To begin configuring an Unscented Kalman Filter estimation process in FreeFlyer, add an UnscentedKalmanFilterOD object to your Mission Plan using the Object Browser. After double-clicking on the new object, you will see the "Estimation Model" page of its object editor. From this page, you can set initial options, such as the maximum allowable residual sigma, the step size for propagating the covariance of the filter, and whether or not to maintain a history of measurements that have been processed.
Estimation Model Page of the Unscented Kalman Filter OD Object Editor
From this page you can also control the initial epoch for the filter, either by explicitly setting the epoch or using the epoch of a Spacecraft object. If the epoch is defined explicitly, the Epoch Details editor will be available. See Parsing Dates and Times for more information on working with the Epoch Details editor.
Epoch Details Editor for the Unscented Kalman Filter OD Object Editor
FreeFlyer also gives you control over the Alpha, Beta, and Kappa properties of the Scaled Unscented Transformation.
For information on configuring an Unscented Kalman Filter with a Smoother, see Setting up a Smoother.
You can also create and configure an UnscentedKalmanFilterOD object through FreeFlyer script. The syntax example below shows how to create the object and set its initial options.
// Create and set up Unscented Kalman Filter UnscentedKalmanFilterOD UKF;
UKF.MaxAllowableSigma = 6; UKF.StepSize = TIMESPAN(300 seconds);
// Set initial filter epoch:
// Specify epoch from Spacecraft UKF.InitialFilterEpochDefitionType = 0; UKF.SetInitialFilterEpochFromSpacecraft(Spacecraft1);
// Define epoch explicitly UKF.InitialFilterEpochDefitionType = 1; UKF.InitialFilterEpoch = TIMESPAN(25364.5 days);
// Set properties of the Scaled Unscented Transformation UKF.Alpha = 0.001; UKF.Beta = 0.5; UKF.Kappa = 1; |
Note: As of FreeFlyer 7.3, the default timing precision mode is nanosecond precision mode. For older Mission Plans that have not yet been converted from millisecond precision mode, the syntax for working with epochs and calendar date/time strings is different. See the timing precision mode page for more information.
Once this initial setup is complete, continue configuring your OD system by:
•Defining the A Priori States •Defining the Measurement Model •Defining Thrust Events •Defining the Properties to Estimate •Including Tracking Data |
See Also
•UnscentedKalmanFilterOD Properties and Methods |