Admission for Btech courses at IIIsT Thiruvanthapuram is via Jee Advanced exam. 

Hence first students need to clear Jee Main exam and be amonsgt top 2.31lakh candidates to qualify and apear for jee Advanced exam and rnaks within 5000 in Jee Advanced shall hav egood chances of IIST Thiruvanthapuram. 

Cutoff shared below for Btech  

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