Spacecraft Propagation

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FreeFlyer is a tool for spacecraft mission design and analysis. As spacecraft are dynamic objects, a mission design and analysis tool must simulate the motion of the spacecraft, both spatially and temporally. FreeFlyer uses a "Propagator" object to model spacecraft motion. There are two ways to propagate, or "step", the Spacecraft: an integration algorithm can be used in conjunction with a force model to step the Spacecraft through time, or an external ephemeris file can be used to specify spacecraft state information including epoch, location, attitude, and rates of change. There are many Propagators available in FreeFlyer. Propagators can be divided into two main categories, Ephemerides and Integrators.


Continue to the pages linked below for examples of how to set up and use a Spacecraft propagator. There are two ways to do most of this set up: via Object Editor, or via FreeFlyer Script. In general, Object Editors are a GUI-based system for speedy set up, and FreeFlyer Script gives more complete control of the properties and methods available for an object. For more on using Object Editors, see Creating/Editing Objects. For more on FreeFlyer Script, see Syntax and the FreeForm Script Editor.


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



Table of Contents

See the pages listed below for more information on spacecraft propagation and other related topics.


The Spacecraft Object

Stepping the Spacecraft

Physical Properties

Spacecraft Propagators

Spacecraft Subsystems

Spacecraft Visualization


Orbit State

oOrbit Element Types

oOrbit Reference Frames

oOrbit Wizard

Attitude State

oAttitude Systems

oAttitude Reference Frames

Working with Integrators

oSetting up an Integrator

oSetting up a Force Model

Gravitational Forces

Point Masses

Zonals and Tesserals

Solid Tides

Atmospheric Forces

Analytic Density Model

Harris Priester Density Model

Jacchia Roberts Density Model

MSIS Density Models

Solar Radiation Pressure

Other Accelerations

Working with Ephemerides

oCreating an Ephemeris File

oImporting an Ephemeris File

oAccessing Data in an Ephemeris

oUsing a SPICE Ephemeris

Working with TLEs and the SGP4 Propagator

oImporting Two Line Element Sets

oUsing the SGP4 Propagator

oGenerating TLEs Using the SGP4StateEstimator

oExporting Two Line Element Sets

Relative Motion

oHCW Propagation

oRelative Motion Orbit Wizard

oWorking with Relative Motion States