Tests a gimbaled thruster stationkeeping control system.

This is the type of system used with the Shuttle OMS engines. ------------------------------------------------------------------------- See also PIDMIMO, Plot2D, TimeGUI, RK4, GimbalControl -------------------------------------------------------------------------

Global for the TimeGUI
Controller sample period
PID Controller
Spacecraft properties
The 2 inch offset will cause a disturbance
Control moment arms of the gimbaled thrusters
Control torque matrix
Pseudo inverse to distribute control
Control state
Disturbance torque matrix
Plot Arrays
Initial state
The simulation
Initialize the time display
Limit the arrays to the actual length of the sim
Plot

%--------------------------------------------------------------------------
%   Copyright (c) 1995-2006 Princeton Satellite Systems, Inc.
%   All rights reserved.
%--------------------------------------------------------------------------

Global for the TimeGUI

%------------------------
global simulationAction
simulationAction = ' ';

Controller sample period

%--------------------------
tSamp = 0.5;
nSim  = 250;
inr   = [40000,0,0;0,50000,0;0,0,60000];

PID Controller

%---------------
zeta          = 1.5*ones(3,1);
omega         = [0.1;0.1;0.1];
tauInt        = 10*ones(3,1);
omegaR        = 5.0*ones(3,1);

[aC,bC,cC,dC] = PIDMIMO(inr,zeta,omega,tauInt,omegaR,tSamp,'Delta');

Spacecraft properties

%-----------------------
thrust  = 0.5;
invInr  = inv(inr);

% Position vectors of gimbaled thrusters

The 2 inch offset will cause a disturbance

%-------------------------------------------
r1 = [ -12 -12 45 ];
r2 = [  10  10 45 ];

Control moment arms of the gimbaled thrusters

%----------------------------------------------
b1 = [ r1(3) 0; 0 -r1(3); -r1(1) r1(2) ];
b2 = [ r2(3) 0; 0 -r2(3); -r2(1) r2(2) ];

Control torque matrix

%----------------------
bT = thrust*[ b1 b2 ];

Pseudo inverse to distribute control

------------------------------------

pB = pinv(bT);

Control state

%--------------
xC = [ 0 0 0 0 0 0 ]';

Disturbance torque matrix

-------------------------

tDist = thrust*[r1(2)+r2(2);-(r1(1)+r2(1));0]

tDist =
    -1
     1
     0

Plot Arrays

%------------
xPlot = zeros(3,nSim);
uPlot = zeros(4,nSim);
dPlot = zeros(3,nSim);

Initial state

%--------------
x = [ 1 0 0 0 0 0 0 ]';

The simulation

%---------------
t = tSamp*0:(nSim-1);

Initialize the time display

%----------------------------
[ ratioRealTime, tToGoMem ] =  TimeGUI( nSim, 0, [], 0, tSamp, 'TGimbal' );

for k = 1:nSim

  % Display the status message
  %---------------------------
  [ ratioRealTime, tToGoMem ] = TimeGUI( nSim, k, tToGoMem, ratioRealTime, tSamp );

  % Controller
  %------------
  att       = 0.5*x(2:4);
  [u,xC,y]  = GimbalC(aC,bC,cC,dC,pB,xC,att);

  tExt      = bT*u + tDist;

  % Plot Arrays
  %------------
  xPlot(:,k) = x(2:4);
  uPlot(:,k) = u;
  dPlot(:,k) = tExt;

  % Dynamics
  %---------
  x = RK4('FRB',x,tSamp,t(k),inr,invInr,tExt);

  % Time control
  %-------------
  switch simulationAction
    case 'pause'
      pause
      simulationAction = ' ';
    case 'stop'
      return;
    case 'plot'
      break;
  end

end

Limit the arrays to the actual length of the sim

%-------------------------------------------------
j = 1:k;
t = t(j);

Plot

%-----
Plot2D(t,(360/pi)*xPlot(:,j),'Time (sec)','Attitude Error (deg)','Attitude')
Plot2D(t,uPlot(:,j)*180/pi,'Time (sec)','Gimbal angles (deg)','Gimbal Commands')
Plot2D(t,dPlot(:,j),'Time (sec)','Torques (inlb)','Total Torque')


%--------------------------------------