Okay, this works and makes the rocket point toward the mouse.
            mouseDirection = rotation2D(Math.atan2(gMouse.y-_y, gMouse.x-_x))*180/Math.PI;
            //_rotation = mouseDirection; <This works Perfectly, but no easing...
//My failing attempts at easing...
            Radians = _rotation*Math.PI/180;
            _x += Math.sin(Radians)*5;
            _y -= Math.cos(Radians)*5;
//ANother...
            _x -= _root.rocketSpeed*Math.cos(mouseDirection*Math.PI/180);
            _y -= _root.rocketSpeed*Math.sin(mouseDirection*Math.PI/180);