gandalf@pro-canaveral.cts.com (Ken Hollis) (11/12/90)
Greetings and Salutations: I have rearranged the message parts to more closely conform to the series of events: >From: andy@syma.sussex.ac.uk (Andy Clews) >Subject: Hypothetical Payload Bay Door problems >On a related note, suppose the payload bay doors cannot be _opened_ once the >vehicle is in orbit. Would this pose serious problems, given that the >door-mounted radiators would be unable to vent excess heat into space? The payload bay doors are opened shortly after orbit is achieved to allow exposure of the environmental control and life support system radiators for heat rejection of the orbiters systems. The forward radiators are deployable to allow heat rejection from both sides of the radiators. The aft panels are not deployable. The baseline heat rejection is 21,500 BTU per hour. Previous to this the flash evaporator is working, boiling off water to allow heat rejection. This system is only good down to 100,000 feet, when the Ammonia boiler takes over until landing. This would, of course, cause a mission to return back to earth. >Suppose, for some reason, the payload bay doors fail to close under their >own mechanism whilst the orbiter is in orbit. Does a mechanism exist for >members of the crew to attempt to close the doors manually? The payload bay doors are driven by rotary a actuator consisting of two electrical three phase reversible ac motors per power drive unit. There is one power drive unit for the right doors and one for the left doors. When both of the motors are operating, the nominal time for payload bay door opening or closing is 63 seconds. If only one motor is operating, the time is 126 seconds. Two bolts on the bellcrank and the bolt connecting the link to the rotary actuator can be EVA disconnect points if the linkage fails when the doors close. The power drive unit can be disengaged manually on the ground or on orbit. >Suppose also, that the doors close but cannot be locked for some reason (as >I assume they are in the normal course of events). Would this be a fatal >mishap, i.e. would it prevent the orbiter from attempting a re-entry and >landing? Each centerline latch group consists of two ac reversible electric motors that drive a rotary shaft and a bellcrank and four hooks to engage a corresponding passive roller to latch the door closed or disengage the passive roller to unlatch the door. When both motors are operating, the nominal operating time is 20 seconds. If only one motor is operating, the time is 40 seconds. EVA disconnects in a centerline latch group can be used to isolate a jammed latch. There are 16 bulkhead latches (8 forward, 8 aft) and 16 payload bay door centerline latches. >A lighter note. I have just completed a 1/72 scale model of Columbia (the >Revell one). The payload bay doors do not close properly. I have >instigated an inquiry into why this is so, how it can be corrected and how >to prevent it happening again. My Mum and my Uncle Norman are on the board >of inquiry. ;-) We all expect a complete & satisfactory report on your inquiry. "If these opinions were NASA's, they'd be 100 pages long and unreadable." Basically what you will find on most all systems aboard the Orbiter is that they are redundant (except where feasibly impossible). There is no real plan for a double failure, so therefore you will find a plan around for the single failure, but not for a double failure. You find two ac motors that have torque limiters in case the limit switches (telling the vehicle that the doors are close) fails. The basic idea being that one motor may fail, but not both. If this adds to the confusion (rather than takes away) send another question. Ken Hollis ProLine: gandalf@pro-canaveral Internet: gandalf@pro-canaveral.cts.com UUCP: crash!pro-canaveral!gandalf