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 in space.

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 feet.

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 closed.

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.




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Last Updated Wednesday January 12 09:54:53 EDT 1994
Jim Dumoulin (