Hi 

To become a cosmologist firstly complete your class 10 then +2 with science stream and then get admission in universities which offer B.Tech, M.Tech, MS, PhD programs in Avionics & Aerospace engineering. To become a cosmologist, take a UG programme offered by IIST. To get into IIST, one should write the entrance exam for which the eligibility criteria is minimum 70% of maximum marks in 11th and 12th. 

To become a space researcher, you should be opting for PCM in 11 and continue with it as space study requires deeper concepts of mathematics. 

Thank you and keep asking:)