Can you clarify what you mean by that please?
What protects from radiation?
What are "sub-surface tracks" and the "acceleration" they provide?
And then, how much energy would it even take to spin such a huge rock? I think you’d need a new exotic propulsion system just to rotate it. Maybe nuclear or a sustained ion propulsion.
Being beneath the surface provides radiation protection.
Specifically by digging out tunnels beneath the surface of moderates size asteroids, putting down butyl ruber tubes, and laying tracks within. By having the cars on the track go around the curved track an artificial gravity is induced.
But you can stop the space train cars, step outside, and there's no deep gravity well to make getting things to and from there so expensive.
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I'd also like to make it clear that the Asteroid Retrieval Bus, the mission that was canceled, is the reason the lunar gateway concept exists. Having the lunar gateway but not asteroid de-spin and retrieval is putting the cart before the horse without intentions of getting a horse.
https://en.wikipedia.org/wiki/Power_and_Propulsion_Element#A...
>The Asteroid Redirect Vehicle... ...mission was cancelled in early 2017 and the spacecraft's propulsion segment became the Power and Propulsion Element (PPE) for the Deep Space Gateway, now known as the Gateway.