---------------------------------------------------------------------------
   Build a model of a spacecraft.
   This GUI displays results of a script.
   It is not designed to allow you to interactively modify the design.
   With no inputs it returns a list of actions. All 'add ...' require
   data and most return an index to the new body or component(s).

   The basic structure of a script using BuildCADModel is

           BuildCADModel('initialize',...)
   kBody = BuildCADModel('add body',...)
           BuildCADModel('compute paths')
   kComp = BuildCADModel('add component',...)
           BuildCADModel('add subsystem',...)

   g = BuildCADModel( 'get cad model' )

   The mass properties for the spacecraft may either be set manually or
   computed from the mass properties of the components. To set them 
   manually, enter: 
			BuildCADModel('set mass',mass); 
   where mass is a struct with fields mass (scalar), cM (3x1 vector) and 
   inertia (3x3 matrix). The mass properties are otherwise automatically  
   updated when the model is retrieved or saved. To command an update, enter: 
 			BuildCADModel('update spacecraft mass properties');
   If the mass properties are set manually, they are considered "locked", 
   and they cannot be overwritten by an automatic update until they are un-
   locked. To lock or unlock the mass properties at any time, enter:
        BuildCADModel('lock mass properties');
    -or-
        BuildCADModel('unlock mass properties');

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

   -------
   Inputs
   -------
   action    (1,:)   Action string. These are not case sensitive.
   modifier  ()      Data for the action
   mod2      ()      Second modifier
   mod3      ()      Third modifier
   mod4      ()      Fourth modifier

   -------
   Outputs
   -------
   g         (1,1)   The CAD data structure

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