After announcing the GATE result you can seat for a centralized counselling where depending on your score you will be shortlisted and will be called for interview. 

Respected Sir,

if you want to go IIST for ISRO in Mtech it is a little bit tough competition but yes if you have the capability to dream of it you have the capability to get it also.

As the rules have changed a lot and for Mtech it was never there. Mostly if you have a gate score of 650+ the chances are high and then it depends upon the interview panel. But weightage is given on gate score, interview and career marks while the interview and gate score is given more weightage.