An airlock is located in the crew cabin middeck. The airlock
and airlock hatches permit EVA flight crew members to transfer
from the middeck crew compartment into the payload bay in EMUs
without depressurizing the orbiter crew cabin.
Normally, two EMUs are stowed in the airlock. The EMU is an integrated
space suit assembly and life support system that enables flight
crew members to leave the pressurized orbiter crew cabin and work
The airlock has an inside diameter of 63 inches, is 83 inches
long and has two 40-inch- diameter D-shaped openings that are
36 inches across, plus two pressure sealing hatches and a complement
of airlock support systems. The airlock's volume is 150 cubic
The airlock is sized to accommodate two fully suited flight crew
members simultaneously. The airlock support provides airlock depressurization
and repressurization, EVA equipment recharge, liquid-cooled garment
water cooling, EVA equipment checkout, donning and communications.
All EVA gear, checkout panel and recharge stations are located
against the internal walls of the airlock.
The airlock hatches are mounted on the airlock. The inner hatch
is mounted on the exterior of the airlock (orbiter crew cabin
middeck side) and opens into the middeck. The inner hatch isolates
the airlock from the orbiter crew cabin. The outer hatch is mounted
in the interior of the airlock and opens into the airlock. The
outer hatch isolates the airlock from the unpressurized payload
bay when closed and permits the EVA crew members to exit from
the airlock to the payload bay when open.
Airlock repressurization is controllable from the orbiter crew
cabin middeck and inside the airlock. It is performed by equalizing
the airlock and cabin pressure with airlock-hatch-mounted equalization
valves on the inner hatch. Depressurization of the airlock is
controlled from inside the airlock. The airlock is depressurized
by venting the airlock pressure overboard. The two D-shaped airlock
hatches are installed to open toward the primary pressure source,
the orbiter crew cabin, to achieve pressure-assist sealing when
Each hatch has six interconnected latches with gearbox and actuator,
a window, a hinge mechanism and hold-open device, a differential
pressure gauge on each side and two equalization valves.
The window in each airlock hatch is 4 inches in diameter. The
window is used for crew observation from the cabin and airlock
and the airlock and payload bay. The dual window panes are made
of polycarbonate plastic and are mounted directly to the hatch
using bolts fastened through the panes. Each hatch window has
dual pressure seals with seal grooves located in the hatch.
Each airlock hatch has dual pressure seals to maintain the airlock's
pressure integrity. One seal is mounted on the airlock hatch and
the other on the airlock structure. A leak check quick disconnect
is installed between the hatch and the airlock pressure seals
to verify hatch pressure integrity before flight.
The gearbox with latch mechanisms on each hatch allows the flight
crew to open or close the hatch during transfers and EVA operations.
The gearbox and the latches are mounted on the low-pressure side
of each hatch, and a gearbox handle is installed on both sides
to permit operation from either side of the hatch.
Three of the six latches on each hatch are double-acting. They
have cam surfaces that force the sealing surfaces apart when the
latches are opened, thereby acting as crew assist devices. The
latches are interconnected, with push-pull rods and an idler bell
crank installed between the rods for pivoting the rods. Self-aligning
dual rotating bearings are used on the rods to attach the bellcranks
and the latches. The gearbox and hatch's open support struts are
also connected to the latching system, using the same rod and
bellcrank and bearing system. To latch or unlatch the hatch, a
rotation of 440 degrees on the gearbox handle is required.
The hatch actuator and gearbox are used to provide the mechanical
advantage to open and close the latches. The hatch actuator lock
lever requires a force of 8 to 10 pounds through an angle of 180
degrees to unlatch the actuator. A minimum rotation of 440 degrees
with a maximum force of 30 pounds applied to the actuator handle
is required to operate the latches to their fully unlatched positions.
The hinge mechanism for each hatch permits a minimum opening
sweep into the airlock or the crew cabin middeck. The inner hatch
(airlock to crew cabin) is pulled and pushed forward into the
crew cabin approximately 6 inches. The hatch pivots up and to
the right side. Positive locks are provided to hold the hatch
in both an intermediate and a full-open position. To release the
lock, a spring-loaded handle is provided on the latch hold-open
bracket. Friction is also provided in the linkage to prevent the
hatch from moving if released during any part of the swing.
The outer hatch (in airlock to payload bay) opens and closes
to the contour of the airlock wall. The hatch is hinged to be
pulled first into the airlock and then pulled forward at the bottom
and rotated down until it rests with the low-pressure (outer)
side facing the airlock ceiling (middeck floor). The linkage mechanism
guides the hatch from the close/open, open/close position with
friction restraint throughout the stroke. The hatch has a hold-open
hook that snaps into place over a flange when the hatch is fully
open. The hook is released by depressing the spring-loaded hook
handle and pushing the hatch toward the closed position. To support
and protect the hatch against the airlock ceiling, the hatch incorporates
two deployable struts. The struts are connected to the hatch linkage
mechanism and are deployed when the hatch linkage mechanism is
rotated open. When the hatch latches are rotated closed, the struts
are retracted against the hatch.
The airlock hatches can be removed in flight from the hinge mechanism
via pip pins, if required.
An air circulation system provides conditioned air to the airlock
during non-EVA operation periods. The airlock revitalization system
duct is attached to the outside airlock wall at launch. When the
airlock hatch is opened in flight, the duct is rotated by the
flight crew through the cabin and airlock hatch and installed
in the airlock. It is held in place by a strap holder. The duct
has a removable air diffuser cap on the end of the flexible duct
that can adjust the air flow from zero to 216 pounds per hour.
The duct must be rotated out of the airlock before the cabin and
airlock hatch is closed for airlock depressurization. During the
EVA preparation period, the duct is rotated out of the airlock
and can be used as supplemental air circulation in the middeck.
To assist the crew member in pre- and post-EVA operations, the
airlock incorporates handrails and foot restraints. Handrails
are located alongside the avionics and environmental control and
life support system panels. Oval aluminum alloy handholds 0.75
by 1.32 inches are mounted in the airlock. They are painted yellow.
The handrails are bonded to the airlock walls with an epoxyphenolic
adhesive. Each handrail has a clearance of 2.25 inches from the
airlock wall to allow gripping in a pressurized glove. Foot restraints
are installed on the airlock floor nearer the payload bay side.
A ceiling handhold installed nearer the cabin side of the airlock
was removed to make room to stow a third EMU. The foot restraints
can be rotated 360 degrees by releasing a spring-loaded latch
and lock every 90 degrees. A rotation release knob on the foot
restraint is designed for shirt-sleeve operation; therefore, it
must be positioned before the suit is donned. The foot restraint
is bolted to the floor and cannot be removed in flight. It is
sized for the EMU boot. The crew member first inserts his foot
under the toe bar and then rotates his heel from inboard to outboard
until the heel of the boot is captured.
There are four floodlights in the airlock. The lights are controlled
by switches in the airlock on panel AW18A. Lights 1, 3 and 4 are
controlled by a corresponding on/off switch on panel AW18A. Light
2 can be controlled by an on/off switch on panels AW18A and M013Q,
allowing illumination of the airlock prior to entry. Lights 1,
3 and 4 are powered by main buses A, B and C, respectively, and
light 2 is powered by essential bus 1 BC. The circuit breakers
are on panel ML86B.
The airlock provides stowage for two EMUs, two service and cooling
umbilicals and miscellaneous support equipment. Both EMUs are
mounted on the airlock walls by means of an airlock adapter plate.
The prime contractor to NASA for the space suit and life support
system is United Technologies' Hamilton Standard Division in Windsor
Locks, Conn. Hamilton Standard is program systems manager, designer
and builder of the space suit and life support system. Hamilton
Standard's major subcontractor is ILC Dover of Frederica, Del.,
which fabricates the space suit.