Comparison of CubeSat and SCT Disturbance models

Generate a 3U sized model using both the full CAD model and the simplified CubeSat model and compare the results.

See also ECIToEF, AtmDens2, InertiaCubeSat, Disturbances, CubeSatFaces CubeSatDisturbanceAnalysis

Parameters
Initialize
Perform the disturbance analysis using the Disturbances function
CubeSat model
Plotting

%--------------------------------------------------------------------------
%  	Copyright (c) 2016 Princeton Satellite Systems, Inc.
%   All rights reserved.
%--------------------------------------------------------------------------
%   Since 2016.1
%--------------------------------------------------------------------------

Parameters

To generate interesting torques, give a non-zero center of mass offset.

cMOffset = 0*[0.02;0;0.01]; % m

Initialize

% Orbit and time step
el    = [7000 0 0 0 0 0];
nSamp	= 100;
jD0   = FindSolsticeOrEquinox( 'spring equinox', 2015 );

% CAD Model
BuildCADModel( 'initialize' );
BuildCADModel( 'set name' , '3UCubeSat' );
BuildCADModel( 'set units', 'm'         );

% Core
m = CreateBody('make','name','Core');
BuildCADModel('add body', m );

% This creates the connections between the bodies
BuildCADModel( 'compute paths' );

% Core component
mass.mass           = 3;
mass.inertia        = InertiaCubeSat( '3u', mass.mass );
mass.cM             = cMOffset;  % Relative to the geometric center
optical.sigmaT      = 0;
optical.sigmaA      = 0;
optical.sigmaD      = 1; % Only diffuse reflection
optical.sigmaS      = 0;
thermal.temperature = 300;
thermal.emissivity   = 0.8;
thermal.absorptivity = 0.4;
m = CreateComponent( 'make', 'box', 'x', 0.1, 'y', 0.1, 'z', 0.3,...
                     'name', 'Core', 'body', 1, 'mass', mass, ...
                     'faceColor', 'gold foil', 'emissivity', thermal.emissivity,...
                     'absorptivity', thermal.absorptivity, 'sigmaT', optical.sigmaT,...
                     'sigmaA', optical.sigmaA, 'sigmaD', optical.sigmaD, 'sigmaS', optical.sigmaS,...
                     'inside', 0);
BuildCADModel( 'add component', m );

g = BuildCADModel('get model');
ShowCAD( g );

Warning: Struct field assignment overwrites a value with class "double". See
MATLAB R14SP2 Release Notes, Assigning Nonstructure Variables As Structures
Displays Warning, for details. 
Warning: Struct field assignment overwrites a value with class "cell". See
MATLAB R14SP2 Release Notes, Assigning Nonstructure Variables As Structures
Displays Warning, for details.

Perform the disturbance analysis using the Disturbances function

We use the EarthEnvironment function which uses AtmDens2

% Get the default data structure to fill in
d = Disturbances( 'defaults' );

% Generate the orbit
period    = Period( el(1) );
d.tSamp   = period/nSamp;
t         = linspace(0,period,nSamp);
[r,v]     = RVOrbGen(el,t);
PltOrbit( el, jD0 );

% Initialize the disturbance model
jD = JD2Array( jD0, t );
e  = EarthEnvironment( r, v, jD, d );
hD = Disturbances( 'init', g, e );

% Create the transformation matrix arrays
for k = 1:nSamp
	g.body(1).bHinge(k).b = eye(3);
end

% Run the analysis
[fD,tD] = Disturbances( 'run', g, e, hD );

CubeSat model

c = RHSCubeSat;
c.mass            = 3;
c.inertia         = InertiaCubeSat( '3U', c.mass );
[a,n,rho]         = CubeSatFaces('3U',1);
c.surfData.cM     = cMOffset;
c.surfData.nFace  = n;
c.surfData.area   = a;
c.surfData.rFace  = rho;
for k = 1:6
  % Radiation coefficients [absorbed; specular; diffuse]
  c.surfData.sigma(:,k) = [optical.sigmaA;optical.sigmaS;optical.sigmaD];
end
c.atm = []; % Force use of AtmDens2 for comparison
q = [ones(1,size(r,2));zeros(3,size(r,2))];
[tC, fC, h, hECI, fr, tq] = CubeSatDisturbanceAnalysis( c, q, r, v, jD );

Plotting

The remaining difference in the drag models is due to a difference in the transformation between the inertial frame and Earth-fixed frame between the two models. CubeSat uses uses a fast almanac function, ECIToEF, while Pro uses VAtm, which ignores the Z component of the Earth rotation due to nutation. The solar pressure forces are a bit different due to different solar ephemeris functions: CubeSat uses SunV1 while Pro uses the higher fidelity SunV2.