-------------------------------------------------------------------------------
   Computes the semi-latus rectum.
-------------------------------------------------------------------------------
   Form:
   p = SLR( e, a )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   e                     Eccentricity
   a                     Semi major axis (or perigee radius for parabola)

   -------
   Outputs
   -------
   p                     Semi-latus rectum

-------------------------------------------------------------------------------
	References:   Bates, R.B. Fundamentals of Astrodynamics, pp. 28,34.
-------------------------------------------------------------------------------