Acceleration History File Format

You can use an acceleration history file (*.accelhist) to specify a finite maneuver in Astrogator and for use in Orbit Determination Tool Kit (ODTK). Each data point provides the time (relative to a start time), an acceleration vector, and the rate of loss of mass.

Keywords

Each acceleration history file table contains some common elements called keywords. Keywords and their associated values (except END) must precede the specification of the data and the actual data points.

Keyword	Required	Description
stk.v.<major release number>.<minor release number>	Yes	This is the version of STK software for which the file is formatted to be used. You can create files in and import them to STK software versions consistent with the file version stamp or higher. The version stamp must be the first line in the data file. Example: stk.v.11.0
BEGIN AccelHistory END AccelHistory	Yes	Sets off the beginning and end of the acceleration history file table, including all other keyword phrases and data point specification (except the version stamp).
NumberOfEphemerisPoints	Yes	Enter the total number of data points in the file.
ScenarioEpoch	Yes	Specify the reference epoch time for the time values of the acceleration history data in the table. Specify the scenario epoch using Gregorian UTC time (`dd mmm yyyy hh:mm:ss.s`). There is no relationship between the scenario epoch specified here and the actual scenario epoch in your STK scenario. Example: ScenarioEpoch 1 Jan 2003 00:00:00.0 In this case, a time of `5.5` for a particular acceleration history data point would correspond to a time of `1 Jan 2003 00:00:05.5`.
CentralBody	No	Specify the central body associated with the CoordinateSystem (see below). The keyword value that completes the phrase can be the name of any registered central body. Registered central bodies are in the `STKData\CentralBodies` directory. Example: CentralBody Earth The default is the central body for the vehicle, and Earth is the default for the vehicle.
CoordinateSystem	Yes	Specify the coordinate system in which the acceleration vectors in the data table are expressed. Normally, the coordinate system is the name of a valid coordinate system for the central body specified above (see Central Body Coordinate Systems). Typically, each central body supports Fixed, J2000, ICRF, and Inertial. You can also use the Vector Geometry Tool (VGT) by specifying the name of the system and the name of the STK object to which it corresponds. A VGT-created system must use the keyword CoordinateSystem AWB. Examples: CoordinateSystem TrueOfEpoch CoordinateSystem AWB RIC The name of the STK object is optional if the object that is importing the data is the object to which the coordinate system corresponds. If you choose a VGT coordinate system, you cannot export that maneuver to ODTK.
InterpolationOrder	No	This is the interpolation order for the Lagrange interpolation between data points. The default is 1 (linear). Example: InterpolationOrder 3
(format keyword)	Yes	The only option for this is EPHEMERISTIMEACCMASSRATE. See the data format section of this topic.

Acceleration History File data format

Use this format to specify actual data points in the acceleration history file data table. You must include the format keyword EPHEMERISTIMEACCMASSRATE in the file on its own line, after the header keywords and before the actual data point array.

Individual data points follow the keyword and look like this:

where,

`<Time>`	This is the time value of the data point, expressed as seconds since the reference epoch specified in the keyword ScenarioEpoch. For central body coordinate systems, Astrogator will transform the accelerations in the file into central body inertial, assuming the times in the file are relative to the maneuver start time. However, Astrogator will execute the maneuver to follow the accelerations assuming the first point in the file is exactly at the maneuver start time. Therefore, when using central body coordinate systems, ensure that the first data point in the file has Time = 0 sec, so that the executed thrust matches the planned thrust. This will always be true when exporting an acceleration history file from STK.
`<ACCELx> <ACCELy> <ACCELz>`	These are the acceleration vector components in the X, Y, and Z axes of the coordinate system specified in the keyword CoordinateSystem.
`<MassChangeRate>`	This is the rate of loss of mass (in kg) of the vehicle for that point in time (<Time>) due to burning of fuel during the maneuver.

Example file

The following example shows all the keywords as well as some data points from the beginning and end of a 3600-second-long maneuver (3601 data points).

stk.v.12.5

BEGIN AccelHistory

NumberOfEphemerisPoints    3601
ScenarioEpoch              20 Aug 2022 16:00:00.000
CentralBody		    Earth
CoordinateSystem           ICRF
InterpolationOrder         3

EPHEMERISTIMEACCMASSRATE

0.000000000000000e+00       0.000000000000000e+00       2.197042781654913e-01       1.192896900649021e-01      -1.699527021629881e-01
1.000000000000000e+00      -2.896772410142835e-04       2.197228034889743e-01       1.192997448111858e-01      -1.699527021629881e-01
2.000000000000000e+00      -5.793939305753698e-04       2.197410372057922e-01       1.193096407467934e-01      -1.699527021629881e-01
3.000000000000000e+00      -8.691496897514908e-04       2.197589792708467e-01       1.193193778472522e-01      -1.699527021629881e-01
4.000000000000000e+00      -1.158944139533764e-03       2.197766296394189e-01       1.193289560882967e-01      -1.699527021629881e-01
5.000000000000000e+00      -1.448776900836650e-03       2.197939882671698e-01       1.193383754458691e-01      -1.699527021629881e-01
6.000000000000000e+00      -1.738647594498405e-03       2.198110551101410e-01       1.193476358961194e-01      -1.699527021629881e-01
7.000000000000000e+00      -2.028555841281543e-03       2.198278301247539e-01       1.193567374154049e-01      -1.699527021629881e-01
8.000000000000000e+00      -2.318501261873292e-03       2.198443132678102e-01       1.193656799802909e-01      -1.699527021629881e-01
9.000000000000000e+00      -2.608483476886062e-03       2.198605044964930e-01       1.193744635675506e-01      -1.699527021629881e-01
1.000000000000000e+01      -2.898502106857897e-03       2.198764037683653e-01       1.193830881541649e-01      -1.699527021629881e-01
1.100000000000000e+01      -3.188556772252942e-03       2.198920110413714e-01       1.193915537173227e-01      -1.699527021629881e-01

			...
			...
			...
			
3.589000000000000e+03       1.405954716005868e-01      -2.911186305149715e-01      -1.576970016446098e-01      -1.699527021629881e-01
3.590000000000000e+03       1.408564264319978e-01      -2.910634090766518e-01      -1.576663926359584e-01      -1.699527021629881e-01
3.591000000000000e+03       1.411173231751882e-01      -2.910080333977036e-01      -1.576356999155639e-01      -1.699527021629881e-01
3.592000000000000e+03       1.413781617286161e-01      -2.909525035558630e-01      -1.576049235260159e-01      -1.699527021629881e-01
3.593000000000000e+03       1.416389419908580e-01      -2.908968196288945e-01      -1.575740635099186e-01      -1.699527021629881e-01
3.594000000000000e+03       1.418996638606102e-01      -2.908409816945916e-01      -1.575431199098921e-01      -1.699527021629881e-01
3.595000000000000e+03       1.421603272366878e-01      -2.907849898307766e-01      -1.575120927685715e-01      -1.699527021629881e-01
3.596000000000000e+03       1.424209320180249e-01      -2.907288441153006e-01      -1.574809821286073e-01      -1.699527021629881e-01
3.597000000000000e+03       1.426814781036745e-01      -2.906725446260424e-01      -1.574497880326649e-01      -1.699527021629881e-01
3.598000000000000e+03       1.429419653928089e-01      -2.906160914409101e-01      -1.574185105234250e-01      -1.699527021629881e-01
3.599000000000000e+03       1.432023937847191e-01      -2.905594846378396e-01      -1.573871496435833e-01      -1.699527021629881e-01
3.600000000000000e+03       1.434627631788145e-01      -2.905027242947949e-01      -1.573557054358502e-01      -1.699527021629881e-01


END AccelHistory