Hi there
I am trying to analyze drag effect on LEO satellite.When I plot it, of
course the altitude get decreased.
Yet, we have a problem here. Since there is flattening of earth, altitude
changes about 20 km from equator to polar, where the inclination is 90
degrees.
But when I do it 0 degree, which is equatorial, the altitude still changes
as 20 km. It is not normal. It shouldnt oscillate, it should only get down
with time.
Please check it. I just attached the file. If I have a mistake let me know
please. How can I stop it oscillating?
Thanks
Kadir
[image: Ekran görüntüsü 2025-02-18 001529.png]
%General Mission Analysis Tool(GMAT) Script
%Created: 2025-02-17 22:49:52
%----------------------------------------
%---------- Spacecraft
%----------------------------------------
Create Spacecraft DefaultSC;
GMAT DefaultSC.DateFormat = UTCGregorian;
GMAT DefaultSC.Epoch = '01 Jan 2000 11:59:28.000';
GMAT DefaultSC.CoordinateSystem = EarthMJ2000Eq;
GMAT DefaultSC.DisplayStateType = Keplerian;
GMAT DefaultSC.SMA = 6677.999999999996;
GMAT DefaultSC.ECC = 2.38175004414415e-16;
GMAT DefaultSC.INC = 0;
GMAT DefaultSC.RAAN = 0;
GMAT DefaultSC.AOP = 0;
GMAT DefaultSC.TA = 0.6931030628374474;
GMAT DefaultSC.DryMass = 10;
GMAT DefaultSC.Cd = 2.2;
GMAT DefaultSC.Cr = 1.8;
GMAT DefaultSC.DragArea = 0.06;
GMAT DefaultSC.SRPArea = 1;
GMAT DefaultSC.SPADDragScaleFactor = 1;
GMAT DefaultSC.SPADSRPScaleFactor = 1;
GMAT DefaultSC.AtmosDensityScaleFactor = 1;
GMAT DefaultSC.ExtendedMassPropertiesModel = 'None';
GMAT DefaultSC.NAIFId = -10000001;
GMAT DefaultSC.NAIFIdReferenceFrame = -9000001;
GMAT DefaultSC.OrbitColor = Red;
GMAT DefaultSC.TargetColor = Teal;
GMAT DefaultSC.OrbitErrorCovariance = [ 1e+70 0 0 0 0 0 ; 0 1e+70 0 0 0 0 ; 0 0
1e+70 0 0 0 ; 0 0 0 1e+70 0 0 ; 0 0 0 0 1e+70 0 ; 0 0 0 0 0 1e+70 ];
GMAT DefaultSC.CdSigma = 1e+70;
GMAT DefaultSC.CrSigma = 1e+70;
GMAT DefaultSC.Id = 'SatId';
GMAT DefaultSC.Attitude = CoordinateSystemFixed;
GMAT DefaultSC.SPADSRPInterpolationMethod = Bilinear;
GMAT DefaultSC.SPADSRPScaleFactorSigma = 1e+70;
GMAT DefaultSC.SPADDragInterpolationMethod = Bilinear;
GMAT DefaultSC.SPADDragScaleFactorSigma = 1e+70;
GMAT DefaultSC.AtmosDensityScaleFactorSigma = 1e+70;
GMAT DefaultSC.ModelFile = 'aura.3ds';
GMAT DefaultSC.ModelOffsetX = 0;
GMAT DefaultSC.ModelOffsetY = 0;
GMAT DefaultSC.ModelOffsetZ = 0;
GMAT DefaultSC.ModelRotationX = 0;
GMAT DefaultSC.ModelRotationY = 0;
GMAT DefaultSC.ModelRotationZ = 0;
GMAT DefaultSC.ModelScale = 1;
GMAT DefaultSC.AttitudeDisplayStateType = 'Quaternion';
GMAT DefaultSC.AttitudeRateDisplayStateType = 'AngularVelocity';
GMAT DefaultSC.AttitudeCoordinateSystem = EarthMJ2000Eq;
GMAT DefaultSC.EulerAngleSequence = '321';
%----------------------------------------
%---------- ForceModels
%----------------------------------------
Create ForceModel DefaultProp_ForceModel;
GMAT DefaultProp_ForceModel.CentralBody = Earth;
GMAT DefaultProp_ForceModel.PrimaryBodies = {Earth};
GMAT DefaultProp_ForceModel.SRP = On;
GMAT DefaultProp_ForceModel.RelativisticCorrection = Off;
GMAT DefaultProp_ForceModel.ErrorControl = RSSStep;
GMAT DefaultProp_ForceModel.GravityField.Earth.Degree = 10;
GMAT DefaultProp_ForceModel.GravityField.Earth.Order = 10;
GMAT DefaultProp_ForceModel.GravityField.Earth.StmLimit = 100;
GMAT DefaultProp_ForceModel.GravityField.Earth.PotentialFile = 'JGM2.cof';
GMAT DefaultProp_ForceModel.GravityField.Earth.TideModel = 'None';
GMAT DefaultProp_ForceModel.Drag.AtmosphereModel = JacchiaRoberts;
GMAT DefaultProp_ForceModel.Drag.HistoricWeatherSource =
'ConstantFluxAndGeoMag';
GMAT DefaultProp_ForceModel.Drag.PredictedWeatherSource =
'ConstantFluxAndGeoMag';
GMAT DefaultProp_ForceModel.Drag.CSSISpaceWeatherFile =
'SpaceWeather-All-v1.2.txt';
GMAT DefaultProp_ForceModel.Drag.SchattenFile = 'SchattenPredict.txt';
GMAT DefaultProp_ForceModel.Drag.F107 = 150;
GMAT DefaultProp_ForceModel.Drag.F107A = 150;
GMAT DefaultProp_ForceModel.Drag.MagneticIndex = 3;
GMAT DefaultProp_ForceModel.Drag.SchattenErrorModel = 'Nominal';
GMAT DefaultProp_ForceModel.Drag.SchattenTimingModel = 'NominalCycle';
GMAT DefaultProp_ForceModel.Drag.DragModel = 'Spherical';
GMAT DefaultProp_ForceModel.SRP.Flux = 1367;
GMAT DefaultProp_ForceModel.SRP.SRPModel = Spherical;
GMAT DefaultProp_ForceModel.SRP.Nominal_Sun = 149597870.691;
%----------------------------------------
%---------- Propagators
%----------------------------------------
Create Propagator DefaultProp;
GMAT DefaultProp.FM = DefaultProp_ForceModel;
GMAT DefaultProp.Type = RungeKutta89;
GMAT DefaultProp.InitialStepSize = 60;
GMAT DefaultProp.Accuracy = 9.999999999999999e-12;
GMAT DefaultProp.MinStep = 0.001;
GMAT DefaultProp.MaxStep = 2700;
GMAT DefaultProp.MaxStepAttempts = 50;
GMAT DefaultProp.StopIfAccuracyIsViolated = true;
%----------------------------------------
%---------- Solvers
%----------------------------------------
Create DifferentialCorrector DC1;
GMAT DC1.ShowProgress = true;
GMAT DC1.ReportStyle = Normal;
GMAT DC1.ReportFile = 'DifferentialCorrectorDC1.data';
GMAT DC1.MaximumIterations = 25;
GMAT DC1.DerivativeMethod = ForwardDifference;
GMAT DC1.Algorithm = NewtonRaphson;
%----------------------------------------
%---------- Subscribers
%----------------------------------------
Create OrbitView DefaultOrbitView;
GMAT DefaultOrbitView.SolverIterations = Current;
GMAT DefaultOrbitView.UpperLeft = [ 0.2505882352941177 0.5533742331288344 ];
GMAT DefaultOrbitView.Size = [ 0.1658823529411765 0.2049079754601227 ];
GMAT DefaultOrbitView.RelativeZOrder = 352;
GMAT DefaultOrbitView.Maximized = true;
GMAT DefaultOrbitView.Add = {DefaultSC, Earth};
GMAT DefaultOrbitView.CoordinateSystem = EarthMJ2000Eq;
GMAT DefaultOrbitView.DrawObject = [ true true ];
GMAT DefaultOrbitView.DataCollectFrequency = 1;
GMAT DefaultOrbitView.UpdatePlotFrequency = 50;
GMAT DefaultOrbitView.NumPointsToRedraw = 0;
GMAT DefaultOrbitView.ShowPlot = true;
GMAT DefaultOrbitView.MaxPlotPoints = 20000;
GMAT DefaultOrbitView.ShowLabels = true;
GMAT DefaultOrbitView.ViewPointReference = Earth;
GMAT DefaultOrbitView.ViewPointVector = [ 30000 0 0 ];
GMAT DefaultOrbitView.ViewDirection = Earth;
GMAT DefaultOrbitView.ViewScaleFactor = 1;
GMAT DefaultOrbitView.ViewUpCoordinateSystem = EarthMJ2000Eq;
GMAT DefaultOrbitView.ViewUpAxis = Z;
GMAT DefaultOrbitView.EclipticPlane = Off;
GMAT DefaultOrbitView.XYPlane = On;
GMAT DefaultOrbitView.WireFrame = Off;
GMAT DefaultOrbitView.Axes = On;
GMAT DefaultOrbitView.Grid = Off;
GMAT DefaultOrbitView.SunLine = Off;
GMAT DefaultOrbitView.UseInitialView = On;
GMAT DefaultOrbitView.StarCount = 7000;
GMAT DefaultOrbitView.EnableStars = On;
GMAT DefaultOrbitView.EnableConstellations = On;
Create GroundTrackPlot DefaultGroundTrackPlot;
GMAT DefaultGroundTrackPlot.SolverIterations = Current;
GMAT DefaultGroundTrackPlot.UpperLeft = [ 0.4370588235294118 0.4466257668711656
];
GMAT DefaultGroundTrackPlot.Size = [ 0.1658823529411765 0.2049079754601227 ];
GMAT DefaultGroundTrackPlot.RelativeZOrder = 22;
GMAT DefaultGroundTrackPlot.Maximized = false;
GMAT DefaultGroundTrackPlot.Add = {DefaultSC};
GMAT DefaultGroundTrackPlot.DataCollectFrequency = 1;
GMAT DefaultGroundTrackPlot.UpdatePlotFrequency = 50;
GMAT DefaultGroundTrackPlot.NumPointsToRedraw = 0;
GMAT DefaultGroundTrackPlot.ShowPlot = true;
GMAT DefaultGroundTrackPlot.MaxPlotPoints = 20000;
GMAT DefaultGroundTrackPlot.CentralBody = Earth;
GMAT DefaultGroundTrackPlot.TextureMap = 'ModifiedBlueMarble.jpg';
Create ReportFile ReportFile1;
GMAT ReportFile1.SolverIterations = All;
GMAT ReportFile1.UpperLeft = [ 0 0 ];
GMAT ReportFile1.Size = [ 0 0 ];
GMAT ReportFile1.RelativeZOrder = 0;
GMAT ReportFile1.Maximized = false;
GMAT ReportFile1.Filename = 'alt_vs_time.txt';
GMAT ReportFile1.Precision = 16;
GMAT ReportFile1.Add = {DefaultSC.ElapsedSecs, DefaultSC.Earth.Altitude};
GMAT ReportFile1.WriteHeaders = true;
GMAT ReportFile1.LeftJustify = On;
GMAT ReportFile1.ZeroFill = Off;
GMAT ReportFile1.FixedWidth = true;
GMAT ReportFile1.Delimiter = ' ';
GMAT ReportFile1.ColumnWidth = 23;
GMAT ReportFile1.WriteReport = true;
Create XYPlot XYPlot1;
GMAT XYPlot1.SolverIterations = Current;
GMAT XYPlot1.UpperLeft = [ 0.03352941176470588 0.5006134969325153 ];
GMAT XYPlot1.Size = [ 0.4976470588235294 0.445398773006135 ];
GMAT XYPlot1.RelativeZOrder = 392;
GMAT XYPlot1.Maximized = false;
GMAT XYPlot1.XVariable = DefaultSC.ElapsedSecs;
GMAT XYPlot1.YVariables = {DefaultSC.Earth.Altitude};
GMAT XYPlot1.ShowGrid = true;
GMAT XYPlot1.ShowPlot = true;
%----------------------------------------
%---------- Mission Sequence
%----------------------------------------
BeginMissionSequence;
Propagate DefaultProp(DefaultSC) {DefaultSC.ElapsedDays = 10};
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