IIT

The Indian Institute of Space Science and Technology (IIST) is a leading government-aided institute and deemed university for the study and research of space Science. It is third in ranking after IIT and PEC Chandigarh for doing B.Tech Aerospace engineering. It is a good option to doing Aerospace engineering and joining ISRO.
An astronaut is a person trained by a human space flight program to command, pilot, or serve as a crew member of a spacecraft. Although generally reserved for professional space travellers, the terms are sometimes applied to anyone who travels into space, including scientists also. Following are the general eligibility criteria to become astronaut:
(a)Bachelor's degree from a recognised university in engineering, Science, or mathematics etc. An advanced degree is desirable.
(b)At least 1,000 hours pilot-in-command time in jet aircraft. Flight test experience is highly desirable.
(c)Medically fit
In order to become astronaut you will have to learn flying in addition to B.Tech Aerospace engineering degree. By the way, first and only two astronauts of India are from Fighter branch of Indian Air Force.