Sensitivity of Mars Entry Navigation Errors to Sensed Acceleration Threshold

The results of an investigation to quantify the sensitivities of the MSL ’09 entry navigation performance associated with selection of the sensed acceleration threshold in the navigation fllter are presented. During the pre-parachute deploy phase, the dead-reckoning process beneflts by appropriately removing low-level accelerometer noise and biases prior to integration. This is accomplished with the sensed acceleration threshold setting. Setting the threshold level too low allows undesired noise and bias to corrupt the state estimate. Setting the threshold too high may result in missing actual nongravitational accelerations in the state integration. Neither situation is acceptable. This study aims to deflne the relationships, if any, between the fllter performance for several early cruise separation cases and the selected sensed threshold value. The fllter performance was deflned to be the state uncertainty at supersonic parachute deploy. The analysis of the results presented include the behavior of the altitude, range, and attitude navigation errors for selected values of the sensed acceleration threshold and orbital cruise separation times. All conclusions are supported by Monte Carlo experiments. It was found that there exists acceptable values for the sensed acceleration threshold to provide accurate state estimation to support parachute deploy for the range of cruise separation considered.