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+memo from docking manoeuvre office to as test flight space systems re as docking collar tests
+preliminary testing of the docking collar system has revealed a potentially serious flaw in the
+design which must be addressed before the system can be certified the issue concerns the emergency
+release system background the docking system performs the following functions impact energy
+absorption mechanical connection spacecraft alignment and retraction spacecraft hard mechanical
+connection and docking interface sealing spacecraft undocking and separation in order to achieve
+these functions the docking system consists of three principle parts the base a structural ring and
+the latching ring the docking system base is the main structural member to which the docking system
+assemblies are attached the structural ring carries the body latches which provide a hard pressure
+tight connection between the two spacecraft together with the capture latches which operate during
+the docking manoeuvre these perform the docking function they consist of eight active and eight
+passive hooks with an electrical drive installed on one of the latches and closed loop cables
+connecting them each active hook has a cam operated mechanism which performs its opening and
+tightening corresponding hooks of the passive docking system are captured by active hooks each
+passive hook has a stack of preloaded bellville springs providing a definite force for the docking
+interface preloading the docking interface seal will provide pressure integrity of the docking
+interfaces this consists of two concentric rubber ring seals on each system and a manhole cover is
+used to close the transfer tunnel of the spacecraft hatch locking and unlocking is manually
+performed by the crew it is sealed by a mechanism which has a further eight eccentric latches these
+being connected with each other by means of closed cable connection the docking system is equipped
+with alarm and meter system which provide telemetry to the ships and to ground control in standard
+operational mode undocking is performed by release of the active spacecraft capture latches and then
+by opening the structure latch hooks if necessary undocking can be performed by the passive
+spacecraft by releasing the body mounted latches and opening the structure latch passive hooks
+spacecraft separation is performed by spring thrusters symmetrically located on the structural rings
+of both systems after the latches release the principle difference between the russian and us
+docking system designs can be seen in the guide ring system unlike the russian electromechanical
+docking system apollo is equipped with an electric drive which uses cable connections to trigger the
+latches another essential difference is the russian emergency release system ers a backup provided
+by pyro bolts attached to each passive and active hook which operates in passive mode and provides
+practically instantaneous undocking in the event of a system malfunction or accident onboard one or
+both of the docked spacecraft situations in which the ers might be initiated include i uncontrolled
+fire or explosion onboard one of the spacecraft during docked operations ii failure of the docking
+control system preventing standard release operation iii attitude control failure of or unplanned
+firing on one or both spacecraft imposing high stresses on the docking mechanism while the ers
+provides an effective backup for emergency situations simulations and tests on the huntsville
+docking testbed show that the effectiveness of the pyrotechnic bolts is a critical issue too much
+explosive could cause critical damage to the pressure seals around the hatch while too little can
+leave the spacecraft attached with a damaged mechanism the ers was designed for operation on ussr
+missions and is therefore tuned to the structural constraints on the soviet platform since the
+latches are electromagnetic on that spacecraft they are less prone to damage under vibrational
+forces the motor and cable mechanism used on the apollo platform is more vulnerable to shock and
+under certain test conditions has been shown to fail following the triggering of the erson the
+soviet end of the docking mechanism shockwaves will not of course propagate through the vacuum of
+space but the forces can be transmitted through the tunnel to the apollo latches and if the bolts
+fire asymmetrically this places a torsion loading on the mechanism which can unseat the drive cables
+in five of the seven tests where this phenomenon was observed the engineers were able to reseat the
+cables by repeatedly operating the mechanism but in the remaining two cases the mechanism was beyond
+repair without manual intervention unfortunately in these two cases the safety interlock also
+prevented the hatch from being opened which could make it difficult for the astronauts to carryout a
+spacewalk to execute the required repair in this case it would normally be possible for the
+astronauts to manually operate the manhole latches by disassembling and subsequently assembling the
+hatch cover however if the latching mechanisms have been sufficiently damaged by the pyro bolts this
+might prove a risky option and it is even possible that the cover latches would fail to retract
+manually we have asked queens team to take a look at this and she assures me that they can sort it
+out she has worked on most of the apollo mission design teams so i am pretty confident that she can
+make sure everything is ok for this one
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