Activity Mobility Units
The EMUs provide the necessities for life support, such as oxygen,
carbon dioxide removal, a pressurized enclosure, temperature control
and meteoroid protection during EVA.
The EMU space suit comes in various sizes so that flight crew
members can pick their suits before launch. Components are designed
to fit men and women from the 5th to the 95th percentiles of body
The self-contained life support system contains seven hours of
expendables, such as oxygen, a battery for electrical power, water
for cooling, lithium hydroxide for carbon dioxide removal and
a 30-minute emergency life support system during an EVA.
The airlock adapter plate in the airlock also provides a fixed
position for the EMUs to assist the crew member during donning,
doffing, checkout and servicing. The EMU weighs approximately
225 pounds, and its overall storage envelope is 26 by 28 by 40
inches. For launch and entry, the lower torso restraint, a cloth
bag attached to the airlock adapter plate with straps, is used
to hold the lower torso and arms securely in place.
The EMU is pressurized to 4 psid. It is designed for a 15-year
life with cleaning and drying between flights. The EMU consists
of a hard upper torso, lower torso assembly, gloves, helmet and
visor assembly, communications carrier assembly, liquid cooling
and ventilation garment, urine collection device and operational
bioinstrumentation system. The upper torso, including arms, is
that portion of the pressure suit above the waist, excluding the
gloves and helmet. It provides the structural mounting for most
of the EMU-helmet, arms, lower torso, portable life support system,
display and control module and electrical harness. The arm assembly
contains the shoulder joint and upper arm bearings that permit
shoulder mobility as well as the elbow joint and wrist bearing.
The PLSS is made of fiberglass and provides a mounting for other
EMU components. It includes oxygen bottles; water storage tanks;
a fan, separator and pump motor assembly; a sublimator; a contaminant
control cartridge; various regulators, valves and sensors; communications;
bioinstrumentation; and a microprocessor module. The secondary
oxygen pack attaches to the bottom of the PLSS. The PLSS expendables
include 1.2 pounds of oxygen pressurized to 850 psia in the primary
bottles, 2.6 pounds of oxygen at 6,000 psia in the secondary pack,
10 pounds of water for cooling in three bladders and lithium hydroxide
in the contaminant control cartridge.
The primary oxygen system and water bladders provide enough of
these expendables for seven hours inside the EMU, including 15
minutes for checkout, six hours of EVA, 15 minutes for EMU doffing
and 30 minutes for reserve. The SOP will supply oxygen and maintain
suit pressure for 30 minutes in the event of a failure in the
primary system or depletion of the primary oxygen system.
The lower torso assembly is that portion of the EMU below the
waist, including boots. It consists of pants and hip, knee and
ankle joints. The lower torso comes in various sizes and connects
to the hard upper torso by a waist ring. It is composed of several
layers, beginning with a pressure bladder of urethane-coated nylon,
a restraining layer made of Dacron, an outer thermal garment made
of neoprene-coated nylon, four layers of aluminized Mylar and
a surface layer of Gortex and Nomex. The foot section consists
of specialized socks that contain return air ports. The EVA crew
members' feet are fitted with boot inserts that fit into the boots.
The gloves contain the wrist connection, wrist joint and insulation
padding for palms and fingers. They connect to the arms and are
available in 15 sizes.
The helmet is a clear polycarbonate bubble with a neck disconnect
and ventilation pad that provides pressurization for the head.
An assembly that goes over the helmet contains visors that are
manually adjusted to shield the EVA crew members' eyes from micrometeoroids
and from ultraviolet and infrared radiation from the sun. Two
EVA lights are attached on each side of the helmet. A TV camera
can also be attached to the helmet.
A cap, known as the Snoopy cap, is worn under the EMU helmet.
It fits over the crew member's head and is held in place by a
chin guard. It contains a microphone and headphones for two-way
communications and receiving caution and warning tones.
The liquid cooling and ventilation garment worn by the EVA crew
member under the pressure suit has sewn-in tubes. It provides
circulation of cooling water and pickup of vent flow at the extremities.
It is a mesh one-piece suit made of spandex and has a zipper in
the front for entry. It has 300 feet of plastic tubing that carries
cooling water at a rate of 240 pounds per hour. It is controlled
by a valve on the display and control module. Ducting along the
garment's arms and legs directs oxygen and carbon dioxide from
the suit to the life support system for purification and recirculation.
The garment weighs 6.5 pounds and provides cooling to maintain
desired body temperature and physical activity that nominally
generates 1,000 Btu per hour and can generate up to 2,000 Btu
per hour, which is considered extremely vigorous.
The urine collection device collects urine. It can store approximately
1 quart of urine. It consists of adapter tubing, a storage bag
and disconnect hardware for emptying after an EVA to the orbiter
waste water tank.
The bioinstrumentation system monitors the EVA crew member's
heart rate (electrocardiogram) during an EVA.
An in-suit drink bag stores approximately 0.5 of a quart of drinking
water in the upper torso. A tube from the upper hard torso to
the helmet permits the EVA crew member to drink water while suited.
The life support system consists of the portable life support
system, display and control module, contaminant control cartridge,
battery, secondary oxygen pack, and EVA communicator and EMU antenna.
The PLSS is also referred to as a backpack. The PLSS normally
provides the EVA crew member with oxygen for breathing, ventilation
and pressurization and water for cooling.
The contaminant cartridge consists of lithium hydroxide, charcoal
and filters to remove carbon dioxide, odors, particulates and
other contaminants from the ventilation circuit. It is replaceable
upon completion of an EVA.
A silver-zinc battery provides all electrical power used by the
EMU and life support system. It is stored dry, filled, sealed
and charged before flight. It is rechargeable upon completion
of an EVA and is rated at 17 volts dc.
The SOP provides oxygen for breathing, ventilation, pressurization
and cooling in the event of a PLSS malfunction. It is mounted
at the base of the PLSS and contains a 30-minute oxygen supply,
a valve and a regulator assembly.
The EVA communicator and EMU antenna provide EVA communications
via its transceiver and antenna between the suited crew member
and the orbiter. In addition, the crew member's electrocardiogram
is telemetered through the communicator to the orbiter. It is
a separate subassembly that attaches to the upper portion of the
life support system at the back of the hard upper torso. The controls
are located on the display and control module mounted at the front
of the upper torso.
The radios for space walk communications have two single-UHF-channel
transmitters, three single-channel receivers and a switching mechanism.
In addition, telemetry equipment is included so that ground personnel
can monitor the astronaut's heart beat. These backpack radios
have a low-profile antenna, a 1-foot-long rectangular block fitted
to the top of the packs. The radios weigh 8.7 pounds and are 12
inches long, 4.3 inches high and 3.5 inches wide.
The EMU electrical harness provides biomedical instrumentation
and communications connections to the PLSS. The harness connects
the communications carrier assembly and the biomedical instrumentation
subsystem to the hard upper torso, where internal connections
are routed to the EVA communicator. The cable routes signals from
the electrocardiogram sensors, which are attached to the crew
member, through the bioinstrumentation system to the EVA communicator.
It also routes caution and warning signals and communications
from the communicator to the crew member's headset.
The DCM is an integrated assembly that attaches directly to the
front of the hard upper torso. The module contains a series of
mechanical and electrical controls, a microprocessor, and an alphanumeric
LED display easily seen by a crew member wearing the space suit.
It contains the displays and controls associated with the operation
of the EMU.
The function of the display and control module is to enable the
crew member to control the PLSS and the secondary oxygen pack.
It also indicates the status of the PLSS, the suit and, the manned
maneuvering unit (when it is attached) visibly and audibly.
The mechanical controls consist of a suit purge valve, the liquid
cooling and ventilation garment cooling valve, and the oxygen
actuator control, which has four positions: off , iv (which turns
primary oxygen on to a 0.5-psid suit pressure setting), press
(which turns primary oxygen on to a 4.1-psid suit pressure setting),
and ev (which leaves primary oxygen on the 4.1-psid setting and
turns the secondary oxygen pack on). The electrical controls include
a voice communications mode switch, dual volume controls, push-to-talk
switches, a power mode switch, feedwater and C/W switches and
the LED display brightness control. The displays on the module
are a 12-digit LED display, a built-in test equipment indicator
and an analog suit pressure gauge.
The display and control module is connected to the hard upper
torso and to the PLSS by both internal and external hookups. A
multiple-function connector links the display module to the service
and cooling umbilical, thus enabling the use of the display module
controls during suit checkout inside the airlock station.
The display module interacts with a microprocessor in the PLSS
that contains a program that enables the crew member to cycle
the display through a series of systems checks and thereby determine
the condition of a variety of components. The microprocessor monitors
oxygen pressure and calculates the time remaining at the crew
member's present use rate. It signals an alarm at high oxygen
use in the primary oxygen tanks. It also monitors water pressure
and temperature in the cooling garment. The carbon dioxide level
is monitored and an alarm is signaled when it reaches high concentrations
in the suit. The microprocessor monitors the power consumed and
signals at high current-drain rates and also when an estimated
30 minutes of battery power is left. All the warnings are displayed
on the LED display.
The display module also has a fiber-optic cable that is used
when the MMU is connected to the EMU. The fiber-optic cable connects
the display unit to the MMU. A fiber-optic cable is more reliable
and more covenient and safer to use than an electrical connector
for extravehicular applications. The MMU is mounted on the back
of the portable life support system. When the MMU is connected,
the display module also provides a cycled readout of propellant
pressures, temperatures, and battery condition (in the MMU) and
an audible thruster cue. The C/W system warns of low propellant,
low battery, and failed components.
Oxygen from the system enters the suit at the helmet and flows
from behind the head down through the suit. Oxygen and carbon
dioxide are removed from the suit through the liquid cooling and
ventilation garment at ports near the crew member's wrists and
feet. Return air goes first through the contaminant control cartridge,
where activated charcoal and lithium hydroxide beds remove carbon
dioxide, odors and dust. From there the return air goes through
a water separator, where moisture from exhalation and the lithium
hydroxide and carbon dioxide reaction is removed. The oxygen then
goes through the fan, which maintains air flow at 6 cubic feet
per minute. It is then routed through the sublimator, where it
is cooled to 85º F, and then passes through a vent and flow detector
and back to the suit. Oxygen for the air system is fed from the
primary oxygen containers through regulators that maintain suit
pressure at 4.1 psid.
The system is protected from suit overpressure, primary oxygen
supply depletion or mechanical failure by regulators, sensors
and the secondary oxygen pack. The secondary oxygen pack can maintain
suit pressure at 3.45 psid. A purge valve on the display and control
module allows a crew member to completely replace system oxygen
in the suit if, for instance, the carbon dioxide level rises too
high too quickly.
The cooling water system takes the warm water from the cooling
garment and divides it into two loops. One loop goes to the sublimator,
where the water in that loop is cooled and sent back to the cooling
control valve. The other loop goes directly back to the cooling
control valve, where the loops are recombined and full flow goes
back to the cooling garment. Thus, the cooling garment has a constant
flow of cooling water at a temperature set by the crew member
using the cooling control valve. During the process, the full
flow from the cooling garment goes through a gas separator, where
gas is removed from the loop, and then through a pump that maintains
a flow of 260 pounds per hour. Another side loop circulates 20
pounds per hour through the contaminant control cartridge to cool
the lithium hydroxide canister since the lithium hydroxide and
carbon dioxide reaction produces heat and needs to be kept cool
for an efficient reaction.
Since the system is a closed-loop design, water from the water
separator is fed back to the water system, and air from the gas
trap is fed back to the oxygen system. Water from the water tanks
is also fed, through regulators, into the cooling system. However,
the primary purpose of the water tanks is to feed water to the
sublimator. The sublimator works on the principle of sublimation,
that is, the process by which a solid turns directly into a vapor,
bypassing the liquid phase. In this case, ice is formed on the
sublimator evaporator sieve and is allowed to vaporize to space,
removing heat with it. Air and cooling water are passed through
fins in the sublimator, which extracts heat from each system.
PLSS sensors detect system air flow, air pressure, water flow, water
pressure, differential water pressure (between the circulating system
and the water tanks), water temperature and carbon dioxide content
in the return air. In addition, there are a number of crew-selectable
valves, including a purge valve, a cooling control valve (infinitely
variable), oxygen supply and a direct-reading air pressure gauge.
The sensors supply information to the display and control module,
where a microprocessor maintains an automatic watch over system
day before an EVA, the orbiter crew compartment cabin pressure is
allowed to decrease from 14.7 psia to 12.5 psia through metabolic
usage. One hour before depressurizing the crew compartment from
12.5 psia to 10.2 psia, the EVA crew member and prebreathes 100-percent
oxygen for 45 minutes. There are two PEAPs in the airlock. The crew
compartment is then depressurized from 12.5 psia to 10.2 psia and
remains at this pressure until after the EVA is completed. This
is necessary to remove nitrogen from the EVA crew member's blood
before the EVA crew member works in the pure oxygen environment
of the EMU. Without the prebreathing, bends can occur. When an individual
fails to reduce nitrogen levels in the blood before working in a
pressure condition, it can result in nitrogen coming out of solution
in the form of bubbles in the bloodstream. This condition results
in pain in the body joints, possibly because of restricted blood
flow to connective tissues or because of the extra pressure caused
by bubbles in the blood in the joint area.
for an EVA, the crew member dons the liquid cooling and ventilation
garment first, enters the airlock and dons the lower torso assembly.
The crew member then squats under the hard upper torso mounted on
the airlock adapter plate and slides up into the upper torso. The
upper and lower torsos are connected with a waist ring. The gloves
and helmet are then put on, and the EMU is disconnected from the
provides electrical power, oxygen, liquid cooling and ventilation
garment cooling and water to the EMUs in the airlock via the service
and cooling umbilical for EVA preparation and after EVA operations.
and cooling umbilical contains communication lines, electrical power,
water, water drain line and oxygen recharge lines. The umbilical
permits the EVA crew member to check out the suit in the airlock
without using the EMU supply of water, oxygen and battery power.
The SCU is
launched with the orbiter end fittings permanently connected to
the appropriate ECLSS panels in the airlock and the EMU connected
to the airlock adapter plate stowage connector. It allows all supplies
(oxygen, water, electrical and communication) to be transported
from the airlock control panels to the EMU before and after EVA
without using the EMU expendable supplies of water, oxygen and battery
power that are scheduled for use in the EVA. The SCU also provides
EMU recharge. The SCU umbilical is disconnected just before the
crew member leaves the airlock on an EVA and is reconnected when
he returns to the airlock. Each SCU is 144 inches long, 3.5 inches
in diameter and weighs 20 pounds. Actual usable length after attachment
to the control panel is approximately 7 feet.
has two display and control panels. The airlock control panels are
basically split to provide either ECLSS or avionics operations.
The ECLSS panel provides the interface for the SCU waste and potable
water, liquid cooling and ventilation garment cooling water, EMU
hardline communications, EMU power and oxygen supply. The avionics
panel includes the airlock lighting, airlock audio system and EMU
power and battery recharge controls. The avionics panel is located
on the right side of the cabin airlock hatch and the ECLSS panel
is on the left side. The airlock panels are designated AW18H, AW18D
and AW18A on the left side and AW82H, AW82D and AW82B on the right
side. The ECLSS panel is divided into EMU 1 functions on the right
side and EMU 2 functions on the left.
are provided with the orbiter audio system at airlock panel AW82D,
where connectors for the headset interface units and the EMUs are
located at airlock panel AW18D, the airlock audio terminal. The
HIUs are inserted in the crew member communications carrier unit
connectors on airlock panel AW82D. The CCUs are also known as the
Snoopy caps. The adjacent two-position switches labeled CCU1 and
CCU2 power enable transmit functions only, as reception is normal
as soon as the HIUs are plugged in. The EMU 1 and EMU 2 connectors
on the panel to which the SCU is connected include contacts for
EMU hardline communications with the orbiter before EVA. Panel AW18D
contains displays and controls used to select access to and control
the volume of various audio signals. Control of the airlock audio
functions can be transferred to the middeck ATUs on panel M042F
by placing the control knob to the middeck position.
the EVA communicator is part of the same UHF system that is used
for air-to-air and air-to-ground voice communications between the
orbiter and landing site control tower. The EVA communicator provides
full duplex (simultaneous transmission and reception) communications
between the orbiter and the EVA crew members. It also supplies continuous
data reception of electrocardiogram signals from each crew member
by the orbiter and processing by the orbiter and relay of electrocardiogram
signals to the ground. The UHF airlock antenna in the forward portion
of the payload bay provides the UHF EVA capability.
in the airlock provides 17 volts dc, plus or minus 0.5 volt dc,
at 5 amperes at both EMU electrical connector panels on panel AW82D
and in EVA preparation. Main bus A or B can be selected on the bus
select switch; then the mode switch is positioned to power . The
bus select switch provides a signal to a remote power controller
that applies 28 volts dc from the selected bus to the power and
battery recharger. The mode switch in the power position makes the
power available at the SCU connector and also closes a circuit that
provides a battery feedback voltage charger control that inhibits
EMU power when any discontinuity is sensed in the SCU/EMU circuitry.
The mode switch in the power position also applies power through
the SCU for the EMU microphone amplifiers for hardline communication.
When the SCU umbilical is disconnected for EVA, the EMU operates
on its self-contained battery power. After EVA, when the SCU is
reconnected to the EMU, selecting a bus and the charge position
on the mode switch charges the PLSS battery at 1.55 amps, plus or
minus 0.05 amp. When the battery reaches 21.8 volts dc, plus or
minus 0.1 volt dc, or the charging circuit exceeds 1.55 amps, plus
or minus 0.05 amp, a solenoid-controlled switch internal to the
battery charger removes power to the charging circuitry.
flight crew members before and after the EVA is provided by the
liquid-cooled garment circulation system via the SCU and LCG supply
and return connections on panel AW82B. These connections are routed
to the orbiter LCG heat exchanger, which transfers the collected
heat to the orbiter Freon-21 coolant loops. The nominal loop flow
of 250 pounds per hour is provided by the EMU and PLSS water loop
pump. The system circulates chilled water at 50º F maximum to the
liquid cooling and ventilation garment inlet and provides a heat
removal capability of 2,000 Btu per hour per crew member. When the
SCU is disconnected, the PLSS provides the cooling. Upon return
from the EVA, the PLSS is reconnected to the SCU, and crew member
cooling is as it was in the EVA preparation.
With the suit
connected to the SCU, oxygen at 900 psia, plus or minus 500 psia,
is supplied through airlock panel AW82B from the orbiter's oxygen
system when the oxygen valve is in the open position on the airlock
panel. This provides the suited crew member with breathing oxygen
and prevents depletion of the PLSS oxygen tanks before the EVA.
Before the crew member seals the helmet, an oxygen purge adapter
hose is connected to the airlock panel to flush nitrogen out of
When the SCU
is disconnected, the PLSS provides oxygen for the suit. When the
EVA is completed and the SCU is reconnected, the orbiter's oxygen
supply begins recharging the PLSS, assuming that the oxygen valve
on panel AW82B is open. Full oxygen recharge takes approximately
one hour (allowing for thermal expansion during recharge), and the
tank pressure is monitored on the EMU display and control panel
as well as on the airlock oxygen pressure readout.
The EMU water
supply and waste valves are opened during the EVA preparation by
switches on panel AW82D. This provides the EMU, via the SCU, access
to the orbiter's potable water and waste water systems. The support
provided to the EMU PLSS is further controlled by the EMU display
and control panel. Potable water (supplied from the orbiter at 16
psi, plus or minus 0.5 psi; 100 to 300 pounds per hour; and 40º
to 100º F) is allowed to flow to the feedwater reservoir in
the EMU that provides pressure, which would top off any tank not
completely filled. Waste water condensate developed in the PLSS
is allowed to flow to the orbiter waste water system via the SCU
whenever the regulator connected at the bacteria filters (airlock
end of the SCU) detects upstream pressure in excess of 16 psi, plus
or minus 0.5 psi.
When the SCU
is disconnected from the EMU, the PLSS assumes its functions. When
the SCU is reconnected to the EMU upon completion of the EVA, it
performs the same functions it did before the EVA except that the
water supply is allowed to continue until the PLSS water tanks are
filled, which takes approximately 30 minutes.
for the EVA, the airlock hatch to the orbiter crew cabin is closed
and depressurization of the airlock begins.
is accomplished in two stages by a three-position valve located
on the ECLSS panel AW82A in the airlock. The airlock depressurization
valve is covered with a pressure and dust cap. Before the cap is
removed from the valve, it is necessary to vent the area between
the cap and valve by pushing the vent valve on the cap. In flight
the pressure and dust cap is stored next to the valve. The airlock
depressurization valve is connected to a 2-inch-inside-diameter
stainless steel overboard vacuum line. The airlock depressurization
valve controls the rate of depressurization by varying the valve's
diameter. Closing the valve prevents any air flow from escaping
to the overboard vent system.
When the crew
members have completed the 40-minute prebreathe in the EMUs, the
airlock is depressurized from 10.2 psia to 5 psia by moving the
airlock depressurization valve to the 5 position, which opens the
depressurization valve and allows the pressure in the airlock to
decrease at a controlled rate. The airlock depressurization valve
must be closed to maintain 5 psia. During depressurization, pressure
can be monitored by the delta pressure gauge on either airlock hatch.
A delta pressure gauge is installed on each side of both airlock
At this time,
the flight crew performs an EMU suit leak check, electrical power
is transferred from the umbilicals to the EMU batteries, the umbilicals
are disconnected, and the suit oxygen packs are brought on-line.
stage of airlock depressurization is accomplished by positioning
the airlock depressurization valve to 0 , which increases the valve's
diameter and allows the pressure in the airlock to decrease from
5 psia to zero psia. The suit sublimators are activated for cooling,
EMU system checks are performed, and the airlock and payload bay
hatch can be opened. The hatch is capable of opening against a 0.2
psia differential maximum.
are installed in the orbiter payload bay for use by the crew member
during the EVA.
tether points are located on the payload bulkheads, forward bulkhead
station Xo 576 and aft bulkhead station Xo 1307 along the sill longeron
on both sides of the bay to provide translation and stabilization
capability for EVA crew members and facilitate movement in the payload
bay. The handrails are designed to withstand a load of 200 pounds,
or 280 pounds maximum, in any direction. Tether attach points are
designed to sustain a load of 574 pounds, 804 pounds maximum, in
have a cross section of 1.32 inches by 0.75 of an inch. They are
made of aluminum alloy tubing and are painted yellow. The end braces
and side struts of the handrails are constructed of titanium. An
aluminum alloy end support standoff functions as the terminal of
the handrail. Each end support standoff incorporates a 1-inch- diameter
A 25-foot safety
tether is attached to each crew member at all times during an EVA.
consists of a reel case with an integral D-ring, a reel with a light
takeup spring, a cable and a locking hook. The safety tether hook
is locked onto the slidewire before launch, and the cable is routed
and clipped along the left and right handrails to a position just
above the airlock and payload bay hatch. After opening the airlock
hatch but before leaving the airlock, the crew member attaches a
waist tether to the D-ring of the safety tether to be used. The
other end of the waist tether is hooked to a ring on the EMU waist
bearing. The crew member may select either the left or the right
safety tether. With the selector on the tether in the locked position,
the cable will not retract or reel out. Moving the selector to the
unlocked position allows the cable to reel out and the retract feature
to take up slack. The cable is designed for a maximum load of 878
pounds. The routing of the tethers follows the handrails, which
allows the crew member to deploy and restow his tether during translation.
The two slidewires,
approximately 46.3 feet long, are located in the longeron sill area
on each side of the payload bay. They start approximately 9.3 feet
aft of the forward bulkhead and extend approximately 46.3 feet down
the payload bay. The slidewires withstand a tether load of 574 pounds
with a safety factor of 1.4 or 804 pounds maximum.
equipment may consist of a small work station, tool caddies and
equipment tethers. The work station contains a universal attachment
tether for crew member restraint and a carrying location for the
tool caddies. The caddies hold the tools and provide tethers for
them when they are not in use.
A cargo bay
stowage assembly installed in the orbiter payload bay contains miscellaneous
tools for use in the payload bay during an EVA. The CBSA is approximately
42 inches wide, 24 inches deep and 36 inches high. The CBSA weighs
and cabin hatch has two pressure equalization valves that can be
operated from both sides of the hatch to repres surize the airlock
volume. Each valve has three positions- closed , norm (normal) and
emerg (emergency)-and is protected by a debris pressure cap on the
intake (high-pressure) side of the valve. The pressure cap on the
outer hatch must be vented for removal. The caps are tethered to
the valves and also have small Velcro spots that allow them to be
stored temporarily on the hatch. The exit side of the valve contains
an air diffuser to provide uniform flow out of the valve.
use of the equalization valves, the airlock is initially pressurized
to 5 psia, and the space suit is connected to the umbilical in the
airlock and electrical power is transferred back to umbilical power.
After the airlock is pressurized to the 10.2-psia cabin pressure,
the EVA crew members remove and recharge their EMUs. Shortly thereafter,
the crew compartment cabin is pressurized from 10.2 psia to 14.7
can accommodate three six-hour EVAs by two crew members per flight
at no weight or volume cost to the payload. Two of the EVAs are
for payload support; the third is reserved for orbiter contingency.
Additional EVAs can be considered with consumables charged to payloads.
with a tunnel adapter, hatches, tunnel extension and tunnel, the
middeck airlock permits flight crew members to transfer from the
orbiter middeck into the Spacelab pressurized modules, where they
can work in a pressurized shirt-sleeve environment. The airlock,
tunnel adapter and hatches also permit EVA flight crew members to
transfer into the payload bay from the tunnel adapter in the space
suit assembly without depressurizing the spacecraft crew cabin and
adapter is located in the payload bay and is attached to the airlock
at orbiter station Xo 576 and to the tunnel extension at Xo 660,
thus attaching it to the Spacelab tunnel and Spacelab. The tunnel
adapter has an inside diameter of 63 inches at the widest section
and tapers in the cone area at each end to two 40-inch-diameter
D-shaped openings, 36 inches across. An identical D-shaped opening
is located at the top of the tunnel adapter. Two pressure-sealing
hatches are located in the tunnel adapter: one at the upper area
of the tunnel adapter and one at the aft end of the tunnel adapter.
The tunnel adapter is constructed of 2219 aluminum and is a welded
structure with 2.4- by 2.4-inch exposed structural ribs on the exterior
surface and external waffle skin stiffening.
The hatch located
in the aft end isolates the tunnel adapter and airlock from the
extension tunnel and Spacelab. This hatch opens into the tunnel
adapter. The hatch located in the tunnel adapter at the upper D-shaped
opening isolates the airlock and tunnel adapter from the unpressurized
payload bay when closed and permits EVA crew members to exit the
airlock and tunnel adapter to the payload bay when open. This hatch
opens into the tunnel adapter.
The two hatches
in the tunnel adapter are installed to open toward the primary pressure
source and the orbiter crew cabin to achieve pressure-assist sealing
has six interconnected latches (with the exception of the aft hatch,
which has 17) with a gearbox and actuator, window, hinge mechanism
and hold-open device, differential pressure gauge on each side and
two equalization valves.
in each hatch is 4 inches in diameter. The window is used for crew
observation from the cabin and airlock, tunnel adapter to tunnel,
and tunnel adapter to 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.
has dual pressure seals to maintain pressure integrity. One seal
is mounted on the hatch and the other on the structure. Leak check
quick disconnects are installed between the hatches and the pressure
seals to verify the hatches' pressure integrity before flight.
with latch mechanisms on each hatch allows the flight crew to open
or close the hatch during transfers and EVA operation. 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.
The aft hatch
is hinged to be first pulled into the tunnel adapter and then pulled
forward at the bottom. The top of the hatch is rotated toward the
tunnel and downward until the hatch rests with the Spacelab side
facing the tunnel adapter's floor. The linkage mechanism guides
the hatch from the close/open, open/close position with friction
restraint throughout the stroke. The hatch is held in the open position
by straps and Velcro.
The upper (EVA)
hatch in the tunnel adapter opens and closes to the left wall of
the tunnel adapter. The hatch is hinged to be pulled first into
the tunnel adapter and then pulled forward at the hinge area and
rotated down until it rests against the left wall of the tunnel
adapter. The linkage mechanism guides the hatch from the close/open,
open/close position with friction restraint throughout the stroke.
The hatch is held in the open position by straps and Velcro. The
hatches can be removed in flight from the hinge mechanism via pip
pins, if required.
When the airlock
hatch is opened on orbit, a duct is connected to the cabin air system
to provide conditioned air to the airlock, tunnel adapter and tunnel
during non-EVA-operation periods. The duct must be disconnected
before the airlock hatch is closed for entry.
For an EVA
during a mission with pressurized Spacelab modules, all hatches
are closed and depressurization of the airlock tunnel adapter begins.
The prebreathe requirements, lowering of cabin pressure to 10.2
psia and space suit preparations, etc., remain the same as for an
EVA from the airlock. The difference is that the EVA crew member
enters the payload bay from the upper tunnel adapter hatch.
installed in the orbiter payload bay and in the tunnel adapter,
tunnel and Spacelab for use by the crew member during the EVA.
When EVA is
completed, the crew member enters the upper tunnel adapter hatch
and closes it. The airlock and tunnel adapter are repressurized
in the same manner as when the airlock alone is used.