FreeFlyer Attitude History File

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The FreeFlyer Attitude History File (AHF) is a file format native to FreeFlyer that can be used for both input and output of Spacecraft attitude data. Attitude history files are useful when the Spacecraft attitude is not fixed or varying with a constant rate.


The data in the FreeFlyer-created Attitude History File is always specified in Quaternions with respect to the MJ2000 reference frame. The AHF is an extension of the FreeFlyer Ephemeris file and the content of the file may be specified to include attitude-only data or a combination of orbit and attitude data.


You can configure a Spacecraft to use an AHF by specifying the file through the Spacecraft Object Editor on the Attitude page, or via FreeFlyer Script. When an AHF is used, FreeFlyer will set the initial attitude state by finding the attitude in the AHF that corresponds to the Spacecraft's existing epoch, or interpolate the data points to that epoch if necessary. The spacecraft’s orientation at any time will be then be interpolated from the states in the AHF.



Format: Attitude Only Data

A FreeFlyer Attitude History File contains two sections, a header and body.



The header contains information about the attitude history file itself such as the version of FreeFlyer that created the file, start and stop epochs of the data, Spacecraft name, reference frame, etc.


FreeFlyer 7.4 Ephemeris

Spacecraft = "Spacecraft1"

StartTime = Jan 01 2020 00:00:00.000 UTC (Julian TAI:    28849.500428241)

StopTime = Jan 01 2020 00:00:00.000 UTC (Julian TAI:    28849.500428241)

CentralBody = Earth

ReferenceFrame = Mean of J2000

PrincipalPlane = Equatorial

UseAttitude = ON

Project = CreateSingleStateEphem.MissionPlan

FileCreationDate = Nov 14 2018 17:32:27.000 UTC



The body of the attitude history file contains all or a user-specified subset of data records of the spacecraft’s attitude, angular velocity and angular acceleration for a given epoch.


The output file will be of the format:

Epoch (UTC Calendar)    Q1    Q2    Q3    Q4    Epoch (TAI Julian)



Q1, Q2, Q3, Q4 is the MJ2000-to-BCS attitude quaternion



Format: Combination of Both Attitude and Orbit Data

When orbital ephemeris data is included with the attitude data, the orbital data is always listed in the columns prior to the attitude data. The TAI epoch is always the last column in the file. The format is:

Epoch(UTC Calendar)  X  Y  Z  Vx  Vy  Vz  Mass  Ax  Ay  Az  Q1  Q2  Q3  Q4  Wx  Wy  Wz  AlphaX  AlphaY  AlphaZ  Epoch(TAI Julian)



X, Y, Z are positions are in km

Vx, Vy, Vz are velocities in km/s

Mass is in kg

Ax, Ay, Az are accelerations in km/s2

Q1, Q2, Q3, Q4 is the MJ2000-to-BCS attitude quaternion

Wx, Wy, Wz is the angular velocity of the BCS with respect to MJ2000 in deg/s

AlphaX, AlphaY, AlphaZ is the angular acceleration of the BCS with respect to MJ2000 in deg/s2


For more information on the contents of the orbital data see the FreeFlyer ephemeris file format page.



See Also

Ephemeris Properties and Methods

The Put Command

Working with Ephemerides

oCreating an Ephemeris File

oImporting an Ephemeris File