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