Orbiter Umbilical Doors

An electromechanical actuation system on each umbilical door closes the left and right umbilical cavities after the external tank is jettisoned and the umbilical plates retracted inside the orbiter's aft fuselage. Each umbilical door is approximately 50 inches square.

The doors are held in the full-open position by two centerline latches, one forward and one aft. They are opened before the mating of the orbiter to the external tank in the Vehicle Assembly Building.

The orbiter umbilical doors normally are controlled by the flight crew with switches on panel R2. In return-to-launch-site aborts, the doors are controlled automatically. The ET umbilical door mode switch on panel R2 positioned to GPC enables automatic control of the doors. The GPC/man position enables manual flight crew control of the doors.

The ET umbilical door centerline latch switch on panel R2 positioned to gnd permits ground control of the door centerline latches during ground turnaround operations. The stow position, enables flight crew manual control of the door centerline latches. The talkback indicator above the switch indicates sto when the door centerline latches are stowed, which permits closure of the doors, and barberpole when the latches are latched or the doors are in transit.

The ET umbilical door left and right latch, off, release switches on panel R2 are used by the flight crew to unlatch the corresponding centerline latches during normal operations. Positioning the respective switch to release provides electrical power to redundant ac reversible motors which operate an electromechanical actuator for each centerline latch that causes the latch to rotate and retract the latch blade flush with the reusable thermal protection system mold line. It takes approximately six seconds for the latches to complete their motion. The talkback indicator above the respective switch indicates rel when the corresponding latches are released. The latch position of each switch is used during ground turnaround operations to latch the respective door open, and the talkback indicator indicates lat when the latches have latched the doors in the open position. The talkback indicators indicate barberpole when the latches are in transit. The off position of the switches removes power from the motors, which stops the latches.

The ET umbilical door left and right , open , off , latch switches on panel R2 normally are used by the flight crew to close the umbilical doors. Positioning the switches to close provides electrical power to redundant ac reversible motors, which position the doors closed through a system of bellcranks and push rods. It takes approximately 24 seconds for the doors to close; and when they are within 2 inches of the closed position, ready-to-latch indicators activate the door uplatch system. Three uplatch hooks for each door engage three corresponding rollers near the outboard edge of the door and lock the door in preparation for entry. The motors are automatically turned off. The talkback indicator above the respective switch indicates cl when two of the three ready-to-latch switches for that door have sensed door closure. The open position of the switches is used during ground turnaround operations to open the doors. The talkback indicator indicates op when the doors are open and barberpole when they are in transit. The off position removes power from the motors, which stops the doors' movement.

The ET umbilical door switch on panel R2 positioned to GPC provides a backup method of releasing the centerline latches and closing the umbilical doors through guidance, navigation and control software through cathode ray tube display item entry during an RTLS abort. The operation of the centerline latches and closing of the umbilical doors are completely automated after external tank separation when the ET umbilical door switch on panel R2 is positioned to GPC . Two seconds after external tank separation, the centerline latches release the doors and the latches are stowed. The ET umbilical door centerline latch talkback indicator indicates sto when the centerline latches complete their motion eight seconds after external tank separation. The left and right umbilical doors are closed, and the ET umbilical door left and right talkback indicates cl 32 seconds after separation. The left and right umbilical door latches latch the doors closed, and the ET umbilical door left and right talkback indicates lat 38 seconds after separation.

Each umbilical door is covered with reusable thermal protection system in addition to an aerothermal barrier that required approximately 6 psi to compress to seal the door with adjacent thermal protection system tiles.

A closeout curtain is installed at each of the orbiter/external tank umbilicals. After external tank separation, the residual liquid oxygen in the main propulsion system is dumped through the three space shuttle main engines and the residual liquid hydrogen is dumped overboard. The umbilical curtain prevents hazardous gases (gaseous oxygen and hydrogen) from entering the orbiter aft fuselage through the umbilical openings before the umbilical doors are closed. The curtain also acts as a seal during the ascent phase of the mission to permit the aft fuselage to vent through the orbiter purge and vent system, thereby protecting the orbiter aft bulkhead at station Xo 1307. The curtain is designed to operate in range of minus 200 F to plus 250 F. The umbilical doors are opened when the orbiter has stopped at the end of landing rollout.

Various parameters are monitored and displayed on the flight deck control panel and CRT and transmitted by telemetry.