Lyapunov:

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   Compute a constant gain feedback controller for relative orbital motion.

   Takes the orbital elements "el", constructs a linearized plant for the
   relative motion, and finds a constant gain feedback controller such that 
   the linear, closed-loop system is asymptotically stable.

   Use "k" to compute the control acceleration "acc" as follows:

           acc = k*(xD - xM)

   where "xM" is the measured relative state, and "xD" is the desired
   relative state. Each state is a 6x1
   vector of the form: [x; y; z; Vx; Vy; Vz]

   Since version 7.
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   Form:
   k = Lyapunov( el );    % where "el" is element vector: [a,i,W,w,e,M]
        -or-
   k = Lyapunov( a );     % where "a" is semi-major axis. assumes e = 0
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   ------
   Inputs
   ------
   el               (1,6) Reference orbital elements [a,i,W,w,e,M]

   -------
   Outputs
   -------
   k                (3,6) Constant gain feedback controller

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	References: This is based on Terry Alfriend's paper, AIAA 2000-4131.
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Children:

OrbitMiniToolbox: Support/M2Nu
SC: BasicOrbit/OrbRate