▁windows ▁measured ▁, ▁used ▁to ▁aid ▁in ▁rende z vous ▁and ▁dock ing ▁with ▁the ▁L M . ▁The ▁circular ▁h atch ▁window ▁was ▁ 1 0 ▁ 5 / 8 ▁in . ▁diameter ▁( 2 7   cm ) ▁and ▁was ▁directly ▁over ▁the ▁center ▁c ouch . ▁Each ▁window ▁assembly ▁consisted ▁of ▁three ▁thick ▁pan es ▁of ▁glass . ▁The ▁inner ▁two ▁pan es , ▁which ▁were ▁made ▁of ▁al um inos il icate , ▁made ▁up ▁part ▁of ▁the ▁module ' s ▁pressure ▁vessel . ▁The ▁f used ▁sil ica ▁outer ▁p ane ▁served ▁as ▁both ▁a ▁de br is ▁shield ▁and ▁as ▁part ▁of ▁the ▁heat ▁shield . ▁Each ▁p ane ▁had ▁an ▁anti - reflect ive ▁co ating ▁and ▁a ▁blue - red ▁reflect ive ▁co ating ▁on ▁the ▁inner ▁surface . ▁ ▁Spec ifications ▁▁ ▁C rew : ▁ 3 ▁ ▁C rew ▁cabin ▁volume : ▁ ▁living ▁space , ▁press ur ized ▁▁ ▁L ength : ▁▁ ▁Diam eter : ▁▁ ▁Mass : ▁▁ ▁Str ucture ▁mass : ▁▁ ▁He at ▁shield ▁mass : ▁▁ ▁R CS ▁engine ▁mass : ▁twelve ▁x ▁▁ ▁Rec overy ▁equipment ▁mass : ▁▁ ▁Navigation ▁equipment ▁mass : ▁▁ ▁Te lem etry ▁equipment ▁mass : ▁▁ ▁Elect rical ▁equipment ▁mass : ▁▁ ▁Communic ations ▁systems ▁mass : ▁▁ ▁C rew ▁c ouch es ▁and ▁prov isions ▁mass : ▁▁ ▁Environment al ▁Control ▁System ▁mass : ▁▁ ▁M isc . ▁cont ing ency ▁mass : ▁▁ ▁R CS : ▁twelve ▁ ▁thrust