▁the ▁tang ential ▁velocity ▁around ▁the ▁Earth ▁is ▁as ▁important ▁as ▁alt itude . ▁In ▁order ▁to ▁perform ▁a ▁stable ▁and ▁last ing ▁flight ▁in ▁space , ▁the ▁space craft ▁must ▁reach ▁the ▁minimal ▁orb ital ▁speed ▁required ▁for ▁a ▁closed ▁orbit . ▁ ▁Inter plan et ary ▁▁ ▁Inter plan et ary ▁travel ▁is ▁travel ▁between ▁plan ets ▁within ▁a ▁single ▁planet ary ▁system . ▁In ▁practice , ▁the ▁use ▁of ▁the ▁term ▁is ▁conf ined ▁to ▁travel ▁between ▁the ▁plan ets ▁of ▁our ▁Sol ar ▁System . ▁ ▁Inter stell ar ▁▁ ▁‘ ’ New ▁Hor iz ons ’ ’ ▁is ▁the ▁fifth ▁space craft ▁put ▁on ▁an ▁escape ▁traject ory ▁leaving ▁the ▁Sol ar ▁System . ▁ ▁Vo y ager ▁ 1 , ▁Vo y ager ▁ 2 , ▁P ione er ▁ 1 0 , ▁P ione er ▁ 1 1 ▁are ▁the ▁earlier ▁ones . ▁ ▁The ▁one ▁far th est ▁from ▁the ▁Sun ▁is ▁Vo y ager ▁ 1 , ▁which ▁is ▁more ▁than ▁ 1 0 0 ▁A U ▁distant ▁and ▁is ▁moving ▁at ▁ 3 . 6 ▁A U ▁per ▁year . ▁In ▁comparison , ▁Pro xim a ▁Cent a uri , ▁the ▁closest ▁star ▁other ▁than ▁the ▁Sun , ▁is ▁ 2 6 7 , 0 0 0 ▁A U ▁distant . ▁It ▁will ▁take ▁Vo y ager ▁ 1 ▁over ▁ 7 4 , 0 0 0 ▁years ▁to ▁reach ▁this ▁distance . ▁Ve h icle ▁designs ▁using ▁other ▁techniques , ▁such ▁as