# This model is focused around the evaluation of an arbitrary Fourier series to 
# recover Solar Radiation Pressure accelerations, with specialized options for  
# handling satellites in eclipse. 
#
# Any line starting with a "#" is ignored and considered a comment.
# E.g. This is a comment line.
#
# Comments may also occur at the end of lines, from the first occurrence of a "#"
# character onwards.
#
# Blank lines are ignored.
#
# The model has 2 main types of input:
# 
#     1) force coefficients
#     2) special variables
#
# (1) Each entry in a "table" of coefficients should have the following format:
#    
#     Type ModeNumber Evaluate Direction Value(s) [NoInflate] [NoSunScale]
#
#     "Type" can be:
#        Constant 
#          a bias used *only* in umbra [full shadow] - if specified, this will 
#          be the *only* force applied from this model during umbra. It will 
#          not be scaled for distance and all partials will be zeroed to avoid 
#          these values from polluting the "real" e.g. solar scale estimates. 
#          This parameter is not expected to get much use, but is provided to 
#          allow some GIPSY models to be implemented which have originated
#          from third party sources. Its "Evaluate" parameter *must* be V. The 
#          ModeNumber parameter is ignored.
#        Sine     
#          sine coefficient, as a function of Earth-Satellite-Sun angle
#        Cosine   
#          cosine coefficient, as a function of Earth-Satellite-Sun angle
#
#     "Mode" is the mode number (n), or harmonic. For example, a Sine value will be 
#     evaluated as:
#       sin( n * angle )
#
#     "Evaluate" indicates how the coefficient should be evaluated, and can take  
#     one of several values, including:
#        V 
#          interpret the value provided as a coefficient directly
#        P+ 
#          interpret the values as polynomial coefficients used to recover the
#          Fourier coefficient for positive beta angles (B), i.e.:
#             coeff = (a0 + a1B + a2B^2 ... + anB^n) 
#          where the independent argument of the polynomial (B) is expected  
#          to be in degrees
#        P- 
#          interpret the values as polynomial coefficients used to recover the
#          Fourier coefficient for negative beta angles (B), i.e.:
#             coeff = (a0 + a1B + a2B^2 ... + anB^n) 
#          where the independent argument of the polynomial (B) is expected 
#          to be in degrees
#        BK 
#          interpret the values as coefficients of the beta-angle (B) dependent 
#          equation 4 from Bar-Sever & Kuang (2004), "IPN Progress Report 42-159":  
#             coeff = C + DsinB + E/sinB + FcosB
#
#     "Direction" is used to indicate the direction along which the acceleration 
#     resulting from the coefficient acts. It can be *one* of X, Y, Z or, if and only
#     if Evaluate == V, any combination thereof, e.g. XYZ or YZ. These directions
#     are assumed to apply to the default spacecraft body-fixed attitude specified
#
#     "Value(s)" is either the coefficient itself, or a series of further coefficients
#     used to instantaneously evaluate the Fourier coefficient's value, expressed
#     in Newtons (kg.m/s^2).
#
#     "NoInflate" is an optional keyword that indicates a certain coefficient
#     or coefficients should not be scaled by an axis-independent factor, i.e.
#     an "overall" solar scale; this may affect both the computed acceleration
#     and its partials. If more than one direction is supplied and "NoInflate" 
#     is specified, none of the coefficients on that line will be scaled. This
#     keyword does not affect axis-dependent scalars, e.g. solar scale X. By
#     default, all coefficients will be inflated.
#
#     "NoSunScale" is an optional keyword that indicates a certain coefficient
#     or coefficients should not be scaled by the shadow factor *nor* the inverse
#     distance between the Sun and the spacecraft. 
#
# (2) Special variables typically separate coefficient tables and values used in  
#     different regimes. Coefficients specified prior to any special variables 
#     will be used by default. Several special variables are available for use:
#
#     FixBeta <degrees>
#       When computing beta-angle-dependent coefficients (e.g. P+, P-, BK), the 
#       beta angle is set to the value of FixBeta (original sign preserved) if
#       |beta| < FixBeta. If not specified, a default value of 14.5 degrees is
#       used.
#
#     EclipseBeta <degrees> 
#       The absolute beta angle value in degrees below which the model considers 
#       itself to be in eclipse. ***Any coefficients defined after EclipseBeta 
#       are interpreted as applying solely to the EclipseBeta regime. If no 
#       coefficients are found after EclipseBeta, the prior standard coefficients 
#       (which *must* be provided) are used. 
#
#     SplitAt <value> <degrees> <arrayFraction> <arrayDiffusivity> <arraySpecularity>
#       If the absolute value of the satellite's mis-pointing (the angle between 
#       its solar panel normal and the Sun-satellite vector) is greater than 
#       SplitAt <degrees>,  then only SplitAt <value> is used to compute the 
#       acceleration. The split acceleration is taken to result from two forces:
#         1) a bus force with magnitude (1-arrayFraction)*value, which acts
#            wholly along the direction from the spacecraft to the Sun.
#         2) a solar array force with magnitude arrayFraction*value, which acts
#            mostly along the solar panel normal, but also along the direction 
#            from the spacecraft to the Sun. 
#         <value> [REQUIRED]
#           The value of the coefficient in Newtons (kg.m/s^2) that best 
#           represents the force in the Satellite-Sun direction (default = 0.0, 
#           i.e. *NO* SRP acceleration). This is typically set to the first 
#           (mode=1) cosine harmonic in Z from the coefficients used when the 
#           absolute beta angle value is below EclipseBeta.
#         <degrees> [OPTIONAL, default = 1.0]
#           the absolute SplitAt angle, in degrees
#         <arrayFraction> [OPTIONAL, default = 0.9]
#           The fraction of <value> believed to result from the solar array.
#           The bus is responsible for (1.0 - arrayFraction). Must be <= 1.0
#         <arrayDiffusivity> [OPTIONAL, default = 0.3]
#           the proportion of radiation incident on the solar array that is 
#           reflected diffusely 
#         <arraySpecularity> [OPTIONAL, default = 0.25]
#           the proportion of radiation incident on the solar array that is 
#           reflected specularly 
#       In order to be physically meaningful, diffusivity + specularity + absorptivity 
#       for the array should = 1. Therefore, diffusivity + specularity should 
#       definitely be <= 1. However, sometimes non-physical values are required
#       for various reasons, so we do not perform any bounds checking on these values.
#
#     SplitAtEcl <value> <degrees> <arrayFraction> <arrayDiffusivity> <arraySpecularity>       
#       For parameter definition, see "SplitAt" above. This model is used if the
#       "EclipseBeta" criterion is defined *and* met, *and* the absolute value 
#       of the satellite's mis-pointing (the angle between its solar panel normal 
#       and the Sun-satellite vector) is greater than SplitAtEcl <degrees>. If 
#       "EclipseBeta" and "SplitAt" were input, but "SplitAtEcl" was not, then
#       "SplitAtEcl" will be set equal to "SplitAt".
#