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2.11-22
Description
An EVA occurs when a crewmember leaves the
protective environment of a spacecraft's pres-
surized cabin and ventures out into the vacuum
of space wearing a space suit. An EVA is com-
monly referred to as a spacewalk. The current
space suit, designed for a total maximum dura-
tion of 7 hours, provides environmental protec-
tion, mobility, life support, and communica-
tions. Two suits are included in each baseline
orbiter mission, and consumables are provided
for three two-person, 6-hour EVAs. Two EVAs
are available for payload use, with the third
reserved for orbiter contingency operations.
EVA has been demonstrated to be useful in
satellite repair, retrieval, and refueling as well
as with space station development.
There are three basic categories of EVA:
scheduled, unscheduled, and contingency. A
scheduled EVA is defined as any EVA incorpo-
rated into the nominal flight plan in order to
complete a specific mission objective. An
unscheduled EVA is not part of the flight plan;
rather, it is conducted to achieve payload opera-
tion success or to advance overall mission
accomplishments. A contingency EVA is also
unscheduled, but is required to ensure safe
return of the orbiter and flight crew.
A subcategory of scheduled EVA is the quick-
response EVA. A quick-response EVA must be
performed within a few hours after a problem is
discovered, and it is usually associated with
payload deployment. Quick-response EVAs are
planned pre-flight, and the crew prepares for
the EVA even though it may not be performed.
Mission
Date
Purpose of EVA
EVA crew
No. EVA/
mission
Duration,
man-hours
STS-6
Apr 4-9, 83
System Functional Demo
Musgrave/Peterson
1
8 hr, 34 min
STS-41B
Feb 3-11, 84
MMU Capability Demo
NcCandless/Stewart
2
23 hr, 14 min
STS-41C
Apr 6-13. 84
Solar Max Satellite Repair
Van Hoften/Nelson
2
20 hr, 12 min
STS-41G
Oct 5-13, 84
Orbiter Fuel Transfer Demo
Leestma/Sullivan
1
6 hr, 58 min
STS-51A
Nov 8-16, 84
Westar/Palapa Satellite Retrieval
Allen/Gardner
2
24 hr, 28 min
STS-51D
Apr 12-19, 85
Syncome F3 Satellite Repair
Griggs/Hoffman
1
6 hr, 20 min
STS-51I
Aug 27-Sep 3, 85
Syncome F3 Satellite Repair
Fisher/Van Hoften
2
23 hr, 42 min
STS-61B
Nov 26-Dec 3, 85
Large Structure Assembly
Spring/Ross
2
24 hr, 40 min
STS-37
Apr 5-10, 91
GRO Satellite Repair/Locomotion Studies
Ross/Apt
2
20 hr, 58 min
STS-49
May 10-14, 92
Intelsat Repair and Assembly of Station by
EVA Methods (ASEM)
Thuot, Hieb, Akers,
Hornton,
4
59 hr, 51 min
STS-54
Jan 17, 93
First EVA Detailed Test Objective (DTO
1210)
Harbaugh, Runco
1
8 hr, 56 min
STS-57
Jun 25, 93
EURECA Antenna Stow and Second EVA
DTO (1210)
Low, Wisoff
1
11 hr, 40 min
STS-51
Sep 16, 93
Third EVA DTO (1210)
Walz, Newman
1
14 hr, 10 min
STS-61
Dec 4-8, 93
Hubble Space Telescope Repair Mission
Musgrave, Hoffman,
Akers, Thornton
5
70 hr, 58 min
STS-64
Sep 16, 94
SAFER First Flight
Lee, Meade
1
13 hr, 42 min
STS-63
Feb 9, 95
First EVA Development Flight Test (EDFT)
(Spartan Mass Handling)
Foale, Harris
1
13 hr, 18 min
STS-69
Sept 16, 95
Second EDFT (Task board with station EVA
interfaces)
Voss, Gernhardt
1
13 hr, 32 min
STS-72
Jan 14-16, 95
Third EDFT (Station assembly and
maintenance hardware)
Chiao, Barry, Scott
2
26 hr, 4 min
STS-76
Mar 27, 96
Fourth EDFT (MEEP - Mir Environmental
Effects Payload)
Godwin, Clifford
1
12 hr, 4 min
Space Shuttle EVA Chronology Extravehicular Mobility Unit
Extravehicular activities are classified according
to level of complexity: simple, intermediate, or
complex. A simple payload EVA requires mini-
mal unique tools, mockups, or mobility aids.
Existing procedures and techniques may be
adapted to particular EVA needs, thus requiring
minimal crew training. An intermediate pay-
load EVA requires development of new tools
and equipment. Some procedure and technique
development is required, with more extensive
training necessary. A complex payload EVA
requires the design and development of com-
plex or elaborate tools and equipment. The
tasks require extension of basic capabilities and
may pose difficulty in access or restraint. Proce-
dure and technique development is extensive, as
are crew training requirements.
Extravehicular Mobility Unit
The extravehicular mobility unit (EMU) is an
independent anthropomorphic system that pro-
vides environmental protection, mobility, life
support, and communications for the crewmem-
ber to perform EVA in Earth orbit. For EMU
design considerations, an EVA is defined as any
time the EMU external environmental pressure
is below 4.0 psia. The EMU is designed to accommodate an EVA mission with a total
maximum duration of 7 hours, consisting of 15
minutes for egress, 6 hours for useful EVA
tasks, 15 minutes for ingress, and a 30-minute
reserve. The EMU also accommodates specific
metabolic rate limits, including (1) an average
metabolic rate not exceeding 1600 Btu/hr in any
given EVA hour and not exceeding 1000 Btu/hr
for the entire duration, (2) a peak metabolic rate
not exceeding 2000 Btu/hr for a period of 15
minutes, and (3) a minimum metabolic rate not
less than 400 Btu/hr for a period of 30 minutes.
The EMU is an integrated assembly, primarily
composed of the space suit assembly, life
support system, and numerous items of associ-
ated support and ancillary equipment.
Space Suit Assembly
The space suit assembly (SSA) is the anthro-
pomorphic pressure vessel that encloses the
crewmember's torso, limbs, and head. The SSA
provides a variety of functions while the
crewmember performs an EVA, including suit
pressure retention, crewmember mobility, crew-
member liquid cooling distribution, oxygen
ventilation gas circulation, downlink of crew-
member's electrocardiogram data via EMU
radio, crewmember interface with EMU radio,
crewmember in-suit drinking water, and urine
containment. The SSA operates under specific
pressure requirements and leakage criteria.
The space suit assembly consists of the
following:

Hard upper torso/arms

Lower torso assembly

Extravehicular gloves

Helmet/extravehicular visor assembly

Liquid cooling and ventilation garment

Operational bioinstrumentation system

Communications carrier assembly

In-suit drink bag

Urine collection device

Maximum absorption garment.
The hard upper torso (HUT) provides pressure
containment for the upper torso as well as being
the central component from which the mechani-
cal, electrical, and fluid interfaces of the EMU
branch. The HUT is available in four sizes to
accommodate 5th through 95th percentile-sized
crewmembers. The planar HUT, which deletes
the arm gimbal and bellows assembly, will be
available in two sizes. The HUT includes the
following components: fiberglass shell (with
water tubes and oxygen ducts), assorted
mounting brackets, waterline and vent tube
assembly, multiple water connector, EMU
electrical harness, shoulder bearing assemblies,
waist disconnect ring (passive half), helmet
disconnect ring, and thermal micrometeoroid
garment (TMG). The right and left arm assem-
blies are flexible, anthropomorphic pressure
vessels that encompass the arms. Each arm
assembly includes the following components:
upper arm assembly, rotating scye bearing,
lower arm assembly, rotating arm bearing, wrist
disconnect ring, urethane pressure bladders,
cloth restraint systems, and TMGs for the upper
and lower arm assemblies.
The lower torso assembly (LTA) consists of a
flexible anthropomorphic pressure vessel that
encompasses the waist, lower torso, legs, and
feet. The LTA includes the following compo-
nents: waist assembly, waist disconnect ring,
trouser assembly, rotating waist bearing
between the waist and trouser assemblies, boot
assembly, urethane pressure bladders, cloth
restraint systems, and TMGs for the waist,
trouser, and boot assemblies.
The current sizing of the arm/leg assemblies is
accomplished on the ground using different
sizes of each assembly for a particular crew-
member. An enhanced EMU has been devel-
oped to provide an on-orbit capability of EMU
resizing by using various arm/leg segments and
sizing rings. The on-orbit quick-sizing capabil-
ity, uses threaded quick-disconnects, softgood
sizing elements, aluminum sizing rings, and
adjustable-length restraint lines. This suit incor-
porates dual lip seal mobility bearings and low-
torque fabric joints. The enhanced EMU will
phase out the current space suit for future
station and shuttle operations. SSA Arm Assembly
Lower Torso Assembly with TMG Removed The extravehicular gloves consist of a detach-
able, flexible pressure vessel, encompassing
each hand for use during EVA. The extrave-
hicular gloves include the following compo-
nents: urethane pressure bladder and cloth
restraint system, wrist disconnect ring with
rotating wrist bearing, wrist gimbal ring,
adjustable palm restraint bar/strap, wrist tether
strap, and TMG with palm restraint bar. The
current 4000 series gloves incorporate a stan-
dard nine-size system to size the gloves for a
comfortable fit. The glove fingers use a sizing
feature that consists of a pair of polyester
dacron cords to provide finger length adjust-
ments. Customized gloves can be manufactured
for the crewmember if a proper fit cannot be
obtained from the standard size glove.
Enhanced Arm Assembly
The helmet, a "one-size-fits-all" model, consists
of a detachable, transparent, hard