e_zAhVzzDgGHeXsDDEQFnoECAYQAQ&usg=AOvVaw3nYDvGA2a4zwYsaZdUTUu0&ampcf=1