In theory, if the force field is just taking less damage than we can repair, 2 force fields is possible to stay up forever
2 mk 1 force fields, put one in low power mode, when the one working is gonna die, turn on the low power mode and switch, engineer fix the force field, AND REPEAT, profit..
why? might be useful for a beach head, course, a better engi and a higher lvl ff is better to do this. also good for a control node.
(turning off the force field is not to damage the one you're repairing be4 it's full health)