[douglas]

The sweep mines button is only really useful if someone launched mines where the ship is after it got there or if someone who already had a minefield there breaks a treaty with you after your ship got there. In those situations, you would have to move away and back in order to sweep the mines if not for the sweep mines button.

You keep losing your minesweepers because they don't have enough minesweeping ability. Each minesweeping component has a limited number of mines it can sweep each time it is used. When a ship enters a minefield, it sweeps as many as it can and then any remaining mines can blow up to destroy it. If multiple ships are in a fleet together, they all get to sweep before the minefield triggers. In stock (and TDM, which is only an AI mod), there is a maximum of 100 mines per sector for each player, so a fleet with at least 100 minesweeping ability can sweep any minefield that doesn't involve multiple empires without taking damage.