Mechanical Systems refer to a certain system in which there is an interaction among elements based on mechanical principles. The components in these systems are those that are continuously opened, deployed, stowed and closed. An electric or hydraulic actuator is used to enhance movement of each of these systems. Mechanical Systems entail payload bay doors, landing/deceleration systems and radiators. The way electromechanical actuators are designed is basically the same.
The assembly of every actuator contains a gearbox, two-three phase ac motors, limit switches and a differential. Torque limiters are part of all actuator assemblies except for the ET door centerline latches. Motor control assemblies are the ones that power the limit switches and actuator motors. The motors in this power sources are operated using commands. These commands are directed by Multiplexer/demultiplexers (MDM). A command from to every actuator is sent by a different MDM. A given actuator cannot be lost when one MDM is lost. Engineering in Kenya has more articles.
Active Vent System and Vent Operations as Part of Mechanical Systems
This system ensures that the orbiter compartments that are unpressurized are equal to the ambient environment. Within the orbiter fuselage, the active vent system has eighteen vent ports. Every door has been numbered and there is a dedicated vent found on each compartment. This is for purposes of easy identification. Both thermal and pressure seals are found in every vent door while an elctromechanical actuator drives it inside. The volume that requires venting determines the size of the vent openings within the Mechanical Systems. The vent doors are protected against harmful gases and other sources of contamination. There are two electromagnetic actuators in each of the six groups of the 18 doors. There is sequencing prelaunch after every 2.5 seconds between the groups. On the other hand, the normal closing time for vents is 5 seconds. A master unit of timing starts the GNC software which controls the vent doors.
All the doors of the orbiter get open at a time when the orbiter’s relative velocity is about 2400ft/s. Ground cooling becomes necessary after the orbiter stops on the runaway. This is done through purging of the vehicle with nitrogen or cool air along the vent doors. With the exemption of the preentry configuration which at the right moment gets commands from the orbiter crew, the Mechanical Systems function automatically.
External Tank Umbilical Doors and ET door Positions in Mechanical Systems
The umbilical openings on the orbiter’s openings have a shuttle through which fuel and electrical umbilicals and the orbiter pass through. The electrical and fuel disconnects, and the orbiter/ET attachments are the main components of umbilical cavities within Mechanical Systems. There is an exposure of the umbilical openings after the separation between the ET and the orbiter. The exposed areas are shielded from direct heating by the two main ET umbilical doors. Both an aerothermal barrier and a system of thermal protection are used to cover the umbilical door. The liquid hydrogen umbilical and the liquid oxygen umbilical are covered by the left door and the right door respectively. The three phase motors are responsible for opening and closing of each door.
External Tank Umbilical Doors and ET door Positions in Mechanical Systems Continued
Two hinges connect each door towards the orbiter. Unplock and centerline latches are the main types of latches that enable the door to close and open respectively. Prior to closing both the ET doors, the centerline latches are supposed to be disengaged from the doors. After unlatching, the two centerline latches get back into the orbiter’s body. While here, they are then termed as stowed. The amount of time required to stow the centerline latches is only six seconds. Two ac-motors (in three – phase) drive the centerline latches to their stowed position. After being stowed, it is not possible to redeploy the centerline latches using crew. However, completion of the task can be done by use of ground crew. This is a brief description of the components and operation of Mechanical System