Ephemerides and AHF

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FreeFlyer can use the data contained in ephemeris files to seed an initial Spacecraft state, and then use an integrator and Force Model to "Step" the Spacecraft forward in time, or FreeFlyer can step the Spacecraft sequentially to the states represented by the data points in the ephemeris file, interpolating Spacecraft states in between data points if desired. See the Importing an Ephemeris File page for more information on stepping the Spacecraft using an ephemeris file.

 

FreeFlyer can write ephemeris data to an external file in several formats. For more information on writing ephemeris data to a file, see the Ephemeris Formats table below, the Creating an Ephemeris File page, and the Put command page of the Help file.

 

 

Ephemeris Formats

FreeFlyer can both read and write:

 

•Orbit Ephemerides (often referred to as simply an Ephemeris)

•Attitude Ephemerides (often referred to as an Attitude History File or AHF)

 

The FreeFlyer ephemeris file is an ephemeris-file format native to FreeFlyer which can contain orbit-only, attitude-only or attitude and orbit data. Later versions of that format also support user-defined columns, user-defined delimiters, adding discontinuities, setting interpolation methods for columns, and setting comments for ephemeris vectors. In addition, FreeFlyer also supports several other ephemeris and attitude history file formats, as shown below.

 

Supported Ephemeris Types

Write?

Format

Extra Pack Required?

FreeFlyer Ephemeris

Yes

(.ephem) or (.FFephem) ASCII Text

No

FreeFlyer AHF

Yes

(.ahf) ASCII Text

No

CCSDS OEM

Yes

ASCII Text

No

STK® Ephemeris

Yes

(.e) ASCII Text

No

STK® AHF

No

(.a) ASCII Text

No

SPICE Ephemeris

Yes

(.bsp)

No

Rinex Nav Files

Yes

(.n) ASCII Text

No

SP3 Ephemeris

Yes

(.sp3) ASCII Text

No

Code 500 PC Ephemeris

Yes

(.eph) Binary

NASA Pack

 

See the Creating an Ephemeris File page and the Put command for information on creating an ephemeris file from the Ephemeris Object.