Sometimes the brain’s auditory cortex can 'misfire' and create sounds or voices that feel 100% real, even when there's no outside signal. It’s actually a documented medical phenomenon.
Comparing this to Dachau suggests you’re feeling a massive amount of psychological pressure. Usually, when the mind is under extreme, prolonged stress, it can start to externalize internal thoughts as voices or 'beamed' messages. It might be worth talking to a professional about the distress this is causing you—they might have ways to help mute those signals.
If we're talking about objects in the asteroid belt, the internal consistency varies wildly. Most smaller objects are indeed rubble piles: boulders, pebbles, and sand-like grains, down to dust. As you'd expect, they're very weak structurally. Notably, the OSIRIS-REx probe was nearly swallowed by its loose material during the sample collection on Bennu.
Some of the other large, iron-rich asteroids like Ceres, Vesta, Pallas, and Interamnia are more like protoplanets than rubble piles.
Besides the concern for structural integrity/stability, they also have reasonable amounts of water ice, volatiles, metals, ad other resources needed to supply an outpost.
I think TM's basic mantra practice would qualify as an Attentional practice. I don't now much about more advanced practices in that school, so I'm not sure.
This type of meditation - a secularized form of Vipassana in which one passively observers mental events - is very popular in the West.
But it's not the only one, and shouldn't be called merely "meditation" without regard to the vast body of practices that exist.
Another form of meditation that's traditionally talked about in Buddhism is shamatha, which translates to something like "concentration" or "tranquility." In this type of practice, the meditator works with a meditation object, commonly the breath, but possibly a sound, mental image, etc. The meditator learns to stabilize the mind and remain fully aware of the object, and in the process learns to debug the mechanisms that direct (and destabilize) conscious attention.
A recently published book called _The_Mind_Illustrated_ by John Yates is fa fantastic resource for this kind of practice.
If you're interested in scientific attempts to categorize and study meditation, the Center for Healthy Minds at UW-Madison does some fantastic neuroscience & psychology research.
In the scientific terminology that is emerging these days, Attentional, Constructive, and Deconstructive types of meditation are mapped onto various types of traditional practices (there's a handy chart in the paper).
Comparing this to Dachau suggests you’re feeling a massive amount of psychological pressure. Usually, when the mind is under extreme, prolonged stress, it can start to externalize internal thoughts as voices or 'beamed' messages. It might be worth talking to a professional about the distress this is causing you—they might have ways to help mute those signals.