It's not the problem of human capital. This will be my first reply on this forum so forgive me if i break any rule. We have very capable people who can be roped in to work on these projects and make them succesful, but the problem is that our government is more focused on winning votes for the next election and as such spends most of its time and (nations) resources in areas where the public is interested in and will give votes seeing the performance (thats just a small percentage of our politics, many more factors are related to our election results which are far from including subects like "Aircraft research'). There is simply not much interest or necessity in the indian political circles to focus on Military stuff (we barely started focusing on civilian research).
Due to this, the government pays peanuts to the scientists and forces them to work in inefficient environments which our DPSUs are famous for. Our scientists literally work in an environent which nerfs their stats (video game language used here). So for what reason will a fresh graduate or an experienced person consider going to these research insitutions when they can have better pay grade, work load, and overall a far better working environment in private firms (even these firms are foreign in most cases, meaning they go to other countries to work). This is one of the main factors of Brain drain. There is a not so popular saying in India,
" Jab padhega India tabhi to aage badhe ga America "
, basically saying that due to brain drain, the best minds of India do not work for the advancement of India, but for the advancement of USA.
Once the government changes its attitude towards sectors like research and starts paying them high enough wages and working consitions and infrastructure to match the private and foreign cos., then only can we advance at the rate mirroring the advanced countries.