Orbit Determination

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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.


Note: This feature is unavailable for students using FreeFlyer Engineer-tier licenses as part of the FreeFlyer University program. If you are a student and have a need for the use of this feature, reach out to our FreeFlyer University team at ffuniversity@ai-solutions.com to discuss options.


There are a variety of Sample Mission Plans (included with your FreeFlyer installation) that demonstrate various applications of these topics. Continue to the Orbit Determination Samples page to view descriptions and images of these examples.


Table of Contents

The FreeFlyer orbit determination system guide covers the following topics:


Covariance Propagation and Visualization

Covariance Utilities

Setting up an OD System

oSpacecraft OD Setup

GNSS Receiver


TDRS Transponder


oGroundStation OD Setup


oThrust Event OD Setup

ImpulsiveBurn Setup

FiniteBurn Setup

OutgassingEvent Setup

oEstimation Techniques

Setting up Batch Least Squares Estimator

Setting up an Extended Kalman Filter

Setting up a Square Root Information Filter

Setting up an Unscented Kalman Filter

Setting up a Smoother

oDefining A Priori States

oDefining Measurement Model

oDefining Thrust Events

oDefining Properties to Estimate

oIncluding Tracking Data in an Estimation Process

Tracking Data

oSimulating Tracking Data

oGenerating Tracking Data Files

oUsing the Tracking Data Editor

oObservations and Measurements

BRTS Observations

Custom Observations

Deep Space Network (DSN) Observations

Ground Station Observations

Point Solution Observations

GNSS Observations

Spacecraft Observations

TDRS Observations

Performing State Estimation

oBatch Least Squares

oKalman Filter, Square Root Information Filter, and Unscented Kalman Filter