Hello there!

hope you are doing well.

Yes, ofcourse!

you can apply for M.tech in astronomy after B.Tech in computer science engineering

You can sit for the GATE exam, which offers admission into IITs and IISc, and most other government colleges. There is also TANCET exam, which offers admission into universities in Tamil Nadu.

you can also do aerospace engineering which is also similar course

You can find the list of colleges offering M.Tech in Aerospace Engineering here

https://engineering.careers360.com/colleges/list-of-me-mtech-in-aerospace-engineering-colleges-in-india

i hope this helps

goodluck!