For retraction, each gear is hydraulically rotated forward and up during ground operations until it engages an uplock hook for each gear in its respective wheel well. The uplock hook locks onto a roller on each strut. Mechanical linkage driven by each landing gear mechanically closes the respective landing gear doors. All three landing gear doors have high-temperature reusable surface insulation thermal protection system tiles bonded to their outer surface with thermal barriers to protect and prevent the landing gear and wheel well from the high-temperature thermal loads encountered during the shuttle's entry into the atmosphere.
For deployment of the landing gear, the uplock hook for each gear is activated by the flight crew initiating a gear-down command. The uplock hook is hydraulically unlocked by hydraulic system 1 pressure applied to release it from the roller on the strut to allow the gear, assisted by springs and hydraulic actuators, to rotate down and aft. Mechanical linkage released by each gear actuates the respective doors to the open position. The landing gear reach the full-down and extended position within 10 seconds and are locked in the down position by spring-loaded downlock bungees. If hydraulic system 1 pressure is not available to release the uplock hook, a pyrotechnic initiator at each landing gear uplock hook automatically releases the uplock hook on each gear one second after the flight crew has commanded gear down. All Rights Reserved: Not for use in any form without the express written permission of the photographer