Astronomer

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
India's first two astronauts were from Indian Air Force Fighter Pilot branch. B.Tech Aerospace Engineering can be a good choice to fulfil your dream of becoming Astronaut or alternatively Space engineer.

Pilot Astronaut minimal requirements:-
Pilot astronauts need a minimum of a bachelors degree in engineering, biological/physical sciences or mathematics. They also require a minimum of 1,000 hours pilot-in-command time in a jet aircraft.
Pilot astronauts need to be able to pass a NASA space physical, which includes the following items:
Distant visual acuity: 20/100 or better uncorrected, correctable to 20/20 each eye
Blood pressure: 140/90 measured in a sitting position
Height between 62 and 75 inches
For applicants applying to be Pilot astronauts, NASA strongly recommends flight test experience. While it is theoretically possible to obtain these credentials without going into the military, the majority of NASA Pilot astronauts come from either the Air Force or Navy.
Mission Control Astronaut Minimal Requirements:-
Mission Control astronauts are required to have the same education as Pilot astronauts: a bachelors degree in engineering, biological/physical sciences or mathematics. However, Mission Control astronauts must also have at least three years of related, progressively responsible, professional experience in their chosen field of study. Advanced education is highly recommended for both Pilot and Mission Control astronauts, and can even replace some of the three year work requirement. A masters degree is equal to one year of experience, and a doctoral degree is equal to three years of experience.
Mission Control applicants must also be able to pass a NASA space physical including the following items:
Distance visual acuity: 20/200 or better uncorrected, correctable to 20/20, each eye
Blood pressure: 140/90 measured in a sitting position
Height between 58.5 and 76 inches
Payload Specialist Astronaut Minimal Requirements:-
A third and far less common path is that of a Payload Specialist astronaut. Payload Specialists are non-NASA personnel who are brought in to perform specialized onboard duties. They can be brought in from private companies, research universities and even other countries. Although they do not undergo the NASA astronaut selection process, they are required to have an appropriate education/training for their payload or experiment. Of course, they must also be physically fit for space travel. Payload specialists were far more common on the Space Shuttle missions than they are now on the Soyuz missions, due to the larger crew capacity of the Space Shuttle.