N Plate (*.nplate) File Format
The N Plate (*.nplate) file is an ASCII-formatted file with a header section. The file specifies the following for a set of flat plates:
- size
- orientation
- physical characteristics
The purpose of the file is to allow STK to model environmental factors on the outer surfaces of a spacecraft. The header section contains information describing the content of the data section.
Header information inside the (*.nplate) file is in keyword-value pairs. White space separates the keywords and values. Anywhere in the file, a # symbol in the first column of a line indicates a comment.
Header information
| Keyword | Value Description |
|---|---|
| Version | Enter the version of file format, which is the value 1.0. |
| Formulation |
Specifies the type of force modeled using the provided information. The options are:
|
The beginning and end of the plate definition are marked with Begin Plates and End Plates. Format the data rows as a combination of common plate characteristics and formulation-specific parameters; see the following sections. Values in the data rows are white space separated. Do not use white space characters in the specification of names.
Plate Definition for Solar Pressure Modeling (Formulation = SRP)
| Column | Value Description |
|---|---|
| Plate Name | Enter a name for the plate in ASCII text. It is for reference only. |
| Group Name | Enter a name in ASCII text. This keyword is relevant to estimation within ODTK. You must specify a value, but STK will not use it for estimation. |
| Plate Type | Enter a single ASCII character. The plate type determines the method for determining the orientation of the plate during force computations. Valid choices are:
|
| Area | Enter a real number to specify the surface area of the plate in m2. |
| Reference Vector | Enter three real numbers to specify a reference vector that is the direction of either the normal to plate (Plate Type = B) or the rotation axis of the plate (Plate Type = A) in the body frame of the spacecraft. STK will normalize the vector upon reading, so you don't need to enter a unit vector. You must enter a vector for sun pointing plates (Plate Type = S), but STK will not use it in the computations. |
Plate parameters for drag modeling (Formulation = DragCd)
| Column | Value Description |
|---|---|
| Drag Coefficient | Enter a real number to specify the drag coefficient (Cd) for a specific plate. The drag force on the plate is computed using the cosine of the angle between the plate normal and central body-fixed velocity direction to determine the area of plate projected in the velocity direction. |
Plate parameters for Solar Pressure Modeling (Formulation = SRP)
| Column | Value Description |
|---|---|
| Specular Reflection Coefficient | Enter a real number between 0 and 1 to specify the fraction on incident radiation that will be reflected in a specular sense. The sum of the specular reflection and diffuse reflection coefficients must be less than or equal to one. |
| Diffuse Reflection Coefficient | Enter a real number between 0 and 1 to specify the fraction on incident radiation that will be reflected in a diffuse sense. The sum of the specular reflection and diffuse reflection coefficients must be less than or equal to one. |
Example SRP file
# N-Plate SRP model plate definition file
# The choice of frames are
# B = Body frame
# S = 2 Degree of freedom solar panel frame (normal always toward Sun)
# A = 1 Degree of freedom solar panel frame (normal towards Sun but
# constrained by single rotation axis)
Version 1.0
# This example contains 8 plates: 6 fixed in the body, one solar panel free to point
# directly at the Sun and one solar panel constrained to rotate about a body axis.
# Furthermore, all of the body plates are configured to estimate the same scale
# parameter while the solar panels are configured to share a separate scale estimate.
# Use of this file in estimation processes will therefore expose two scale factors for
# estimation.
# SRP formulation indicates that panel size and orientation will be followed by
# specular and diffuse reflectivity coefficients
Formulation SRP
# Beginning of plate definitions
Begin Plates
# The parameters must be space, comma, or tab delimited
# Group names define estimation parameters - 1 scale factor is estimated for each group
# Example record content for Sun pointing panels ('S') and fixed in body plates ('B')
# [Plt Name] [Grp Name] [Type] [Area] [Normal Vector] [Spec.Rflct.] [Diff.Rflct.]
SolarPanel SP S 60.0 0.0 0.0 1.0 0.30 0.5
PlusZ Body B 5.0 0.0 0.0 1.0 0.10 0.7
MinusZ Body B 5.0 0.0 0.0 -1.0 0.10 0.7
PlusY Body B 5.0 0.0 1.0 0.0 0.10 0.7
MinusY Body B 5.0 0.0 -1.0 0.0 0.10 0.7
PlusX Body B 5.0 1.0 0.0 0.0 0.10 0.7
MinusX Body B 5.0 -1.0 0.0 0.0 0.10 0.7
# For constrained solar panels which rotate about an axis,
# the axis definition replaces the normal vector in the row definition
# [Plt Name] [Grp Name] [Type] [Area] [Axis Vector] [Spec.Rflct.] [Diff.Rflct.]
AxisPanel SP A 5.0 0.0 0.0 1.0 0.40 0.4
End Plates
Example DragCd file
# N-Plate model plate definition file
# The choice of frames are
# b=body
# S= 2 degree of freedom solar panel frame (normal always toward the sun)
# A= 1 degree of freedom solar panel frame (normal towards the Sun but constrained by single rotation axis)
Version 1.0
# This example contains eight plates: six fixed in the body, one solar panel free to point
# directly at the Sun and one solar panel constrained to rotate about a body axis.
# Furthermore, all of the body plates are configured to estimate the same scale
# parameter while the solar panels are configured to share a separate scale estimate.
# Use of this file in estimation processes will therefore expose two scale factors for
# estimation.
# DragCD formulation indicates that panel size and orientation will be followed by
#a drag coefficient
Formulation DragCd
# Beginning of plate definitions
Begin Plates
# The parameters must be space, comma, or tab delimited
# Group names define estimation parameters - 1 scale factor is estimated for each group
# Example record content for Sun pointing panels ('S') and fixed in body plates ('B')
# [Plt Name] [Grp Name] [Type] [Area] [Normal Vector] [Cd]
SolarPanel SP S 60.0 0.0 0.0 1.0 2.0
PlusZ Body B 5.0 0.0 0.0 1.0 1.8
MinusZ Body B 5.0 0.0 0.0 -1.0 1.8
PlusY Body B 5.0 0.0 1.0 0.0 1.8
MinusY Body B 5.0 0.0 -1.0 0.0 1.8
PlusX Body B 5.0 1.0 0.0 0.0 1.8
MinusX Body B 5.0 -1.0 0.0 0.0 1.8
# For constrained solar panels which rotate about an axis,
# the axis definition replaces the normal vector in the row definition
# [Plt Name] [Grp Name] [Type] [Area] [Axis Vector] [Cd]
AxisPanel SP A 5.0 0.0 0.0 1.0 2.3
End Plates