▁and ▁y aw ▁movements ▁in ▁the ▁two ▁vehicles ▁to ▁sub side . ▁Ex cess ▁movement ▁in ▁the ▁vehicles ▁during ▁the ▁' hard ▁dock ' ▁process ▁could ▁cause ▁damage ▁to ▁the ▁dock ing ▁ring ▁and ▁put ▁stress ▁on ▁the ▁upper ▁tunnel . ▁A ▁de pressed ▁lock ing ▁trigger ▁link ▁at ▁each ▁l atch ▁allowed ▁a ▁spring - loaded ▁sp ool ▁to ▁move ▁forward , ▁maintain ing ▁the ▁toggle ▁link age ▁in ▁an ▁over - center ▁locked ▁position . ▁In ▁the ▁upper ▁end ▁of ▁the ▁lun ar ▁module ▁tunnel , ▁the ▁dro gue , ▁which ▁was ▁constructed ▁of ▁ 1 - inch - thick ▁al umin um ▁h oney comb ▁core , ▁bond ed ▁front ▁and ▁back ▁to ▁al umin um ▁face ▁sheets , ▁was ▁the ▁receiving ▁end ▁of ▁the ▁pro be ▁head ▁capture ▁l atch es . ▁ ▁Ret raction ▁After ▁the ▁initial ▁capture ▁and ▁stabil ization ▁of ▁the ▁vehicles , ▁the ▁pro be ▁was ▁capable ▁of ▁ex ert ing ▁a ▁closing ▁force ▁of ▁ ▁to ▁draw ▁the ▁vehicles ▁together . ▁This ▁force ▁was ▁generated ▁by ▁gas ▁pressure ▁acting ▁on ▁the ▁center ▁p ist on ▁within ▁the ▁pro be ▁cyl inder . ▁P ist on ▁retra ction ▁com pressed ▁the ▁pro be ▁and ▁interface ▁se als ▁and ▁actu ated ▁the ▁ 1 2 ▁automatic ▁ring ▁l atch es ▁which ▁were ▁located ▁radial ly ▁around ▁the ▁inner ▁surface ▁of ▁the ▁C SM ▁dock ing ▁ring . ▁The ▁l atch es ▁were ▁manually ▁re - cock ed ▁in ▁the ▁dock ing ▁tunnel ▁by ▁an ▁astr onaut