Dear,

Both aeronautical engg and aerospace engg are emerging fields of engineering education in India. However, Aeronautical engineers are in demand in some of the most reputed space centers in the world such as NASA.Aerospace engineering also offers bright career opportunities. Both fields can get you a job in ISRO. Aeronautical engineering is a field of Aerospace Engineering. It can also be understood as a specialization of in the field of aerospace. You can apply for a job at ISRO right after you acquire the relevant Degree, with no experience, if there is an ongoing recruitment drive for freshers. Both are 4 year courses. So, lastly it depends on your choice.

Hope this helps!