 The launch simulation on January 27 , 1967 , on pad 34 , was a " plugs @-@ out " test to determine whether the spacecraft would operate nominally on ( simulated ) internal power while detached from all cables and <unk> . Passing this test was essential to making the February 21 launch date . The test was considered non @-@ hazardous because neither the launch vehicle nor the spacecraft was loaded with fuel or cryogenics , and all pyrotechnic systems were disabled . 
