Wales.Larrison@ofa123.fidonet.org (Wales Larrison) (11/16/90)
>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? Recently had to look into this problem for a project I was working on.... There are 8 gangs of 4 latches each on the shuttle - 2 (port and starboard) on each bulkhead (forward and aft), and 4 down the centerline of doors. These latches must be closed since the doors take a shear moment in reentry. First of all, the doors will close - there are redundant drives, latches, wiring, and power systems to get the doors closed. Even if the drives don't work, the crew can manually winch the doors shut using either the forward bulkhead winch, or the aft bulkhead winch by going EVA. This is checked each flight so there is no interference with a payload location. Now what if you can shut the doors, and run the latch motors, but it still won't latch? Again, the latch drives and actuators and their supporting systems are redundant. And beyond that, the shuttle has been analyzed, tested, and qualified to return with any single latch gang (group of 4 latches) failed. So if only 1 gang has failed - no sweat. If the wrong 2 fail, you might have to go out and manually latch a gang- and again there are a variety of ways to do this which the crew is trained on. They can manually clamp the latches shut with either a centerline or bulkhead latch clamp, which would replace the failed latch on each gang (you don't need every latch on each gang - just one or two to work), or you can (depending on the failure) cut the drive shaft and drive 1, 2 or 3 of the remaining latches electrically or manually. And remember, you can return with any gang of four out, so you only have to fix 1 of the 2 failed gangs. Has a failure ever happened on a flight? Yes - but it was on flight 1, and they were intentionally trying to "warp" a door by thermally heating one and cooling one in the sun and shadow to see if they could warp the door out of true enough to cause a concern. The math analysis said it should be a problem, and after thermally soaking the doors for several orbits, they tried to close and latch the doors and had 1 gang fail - as expected. No sweat, they put the shuttle into a slow roll ("barbeque mode", they call it) to get the doors each to about the same temperature, tried it again, and it latched - to no one's surprize. ------------------------------------------------------------------ Wales Larrison Space Technology Investor -- Wales Larrison Internet: Wales.Larrison@ofa123.fidonet.org Compuserve: >internet:Wales.Larrison@ofa123.fidonet.org --------------------------------------------------------------------------