ISRO Annually releases vacancies for Electronics and Mechanical Engineer/Scientists, you may apply after BTech in ECE. You probably require appearing for a Examination by ISRO, besides Producing GATE Score and Other eligibility criteria. Other option maybe pursuing MTech/MS from IITs/IISc Bangalore followed by applying fot vacancies in ISRO. ISRO and Other Public Research Organizations like DRDO, have more vacancies for Postgraduates than Graduates.