hou_config.cfg

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[Gravity Parameter]
# This section specifies the gravity parameter G
# in units of [METERS^3/SECONDS^2]
G: 6.67e-11

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[Initial Conditions]
# This section defines the initial conditions to 
# be integrated. The units of all inputs here
# are defined as [MKS]

# The Fahnestock Input File Flag Toggles the use
# of a predefined input file which will cause the 
# software to ignore the initial conditions, 
# gravity parameter, and densities defined in
# this config file. For documentation on this 
# file format see the {NAME TBD} file as 
# described in the documentation.
# BE SURE THIS VALUE IS SET TO 0 IF USING USER
# DEFINED INITIAL CONDITIONS, GRAVITY PARAMETER,
# OR DENSITY VALUES 
Fahnestock Input File Flag: 0

# FRAME DEFINITIONS--------------------------
# The N Frame is defined as the inertial frame
# The A Frame is defined as the primary's body-
# fixed frame
# The B Frame is defines as the secondary's
# body fixed frame
# All frames are initially aligned unless a non-
# identity rotation matrix is specified below.
# The body frames are defined based on the 
# orientation of the vertex file input for the 
# body shape or for the cases of ellipsoid and
# sphere shaped bodies such that the x-axis is
# aligned with the major axis and the z-axis is
# aligned with the minor axis
# FRAME DEFINITIONS--------------------------

# The Relative Position is defined as the vector
# from the primary's center of mass to the 
# secondary's center of mass. The vector is defined
# in the A frame
Relative Position X: 1200.0
Relative Position Y: 0.
Relative Position Z: 0.

# The Relative Velocity is defined as the velocity
# of the secondary's center of mass relative to the
# primary's center of mass. The vector is defined
# in the A frame not considering the frame rotation
Relative Velocity X: 0.
Relative Velocity Y: 0.175704287113523
Relative Velocity Z: 0.

# The Angular Velocities are defined in the body
# fixed frames A or B respecively
Primary Angular Velocity X: 0.0
Primary Angular Velocity Y: 0.0
Primary Angular Velocity Z: 0.000772269580528
Secondary Angular Velocity X: 0.0
Secondary Angular Velocity Y: 0.0
Secondary Angular Velocity Z: 0.000146420239261

# The B into A values define the rotation matrix
# which maps a column vector expressed in the B
# frame into the A frame and thus describe the
# relative attitude of the two bodies. If Euler
# Angles are a prefered attitude representation 
# see the B into A Euler descriptions below
B into A (1,1): 1.0
B into A (1,2): 0.0
B into A (1,3): 0.0
B into A (2,1): 0.0
B into A (2,2): 1.0
B into A (2,3): 0.0
B into A (3,1): 0.0
B into A (3,2): 0.0
B into A (3,3): 1.0

# To toggle the Euler Angle description of the 
# B into A rotation matrix set the B into A Euler
# Flag to 1. The Euler angles 1, 2, and 3 are
# ordered such that the Euler 1 is a rotation about
# the Body B x-axis, the second is a rotation about
# the Body B y-axis and the third is a rotation about
# the Body B z-axis. All rotations are in radians

B into A Euler Flag: 1
B into A Euler 1 X: 0.
B into A Euler 2 Y: 0.
B into A Euler 3 Z: 0.

# The A into N values define the rotation matrix 
# which maps a column vector expressed in the A
# frame into the N frame and thus describes the 
# inertial orientation of the primary, functionally
# it is used to define the orientation of the 
# system in the ecliptic. If Euler
# Angles are a prefered attitude representation 
# see the A into N Euler descriptions below
A into N (1,1): 1.0
A into N (1,2): 0.0
A into N (1,3): 0.0
A into N (2,1): 0.0
A into N (2,2): 1.0
A into N (2,3): 0.0
A into N (3,1): 0.0
A into N (3,2): 0.0
A into N (3,3): 1.0

# To toggle the Euler Angle description of the 
# A into N rotation matrix set the A into N Euler
# Flag to 1. The Euler angles 1, 2, and 3 are
# ordered such that the Euler 1 is a rotation about
# the Body A x-axis, the second is a rotation about
# the Body A y-axis and the third is a rotation about
# the Body A z-axis. All rotations are in radians

A into N Euler Flag: 1
A into N Euler 1 X: 0.
A into N Euler 2 Y: 0.
A into N Euler 3 Z: 0.

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[Integration Settings]
# This sections allows the user to select the 
# integration time, scheme, and settings.

# The Start and Final Time values set the integration
# time and are defined in [SECONDS]. 
Start Time: 0.0
Final Time: 7200.

# The Integrator Flag allows the user to toggle
# between a fixed step RK4 integrator, an 
# adaptive RK 7(8) Dormand-Prince Integrator,
# the fixed step LGVI, and a fixed step Adams-
# Bashforth-Moulton predictor-corrector integrator.
# All of the fixed step integrators take in a fixed 
# time step to control their accuracy. The RK4 and ABM 
# do not conserve SO(3) and thus will have worse attitude
# conservation than the LGVI which does conserve
# SO(3). The RK 7(8) integrator will adapt a time
# step based on an absolute tolerance on the state
# integration accuracy and will provide faster
# integration but will only provide coarse 
# time-step outputs. The lGVI is the fastest but cannot
# calculate the effects of perturbations. For external
# pertubations, the RK4 or ABM must be used. For internal
# tidal perturbations, the RK4, RK 7(8), or ABM must
# be used. The ABM is roughly as accurate as the RK4 but
# is twice as fast. The LGVI is limited to pure
# full two-body dynamics.

# For the RK4 set that flag to 1, set the flag to 
# 2 for the LGVI, set the flag to 3 for the RK 7(8), 
# set the flag to 4 for the A-B-M.
Integrator Flag: 2

# The Fixed Time Step defines the time step to be
# used in the RK4, ABM, and LGVI integrators. It is
# defined in [SECONDS]
Fixed Time Step: 30.

# The Absolute Tolerance defines the adaptive state
# tolerance to be used by the RK 7(8) integrator
# and will force the magnitude of the state error
# to remain below the tolerance for each time step
Absolute Tolerance: 1.e-15

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[Output Settings]
# This section allows the user to define the output
# times of the integration. It is of note that at
# this time no interpolation techniques have been
# developed for the RK 7(8) integrator such that 
# all integration steps must be post processed
# for this selection of integrator

# Do any post processing?
# set to 1 if you want to output all the various .csv output files
# if set to 0, only the binary output files are written
# the post-processing to generate ascii output significantly
# increases the run time
Post Processing: 1


# The Fixed Output Frequency allows the user to 
# toggle and select a fixed frequency of post-
# processed data. A value of -1 will signal the
# software to use the Specified Time List below.
# A value of 0 signals the system to process all
# time steps of the integrator (this is the only
# option if the RK 7(8) is being used). The third
# option is to specify a fixed time step of outputs
# to be post processed in seconds (this value must
# be commensurate with with the fixed integration 
# time step used
Fixed Output Frequency: 3600.

# If the Fixed Output Frequency is set to -1 the 
# software will look for a list of time steps
# provided in a .csv file format. If this option is
# selected provide the .csv filename (with the 
# .csv extension) below. The time steps should 
# be specified in seconds and must be commensurate
# with the fixed time step used in the integrator.
# The .csv file should be specified as a single row
# of time values.
Specified Time List Filename: filler.csv

# The Case Name is a file tag which can be input as
# any string value. The standard output file names
# are described in the documentation where the Case
# name is a tag included as part of the name
Case Name: Test

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[Body Model Definitions]
# This section defines the shape and density of the
# bodies. Many of these values are specific to the 
# selected shape definitions, but must still be set
# even if the corresponding shape definition is not
# selected; in this case arbitrary values can be
# input

# The Inertia Integral Generation Flag tells the
# software whether or not to generate inertia
# integral during the run, with 1 being the
# the selection to generate them and 0 telling
# the software to use previously computed values.
# If the bodies have not been simulated previously
# then the value must be set to 1. Unless the 
# inertia integral orders to be computed (see
# Mutual Gravity Expansion Parameters section below)
# are beyond order 6, this parameter should be 
# kept on (with the value of 1). If the value is 
# set to 0, the software will use any files named
# TDP_[N].mat, TDS_[N].mat, IDP.mat, and IDS.mat
# in the local folder (these are the files containing
# the inertia integrals and moments of inertia 
# generated for a given run where [N] is the 
# Gravity Expansion Truncation Order). It is thus
# imperative that the user is very careful about
# these files if this flag is set to 0.
Inertia Integral Generation Flag: 1

# The Primary and Secondary Shape Flags tell the 
# system whether each body is to be modelled as
# either a sphere (Flag=0), an ellipsoid (Flag=1),
# or as a polyhedron shape approximation (Flag=2).
# An oblate spheroid can be simulated via the
# ellipsoid shape selection. There certain limits
# on the inertia integral implementation which 
# can be used for the sphere and ellipse case 
# which are explained in the Mutual Gravity
# Expansion Parameters section below.
Primary Shape Flag: 2
Secondary Shape Flag: 1

# The Primary and Secondary axes are used to define
# the shape for the sphere and ellipsoid selections.
# The semi-axes here are defined from the center of 
# the body to the maximal extent along each of its 
# axes in [METERS]. The semi-major axis is assumed 
# to be along the x-axis of the body frame, the 
# semi-intermediate axis is assumed along the y-axis
# of the body frame and the semi-minor axis is 
# assumed along the z-axis of the body frame. Be sure 
# that your bodies are aligned as intended by reading 
# the frame definitions described in the Initial 
# Conditions section above. If a spherical shape is
# selected simply set all axes to equal values
Primary Semi-Major Axis: 576.7195
Primary Semi-Intermediate Axis: 576.7195
Primary Semi-Minor Axis: 576.7195
Secondary Semi-Major Axis: 103.16
Secondary Semi-Intermediate Axis: 79.35
Secondary Semi-Minor Axis: 66.13

# The Vertex and Tertahedron files are [.CSV] files 
# which define the polyhedron approximation shape 
# models. The Vertex files should be formatted as 4
# columns with the first column being the vertex
# IDs or filler values, and the second through fourth
# columns being the x, y, and z coordinated of the
# vertices in the body fixed frame. The units of the
# coordinates should be [METERS]. The tetrahedron
# files should be 3 columns where each row lists the 
# 3 vertices of a tetrahedron connected to the body
# center of mass (at the origin). The vertex files
# should be aligned with the principal body axes
# such that the body-frame inertia tensor is diagonal.
Primary Vertex File: Didymos_A_vert_met.csv
Primary Tetrahedron File: Didymos_A_facet.csv
Secondary Vertex File: Didymos_B_vert_met.csv
Secondary Tetrahedron File: Didymos_B_facet.csv

# All bodies are assumed to be of constant density.
# The densities should be described as [GRAMS/CENIMETER^3]
Primary Density: 2.203111036687207
Secondary Density: 2.203111036687207

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[Mutual Gravity Expansion Parameters]
# This section defines the expansion order used when
# mutual gravity and inertia integrals are computed
# values should be integers from 0-N, where order 0
# is equivalent to a point mass, order 2 will account
# obliquity effects such as J2, C22, etc, orders higher
# than 2 will similarly capture the behaviors of the 
# equivalently ordered spherical harmonics

# The Gravity Expansion Truncation Order defines the 
# order that the mutual gravity potential will be 
# computed at, in the Hou paper this is the value N.
# If the primary or secondary shape models selected 
# are polyhedra, their inertia integral truncation 
# order will automatically be increased to match this
# value. Likewise if the either body's inertia integral
# truncation order is higher that the gravity expansion
# order, the gravity expansion truncation order will
# be increased.
Gravity Expansion Truncation Order: 4

# The Primary and Secondary Truncation Orders
# define the order of the inertia integrals to be 
# computed for each body. The selection of shape
# for each body affects the implementation of 
# these parameters. If the body has been set to a
# sphere or ellipsoid the inertia integrals 
# beyond this truncation order for the body will 
# be set to 0. It is also of note that the closed 
# form sphere and ellipsoid inertia integral 
# equations used are only implemented up to 
# order 4; if an ellipsoidal or spherical shape
# is desired with parameters computed beyond
# order 4 then a polyhedron approximation
# will be needed. Additonally if a polyhedron
# shape is selected for either body then the
# truncation order will automatically be raised
# to the Gravity Expansion Truncation Order.
Primary Inertia Integral Truncation Order: 4
Secondary Inertia Integral Truncation Order: 4

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[Additional Forces and Perturbations]
# This section allows the user to toggle and 
# specify parameters for additional modelled 
# forces and perturbations to the binary system

# 3rd body flyby orbit parameters. Flyby is toggle
# to turn on (1) or off (0)
# These should be in km, s, and radians
# Can specify either hyperbolic or elliptic, and
# keplerian dynamics are assumed between the 3rd body
# and the binary system barycenter.
# To use flyby code, integrator must be set to
# 1 (RK4) or 4 (ABM). The perturbation equations are
# outlined in Meyer & Scheeres 2021
Flyby: 0
Planetary Mass: 5.9722e24
Semimajor Axis: -1.1072e+04
Eccentricity: 9.1284
Inclination: 0.1745
RAAN: 0.1745
Argument of Periapsis: 0.1745
Flyby Time: 345600.0

# Heliocentric orbit parameters. Heliocentric Orbit is 
# toggle to turn on (1) or off (0)
# These should be in km, s, and radians.
# Keplerian dynamics are assumed between the sun
# and the binary system barycenter.
# To use heliocentric code, integrator must be set to
# 1 (RK4) or 4 (ABM). The perturbation equations are
# the same as the 3rd body flyby, but allows for the 
# use of 3rd body and heliocentric perturbations
# simulatneously.
Heliocentric Orbit: 0
Sun Mass: 1.989e+30
Heliocentric Semimajor Axis: 246013901.32
Heliocentric Eccentricity: 0.38362664
Heliocentric Inclination: 0.059475759
Heliocentric RAAN: 1.277649080300677
Heliocentric Argument of Periapsis: 5.5732150380
Time of periapsis passage: 2582993.15688

# Model for solar gravity uses Hill's Problem
# to approximate the solar gravity effects from
# a planar circular orbit. The binary is treated
# as a single mass to compute the systems mean 
# motion. Toggle this force by setting Solar 
# Gravity to 1, 0 to toggle off. Solar Orbit 
# Radius specifies the circular orbit radius 
# of the binary in [AU]. AU Definition allows the
# user to specify the number of [m] in an AU.
# Solar Mass should be specified in [kg].
# NOTE this is legacy code. For a more accurate
# solar gravity perturbation use the heliocentric
# orbit toggle above
Solar Gravity: 0 
Solar Orbit Radius: 1.
AU Definition: 149597870700.
Solar Mass: 1.988e30

# Tidal dissipation model assumes each body 
# experiences the tidal torque model defined
# in Murray and Dermott Solar System Dynamics.
# The binary asteroid modification defined in 
# Jacobson and Scheeres 2011 is used to ensure 
# that the model remains consistent as each
# body rotates. 3D considerations are made
# following Meyer et al 2022.
# Tidal Torque can be set to 1 or
# 0 turn toggle it on or off. Primary and Secondary
# Love Number provide the value for each. Primary
# and Secondary Reference Radius are used as
# the body radius value for the torque, enter
# in [m]. The tidal lag angles should be provided
# as [rad].
Tidal Torque: 0
Primary Love Number: 1.e-5
Secondary Love Number: 1.e-5
Primary Reference Radius: 660.
Secondary Reference Radius: 225.
Primary Tidal Lag Angle: .005
Secondary Tidal Lag Angle: .005