An industrial inspection drone control system, the control system comprising: a plurality of radar sensors for placement on the drone to sense the location of one or more object(s) in three dimensions around the drone and provide output signals relating to the sensed location of the object(s); and a controller; wherein the controller is configured to determine a position and a velocity of the drone relative to the object(s) based on the output signals of the radar sensors and without reference to GPS or other satellite positioning signals; and wherein the controller is configured to control flight and collision avoidance of the drone based on the determined position and velocity; and wherein the plurality of radar sensors are configured to be located on the drone so that the location of objects can be sensed in each direction along three orthogonal axes, wherein the drone control system comprises an Inertial Measurement Unit (IMU) configured to sequentially output accelerometer data, wherein the controller is configured to correct the IMU bias, based on tracking of the one or more object(s), wherein the controller is configured to determine an observed distance of the drone relative to the object(s) based on the output signals of the radar sensors , wherein the drone control system further comprises - a third order Kalman filter with bias gain compensation on acceleration, wherein the drone control system is configured for - spawning an instance of the Kalman filter for each of the one or more object(s), - predicting, in a first frame of the Kalman filter, a predicted distance of the object by fusing the observed distance with a first accelerometer data, and for each consecutive accelerometer data - correcting, in a next frame of the Kalman filter, the predicted distance, the predicted velocity and a predicted acceleration bias, by fusing the difference between the predicted and the observed distance with the accelerometer data. a plurality of radar sensors for placement on the drone to sense the location of one or more object(s) in three dimensions around the drone and provide output signals relating to the sensed location of the object(s); and a controller; wherein the controller is configured to determine a position and a velocity of the drone relative to the object(s) based on the output signals of the radar sensors and without reference to GPS or other satellite positioning signals; and wherein the controller is configured to control flight and collision avoidance of the drone based on the determined position and velocity; and - a third order Kalman filter with bias gain compensation on acceleration, wherein the drone control system is configured for - spawning an instance of the Kalman filter for each of the one or more object(s), - predicting, in a first frame of the Kalman filter, a predicted distance of the object by fusing the observed distance with a first accelerometer data, and for each consecutive accelerometer data - correcting, in a next frame of the Kalman filter, the predicted distance, the predicted velocity and a predicted acceleration bias, by fusing the difference between the predicted and the observed distance with the accelerometer data. <EOS>