The answers to my latest question on restarting Mars core have finally convinced me; I have abandoned the concept of doing so. However, whilst morosely browsing other questions on giving Mars a magnetic field, I happened upon Ville Niemi’s answer to What would be best way to re-melt Mars' mantle and core to revive its magnetosphere.
In it, they propose building a pair of giant electromagnets, one at either pole, which together produce a magnetosphere. The system draws electric current from the planet itself; thermocouples buried deep beneath the surface convert geological heat into electricity by the thermoelectric effect.
Now, ordinarily, I would be opposed to putting an entire planet’s habitability on any kind of fallible, man-made generator, where all it takes is for some wiring to blow to render the whole planet uninhabitable. However, I am now seriously considering going with this idea, because:
A: unlike most ideas along these lines, this one does seem like it could work continuously with zero maintenance on a timespan of millions of years
B: I’ve lost Venus; I’m desperate.😭
So, my question is, in essence, how long could this system realistically last without maintenance, and what is the tech-level required of a civilisation to build it?