Hi Vishnu, IIST, Thiruvanandapuram has 3 courses in the under graduate level.
4 year B.Tech in Aerospace Engineering
4 year B.Tech in ECE (Avionics specialisation)
5 year Dual degree (B.Tech + M.S or Mater of Technology) The 5 year Dual degree program leads to B.Tech in Engineering Physics and any one of the PG Degree specialisations:
Master of Science (Astronomy & Astrophysics), Master of Technology (Earth System Science), Master of Science (Solid State Physics), Master of Technology (Optical Engineering) There is no exit option after 4 years.

The admission is through JEE (Advanced) scores.

In case of a PG Degree,

There are various specialisations and admission is through GATE Scores and Interview.

For more info. regarding this, visit https://www.iist.ac.in/admissions/postgraduate/regular

Hope this helps, All the best.