Dear Jyoti ,

Generally ISRO takes trainees/fresher candidates through GATE  or their own internal exam . The average eligibility criteria is minimum B.Tech / ME/ M.Sc/B.Sc  based on the previous year recruitment analysis. As you know , ISRO recruitment for individual categories like technician/ research scientist etc. comes alternatively in every year , so you need to keep aware about their recruitment notices .

Though now GATE allows B.Sc graduates too for applying this exam , but there is no previous records about taking B.Sc graduate trainee for the post of Scientist through any exam in ISRO or GATE.But, yes .. you may get the job for assistant Technician/ Jr Scientist based on the vacancies available on that post.

Hope my answer helps !