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The FreeFlyer orbit determination (OD) system is a robust, easy-to-use, and convenient system for computing a weighted fit between a user's measurements and the propagated a priori state of a Spacecraft. Orbit determination takes many forms and has many options available for designing and tuning a system to minimize residuals and maximize likeliness of convergence. The "estimator" is the core of any OD process. It contains references to the objects to be estimated (Spacecraft, Transponders, etc) as well as references to all tracking data to be processed.
Currently, FreeFlyer supports four kinds of estimators: Batch Least Squares, Extended Kalman Filter, Square Root Information Filter, and the Unscented Kalman Filter. Many objects, including the Spacecraft and GroundStation objects, have properties that can be estimated by these estimators.
An Observation represents a collection of Measurements taken at the same time. All the Measurements in an Observation have the same observer and object being observed. Each Measurement contains its own statistics, such as Pre- and Post-Update Residuals. Currently, FreeFlyer supports several types of Observations, discussed in below guides. Tracking data also comes in many different formats, depending on data type and the observing system (e.g. DSN, USN, TDRS). FreeFlyer currently supports natively reading and writing several tracking data formats, discussed in the guides of this section.
Note: The deprecated orbit determination system from FreeFlyer 6.5 and earlier is not available in versions of FreeFlyer 6.10 and higher.
Table of Contents
The FreeFlyer orbit determination system guide covers the following topics: