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ET_INFO.TXT
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1993-02-06
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"6_2_3_13_4.TXT" (14045 bytes) was created on 12-12-88
ORBITER/EXTERNAL TANK SEPARATION SYSTEM
The orbiter/external tank separation system consists of the oxygen and
hydrogen umbilical disconnects located at the lower left and right aft
fuselage, one forward structural attach point just aft of the nose
landing gear doors and two structural attach points located in the
orbiter/external tank umbilical disconnect cavities. An umbilical
retraction system retracts the orbiter umbilicals within the orbiter
aft fuselage, and umbilical doors close over each of the umbilical
cavities after separation.
The 17-inch liquid oxygen and liquid hydrogen disconnects provide the
propellant feed interface from the external tank to the orbiter main
propulsion system and the three space shuttle main engines. The
respective 17-inch disconnects also provide the capability for
external tank fill and drain of oxygen and hydrogen through the
orbiter main propulsion system and the T-0 umbilicals. The liquid
hydrogen interface between the orbiter and the ground storage tank is
provided by a T-0 umbilical located on the left side of the aft
fuselage. The liquid oxygen interface between the orbiter and the
ground storage tank is provided by a T-0 umbilical on the right side
of the aft fuselage.
17-INCH DISCONNECT.
Each mated pair of 17-inch disconnects contains two flapper valves,
one on the orbiter side of the interface and one on the external tank
side of the interface. Both valves in each disconnect pair are opened
to permit propellant flow between the orbiter and the external tank.
Before the separation of the external tank, both valves in each mated
pair of disconnects are commanded closed by pneumatic (helium)
pressure from the main propulsion system. The closure of both valves
in each disconnect pair prevents propellant discharge from the
external tank or orbiter at separation. Valve closure on the orbiter
side of each disconnect also prevents contamination of the orbiter
main propulsion system during landing and ground operations.
Inadvertent closure of either valve in a 17-inch disconnect during
space shuttle main engine thrusting would stop propellant flow from
the external tank to all three main engines. Catastrophic failure of
the main engines and external tank feed lines would result.
To prevent inadvertent closure of the 17-inch disconnect valves during
the main engine thrusting, a latch mechanism was added in the orbiter
half of the disconnects. The latch mechanism provides a mechanical
backup to the normal fluid-induced-open forces. The latch is mounted
on a shaft in the flowstream so it overlaps both flappers and
obstructs closure for any reason.
In preparation for external tank separation, both valves in each
17-inch disconnect are commanded closed. Pneumatic (helium) pressure
from the main propulsion system causes the latch actuator to rotate
the latch shaft in each orbiter 17-inch disconnect 90 degrees, thus
freeing the flapper valves to close as required for external tank
separation.
If the latch pneumatic actuator malfunctions, a backup mechanical
separation capability is provided. When the orbiter umbilical
initially moves away from the external tank umbilical, the mechanical
latch disengages from the external tank flapper valve and permits the
orbiter disconnect flapper to toggle the latch. This action permits
both flappers to close.
During ground mating of the external tank to the orbiter, the latch
engagement mechanism in each 17-inch disconnect provides a go/no-go
verification that flapper angle rigging is within stability limits.
Misrigged flappers will prevent full engagement of latch. The angle
of each flapper in each disconnect is still carefully rigged within
specific tolerances to assure basic stability independently of the
latch safety feature.
EXTERNAL TANK SEPARATION SYSTEM.
The external tank is separated from the orbiter at three structural
attach points. Separation from the orbiter occurs before orbit
insertion and is automatically controlled by the orbiter's
general-purpose computers. External tank separation can be manually
initiated by the flight crew using the same jettison circuits as the
automatic sequence. Separation is controlled by the ET separation
auto, man switch on panel C3 and the sep push button on panel C3. In
the auto position, the onboard GPCs initiate separation. To manually
initiate separation, the ET separation switch is positioned to man and
the sep push button is depressed.
The forward structural attachment consists of a shear bolt unit
mounted in a spherical bearing. The bolt separates at a break area
when two pressure cartridges are initiated. The pressure from one or
both cartridges drives one of a pair of pistons to shear the bolt,
with the second piston acting as a hole plugger to fill the cavity
left by the sheared bolt. A centering mechanism rotates the unit from
the displacement position to a centered position, aligning the bearing
flush with the adjacent thermal protection system mold line.
The aft structural attachment consists of two special bolts and
pyrotechnically actuated frangible nuts that attach the external tank
strut hemisphere to the orbiter's left- and right-side cavities. At
separation the frangible nuts are split by a booster cartridge
initiated by a detonator cartridge. The attach bolts are driven by
the separation forces and a spring into a cavity in the tank strut.
The frangible nut, cartridge fragments and hot gases are contained
within a cover assembly, and a hole plugger isolates the fragments in
the container.
The aft separation involves right and left umbilical assemblies. Each
assembly contains three dual-detonator frangible nut and bolt
combinations that hold the orbiter and external tank umbilical plates
together during mated flight. Each bolt has a retraction spring that,
after release of the nut, retracts the bolt to the external tank side
of the interface. On the orbiter side, each frangible nut and its
detonators are enclosed in a debris container that captures nut
fragments and hot gases generated by the operation of the detonators,
either of which will fracture the nut.
The right aft umbilical assembly consists of an electrical disconnect,
the gaseous oxygen 2-inch pressurization disconnect used for
pressurization of the external tank's oxygen tank and the 17-inch
liquid oxygen disconnect.
The left aft umbilical assembly consists of an electrical disconnect
plate, the gaseous hydrogen 2-inch pressurization disconnect used for
pressurization of the external tank's hydrogen tank, the 4-inch
recirculation disconnect used during prelaunch to precondition the
main engine and the 17-inch liquid hydrogen disconnect.
After release of the three frangible nuts and bolts at each aft
umbilical, three lateral support arms at each orbiter umbilical plate
hold the plates in the lateral position when the external tank
separates from the umbilical plates. Each 17-inch disconnect has been
commanded closed. The orbiter umbilical plates are retracted inside
the orbiter aft fuselage approximately 2.5 inches by three hydraulic
actuators and locked to permit closure of the umbilical doors in the
bottom of the aft fuselage. Hydraulic system 1 source pressure is
supplied to one actuator at each umbilical, hydraulic system 2 source
pressure is supplied to the second actuator at each umbilical, and
hydraulic system 3 source pressure is supplied to a third actuator at
each umbilical.
The retraction of each umbilical disconnects the external tank and
orbiter electrical umbilical in the first 0.5 of an inch of travel and
releases any fluids trapped between the 17-inch disconnect flappers.
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.
Contractors for the separation system include Hoover Electric, Los
Angeles, Calif. (external tank umbilical centerline latch and
actuator; umbilical door actuator and umbilical door latch actuator);
U.S. Bearing, Chatsworth, Calif. (external tank/orbiter spherical
bearing); Bertea Corp., Irvine, Calif. (umbilical retractor
actuator); Space Ordnance Systems Division, Trans Technology Corp.,
Saugus, Calif. (orbiter/external tank separation bolt/cartridge
detonator assembly, 0.75-inch frangible nut orbiter/external tank
umbilical separation and 2.5-inch frangible nut/pyro components in
orbiter/external tank aft attach separation system).