 circular transfer trajectori descend satellit circular transfer trajectori descend satellit simplifi express describ transfer satellit orbit point atmospher entri deriv express limit altitud chang small compar earth's radiu veloc chang small compar satellit veloc restrict motion spheric nonrot earth transfer orbit applic thrust direct point ellipt orbit consid express error distanc distanc entri angl initi misalin magnitud error deflect thrust present largest potenti contribut factor distanc stem misalin retroveloc increment veloc increment point direct opposit flight path 1 misalin lead distanc 34 5 mile error avoid appli veloc increment angl 120 150 flight-path direct guidanc accuraci requir establish circular orbit addit correct appli transform ellipt orbit circular discuss 