One who wants to become a cosmologist in NASA has to study in science stream then go for UG/PG courses in Astrophysics and then try together a good fellowship in Astrophysics/Cosmology and engage in research and then keep a watch for NASA openings and apply there for an entry level job which is generally in the nature of research associate and then try to become a full fledged cosmologist. To achieve this target one should have a strong base in Physics and Mathematics along with inclination and keen interest in cosmology. This is a very interesting area but there is a tough competition also in this arena as there are so many universities and colleges across the globe which are providing education in Astrophysics/Cosmology and students after completing their PG/B.Tech./PhD courses aspire and seek to become a cosmologist in the global ace organisation in the area of cosmology known as NASA. It is imperative that much efforts and hard work is a prerequisite to become successful in making career line like that.
There are many institutes imparting Astrophysics education in India and some of the worth mentioning are - Raman Research Institute, Bangalore, Institute of Fundamental Research, Tamil Nadu, National Centre for Radio Astrophysics, Pune, Tata Institute of Fundamental Research, Mumbai, Harish Chandra Research Institute, Allahabad, JNTU College of Engineering, Hyderabad, Inter Universities Centre for Astronomy and Astrophysics, Pune, India Institute of Space Science and Technology, Trivandrum, Indian Institute of Astrophysics, Bangalore, Tata Institute of Fundamental Research, Pune, and Physical Research laboratory, Ahmedabad.
It is also to be noted that there is a tough competition for getting admission to these niche courses and one has to prepare for the entrance tests some of which are on all India basis like JEE while others are institute specific.
Some of these institutes have collaboration with some of the foreign reputed cosmology institutes and the meritorious students can get an opportunity to work with foreign scientists also. Some of the leading institutes have links with NASA also especially in some part project completions and that sometimes creates good opportunity to work in collaboration with NASA with a future hope of likely employment there.
In summary, I would like to add that cosmology is an area which has tremendous scope for research and scientific work of high level but it would require a lifetime devotion of a person who wants to make a career in this line. So aspiring for this line would require strong motivation, focus, and determination for one's work.
Knowledge is power.