▁pro be ▁was ▁extended ▁like ▁a ▁sc iss or ▁jack ▁to ▁capture ▁the ▁dro gue ▁on ▁initial ▁contact , ▁known ▁as ▁soft ▁dock ing . ▁Then ▁the ▁pro be ▁was ▁ret ract ed ▁to ▁pull ▁the ▁vehicles ▁together ▁and ▁establish ▁a ▁firm ▁connection , ▁known ▁as ▁" hard ▁dock ing ". ▁The ▁mechanism ▁was ▁specified ▁by ▁NASA ▁to ▁have ▁the ▁following ▁functions : ▁Allow ▁the ▁two ▁vehicles ▁to ▁connect , ▁and ▁at ten uate ▁excess ▁movement ▁and ▁energy ▁caused ▁by ▁dock ing ▁Al ign ▁and ▁center ▁the ▁two ▁vehicles ▁and ▁pull ▁them ▁together ▁for ▁capture ▁Prov ide ▁a ▁rig id ▁struct ural ▁connection ▁between ▁both ▁vehicles , ▁and ▁be ▁capable ▁of ▁removal ▁and ▁re - install ation ▁by ▁a ▁single ▁crew man ▁Prov ide ▁a ▁means ▁of ▁remote ▁separation ▁of ▁both ▁vehicles ▁for ▁the ▁return ▁to ▁Earth , ▁using ▁py rote chn ic ▁fast en ers ▁at ▁the ▁circum ference ▁of ▁the ▁C SM ▁dock ing ▁col lar ▁Prov ide ▁redundant ▁power ▁and ▁logic ▁circ uits ▁for ▁all ▁elect rical ▁and ▁py rote chn ic ▁components . ▁ ▁Cou pling ▁The ▁pro be ▁head ▁located ▁in ▁the ▁C SM ▁was ▁self - centering ▁and ▁g im bal - mount ed ▁to ▁the ▁pro be ▁p ist on . ▁As ▁the ▁pro be ▁head ▁engaged ▁in ▁the ▁opening ▁of ▁the ▁dro gue ▁socket , ▁three ▁spring - loaded ▁l atch es ▁de pressed ▁and ▁engaged . ▁These ▁l atch es ▁allowed ▁a ▁so - called ▁' soft ▁dock ' ▁state ▁and ▁enabled ▁the ▁pitch