▁susp ension ▁arrangement ▁developed ▁in ▁ 1 9 8 8 ▁for ▁use ▁in ▁NASA ' s ▁Mars ▁ro ver ▁So j our ner , ▁and ▁which ▁has ▁since ▁become ▁NASA ' s ▁fav ored ▁design ▁for ▁ro vers . ▁It ▁has ▁been ▁used ▁in ▁the ▁ 2 0 0 3 ▁Mars ▁Ex pl oration ▁R over ▁mission ▁rob ots ▁Spirit ▁and ▁O pport unity , ▁on ▁the ▁ 2 0 1 2 ▁Mars ▁Science ▁Labor atory ▁( MS L ) ▁mission ' s ▁ro ver ▁Cur ios ity , ▁and ▁is ▁sl ated ▁for ▁use ▁in ▁the ▁Mars ▁ 2 0 2 0 ▁ro ver . ▁ ▁The ▁" ro cker " ▁part ▁of ▁the ▁term ▁comes ▁from ▁the ▁rock ing ▁aspect ▁of ▁the ▁larger , ▁forward ▁leg ▁on ▁each ▁side ▁of ▁the ▁susp ension ▁system . ▁These ▁rock ers ▁are ▁connected ▁to ▁each ▁other ▁and ▁the ▁vehicle ▁ch ass is ▁through ▁a ▁differential . ▁Rel ative ▁to ▁the ▁ch ass is , ▁when ▁one ▁ro cker ▁goes ▁up , ▁the ▁other ▁goes ▁down . ▁The ▁ch ass is ▁maintain s ▁the ▁average ▁pitch ▁angle ▁of ▁both ▁rock ers . ▁One ▁end ▁of ▁a ▁ro cker ▁is ▁fitted ▁with ▁a ▁drive ▁wheel , ▁and ▁the ▁other ▁end ▁is ▁p iv oted ▁to ▁the ▁bog ie . ▁ ▁The ▁" b og ie " ▁part ▁of ▁the ▁term ▁refers ▁to ▁the ▁smaller , ▁rear ward ▁leg ▁that ▁p iv ots ▁to ▁the ▁ro cker ▁in ▁the ▁middle ▁and ▁which ▁has ▁a ▁drive ▁wheel ▁at