A system for detecting satellite signal spoofing using error state estimates, the system comprising: at least one satellite receiver to receive satellite signals; at least one memory, the at least one memory configured to store at least operation instructions; and at least one controller in communication with the at least one satellite receiver and the at least one memory, the at least one controller configured to determine state estimates from the received satellite signals, and characterized in that the at least one controller is further configured to determine error state estimates based at least in part on differences in current state estimates and differences in delayed state estimates, the controller further configured to determine if spoofing is occurring in one or more of the received satellite signals when the error state estimates are greater than a select threshold; wherein the system further comprises: at least one sensor (105, 114), wherein the determined state estimates include satellite state estimates determined from the satellite signals and sensor state estimates determined from sensor information from the at least one sensor, the at least one controller configured to determine the error state estimates based on differences between the sensor state estimates and the satellite state estimates; a Kalman filter configured to generate state corrections and, optionally, error covariances based on the sensor state estimates and the satellite state estimates; wherein the at least one controller is further configured to: apply the state corrections to the sensor state estimates to generate current total state estimates; delay one of the current total state estimate and the state corrections to generate delayed total state estimates; and compare the current total state estimates with the delayed total state estimates to determine the error state estimates. at least one satellite receiver to receive satellite signals; at least one memory, the at least one memory configured to store at least operation instructions; and at least one controller in communication with the at least one satellite receiver and the at least one memory, the at least one controller configured to determine state estimates from the received satellite signals, and characterized in that the at least one controller is further configured to determine error state estimates based at least in part on differences in current state estimates and differences in delayed state estimates, the controller further configured to determine if spoofing is occurring in one or more of the received satellite signals when the error state estimates are greater than a select threshold; wherein the system further comprises: at least one sensor (105, 114), wherein the determined state estimates include satellite state estimates determined from the satellite signals and sensor state estimates determined from sensor information from the at least one sensor, the at least one controller configured to determine the error state estimates based on differences between the sensor state estimates and the satellite state estimates; a Kalman filter configured to generate state corrections and, optionally, error covariances based on the sensor state estimates and the satellite state estimates; at least one sensor (105, 114), wherein the determined state estimates include satellite state estimates determined from the satellite signals and sensor state estimates determined from sensor information from the at least one sensor, the at least one controller configured to determine the error state estimates based on differences between the sensor state estimates and the satellite state estimates; a Kalman filter configured to generate state corrections and, optionally, error covariances based on the sensor state estimates and the satellite state estimates; apply the state corrections to the sensor state estimates to generate current total state estimates; delay one of the current total state estimate and the state corrections to generate delayed total state estimates; and compare the current total state estimates with the delayed total state estimates to determine the error state estimates.