See IIST is the only institute in India which have professors who are working professionals at ISRO and are in close quarters with the research of ISRO. You may not be wiling to go for the ISRO but getting your subject education from the professionals who themselves are not only involved with teaching but also in real life Aerospace Engineering research will be a great thing in your professional career. You will get the notion of the real life working and active research going in the field. So if you get a chance to study at IIST, then don't loose it even if you don't want to go for ISRO.

For more information regarding IIST consider the link below:

https://www.careers360.com/university/indian-institute-of-space-science-and-technology-thiruvananthapuram

I hope this helps. Goodnight!