Are these thrusters omni-directional? Conventional stuff would be blasting things upwards giving downward (towards the core/center) momentum and acceleration. Where I understand that 1 thruster might be OP and just split the moon into halves, 2 of them spaced 90 or 120 degrees can provide motion required to push moon further up from the planet.
But putting 3rd thruster in opposite direction is actually counter-productive and can be considered only as fantasy magical physics. And I lack PhD in that area.