For solar pressure, set the following parameters:
Solar Pressure  

Parameter  Description 
Use 
Select among:

WillUseSolarPressure 
This is a readonly field, with a boolean (true/false) value that reflects the result of the selection made in the Use field:

EstimateSRP  A correction to the nominal solar pressure coefficient, (ΔC_{r}), or to the product Δ (C_{r} A / M) will be estimated by the filter if set to true and SRP effects are modeled. Also controls if the nominal solar pressure coefficient can be perturbed by the simulator. The estimate flag must also be set to true if this parameter is to be used as a Least Squares Consider State. When used as a consider state it is modeled as a constant. 
Model  Select either "Spherical" and enter the related parameters
immediately below, or select one of the described after the table,
or select for a userdefined Reflection Plugin model. Options are:

SpecModel 
Specifies the method for input of solar pressure coefficient information.
Available when "Spherical" Model is selected. 
CorrectionType 
Specify the estimation solve for to be used in estimating corrections to acceleration due to solar pressure. The area referenced here, A, is that which is associated with solar pressure modeling. Choose between:
Available when "Variable Area" Model is selected, the correction will be of the Cr Additive form. 
Cr 
Specify the solar pressure coefficient (C_{r}) to be used in calculating acceleration due to solar pressure. Available when "Spherical" and "Variable Area" Model is selected. 
Area 
Crosssectional area of the spacecraft in the selected distance unit squared, for computation of solar radiation pressure. Available when "Spherical" Model is selected. 
CrAoverM 
Specify the product of the solar pressure coefficient and the solar pressure area divided by the mass (C_{r} A / M) to be used in calculating acceleration due to solar pressure. Available when "Spherical" Model is selected. 
Filename 
Text file conforming to the Variable Parameter File format, which provides the evolution of the SRP area as a tabulated function of time or of the argument of latitude of the spacecraft. The ParameterName keyword in the file header must indicate that Area data is specified. 
CrModel 
Identifies the Stochastic sequence to be used to represent the Solar Pressure CrModel Coefficient correction, {ΔC_{r}, Δ(C_{r} A/M), or Δ (C_{r} A / M) / (C_{r} A/M)}.
Reference the Stochastic Model page for the description and inputs associated with each model. Available when "Spherical" or "Variable Area" Model is selected. Note: Constant is a readonly field whose value is defined by the selected SpecMethod for "Spherical" Model. Note: Corrections always take the form of ΔC_{r} when the "Variable Area" model is selected. 
ReflectionModel 
For Spherical SRP model. Select between:
Available when "Spherical" and "Variable Area" Model is selected. 
SunPosMethod  Specifies the algorithm to be used in the computation of the position of the Sun for input to the solar radiation pressure model. Options are to compute the true position of the Sun, apparent position of the Sun to an observer at the center of the Earth or the apparent position of the Sun based on the satellite position. 
EclipsingBodies  Select from a list of available solar system bodies to include in shadowing computations. The entries in this list are in addition to the central body associated with the satellite unless that satellite is the "Sun" in which case it is not considered as an eclipsing body. 
UseInVariationalEquations  Set to true to have solar pressure accelerations included in the variational equations for the propagation of covariance. It is recommended that this flag be set to true for high altitude satellites. 
AddProcessNoise  This controls the addition of white process noise in two components (specified via the EclipticNorthFraction and the EclipticPlaneFraction attributes) normal to the suntosatellite line. This is useful when significant solar pressure accelerations exist in these directions, since the solar pressure model cannot account for such accelerations. Process noise along the suntosatellite line is added when the solar pressure coefficient is estimated. 
EclipticNorthFraction  When SRP process noise is added, the acceleration noise added in the direction normal to the suntosatellite line and normal to the ecliptic plane is computed as the magnitude of the nominal solar pressure acceleration multiplied by the EclipticNorthFraction. For example, to add white noise equal to 50% of the nominal acceleration in the Ecliptic North direction, specify a value of 0.5. 
EclipticPlaneFraction  When SRP process noise is added, the acceleration noise added in the direction normal to the suntosatellite line and in the ecliptic plane is computed as the magnitude of the nominal solar pressure acceleration multiplied by the EclipticPlaneFraction. For example, to add white noise equal to 50% of the nominal acceleration in the Ecliptic Plane, specify a value of 0.5. 
set srp = sat.ForceModel.SolarPressure ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' Use Spherical model represented by a Scalar Gauss Markov sequence ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' srp.Model.Type = "Spherical" srp.Model.Area.Set 6,"m^2" srp.Model.ReflectionModel = "Sphere with perfect absorption" srp.Model.CPModel.Type = "GaussMarkov" srp.Model.CPModel.Constant = 1.1 srp.Model.CPModel.InitialEstimate = 0 srp.Model.CPModel.Sigma = 0.25 srp.Model.CPModel.HalfLife.Set 2880,"min" ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' Use Spherical model represented by a Vasicek sequence ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' srp.Model.Type = "Spherical" srp.Model.Area.Set 6,"m^2" srp.Model.ReflectionModel = "Sphere with perfect absorption" srp.Model.CPModel.Type = "Vasicek" srp.Model.CPModel.LongTerm.Constant = 1.1 srp.Model.CPModel.LongTerm.Sigma = 0.25 srp.Model.CPModel.ShortTerm.InitialEstimate = 0 srp.Model.CPModel.ShortTerm.Sigma = 0.05 srp.Model.CPModel.ShortTerm.HalfLife.Set 60,"min"
The following solar pressure models are intended specifically to be used with GPS satellites.
GPS_BlkIIA_GSPM04a and GPS_BlkIIR_GSPM04a: Implementation of the JPL GSPM.04a models for Block IIA and Block IIR satellites following reference 1, below. This model was derived from a study of noneclipsing satellites. The model is dependent on the angle of the sun out of the orbit plane (the beta angle), but holds the absolute value of the beta angle at 14.5 degrees for cases where the actual beta angle goes below 14.5, as is the case for eclipsing satellites. The form of the model is the same for Block IIA and Block IIR satellites, but the coefficients are different.
GPS_BlkIIA_GSPM04ae and GPS_BlkIIR_GSPM04ae: Implementation of the JPL GSPM.04ae models for Block IIA and Block IIR satellites following reference 2. This model was derived as an extension of the GSPM.04a models (reference 1), where the models deviate from the GSPM.04a models only for eclipsing satellites. The model is dependent on the angle of the sun out of the orbit plane (the beta angle), but drops one term involving division by the sine of the beta angle when the beta angle goes below one degree. The form of the model is the same for Block IIA and Block IIR satellites, but the coefficients are different.
GPS_BlkIIA_AeroT20: Model for use with Block IIA satellites. Implementation follows reference 3. Model originally presented in reference 4.
GPS_BlkIIR_AeroT30: Model for use with Block IIR satellites. Implementation follows reference 3. Model originally presented in reference 4.
The following parameters apply to all of the above models:
GPS Solar Pressure Model Parameters  

Parameter  Description 
K1Model 
"K_{1}" refers to the unitless scale parameter for computed acceleration in the satellite body fixed XZ plane, which contains the sun to satellite line. Nominally the value of K_{1} is near 1.0. Enter the Stochastic sequence to be used to represent the correction to K_{1}, ΔK_{1}

K2Model 
"K_{2}" refers to the scale parameter for acceleration along the bodyfixed Y axis of the satellite. Input is unitless but is multiplied by 1e12 km/sec^2 to give the acceleration, often referred to as the Y bias. The resulting acceleration is perpendicular to the suntosatellite line, and the bodyfixed Y axis points in opposite directions for the Block IIA and Block IIR satellites. Nominally the value of K_{2} is in the range of 1 < K_{2} < 1. Enter the Stochastic sequence to be used to represent the correction to K_{2}, ΔK_{2}

ODTK 6.5