Hello,

It is not necessary for you to study only in IIST to get into ISRO. You can get a job at ISRO with a degree feom other colleges too. If you are passionate and talented enough to get into IIST then you can get into ISRO through campus placements. You can go through more information about your query from the link below-
https://www.iist.ac.in/placementcell
Good luck!