hey anish,
for making weapons you can opt for chemical engineering , if you're interested in this field it is very good stream and quite interesting and many colleges in India offer this stream in this the field of B.Tech.
For a building space crafts you can opt for aeronautical engineering , this is pretigious course offered in the field of B.Tech
Both the fields are unique in their own ways, choose the best and the thing that interests you the best.
hope this helps
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