Setting ExtendedKalmanFilter.ProcessNoiseTimeStep to 0 when using SN measurements yields an error message "Estimator Exception: Unable to find a matching epoch between the forward and backward filter data while smoothing" during the smoother run
See test case Smoother_Filter_ProcessNoiseTimeStep_0sec_SN
Smoother residuals for SN measurements are very large
See test case EKFS_SpacecraftNavigation_SolveFors_CartesianState_SN
Duplicate of GMT-7376.