An example drilling system includes a rotary steerable system (RSS) having an inner shaft configured to rotate during drilling performed by the drilling system. One or more sensors are associated with the inner shaft to obtain one or more readings based on the drilling performed by the RSS. One or more processing devices may receive data based on the sensor readings and process that data in order to generate an output based on the sensor readings. The data may relate to stresses on the inner shaft and the data may be used for purposes including, but not limited to, controlling operation of the RSS in real-time, determining current condition of the RSS, and estimating a potential life expectancy of the RSS.