NAME:
  orbvec
 PURPOSE:   (one line only)
  Computes orbit orientation vectors from angular orbital elements
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
  orbvec,inc,node,peri,p,q,r
 INPUTS:
  inc  - Orbit inclination [scalar, radians]
  node - Longitude of the ascending node [scalar, radians]
  peri - Longitude of periapse [scalar, radians]
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  p,q,r - 3-element orientation vectors
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2011/11/29, Written by Marc W. Buie, Southwest Research Institute
                guided by PQR.F written by David J. Tholen