Demonstrate a 2 satellite CubeSat constellation

Uses ode113 and FOrbitMultiSpacecraft. This simulation just has the central force model. All other models (drag, radiation pressure, thrusters) are off by being empty.

```----------------------------------------------------------------------
See also LabelLine, NewFig, Plot2D, TimeLabl, XLabelS, YLabelS,
Date2JD, FOrbitMultiSpacecraft, TwoSpacecraftOrbitSimulation
----------------------------------------------------------------------```

Contents

```%------------------------------------------------------------------------
%   Copyright (c) 2009 Princeton Satellite Systems, Inc.
%   All rights reserved.
%------------------------------------------------------------------------
%   Since version 8.
%------------------------------------------------------------------------

d = FOrbitMultiSpacecraft;
```

Time and date

```%--------------------
days  = 0.5;
tEnd  = days*86400;
d.jD0 = Date2JD([2012 4 5 0 0 0]);
```

Initial state vector

```%---------------------
x1   = 6500;
x2   = 6500.010;

vY1  = VOrbit(x1);
vY2  = VOrbit(x2);

% State is [position;velocity;mass]
% CubeSats are 1 kg
%---------------------------------
r1   = [x1;0;0];
r2   = [x2;0;0];
v1   = [0;vY1;0];
v2   = [0;vY2;0];
m0   = 1;
x0   = [r1;v1;1;r2;v2;m0];

d(2) = d;
```

ode 113 parameters

```%-------------------
opt   = odeset( 'AbsTol', 1e-7, 'RelTol', 1e-4 );
```

Numerically integrate the orbit

```%--------------------------------
[t,x] = ode113( @FOrbitMultiSpacecraft, [0 tEnd], x0, opt, d );
```

Flip the matrices for plotting

```%-------------------------------
delT   = diff(t);
[t,tL] = TimeLabl( t');
x     = x';
```

Plot the xy-plane

```%------------------
dX    = x([1;2],:) - x([8:9],:);

NewFig('Simulation Timestep')
plot(delT);
YLabelS('Timestep (sec)')
XLabelS('Steps')

Plot2D( dX(1,:)*1000, dX(2,:)*1000, '\Delta x (m)', '\Delta y (m)',...
'Two spacecraft XY-Plane' );
LabelLine( dX*1000, t, 10, ['- %4.1f ' tL(7:end-1)] )

%--------------------------------------
% PSS internal file version information
%--------------------------------------
```