The questions are
Is there any recorded knowledge for how to incite or use Brahmastra or
its likes in Mahabharat or any other scripture, if not, why wasn't
that all recorded or known or passed on?
Why isn't that available like Vedas and other things?
Why does no one have any knowledge regarding those weapons, or transcending in skies with human body, etc.?
I agree with Vimana Shastra, where it's written on how to make spacecrafts using what materials and what a pilot should do. But why isn't there a single human being making use of that book and creating something or understanding those things? Or is there anyone?
Good questions indeed.
Let me start with 2nd point first
- The Veda, to be precise Rig, Yaju and Sama ( I am not taking Atharva into consideration into the core Veda Category) Vedas, contain SPIRITUAL matters, occasionally mentioning some historical facts like Daśarājñá yuddhá, about Manu, Bharata, etc.
It does not mean to say that The Veda do not refer to any weapons. They do refer to Vajra of Indra, Parasu of Varuna, etc. As the Veda contain multi-layered meanings, these weapons can be interpreted in different ways.
The same Vajra was mentioned in Ramayana and Mahabharata also.
- The DIVINE weapons mentioned in Ramayana or Mahabhrata were not Nuclear as many would like to believe. They are of different technology, which was not described in those EPICs.
Further, their usage also mentioned in different ways by different people.
a) Those DIVINE weapons were used either through an arrow made of Iron or Kusa grass, uttering some mantra.
Sri Rama used brahmAstra against a crow, the son of Indra, through a blade of grass
Aswatthama used brahmashira, through a blade of grass, against the descendants of Pandavas, which killed the unborn baby in the womb of Uttara.
b) Indrajit used brahmastra in 2 ways
to catch hold of Sri Hanuman, who was found invincible (Sundara kanda)
to eliminate 67 crores of vanaras in a single day
सप्तषष्टिर्हताः कोट्यो वानराणां तरस्विनाम् | अह्नः पञ्चमशेषेण वल्लभेन
स्वयम्भुवः || (Yuddha Kanda 74 Sarga 12 Sloka)
Sixty seven crores of powerful monkeys were struck down by the
cherished missile of Brahma, the self-born creator, in the fifth and
last period of the day.
In all cases, if we observe closely, we will find that except the targetted people no one else got affected due to impact of that DIVINE weapon.
For example, when Indrajit used the brahmAstra, it affected Vanaras only, but not Rakshasas, who were also present in the war field.
Coming to the aspect of non-availability of those DIVINE weapons now, we have to remember that even in that era also, only a handful of few were described to be in possession of those weapons, but not all.
So to acquire those DIVINE weapons, rigorous training, practice, etc are needed. When those qualities were not found in subsequent generations, they might have lost to the them.
Losing of knowledge in any field occurs not only in one field alone, but in many fields.
One accomplished Guru in Gayatri Mantra said once (Sri Paakalapati Guruvu - Telugu) that mere keeping of hands in a form and touching some parts of body and reciting mantra, does not assure Siddhi in Gayatri mantra.
It needs something else, which will be made known to the eligible aspirants by the NATURE/GOD directly, but not to all.
It is confidential knowledge.
That was why, he added, not many people were able to get the Siddhi in that Mantra.
Same is the case with DIVINE weapons. Only the eligible ones will get the knowledge, but not by everyone.
Who is eligible, will be decided by the God alone.