I recently saw an interesting criticism of this paper: That by the end stages of the disassembly of Mercury, the amount of heat generated would be so much as to melt the surface, calling into question whether the mass driver system could work at such a high rate.
In the open space, shades get very cold, like a few degrees over absolute zero cold, because even without a medium to facilitate convection and (atmospheric contact) conduction, the loss of heat through mere radiation (into the pitch black universe) is very efficient (for normal, non-reflective materials). Thus, for an astral body to remain in a melted state, continuous steams of energy should be poured in (and some thermo-insulating gaseous atmosphere may also help to reduce cooling, if the body in question would have enough gravity to retain it), but that's hardly a thing to worry for a project where the energy itself is carefully controlled and dosed.
Refreshing to see a technical criticism of this paper for a change.