Hello Riya Singh,


Basic requirements to join the NASA are:

• Candidates must have a Bachelor's degree from one of the recognized universities is science stream whether it be biological science, mathematics, physical science, or engineering. However, it is advised that you do your Master's and Ph.D too in order to get an edge over the other people applying.
• Candidates must have a minimum of 1,000 hours of experience as pilot-in-command in jet aircrafts. It is highly desirable in NASA.
• Candidates must pass a test, the NASA space physical. It is very similar to the test which is conducted for military or civilian flight physical. The standard it includes are that the blood pressure of the candidate applying should 140/90 in sitting position, they should have a 20/20 vision in each eye, and the height of the candidate should be between 62 to 75 inches.
• Candidates must be free of ony disease. All his joints must be functional and he should have normal range of motion. The candidate must be independent of drugs, alcohol or tobacco. The candidate should not have any psychiatric disorder i.e. he should be of am sound mind. 
• The candidate must demonstrate mental, cognitive and personality capabilities to enable him to work in highly demanding physical, soical and intellectual environment.

Suggestions:

• It is suggested that in your Bachelor's you do courses in aerospace or aeronautical engineering and avionics and then your Master's and Ph.D in the same.
• Try getting an internship with such fields so that you know the basics of the field experience involved.
• Keep a perfect score in your 12th, Bachelor's and any other degree you pursue. The higher marks you secure the better are your chances. Since there are multiple people applying for this and this job is in huge demand, the chances of you getting in are very low and thus to maximise your chances, you should secure maximum possible marks. 
• You should be physically fit. Physical fitness is very important for this job at it is a very physically demanding job.
• It will be really good if you get a pilot's license. It will give you an edge over other candidates since you will have flying experience.
• It will be advisable to either join the Air Force or Indian Space Research Organisation (ISRO) prelimnarily and then join an atronaut training programme.

College offering Astrophysics/Aeronautic courses are:

• Indian Space and Research Organisation (ISRO), Bangalore
• Osmania University, Hyderabad
• Andhra University, Vishakhapatnam
• Punjabi University, Punjab
• IIT Bombay, Mumbai
• Indian Institute of Science (IISc), Bangalore
• IIT Madras, Chennai
• IIT Delhi, New Delhi
• IIT Kanpur
• Tata Institute of Fundamental Research (TIFR), Mumbai
• Delhi University
• IIT Kharagpur
• IIT Madras
• Indian Institute of Space Science and Technology (IIST), Trivandum
• Indian Centre for Space Physics, Kolkata
• Savtribai Phule Pune University - Department of Atmospheric and Space Science, Pune
• Cochin Institute of Science and Technology - Department of Atmospheric Sciences, Cochin
• IISER, Bhopal
• IISER, Kolkata
• IISER, Pune
• Madras Institute of Technology (MIT Madras), Chennai
• Manipal Institute of Technology (MIT Manipal), Manipal
• Indian Institute of Space Science and Technology (IIST), Thiruvananthpuram

All the best!

I hope this helps!

Do revert back in case of any doubts.