1. A system for providing semi-autonomous control of a mechanical device, the system comprising: a computer control system, configured to combine at least predicted device controller inputs into a scalar threat assessment metric, the computer control system determining the scalar threat assessment metric based at least on predicted stability of the device through the time horizon, the computer control system being further configured to determine a type and degree of operator assistance to provide as a threat response based on at least the scalar threat assessment metric; and an actuator configured to actuate a system of the device to execute operator assistance based on an actuator input, the actuator input being based on at least the threat response determined by the computer control system.