PLBD
Original archive entry. The text, images and links below are kept as they were written.
Payload Bay Doors. These were a critical shuttle item. Failure of them to open would prevent deployment of the shuttle's cooling radiators and lead to an immediate mission abort and return home. Failure of them to close would doom the shuttle to burn up during reentry. Therefore there were redundant electrical systems to close the doors, and if these would fail, a manual method that could be accomplished by astronauts conducting an emergency spacewalk. Even missions with no spacewalk on the flight plan had spacesuits and astronauts aboard trained to manually shut the payload bay doors.