DFFAttitudeController:

------------------------------------------------------------------------
   This routine implements attitude control for the DFF system. PID
   controllers are used for attitude control - momentum control is not
   used. The torque command is applied directly in the simulation,
   without the use of an RWA model. 
   Provision is made for filters of arbitrary order for loop shaping. 
   Inputs are the target quaternion and the true quaternion.
   Small angles are computed from the two quaternions. 
   The target quaternion should be near the true quaternion for best results.

   Since version 7.
------------------------------------------------------------------------
   Form:
   t = DFFAttitudeController( action, d, k )
------------------------------------------------------------------------

   ------
   Inputs
   ------
   action        (1,:)     Action to be performed        
   d             (1,1)     Data structure for inputs
   k             (1,1)     Unique spacecraft identifier

   -------
   Outputs
   -------
   t             (1,1)     Data structure with outputs. Valid only
                           with action 'update' and 'get telemetry'

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

Children:

Common: Control/PIDMIMO
Common: General/FSWClock
Common: General/MessageQueue
Common: Quaternion/AU2Q
Common: Quaternion/Q2AU
Common: Quaternion/QMult
Common: Quaternion/QPose
IntegratedSim: Sensors/StateSensor
IntegratedSim: Software/DFFAttitudeManeuver
IntegratedSim: Software/DFFParameterDatabase
IntegratedSim: Software/DFFRelativeNavigation
Math: Trigonometry/DeltCirc