This answer starts with the assertion:
Sorry to burst your bubble, the simple answer is there was no such technology or knowledge at the time.
Brahmāstra, Vāruṇāstra and Āgneyāstra are all mythical weapons that sprung from the imagination of authors of the two epics and Purāṇas.
To start off, this assertion is utterly disrespectful towards the Rishis whose works are considered as authority here on this site. But that's alright for me as I am accustomed to see such statements and attempts being made by this particular user several times in the past too.
I am concerned about the two sources used in the answer.
- Are those two sources considered valid here? Are opinions of Mr. Sankalia etc considered as valid sources to cite on this site?