Within segments, {HEAD ~ terrestrial interfaces} 143 exist between ground stations 119 and {TAIL ~ the control center} 135 
exist between
Within segments , { HEAD ~ terrestrial interfaces } 143 exist between ground stations 119 and { TAIL ~ the control center } 135
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH