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EVA-EXP-0031

BASELINE

National Aeronautics and

Space Administration

EFFECTIVE DATE: 04/18/2018

EVA OFFICE

EXTRAVEHICULAR ACTIVITY (EVA) AIRLOCKS 

AND ALTERNATIVE INGRESS/EGRESS METHODS

DOCUMENT
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REVISION AND HISTORY PAGE

Revision

No.

Change 

No.

Description Release

Date

EVA-EXP-0031

Baseline Baseline per CR# EVA-CR-00031 04/18/2018

Document dated 03/07/2018 submitted and 

approved through DAA process/DAA # TN54054

approved April 9, 2018

EVA-REF-001

DAA 

33134 Pre Baseline 03/12/2015

Draft EVA-RD-002 05/14/2015

SAA 

DRAFT 12/15/2015
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Executive Summary

This document captures the currently perceived vehicle and EVA trades with high 

level definition of the capabilities and interfaces associated with performing an 

Extravehicular Activity (EVA) using an exploration EVA system and ingress/egress 

methods during future missions. Human spaceflight missions to Cislunar space, 

Mars transit, the moons of Mars (Phobos and Deimos), the Lunar surface, and the 

surface of Mars will include both microgravity and partial-gravity EVAs, and 

potential vehicles with which an exploration EVA system will need to interface. In 

order to build an airlock compatible with the EVA suit, the interfaces must be 

understood. This document captures the current EVA assumptions and the trades 

and details needed from the vehicle-side to provide further detail to these EVA 

interfaces and operational concepts.

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TABLE OF CONTENTS

SECTION PAGE

1.0 INTRODUCTION................................................................................................ 10

1.1 PURPOSE AND SCOPE ................................................................................... 11

1.2 CHANGE AUTHORITY/RESPONSIBILITY....................................................... 12

2.0 BACKGROUND ................................................................................................. 13

3.0 STATE OF THE ART AND KNOWN CHALLENGES........................................ 15

3.1 SUIT ARCHITECTURE...................................................................................... 18

3.2 UNASSISTED DON/DOFF ................................................................................ 18

3.3 RECHARGE OF ALL SUIT CONSUMABLES................................................... 19

3.4 VOLUME FOR IN-FLIGHT SUIT MAINTENANCE AND SPARES ................... 20

3.5 VOLUME FOR DONNING/DOFFING AND PREBREATHE ............................. 20

3.6 MINIMAL CONSUMABLES USAGE WITH VEHICLE INGRESS/EGRESS 

CYCLES............................................................................................................................ 21

3.7 INCREASED CREW AUTONOMY FOR AIRLOCK OPERATIONS ................. 21

3.8 INCREASED QUANTITY AND ACCESS OF EVAs (HARDWARE CYCLE LIFE 

AND OPERATIONS)......................................................................................................... 21

3.9 ALTERNATIVE ATMOSPHERES FOR REDUCED PREBREATHE TIME ...... 22

3.10 DUST MITIGATION AND PLANETARY PROTECTION ................................... 22

4.0 CONCEPTUAL SOLUTIONS ............................................................................ 23

4.1 SUITPORT CONCEPT....................................................................................... 24

4.2 REAR-ENTRY AIRLOCKS................................................................................. 28

4.3 SUITPORT-AIRLOCK ........................................................................................ 31

5.0 PAST TRADE STUDIES.................................................................................... 34

5.1 DRATS................................................................................................................ 35

5.2 AIRLOCK SUITLOCK SUIT PORT ASSESSMENT TEAM (ASPAT) ............... 38

5.3 SUITPORT TESTING......................................................................................... 39

5.4 RAPID EVE METHODS PHASE 1: NEAR TERM DRM QUICK STUDY.......... 40

5.5 CONSTELLATION SPACE SUIT SYSTEM (CSSS) SUITPORT ASSESSMENT

............................................................................................................................ 43

5.6 EXPLORATION ATMOSPHERES..................................................................... 44

5.7 VERTICAL AND HORIZONTAL HABITATS IN STRATEGIC PLANNING ....... 47

5.8 SMALL HABITAT COMMONALITY................................................................... 48

5.9 EXAMPLE INGRESS/EGRESS METHODS...................................................... 51
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5.10 DEEP SPACE GATEWAY AND TRANSPORT................................................. 52

6.0 EVA ASSUMPTIONS FOR FUTURE VEHICLES............................................. 53

6.1 EVA CONTINGENCY SECONDARY INGRESS HATCH AND DUAL 

CHAMBER AIRLOCKS..................................................................................................... 54

6.2 EVA INTERFACES ............................................................................................ 56

6.2.1 EVA Interface Details.......................................................................... 57

6.2.2 EVA Volumes ...................................................................................... 60

6.3 EVA NEEDS FOR TRANSLATION PATHS (μg)............................................... 61

7.0 FUTURE TRADES FOR VEHICLES................................................................. 63

7.1 OVERALL MISSION........................................................................................... 63

7.1.1 Overall Mission Asset Trades ............................................................. 63

7.2 HABITAT AND INGRESS/EGRESS METHOD TRADES ................................. 65

7.2.1 Ingress/Egress Method: Integral to vehicle or separate module?...... 65

7.2.1.1 Ingress/Egress Method as a Separate Add-on Module ..................... 68

7.2.1.2 Ingress/Egress Method Integrated with the Host Vehicle .................. 69

7.2.2 Logistics Module Conversion to Airlock.............................................. 70

7.2.3 Host Vehicle Atmosphere ................................................................... 71

7.2.4 Inflatable Portions of the Ingress/Egress Method .............................. 75

7.2.4.1 Inflatable Structures History................................................................ 75

7.2.4.2 Current Inflatable State of the Art ....................................................... 75

7.2.4.3 Inflatable Development Work to Date................................................. 76

7.2.4.4 Alternate Inflatable Concepts.............................................................. 77

7.2.5 Diameter of Module............................................................................. 81

7.2.6 Hatches ............................................................................................... 83

7.2.6.1 Inward-opening vs. Outward-opening Hatches .................................. 83

7.2.6.2 Hatch Size in Microgravity .................................................................. 84

7.2.6.3 Hatch Size for Surface Operations ..................................................... 87

7.2.6.4 Secondary Hatch Requirement .......................................................... 87

7.2.6.5 Hatch within a Hatch ........................................................................... 88

7.2.7 Dust Mitigation/Planetary Protection Differences between 

Ingress/Egress Concepts................................................................................... 89

7.2.8 Volume Studies and Suit Maintenance .............................................. 92

7.2.8.1 Don/Doff Volume estimate.................................................................. 94

7.2.8.2 Suit Maintenance ................................................................................ 95

7.2.9 Incapacitated Crewmember................................................................ 97
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7.2.10 Add-on to ISS and Integration ............................................................ 98

7.3 SUIT vs. VEHICLE SUITPORT OPERATIONS................................................. 98

7.3.1 Pressurization, Suit Access Hatch Open-Close, PLSS RotationTranslation ......................................................................................................... 99

7.3.2 Ventilation and Water Circulation ..................................................... 100

7.3.3 Thermal Heat Sync ........................................................................... 100

7.3.4 Environmental Protection.................................................................. 100

7.3.5 100% O2 ........................................................................................... 100

7.3.6 Don/Doff ............................................................................................ 100

7.3.7 PGS Impacts and Suit Center of Gravity.......................................... 101

7.3.8 PLSS Impacts ................................................................................... 101

8.0 SUMMARY....................................................................................................... 102

9.0 REFERENCE DOCUMENTS .......................................................................... 104
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APPENDIX

APPENDIX A ACRONYMN LIST ................................................................................... 108

APPENDIX B SUITPORT TESTING OPTIONS............................................................. 111

APPENDIX C CONCEPTUAL SUITPORT INTERFACE DESCRIPTION ..................... 114

APPENDIX D HATCH AND AIRLOCK HISTORY.......................................................... 123

TABLES

TABLE C-1 SIMULATED MICRO-G FUNCTIONAL TASKS AT EVA PRESSURE...... 114

TABLE C-2 1-G FUNCTIONAL TASKS AT EVA PRESSURE ...................................... 115

TABLE C-3 1-G FUNCTIONAL TASKS AT DCS TREATMENT PRESSURE .............. 116

TABLE C2-1 FORWARD WORK ITEMS ...................................................................... 121

FIGURES

FIGURE 1-1 NASA’s EXPANDING HUMAN PRESENCE IN PARTNERSHIP, 2017..... 10

FIGURE 3-1 SOA ISS QUEST JOINT AIRLOCK ............................................................ 15

FIGURE 3-2 CREW LOCK ............................................................................................... 16

FIGURE 3.3 ISS ISLE PREBREATHE PROTOCOL ....................................................... 17

FIGURE 3.2-1 ISS CREW DONNING/DOFFING EMU ................................................... 19

FIGURE 3.3-1 ISS JOINT QUEST AIRLOCK SPCE....................................................... 20

FIGURE 4-1 SCENARIOS INCORPORATING ALTERNATIVE CONCEPTS ............... 23

FIGURE 4.1-1 SUITPORT INTERFACE PLATE ............................................................. 25

FIGURE 4.1-2 SUIT INTERFACING TO SUITPORT ...................................................... 25

FIGURE 4.1-3 SUITPORT CONCEPT IN PRESSURIZED ROVER WITH 

ENVIRONMENTAL COVER ............................................................................................. 27

FIGURE 4.1-4 SUITPORT TESTING IN CHAMBER B ................................................... 28

FIGURE 4.2-1 SUITPORT AND REAR-ENTRY AIRLOCK DIFFERENCES .................. 29

FIGURE 4.2-2 INTERNAL HATCH (OPEN)..................................................................... 30

FIGURE 4.2-3 REGULAR AIRLOCK VS. REAR-ENTRY AIRLOCK CONCEPT............ 31

FIGURE 4.3-1 SUITPORT-AIRLOCK VS. REAR-ENTRY AIRLOCK CONCEPT........... 32

FIGURE 4.3-2 SUITPORT AIRLOCK CONCEPT............................................................ 33

FIGURE 5.1-1 MODULAR MULTI-MISSION SPACE EXPLORATION VEHICLE .......... 37

FIGURE 5.4-1 RAPID EVA METHOD PHASES.............................................................. 41

FIGURE 5.6-1 HEALTH CONCERN DIAGRAM .............................................................. 46

FIGURE 5.7-1 VERTICAL HABITAT CONCEPTS........................................................... 47

FIGURE 5.7-2 HORIZONTAL HABITAT .......................................................................... 48
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FIGURE 5.8-1 SMALL HABITAT COMMONALITY EVA METHOD OPTIONS............... 50

FIGURE 5.9-1 EXAMPLE INGRESS/EGRESS METHODS............................................ 51

FIGURE 6.2-1 GENERIC EVA INTERFACES DIAGRAM ............................................... 57

FIGURE 6.3-2 GENERIC EVA INTERFACES DIAGRAM ............................................... 59

FIGURE 7.2.1-1 INTEGRATED VS. SEPARATE AIRLOCK FUNCTIONS..................... 66

FIGURE 7.2.1-2 SUITPORTS INTEGRATED WITH PRESSURIZED ROVER .............. 66

FIGURE 7.2.1-3 INTEGRATED HORIZONTAL HABITAT CONCEPTS......................... 67

FIGURE 7.2.1-4 SEPARATE MODULE FOR REAR-ENTRY AIRLOCK OR SUITPORTAIRLOCK........................................................................................................................... 67

FIGURE 7.2.1-5 INTEGRATED OR SEPARATE INGRESS/EGRESS CONCEPTS ..... 68

FIGURE 7.2.3-1 A HISTORY OF HSF: HABITABLE ATMOSPHERES EMPLOYED IN 

THE PAST......................................................................................................................... 73

FIGURE 7.2.3-2 HOST VEHICLE ATMOSHPHERE TRADES ASSUMING A 4.3 PSIA 

EVA PRESSURE.............................................................................................................. 74

FIGURE 7.2.5-1 SUITPORT BULKHEAD (SPR APPLICATION).................................... 82

FIGURE 7.2.5-2 REAR-ENTRY AIRLOCK BULKHEAD (HABITAT APPLICATION WITH 

INTERNAL HATCH).......................................................................................................... 82

FIGURE 7.2.5-3 REAR-ENTRY AIRLOCK BULKHEAD (ANGLED 3.5 M DIAMETER 

TRI-PLANER and PLANAR BULKHEADS)...................................................................... 83

FIGURE 7.2.6-1 ISS AIRLOCK EVA INGRESS/EGRESS HATCH with EMU 

(MICROGRAVITY EVA).................................................................................................... 85

FIGURE 7.2.6-2 FGB 800mm HATCH INGRESS/EGRESS HATCH with Z2 CAD 

(MICROGRAVITY EVA).................................................................................................... 86

FIGURE 7.2.6-3 IDA INGRESS/EGRESS HATCH with Z2 CAD (MICROGRAVITY EVA)

............................................................................................................................ 86

FIGURE 7.2.6-2 COMPLEXITY OF HATCH WITHIN A HATCH..................................... 88

FIGURE 7.2.6-3 REAR-ENTRY AIRLOCK BULKHEAD (HABITAT APPLICATION WITH 

INTERNAL HATCH WITHIN a HATCH)........................................................................... 89

FIGURE 7.2.7-1 LAYERED ENGINEERING CONTAMINATION ZONES ...................... 92

FIGURE 7.2.8-1 DON/DOFF VOLUME ESTIMATE ........................................................ 94

FIGURE 7.2.8-2 PLANAR BULKHEAD WITH 1.22 METER CLEARANCE.................... 96

FIGURE 7.2.8-3 “MUDROOM” EXAMPLE....................................................................... 97
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1.0 INTRODUCTION

National Aeronautics and Space Administration’s (NASA’s) EVA Office, EVA 

System Maturation Team (SMT), and the Human Exploration Office have identified 

exploration Extravehicular Activity (EVA) suits as a high priority requirement to 

support any of the Design Reference Missions (DRMs) currently under 

consideration. Many of these DRMs include alternative ingress/egress methods

which aim to provide the capability for high frequency EVAs, or readily available 

EVA capability, with dust mitigation. While there is not an impending need for 

readily available EVAs with dust mitigation in near term DRMs, it could help buy 

down risk to test the end-to-end operations in advance to prove the technology as 

well as the long-term effects of alternative spacecraft atmospheres on the human 

prior to getting to Mars and using it for mission success. Figure 1-1 shows potential 

phases of exploration.

FIGURE 1-1 NASA’S EXPANDING HUMAN PRESENCE IN PARTNERSHIP, 2017

There are many variables to be balanced when evaluating the interfaces for 

alternative airlock concepts and exploration EVA suit compatibility. Ongoing 

technology development efforts are maturing new technologies for new exploration 

EVA suits and Portable Life Support Systems (PLSS) while reducing remaining 

operational risks for the suit. The same must be done for any new ingress/egress

technology. This “stepping stone” approach parallels the current build, test, and 

learn methodology and allows time for agency maturation of flight/mission needs. 
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The EVA Office has assessed interfaces and impacts to the extent possible, 

though the extent of this is limited without a partner on the vehicle side. Currently, 

there are no funded projects/vehicles that are analyzing alternative airlock 

interfaces from a vehicle perspective. An ISS concern (#6458 in the ISS Program’s

Integrated Risk Management Application (IRMA)) describes the high level impacts 

to an exploration EVA suit compatible with current understandings of alternative 

ingress/egress methods, namely the suitport concept. These will be discussed in 

further detail in this document. To understand what can be done to reduce these 

impacts before building a suit compatible with suitport functionality or any other 

alternative airlock concept, a vehicle assessment is necessary. Other airlock 

concepts with less severe suit impact concerns are described in this document 

along with new functional needs for long duration missions in a partial gravity 

surface environment such as suit maintenance and dust mitigation.

In order to support EVA strategic planning for any future missions (with the ultimate 

goal of a Mars surface mission), it is valuable to understand the key Figures of 

Merit (FOM), such as mass, volume, consumables, etc. associated with 

ingress/egress methods from the vehicle perspective. 

1.1 PURPOSE AND SCOPE

This document is intended to record and organize trades for future exploration EVA 

capability that addresses needs for ingress/egress methods and vehicle impacts. 

Once trades have been established/narrowed down, the structures and masses, 

volumes, and consumables can be understood from the vehicle perspective, 

possibly allowing future projects a path forward instead of immediately assuming 

state of the art equipment as appropriate for the future of human space flight. 

Sections 2-5 provide general background details of EVA, alternative airlock 

concepts and other methods of ingress/egress, as well as past trade studies which 

have been performed. These sections are intended to provide a consolidated 

review-form product which fulfills the role of a “primer” for ingress/egress 

methodologies across all of human spaceflight and thus can be used to form a 

basis of conversation for where the state of the art in both flight hardware and 

concept articulation currently is. Section 6 then addresses the current agreed upon 

EVA community assumptions given to each feasibility vehicle concept project that 

arises. Section 7 presents future trades to be considered when planning missions 

and vehicles capable of performing EVAs, with particular emphasis on

documenting the various issues and FOMs that prove particularly difficult to 

resolve without a multi-party analysis that includes spacecraft/vehicle stakeholder 

participation. Section 8 provides a quick summary and Section 9 captures all the 

references that are cited throughout the document. This document does not reflect 

whether or not high frequency, readily available EVAs are a requirement in a 

particular DRM. That is a programmatic level trade and is specific to the 

destination, mission duration, and objectives of the mission. 
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1.2 CHANGE AUTHORITY/RESPONSIBILITY

Proposed changes to this document shall be submitted by an EVA Management 

Office Change Request (CR) to the EVA Configuration Control Board (EVA CCB) 

for consideration and disposition.

The appropriate NASA Office of Primary Responsibility (OPR) identified for this 

document is the EVA Office. As such, the EVA CCB manages this document on 

behalf of the International Space Station (ISS) Program as the delegated authority 

from the Space Station Program Control Board (SSPCB) per ISS MD 1049, 

Charter for the EVA CCB.
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2.0 BACKGROUND

Missions to destinations beyond Low Earth Orbit (LEO) will affect all exploration 

EVA suit subsystems including the suit (or pressure garment), the PLSS, and the 

Informatics system (INFO). In addition, such missions will force the design of an

exploration EVA suit to consider new challenges involving limited

resources/consumables resupply, communication delays, harsher environments 

(e.g. thermal, prolonged radiation exposure, micrometeoroid impingement, 

increased thermal gradients and dust mitigation), and different gravity fields.

Necessary for ISS construction and maintenance, ISS EVAs were implemented 

with repurposed Shuttle EVA suits and a modified Shuttle airlock that includes

additional volume using a shortened pressurized module as an equipment lock. 

As the Agency continues looking at missions in cislunar space, Mars surface, and 

Mars vicinity destinations, it is clear that an exploration EVA suit architecture must 

be more robust, more reliable, and operate more efficiently than the current ISS 

EVA Mobility Unit (EMU) fleet and ISS airlock. The architecture should also be

extensible to Mars surface pioneering efforts and capable of supporting more

frequent, readily available exploration EVAs (including surface and microgravity 

ops) while minimizing needed consumables, spares, crew time, and planetary 

protection impacts. Timely EVA is a key FOM in the efficacy of exploration and a 

primary product for exploration mission success. 

These mission performance improvements are believed to drive a need for an 

ingress/egress method beyond conventional airlocks. For the purpose of this 

document, the various concepts that might meet this need will be collectively 

referred to as ingress/egress methods. Features and capabilities that have been 

widely discussed for an ingress/egress method include:

• A rear-entry suit donned/doffed through a vehicle bulkhead

• Short-duration EVAs which become feasible due to reduced EVA prep time

- Alternative spacecraft atmospheres reduce amount of prebreathe time

(Abercromby, et al., 2015)

• Multiple EVAs during the same day, multiple days per week

- Reduced crew fatigue/injury

- Increased crew autonomy

• Reduced consumables use such as cabin atmosphere (specifically for the 

suitport concept)

• Increased dust mitigation/planetary protection

Concepts including some or all of the features listed above include the suitport 

concept, the rear-entry airlock or suitlock, and a suitport-airlock combination. 

These will each be described in further detail in Section 4. 
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During the Constellation Program (CxP), risks were identified for an exploration 

EVA suit and PLSS compatibility with a suitport. Several trade studies were 

introduced to delve deeper into the operational concepts and mechanisms of 

different concepts. These trades are described in further detail in Section 5. 

While these studies began to point the way to complete solutions, trades and 

implications associated with these concepts need to be further assessed. This

document has been organized to guide the reader through the historical context 

as well as the trades and analyses that need to be performed in order to develop 

an ingress/egress method. 

After Constellation, concentration began to focus more on near term deep space, 

mainly cislunar, with a future destination of Mars. Section 6 was introduced to be 

available to provide a consolidated list of EVA assumptions to feasibility study 

teams in order to guide them in conceptual airlocks and the interfaces needed by 

EVA. 
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3.0 STATE OF THE ART AND KNOWN CHALLENGES

Current State of the Art (SoA) technology is the ISS Quest Joint Airlock (reference 

Figure 3-1). 

FIGURE 3-1 SOA ISS QUEST JOINT AIRLOCK

The ISS Quest Joint Airlock system includes:

• Two isolatable volumes independent of the ISS vehicle (Dual Chamber 

Airlock)

• The total Joint Airlock pressurizable volume is 1108.25 ft3 (31.4 m3), 

the Crew Lock volume is 200.61 ft3 (5.6 m3

), and the Equipment Lock 

volume is 907.64 ft3 (25.7 m3)

• This volume is different from the functional working activity volume 

of the ISS crew lock, which is measured internally 

• Equipment lock CAD models and physical measurements of training 

unit show a 100” x 53”, or a 137.82 ft3 cylindrical functional working 

activity volume with hatch closed

• Dual suit capable (both EMU and Orlan (RS) suits – this has not been 

tested on-orbit as the RS airlock is closer to the RS segment worksites; 

however, it has been ground tested

• There were unresolved questions about how to scrub the water loops 

post RS/Orlan use in order to not contaminate the EMU water loop 

systems (Orlan used silver nitrate, EMU used iodine. Silver nitrate is 

not compatible with EMU water systems)

• The risk to EMU capability was determined too great, and the ISS 3 

Increment Manager directed a stand down from demonstrating the 

Orlans in the US airlock
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The crew lock external volume is shown below (drawing ref. 683-51960):

FIGURE 3-2 CREW LOCK

• 4.25 m3 or 150 ft3 habitable crew lock volume which accommodates two 

suited pressurized crewmembers; however, the shortest distance 

between the top of the UIA to the EVA handrail opposite of it drops the 

internal habitable volume closer to 137.82 ft3 based on measurements 

and CAD (~5.5 m3 or 194.23 ft3 internal pressurized volume, CX reports 

as 200.2 ft3)

- Majority of atmosphere consumables reclaimed into vehicle stack 

during depressurization prior to opening the hatch with a 1.5 kW 

depress pump (two 30 minute cycles during EVA prep) referenced in 

NAS15-10110 Depress Pump Assembly Micron-A Technical 

Description and Operation Manual

- 1.0 lbm Air residual Airlock depress gas loss

- One of the currently limiting factors on ISS EVA tasks is whether the 

required On-Orbit Replaceable Units (ORU) or other equipment such 

as payloads can fit in the airlock with 2 suited crewmembers. The 

program is having to include whether there is room for ORUs in the 

airlock with the 2 crew in their priority decisions on what critical tasks 

get done.

- EVA hatch is 36” x 40” diameter D hatch (XA has determined by 

analysis that pressurized EMU suit operations require at least a 35” 

pass-through). 

• The larger equipment lock volume is 25.7 m3 which provides secondary 

ingress capability, space for prebreathe and assistance from 

Intravehicular Activity (IVA) crewmembers during prep (supporting a waist 

entry suit) as well as equipment stowage and battery charge and stow 

locations

• Limited volume for in-flight suit maintenance 

• Recharge of most suit consumables (does not recharge high pressure O2)

Significant ground operations support for planning and procedures

• Infrequent EVAs 
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• No provision for dust mitigation

• ~14.7 psi with 21% O2 nominal atmosphere, can be brought down to 10.2 

psi with 26.5% O2 (Reference In-Suit Light Exercise (ISLE) Prebreathe 

Protocol Peer Review Assessment”, NASA Technical Memorandum, 

NASA/TM-2011-217062/Volume I, NESC-RP-10-00659 for further 

information)

- 3 hours 10 minute prebreathe with In Suit Light Exercise (ISLE) shown 

in Figure 3.3 (minimal time at 10.2 pounds per square inch (psi)

FIGURE 3.3 ISS ISLE PREBREATHE PROTOCOL

In addition to minimum suited pressurized EMU translation, based on previous 

EVA evaluations and on orbit demonstration, the translation corridor to transfer an 

unpressurized EMU is 31.5". 

Assessing all known DRMs and with the current SoA in mind, the following 

challenges for exploration EVAs and ingress/egress methods beyond LEO were 

identified when considering proposed future capabilities:

• Suit Architecture

• Unassisted Don/Doff 

• Recharge of all suit consumables (incl. high pressure O2)

• Volume for in-flight suit maintenance and spares 

• Volume for donning/doffing and prebreathe

• Minimal consumables usage with vehicle ingress/egress cycles

• Increased crew autonomy for airlock operations

• Increased quantity and access of EVAs

• Alternative atmospheres for reduced prebreathe time

• Dust mitigation and Planetary Protection
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Each of the challenges are expanded upon in the following sections and should 

be considered when evaluating the FOMs for an ingress/egress method.

3.1 SUIT ARCHITECTURE

Missions to destinations such as asteroids, Earth’s Moon, and the Martian System

are long duration missions resulting in needs that exceed current state-of-the-art 

EMU capability. For EVA, these Destination Classes are defined as follows:

• microgravity on a Engineered Surface (Spacecraft)

• microgravity on a natural surface, such as an asteroid or the moons of Mars

• partial gravity in a vacuum, such as the moon (lunar surface), and

• partial gravity in Partial Atmosphere, such as Mars surface

Reference EVA-EXP-0042 Exploration EVA System Concept of Operations for 

further definition of the Destination Classes as it relates to anticipated concept of 

operations for the suit.

The EMU was designed for the mobility required and the operational constraints

present in a microgravity environment on a vehicle and is already performing 

beyond original specifications. The current EMU does not meet the reliability and 

maintainability requirements needed for missions beyond LEO and cannot be used 

as a surface/planetary exploration EVA suit due to lack of mobility for surface 

operations. Also, DRMs under consideration have assumptions that exceed the 

25 EVA certification life of the ISS EMU, and these DRMs will have limited 

opportunities for resupply or maintenance. Available launch mass and volume will 

also be more constrained, so consumables and logistics must be minimized. The 

long duration missions also limit the EMU’s ability to be upgraded to support the 

unique natural and induced environments envisioned for the multiple destinations. 

With all of this under consideration, mass, volume, Center of Gravity (CG), mobility, 

etc. should be as good as, or better than the EMU for a future suit. Interfaces with 

alternative ingress/egress concepts could change suit architecture.

3.2 UNASSISTED DON/DOFF

The EMU is a waist entry suit and is typically donned with the assistance of an IVA 

crewmember to help connect the lower torso assembly. Due to airlock architecture 

with the ISS environment at 1 atmosphere, the IVA crewmember who assists in 

EMU donning must also perform part of the prebreathe with the EVA crewmembers

when the airlock is isolated from the general ISS volume, which is a significant 

crew time impact. A suit that is donned/doffed without assistance will reduce the 

EVA crewmember’s time as well as eliminate the need for an assisting IVA

crewmember’s time. The EMU is a waist entry suit and can only be donned with 
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the assistance of an IVA crewmember to help connect the lower torso assembly 

(reference Figure 3.2-1).

FIGURE 3.2-1 ISS CREW DONNING/DOFFING EMU

3.3 RECHARGE OF ALL SUIT CONSUMABLES

The three primary building blocks associated with an exploration EVA suit are the 

PLSS, the Suit/Pressure Garment, and the Power, Avionics, and Software system. 

Current EMU interfaces are similar to the needs of an Exploration Extravehicular 

Mobility Unit (xEMU). The following International Space Station (ISS) joint airlock 

Servicing, Performance, and Checkout Equipment (SPCE) hardware items

(reference Figure 3.3-1) located in both the equipment lock and crew lock are 

designed to support Extravehicular Activities (EVAs) for the U.S. Extravehicular 

Mobility Unit (EMU) and Russian Orlan space suit:

• Battery Charger Assembly (BCA)

• Battery Stowage Assembly (BSA)

• EMU Don/Doff Assembly (EDDA)

• Umbilical Interface Assembly (UIA)

• Fluid Pumping Unit (FPU)

• Payload Water Reservoir (PWR)

• Power Supply Assembly (PSA)

• Metox Regenerator

• Metox Canisters

• Miscellaneous Maintenance Fixtures
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FIGURE 3.3-1 ISS JOINT QUEST AIRLOCK SPCE

3.4 VOLUME FOR IN-FLIGHT SUIT MAINTENANCE AND SPARES

The EMU was designed to be sent back down to the ground for most major suit 

maintenance at the end of a limited duration Space Shuttle mission. Because of 

this, the ISS Airlock (A/L) was not designed to facilitate every possible suit 

maintenance event that might occur. As transportation logistics evolved, 

workarounds arose out of necessity to include procedures to perform much more 

extensive suit maintenance tasks on the ISS than originally planned. As the crew 

explores further from earth, suit maintenance will have to be performed in-flight or 

at the destination, rather than relying on the luxury of transfer to the ground or 

transfer of tools.

3.5 VOLUME FOR DONNING/DOFFING AND PREBREATHE

Conventional airlocks have partnered with their host spacecraft to provide 

reasonable volume for EVA prep and post activities which include suit donning, 

doffing, and prebreathe. This has typically been solved in one of two ways. For 

relatively small spacecraft, such as the Gemini and Apollo capsules and the Apollo 

lunar lander, the entire habitable volume was used for these activities and 

depressurized as an airlock. Alternatively, spacecraft with much larger habitable 

volumes provided an intermediate partition such that the depressurizable airlock 

volume was minimized and kept separate from the rest of the spacecraft. This was 

done to minimize depressed consumables and interruptions to the rest of the 
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vehicle’s design and operation. On Shuttle, the middeck was used for most prep 

and post activities including partial donning and prebreathe whereas, on ISS, a 

shortened module called the Equipment Lock was added which provided 

bulkheads and storage space in between the airlock and the rest of ISS. This is 

comparable in EVA prep and post function to the Shuttle middeck. Regardless of

stack size, future EVA systems must provide accommodations for don/doff and 

prebreathe activities in some way or another. 

3.6 MINIMAL CONSUMABLES USAGE WITH VEHICLE INGRESS/EGRESS 

CYCLES

In order to transition from cabin pressure to the exterior environment, cabin 

atmosphere must somehow be displaced. Some architectures, such as small 

capsules, have chosen to vent the entire volume of the cabin directly overboard. 

Others have attempted to conserve resources using reclamation pumps. Even 

with minimized volumes and relatively high efficiency pumps, some amount of 

atmosphere is still lost overboard during each ingress/egress cycle. Exploration 

architectures with high numbers of EVAs thus may pay a non-trivial penalty for the 

accumulated mass lost in many cycles. As an example, see Appendix D for current 

SoA consumables via ISS A/L actuals.

3.7 INCREASED CREW AUTONOMY FOR AIRLOCK OPERATIONS

Exploration architectures with increased communications delays from earth-based 

support teams will face challenges conventionally addressed through low-latency 

communications. Items as simple as assisting crew with procedures during airlock 

operations will need to be addressed in new ways. Though this may include 

increased reliance on IV support crewmembers as has been demonstrated on ISS, 

automation of many functions may also be necessary in order to contain crew 

workload to a manageable level. Airlock architecture choices will likely 

dramatically sway the level of manual and autonomous features necessary to 

increase crew autonomy.

3.8 INCREASED QUANTITY AND ACCESS OF EVAs (HARDWARE CYCLE LIFE 

AND OPERATIONS)

Significant effort has historically been needed to ensure safe EVA operations. For 

spacecraft maintenance EVAs, this is reasonably acceptable due to the relatively 

infrequent nature of vehicle failures and planned nature of nominal construction 

and reconfiguration events. However, human spaceflight systems that seek to 

explore and pioneer unknown natural surfaces may be hampered without 

increased quantities and access to EVA. 
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3.9 ALTERNATIVE ATMOSPHERES FOR REDUCED PREBREATHE TIME

A fundamental limitation of human physiology is the potential for acute and chronic 

injury due to Decompression Sickness (DCS). Because of compromises associated 

with suited mobility, conventional EVA systems have operated at pressures reduced 

from that which human beings live at long term. Even with the short duration of the 

EVA event, it is necessary to intentionally control the transition from the habitable 

volume’s saturation atmosphere to that which the EVA suit will run on. Unfortunately, 

the amount of time necessary to make this transition is directly proportional to the 

difference between vehicle saturation and EVA pressures. This amount of time can 

be non-trivial compared to the duration of the EVA itself and is a significant barrier to 

EVA availability because of crew time penalties. If EVA suit design and ops cons 

cannot allow for increased EVA suit pressure, the only other known way to reduce the 

pressure differential is to decrease the nominal vehicle pressure and determine a 

minimal denitrogenation strategy that allows for on-demand EVA capabilities. This 

would require alternative atmospheric blends, the more dramatic of which may pose 

non-trivial issues including new Human Health uncertainties and vehicle design 

challenges such as reduced effectiveness for atmosphere-based avionics cooling. 

3.10 DUST MITIGATION AND PLANETARY PROTECTION

Dust mitigation and resistance to abrasion poses a significant technical challenge 

for many exploration DRMs. Dust can damage suit components and may become 

a crew health hazard if introduced into the crew cabin in sufficient quantities. In 

addition to the basic mechanical design challenge, airlocks provide a significant 

opportunity of controlling or propagating backward and forward contamination. As 

such, planetary protection concerns for human health and science quality partner 

with engineering design at the airlock interface between EVA and the spacecraft. 

Past methods of ingress/egress would have the crewmember 

traversing/translating directly through the dust that was brought in after an EVA 

both after the crewmembers doff their suits and prior to donning their suits. This 

feature alone poses a significant challenge for ingress/egress methods. “The point

at which the dust becomes the greatest threat to safety is in the donning and 

doffing of the space suit, ingress and egress of the EVA airlock.” (Cohen, M. 2000).
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4.0 CONCEPTUAL SOLUTIONS

NASA headquarters chartered the Human Exploration Architecture Team (HAT) in 

2012, which was tasked with examining a flexible path for human exploration and 

refining the notional DRMs, identifying core capabilities and common architectural 

elements needed to support manned missions to multiple destinations (reference 

Figure 4-1). 

FIGURE 4-1 SCENARIOS INCORPORATING ALTERNATIVE CONCEPTS

Through HAT, exploration EVA development was identified as one of the top five 

capabilities required for enabling missions to multiple destinations for tasks ranging 

from spacecraft assembly through maintenance and repair of satellites and 

vehicles to conducting exploration science at natural destinations. This 

prioritization and early need was based on the significant interplay exploration EVA 

systems have with several of the other possible transportation and destination 

elements. 

Many of the conceived DRMs for human exploration are EVA-centric upon arrival 

at the destination and include science-focused EVAs that increase EVA frequency 
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and require a paradigm shift from heritage programs. For these heritage 

programs, NASA has used tightly-controlled and highly-scripted EVA timelines at 

a relatively low annual rate (about 8 EVAs/year on average in the ISS Program)

and relied heavily on interaction between the EVA crew and ground team. For 

exploration missions, a flexible operational paradigm is needed so that the crew 

can make changes to their activities in near real-time to satisfy science and 

maintenance objectives. Such EVA-centric missions are theorized to require a 

capability that is both reliable and robust while accomplishing 3 to 6 EVAs per week

of shorter duration than the construction-focused missions of Shuttle and ISS, 

while maintaining the flexibility to perform long duration EVAs when necessary.

The following sections will discuss the details of multiple systems; such as a rearentry airlock, suitport, and suitport-airlock (suitport in an airlock) configurations that

an exploration EVA suit may interface with during ingress/egress. Operational 

concepts for some of these systems and how they are applied to specific DRMs 

are documented in EVA-EXP-0042, EVA Office Exploration EVA Capabilities and 

Operational Concepts Document.

4.1 SUITPORT CONCEPT

The suitport concept (generally assumed to be on pressurized rovers) allows for a 

15 minute prebreathe when partnered with a reduced saturation pressure vehicle 

atmosphere. This architecture increases the feasibility of frequent EVAs, and 

minimization of the amount of dust that gets inside the cabin where the crew lives. 

An exploration EVA suit would include a Suitport Interface Plate (SIP) in order to 

interface with a suitport as shown in Figure 4.1-1. The following figure shows a

notional suitport interface plate (green) on a suit:
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FIGURE 4.1-1 SUITPORT INTERFACE PLATE 

A suitport includes two pressure sealing interfaces, one between the SIP (shown 

in green on the suit) and the outside of the bulkhead and another between the 

inner vestibule hatch (shown in purple) and the inside of the bulkhead in the 

habitable volume of a host vehicle (reference Figure 4.1-2). 

FIGURE 4.1-2 SUIT INTERFACING TO SUITPORT

Suits are attached to the bulkhead via the SIP attached to the suit. The SIP creates 

a sealing interface with the bulkhead such that the bulkhead vestibule hatch can 

be open to the cabin and the PLSS hatch can be open to the cabin, while the Interior bulkhead
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opposite side of the bulkhead and front of the suit are at vacuum. The outside of 

the suits are not accessible for maintenance nor sizing while on suitport. The 

vestibule hatch is also a sealing interface. While the suitport vestibule hatches are 

open, the exploration suit SIP acts as the pressure barrier between the habitable 

volume and vacuum. The volume around the suits is continuously at 

vacuum/surface atmosphere while the inside of the suit remains at 0.9 (pounds per 

square inch delta (psid) when not in use to maintain thermal conditioning of the 

suit, to inhibit the migration of dust into the suit, and to minimize leakage (some 

low level leakage is expected). When the suit is not docked to the suitport, the 

suitport vestibule hatch (inner hatch/vestibule door) separates the internal 

habitable volume from vacuum. Sample transfer could be performed through a 

Suitport Transfer Module (SPTM). Depending on the design of the suitport, the 

seal interface between the suit and the vestibule may require an EVA to perform 

maintenance or repair in the case that the seal become damaged/contaminated. 

The suit is assumed to be at 8.2 psid during prebreathe, donning/doffing, and part 

of the suit checkout. EVA suit design for nominal operation at a delta pressure of 

8.2 psid is known to be feasible (nominally operated at 4.3 psid during the EVA)

thus suitports can be used if the pressurized cabin can be reduced to 8.2 (pounds 

per square inch absolute) (psia). Vehicle/cabin pressure must be brought down to 

8.2 psid or less in order to ingress the suit without blowing it out. Prior to an EVA, 

the suit must be brought up to cabin pressure and equalized with the vestibule and 

the cabin. The crewmember ingresses the suit unassisted through the suitport 

(which necessitates a rear entry suit), closes the suit/PLSS hatch, closes the 

vestibule hatch, and depresses the vestibule volume between the hatch and the 

PLSS. 

The exploration atmosphere of 8.2 psi/34% O2 enables a significantly shorter 

prebreathe when compared to traditional airlocks operating at 14.7 psia and at 

10.2 psia, and from 21-28% O2, depending on the prebreathe protocol. This would 

be conducted while the crewmember also performs suit leak checks. While models 

have been used to develop a preliminary prebreathe protocol using the exploration 

atmosphere (Abercromby et al., 2015), that protocol has not yet been validated 

through ground trials. Vehicle atmospheres higher than 8.2 psia would likely 

require additional features in order to maintain the maximum delta pressure across 

the suit during ingress/egress, thus emphasizing the value of further investigation 

in reduced pressure vehicle atmospheres. 

Also, it should be noted that surface operations features on the exterior of the 

suitport concept would be required to restrain suit components such as legs, boots,

arms, and gloves during driving. This is necessary to reduce inadvertent cycling, 

abrasion and impacts induced through vehicle motion. Overall, suits are 

envisioned to be protected by an environmental cover as shown in Figure 4.1-3
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FIGURE 4.1-3 SUITPORT CONCEPT IN PRESSURIZED ROVER WITH 

ENVIRONMENTAL COVER

Dust mitigation is maximized greatly compared to a conventional A/L by keeping 

the dustiest parts of the suits on the outside of the 

cabin and thus decreasing exposure of the habitable 

volume to dust, particulates, or other harmful 

materials. However, dust exposure is not completely 

eliminated so a dust defense plan must be in place to 

mitigate dust entrance into the cabin (as discussed 

later in this document). The intent of suitport is to allow for more rapid egress and 

ingress of an exploration vehicle while limiting the amount of dust entry into the 

cabin and reducing consumables. This new technology will result in reduced gas 

loss over standard airlock operations. Gas used would include the gas leaking 

from the suits for the duration the suits are on the suitport (at 0.9 psid), the gas 

used to bring the vestibule volume and the suit up to cabin atmosphere (8.2 psia) 

to allow the crewmember to ingress the suit, and the gas used post EVA to 

increase the vestibule volume and the free volume around the crewmember inside 

the suit from 4.3 psid to 8.2 psia.

It is anticipated that matured versions of suitport-compatible exploration EVA suits 

will not preclude operation in a typical airlock (including ISS Joint Airlock) but will 

allow for operation in multiple airlock, suitport, and/or hybrid suitport-airlock

configurations. 

Early stage suitport development and testing in JSC Chamber B proved the 

feasibility (Figure 4.1-4) of the suitport concept as 

discussed further in Section 5.3 Suitport Testing. An

exploration EVA suit can be designed and scarred 

built to eventually be compatible for possible future 

development of suitport capability; however, to fully 

designate the suit as suitport-compatible a functioning 

suitport will be required for testing and certification.

Suitport compatibility includes the following: rear-entry 

Suitport Benefits

• Reduced Gas Loss

• Decreased exposure of 

habitable volume to dust & 

particulates

• Rapid Ingress/Egress

Suitport Challenges

• Additional on-back mass

• PLSS Outer Mold Line 

(OML)/plumbing

• Environment exposure, 

delta pressure exposure, 

material degradation

• Suit don/doff difficulty
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don/doff capability, the addition of a SIP, mobility taking into consideration the 

mass and CG of the SIP, volumetrically constrained PLSS packaging, plumbing 

and routing designed with the SIP installed, and suit durability/mobility that can 

withstand a constant delta pressure. The port on the suit that allows access to 

vacuum during EVAs and while on suitport should be compatible with a vacuum 

umbilical interface in order not to preclude use in an airlock or a suitlock-airlock 

(suitports within a pressurizable volume). 

FIGURE 4.1-4 SUITPORT TESTING IN CHAMBER B

While the suitport concept works well with a pressurized rover, long duration 

human stays in excess of a few days must provide a pressurized volume large 

enough to allow the crewmembers to bring the suits inside. It is assumed this 

function will reside on a habitat and will allow for regular suit maintenance, suit 

resizing, suit swapping for crew changeout, and suit swapping for suit end of life 

(conservatively, about 2 suits per crewmember over a 500 day mission duration 

with maximum EVA hours). 

4.2 REAR-ENTRY AIRLOCKS

The Rear-Entry Airlock (which has sometimes been referred to as a “Suitlock”)

looks similar in concept to suitport (Figure 4.2-1), except that the suit does not act 

as a pressure sealing interface to the bulkhead and vehicle. Instead, there is one 

internal hatch to access the airlock chamber and two bulkhead suit access 

hatches. The only pressure sealing interfaces are the hatches themselves. Similar 
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to the suitport, the crew dons/doffs their suits through the bulkhead. The volume 

around the suits is pressurizable and would be pressurized during suit don/doff

operations while the hatches are open to the cabin. The EVA suits are at ambient 

pressure (no delta pressure across the suit) inside the rear-entry airlock. The suits 

are not stowed in vacuum between EVAs as they are while on the suitport concept. 

FIGURE 4.2-1 SUITPORT AND REAR-ENTRY AIRLOCK DIFFERENCES

The rear-entry airlock has bulkhead suit access hatches on the bulkhead that allow 

for rear-entry into suits that are contained inside the airlock chamber. In addition

to the two bulkhead suit access hatches, there is an internal hatch (reference 

Figure 4.2-2) that allows the crew to ingress the airlock while at IVA pressure for 

maintenance. 
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FIGURE 4.2-2 INTERNAL HATCH (OPEN)

As mentioned, since the suit interface to the bulkhead itself is not hermetic, the

volume around the suits must remain pressurized in order to open the bulkhead 

suit access hatches and ingress the suits. Thus, all three hatches to the cabin must 

be sealed prior to depressurizing the airlock chamber. Egress occurs once the 

rear-entry airlock chamber is isolated (bulkhead suit access hatches and internal 

hatch sealed) and is depressed. Gas can be reclaimed depending on filtration 

requirements/contamination. 

Because of this arrangement, the Rear-Entry Airlock concept is more similar to a 

traditional airlock than it is to a Suitport (reference Figure 4.2-3). The rear-entry 

airlock does not require the habitable volume behind the suits to reduce to 8.2 psid

like a suitport so as not to blow the suits out. The only significant difference is that, 

assuming a rear-entry suit, the donning hardware is integrated into the bulkhead 

of the airlock. With the addition of the pressure-sealing hatches, this essentially 

places the suits inside a conventional airlock albeit having donned them “through 

the wall” prior to closing the hatch over the rear-entry PLSS to truly isolate the 

airlock from the rest of the vehicle. For this reason, the Rear Entry Airlock concept 

can look very similar to a Suitport. A rear-entry airlock does not require a SIP. 

The Rear-Entry Airlock allows access to suits for maintenance, inspection, 

cleaning and addresses dust contamination concerns by allowing the 

crewmembers to don Personal Protection Equipment (PPE) prior to ingressing at 

IVA pressure through the internal hatch. With a rear-entry airlock on a habitat, the 

crew can clean the suits before bringing them into a maintenance workstation, or 

they can perform maintenance in front of the suits with enough volume as 

discussed in Section 7.2.8.2 Suit Maintenance.
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FIGURE 4.2-3 REGULAR AIRLOCK VS. REAR-ENTRY AIRLOCK CONCEPT

The rear-entry airlock provides similar dust mitigation and contamination protection 

as the Suitport, though without a true hermetic seal it is not assumed to be truly 

equal and may require additional mitigation features to fully break contamination 

chains and ensure human health. Despite this, dust mitigation is increased beyond 

regular airlock capabilities since the crewmembers are not walking directly through 

the dust as they would in a regular airlock. 

4.3 SUITPORT-AIRLOCK

The suitport-airlock concept incorporates suitports into a pressurizable volume and 

combines the benefits of the previously described Suitport and Rear-Entry Airlock 

concepts. Suitport-airlocks are suitports on the bulkhead that access an airlock

and includes an internal hatch (either around a suitport or in between the suitport 

hatches). The volume around the suits can be left depressurized to vacuum that 

acts purely as a suitport to allow for quicker EVA egress/ingress, held at a delta 

pressure to decrease suit leakage during unmanned quiescent mode, or be 

pressurized to operate as an airlock at the same pressure as the habitat, which 

allows shirtsleeve access to suits for maintenance, suit swapping, sterilization, and 

transfer of equipment. The difference between a rear-entry airlock (suitlock) and 
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suitport-airlock are shown in Figure 4.3-1. The dust mitigation for a suitport-airlock 

is the same as for a suitport. If it needs to be stricter, you treat it as a suitport. If 

you have to access the outside of the suits, it's the same dust risk as having to 

bring the suits in from a suitport to maintain them. 

FIGURE 4.3-1 SUITPORT-AIRLOCK VS. REAR-ENTRY AIRLOCK CONCEPT

A suitport-airlock can be incorporated into an asset that can be brought down to

~8.2 psia with 34% O2 in preparation for EVA and during suit donning and doffing 

operations. The cabin must be kept at 8.2 psia while EVA suits are on the suitports

(to limit pressure differential across the suit); however, it could be possible to 

operate the chamber around the suits at a slight pressure to make up the difference

and allow use of a suitport-airlock on a habitat or pressurized rover that goes above 

8.2 psid. The suit could be kept at a delta pressure with a suitport-airlock, such 

that the outer chamber is at 2 psia and the cabin is at 10.2 psia causing an 8.2 

psid. These details have not been examined in full yet, but if successfully analyzed 

and implemented this could be valuable for nominal EVAs from a habitat. It could 

also be an important mitigation step for use on suitports if on-orbit suitport testing 

cannot be accomplished prior to use for the first time in the Mars vicinity (i.e. if 

difficulty or contingency with the suitport, the outer chamber can be repressed). 
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The suitport vestibule is regulated by the vehicle during unsuited ops (i.e., traverse, 

etc.) for suit stowage. The cabin does not need to be depressed in order to perform 

EVA out of another hatch to translate suits onto the suitports since an internal 

hatch is included similar to the rear-entry airlock (hatch around or between suitport 

hatches). Sample transfer could be performed through a Suitport Transfer Module 

(SPTM) or an internal hatch depending on if the outer chamber is pressurized or 

not.

An EVA can be started with the outer chamber still pressurized (rear-entry airlock

mode) or unpressurized (in suitport mode). Figure 4.3-2 shows another rendering 

of a suitport-airlock concept on a habitat. 

FIGURE 4.3-2 SUITPORT AIRLOCK CONCEPT
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5.0 PAST TRADE STUDIES

Many different style airlocks have been used in the past as shown in the 

Appendices. These styles ranged from depressurizing the capsule (as in the 

Apollo lunar missions), to inflatables, to small airlocks, and included additional 

chambers necessary for prebreathe and maintenance. When discussing 

challenges for reduced prebreathe, dust mitigation, and pressurized rover

interfaces, alternative solutions began emerging through Cohen et al. at the NASA 

Ames Research Center in the late 1980s. First patented in 1989 (lapsed), the 

suitport concept (Cohen, M. 1987) on pressurized rovers initially began as an 

interface to a hard suit. Early concepts showed potential for Hazmat application 

and routine space station operations, postulating substantial savings in 

atmosphere loss, crew time, power, pump cooling, and contamination isolation 

(Cohen, M. 1995). Further studies discussed minimum volume airlocks, 

“airlockless airlocks”, and pressurized rover concept design approaches (Cohen, 

M. 2000). 

Another significant discussion in the Cohen papers included the following

discourse:

“Pressurized surface rovers present their own issues of docking, but they differ 

from orbital systems in the degree to which they interact with the design of the

habitats or EVA support modules to which they must connect. The key question 

is whether the EVA airlock can double as the docking port between the mobile

vehicle and the habitat. Perhaps the most salient point on this question is the

lesson from Skylab: that the design should not situate the airlock between the 

vehicle and the habitat, which in Skylab were the Apollo Command Module and

the Saturn Orbital Workshop. The consequence was that whenever two Skylab 

crew members went EVA and depressurized the airlock, the third needed to retreat 

in advance to the Apollo Command Module, lest he be cut off from escape by the 

depressurized airlock.” (Cohen, 1983 & Cohen, 1985)

“The lesson from Skylab is that the crew should not enter the escape vehicle 

through the airlock from the crew habitat applies equally to the design of EVA 

airlocks as it does to the design of docking ports. Although it is tempting to 

“economize” by combining the two functions of docking port and airlock, it is a false 

economy. Combining the airlock and the docking port into a single unit 

compromises the functioning of both, to the benefit of neither.” (Cohen, 2000)

The advanced airlock initiative was deferred when it was decided to continue using 

the EMU for the ISS. Some of the same questions originally highlighted in the 

Cohen papers are extended here. Since the Constellation Program, alternative 

airlocks have been assessed in trade studies and incorporated in mockups for 

limited feasibility testing. 
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The Desert Research and Technology Studies (DRATS) team began using a 

mockup of the suitport during the Constellation Program in 2008 (Romig, B., et al. 

2009). The Airlock Suitlock Suit Port Assessment Team (ASPAT) was formed in 

2008 to determine appropriate ingress/egress methods for pressurized rover and 

habitat during CxP for lunar surface destinations. The team assessed mass, 

power, consumables, time, effect of concept design on EVA system, etc. 

In order to address some of the issues and to advance the concept, the Advanced 

Exploration Systems (AES) Suitport Project was started in Fiscal Year (FY) 12 with 

a focus on system design. Development and testing occurred before the Suitport 

Project funding ended for FY13, concluding with the early stage suitport 

demonstration test discussed in Section 4.1. 

The Exploration Atmospheres Working Group was formulated in 2005 and again 

in 2011 to select the best combination of pressure and oxygen and the associated 

forward work. 

The Near Term DRM Quick Study was performed by the EVA Office in conjunction 

with Engineering Directorate in 2014 to determine if the suitport concept should be 

considered within “near-term” DRMs (2021-2033). The study looked at a proposed 

module that would go both to the ISS and a Lunar Distant Retrograde Orbit (LDRO)

and determined that the suitport-airlock is the ingress/egress method that should 

be tested on this module. Discussions on whether testing on-orbit is prudent are 

still ongoing; however, the current stance is that it is not a requirement prior to 

going to Mars, but needs further ground testing to determine a path forward. 

The Small Habitat Commonality Team was established in 2014 to look into 

possible commonality between certain assets to help reduce cost. This included 

understanding which modules included EVA capability and options for 

ingress/egress commonality.

The following sections examine the crosslinks and implications of these studies in 

further detail.

5.1 DRATS

DRATS used analog testing to evaluate technology, human-robotic systems, and 

EVA equipment for future human exploration missions. These simulated missions 

helped to assess conceptual design, potential technology, and operations. The 

2008 field tests for a pressurized rover concept was held at the Black Point Lava 

Flow in Arizona to gather data on the suitport concept and compare the scientific 

productivity and human factors during a 1-day exploration, mapping, and traverse

mission versus utilizing an unpressurized rover prototype.
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Human factors data was collected on human exertion, discomfort, fatigue, suitport 

operations, handholds, and volume (Romig, B., et al. 2009) and was found to be 

acceptable and provided lessons learned for future designs. Quantitative 

assessment of crew productivity by an on-site team of expert field geologists found

that compared with unpressurized rover traverses, the same crewmembers were 

57% more productive during pressurized rover traverses and used 61% less EVA 

time due to the ability to use EVA only when required by utilizing the visibility from 

inside the Small Pressurized Rover (SPR) combined with the ability to rapidly 

egress and ingress the SPR via suit ports. Further conclusions indicate that the 

travel distance of an unpressurized rover is constrained by the 8 hour consumables 

limit among other observations (Abercromby, A., et al. 2010).

The 2009 field test pressurized rover concept incorporated the suit environmental 

enclosure, or “cabana”, to protect the suits from dust during the field test 

(Abercromby, A., et al. 2012). 2009 also marked the last year DRATS investigated 

partial gravity EVA surface ops within the context of the CxP program.

In 2010, the DRATS field test expanded upon previous investigations by 

incorporating two pressurized rovers as Multi-Mission Space Exploration Vehicles 

(MMSEV) over a 14 day mission (Abercromby, A., et al. 2013), but transitioned to 

simulating microgravity operations concepts appropriate for Near Earth Asteroid

missions. This included renewed focus on a modular vehicle design that could be 

configured for microgravity or partial gravity destinations (Figure 5.1-1). 
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FIGURE 5.1-1 MODULAR MULTI-MISSION SPACE EXPLORATION VEHICLE

The following bullets indicate which challenges (as identified in Section 3) have 

been addressed to some extent in this study:

• Suit Architecture: Yes
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• Unassisted Don/Doff: Yes (unpressurized)

• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: Yes

• Minimal consumables usage with vehicle ingress/egress cycles: Yes

• Increased crew autonomy for airlock operations: Yes 

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: (Alternative 

atmosphere was assumed, not evaluated)

• Volume for in-flight suit maintenance and spares: No

• Dust mitigation and Planetary Protection: Yes

5.2 AIRLOCK SUITLOCK SUIT PORT ASSESSMENT TEAM (ASPAT)

ASPAT was started in 2008 to determine appropriate ingress/egress methods for 

a pressurized rover and habitat during CxP (destination moon) to address suit 

challenges and overall mission benefits. Over the course of the study, many 

alternate concepts were examined with several concepts selected to be 

considered within scope for a pressurized rover and a habitat on the lunar surface. 

The study involved significant participation time over the next year and a half, along 

with cost due to additional resources deployed to properly assess overall lunar 

mission manifest mass, power, consumables, time, safety, and effect of concept 

design on the EVA system. Independently from the Cohen paper (Cohen, M. 

2000), the ASPAT team also determined that the 

conformal, single person “coffin” designs or single 

person chambers were unsafe due to a fundamental 

difference in utilizing the buddy system during a two 

person EVA. Ground rules and assumptions are 

included in the final report along with analyses and 

results. It was determined that the pressurized rover 

traverse distances would be too constrained to have 

to carry the extra mass, power, and consumables for concepts other than the 

suitport. ASPAT and analogs have shown suitport to be preferred on pressurized 

rovers for multiple reasons, such as lower mass, power, and volume and therefore, 

greater drive distance. Suit challenges due to suitport would have to be looked 

into further through testing. The following concepts were chosen for the 

pressurized rover and the habitat:

• Finding 1: Pressurized rover – suitport

• Finding 2: Habitat – rear-entry airlock (called “suitlock” in the ASPAT 

report)

The following bullets indicate which challenges (as identified in Section 3) have 

been addressed to some extent in this study:

Suit Challenges

Additional on-back mass

PLSS Outer Mold Line 

(OML)/plumbing

Environment exposure, delta 

pressure exposure, material 

degradation

Suit don/doff difficulty
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• Suit Architecture: Yes

• Unassisted Don/Doff: No 

• Recharge of all suit consumables (incl. high pressure O2): Yes

• Volume for donning/doffing and prebreathe: Yes

• Minimal consumables usage with vehicle ingress/egress cycles: Yes

• Increased crew autonomy for airlock operations: Yes 

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: Yes

• Volume for in-flight suit maintenance and spares: Yes

• Dust mitigation and Planetary Protection: Yes

5.3 SUITPORT TESTING

Suitport feasibility testing was performed by the Crew and Thermal Systems 

Division (CTSD) using the Johnson Space Center Building 32 Vacuum Chamber 

B and the Z1 prototype space suit with an 8.3 psi differential across the space suit. 

The Z1 suit is a rear-entry suit with soft upper and lower torso with bearings for 

mobility and includes a SIP to interface with the suitport designed for the chamber. 

Design challenges and work-arounds and/or solutions are discussed in an initial 

paper such as aspects of the suit (PLSS and SIP shapes, glove and boot 

adjustment), the donning angle of the suit, alignment guides and suitport 

mechanisms describing the test (Boyle, et al. 2012). The suitport mechanisms

(such as the second generation Marman Clamp and the Pneumatic Flipper), were 

tested in Building 32 Chamber B along with other design solutions in the first ever 

human-in-the-loop test of 8.3 psid pressurized donning with a suitport compatible 

prototype suit. The paper describes the suit, suitport mechanisms, chamber layout 

and systems, don/doff aids, and results.

The test found that some test subjects could not don, or were partially donned and 

unable to doff, the suit until the chamber was repressurized. During donning, some 

crewmembers were unable to don the suits due to difficulty getting the foot past 

the knee break in the suit due to the pressure differential. The introduction of a 

don/doff aid helped; however, this illustrated that further improvements need to be 

made and testing of suitports need to be further demonstrated in 1-g conditions 

(pressurized donning/doffing, the use of don/doff aids, etc.). Doffing also proved 

to be difficult due to bladder fold and ankle and knee joints and the need for 

leverage to get their upper body out of the suit. Microgravity could help with 

doffing, but may further impede donning. Scores based on the Modified CooperHarper Scale showed improvement after several dockings/undockings from the 

suitports, which indicates operational experience and crewmember technique are 

valuable. These could prove to be quite different between 1g and microgravity due 

to the extent of the differences between gravities and how reduced gravity affects 

don/doff. Testing in reduced gravity environments would help identify any currently 
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unknown issues. Continued testing is needed for system maturation (Boyle, et al. 

2013): 

“This design test effort has significantly improved the technology readiness level 

of the suitport, taking it from the concept stage, to a demonstrated prototype in 

ground testing. The next step, when funding and appropriate missions are 

identified is to implement suitport in a human vacuum chamber test with the 

chamber at space vacuum conditions, followed by thermal vacuum testing with a 

prototype space suit and life support system.” 

The following bullets indicate which challenges (as identified in Section 3) have 

been addressed to some extent in this study:

• Suit Architecture: Yes

• Unassisted Don/Doff: Yes 

• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: No

• Minimal consumables usage with vehicle ingress/egress cycles: No

• Increased crew autonomy for airlock operations: No 

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: No

• Volume for in-flight suit maintenance and spares: No

• Dust mitigation and Planetary Protection: (assumed to be addressed by 

the design concept; not explicitly studied)

5.4 RAPID EVE METHODS PHASE 1: NEAR TERM DRM QUICK STUDY

The Rapid EVA Methods (REM) study was a large trade study that would have 

assessed the ingress/egress methods for all exploration vehicle assets and DRMs. 

The first phase of the study incorporated knowledge gained during past suitport 

testing and incorporated recommendations from ASPAT (with a focus on 

commonality and Mars extensibility). The EVA Office determined that further 

integration was required that would take into consideration the following: 

• Tasks/actions coming from Destination Operations Team (DOT) for the

Evolvable Mars Campaign (EMC) including Cislunar and Mars 

assumptions and conops (2014-2016)

• Exploration Augmentation Module (EAM) project kickoff (ISS and LDRO) 

requirements working groups (2014-2015)

• SMT Gap Closure #401 Ingress/Egress Trade Study input

• Exploration EVA suit technology development (suitport compatibility 

requirements under consideration, but no current funding for suitport)
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• Schedule constraints to determine what should be tested on ISS with 

current extension to 2024 and potential 2028 extension 

The study scope had the potential to be large enough that it was split up into 

phases (reference Figure 5.4-1):

FIGURE 5.4-1 RAPID EVA METHOD PHASES

Part of Phase 1 included the Near Term DRM Quick Study (reference the red box 

in Figure 5.4-1). It was kept to a very short paper study due to limited resources 

and funding and was not a study of the same magnitude of ASPAT. The study 

was specifically to determine if suitports should even be considered in any of the 

near term DRMs (in the next 20 years) based on a quick look at the Figures of 

Merit (FOM), especially operational experience, commonality, and extensibility to 

long term DRMs such as Mars surface. The goal was to provide a nonprogrammatic recommendation to help buy down risk and document a draft of what 

can be done in ground testing vs. on-orbit with further work outlined to be done in 

phases 2 and 3. Phases 2 and 3 were not achieved due to lack of resources.

The scope included a timeframe of 2021-2033 that included the ISS, EAM, Mars 

Transit Vehicle (MTV), and Mars Moons (Phobos/Deimos). The main ground rules 

and assumptions included the following:

• Readily available EVA capability with dust mitigation is NOT required for 

the above DRMs although dust mitigation may very well be required for 
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an asteroid and/or moons of Mars EVA, as clouds of dust may form around 

an EVA crewmember taking samples

• Suitport is the ingress/egress method when readily available EVA with 

dust mitigation are required by the DRM

• Suitport needs to be tested on the ground and in microgravity (don/doff, 

vehicle integration, operational experience for future DRMs in microgravity 

and Mars 3/8g)

• Suit designed for 8.2 psid

• Exploration Atmospheres (8.2 psi 34% O2) is required for suitport 

operations and needs to be tested on the ground and in microgravity 

(DCS can be mitigated, but prebreathe protocol model needs to be 

validated, need to run exploration atmospheres in microgravity – hypoxia, 

interstitial fluid and vision impairment); Further information needs to be 

understood about the combined effects in microgravity, which should be 

worst case testing

FOMs were discussed and documented as pros/cons due to limited resources. 

The result of the trade study identified the need to test suitports and exploration 

atmospheres (8.2 psi/34% O2) on-orbit with the most flexibility being in a suitportairlock prior to relying on the suitport for mission success on the surface of Mars. 

After the study, it was discussed that either the rear-entry airlock or 

depressurizable module could work with the MTV and still be common.

The lunar surface could be the most environmentally representative and ideal 

place to test; however, it is only discussed in terms of cooperation with 

International Partners. There are very limited opportunities for testing on-orbit prior 

to Mars, but it could be done on precursor missions. 

Readily available, or high frequency EVAs with dust mitigation are not drivers for 

ISS, LDRO, or Mars transit EVAs; however, all DRMs could benefit, especially 

LDRO if exploration of an asteroid is to take place and dust mitigation is required. 

This is new technology and requires validation testing to ensure mission success 

in the future. The end-to-end operations of the alternative concept atmosphere in 

microgravity or partial gravity with an exploration EVA suit will need to be tested to 

prove the ability to don/doff the suit at a delta pressure, prove vehicle integration

as a new system, show that the combined effects on the crewmember are 

acceptable, and provide operational experience for crewmembers that fly future 

missions in microgravity and Mars surface 3/8g. While decompression sickness 

(DCS) can be mitigated, the prebreathe protocol model for exploration 

atmospheres is different than the ISS prebreathe protocol and needs to be 

validated. The combined effect of microgravity with hypoxia, interstitial fluid and 

vision impairment could be tested in microgravity, which could provide an 

understanding of partial gravity by bounding the problem between 0 g and 1 g
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effects. Many of the testing considerations discussed during this trade study are 

in Appendix B.

The following bullets indicate which challenges (as identified in Section 3) have 

been addressed to some extent in this study:

• Suit Architecture: (in terms of understanding suit interfaces)

• Unassisted Don/Doff: No 

• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: Yes

• Minimal consumables usage with vehicle ingress/egress cycles: Yes

• Increased crew autonomy for airlock operations: No

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: Yes

• Volume for in-flight suit maintenance and spares: Yes

• Dust mitigation and Planetary Protection: Yes

The current thinking in the EVA community is that any testing going forward can 

be completely fulfilled with ground testing and should be tested out to ensure safety 

for the crewmember prior to flight.

5.5 CONSTELLATION SPACE SUIT SYSTEM (CSSS) SUITPORT ASSESSMENT

A study was performed under the CSSS contract in 2014 to determine the impacts 

of suitport interfaces imposed on the EVA suit (TDS #1228, D-0588270 

05/15/2014) finding significant impacts to cost and schedule. “The many 

unknowns with respect to environments, operations, exploration assets and 

external interfaces greatly reduce the ability to adequately assess suit architecture 

options. Furthermore, many of the functions assumed as being performed by the 

exploration EVA suit such as Micro Meteoroid Debris (MMD), dust, radiation and 

thermal protection, stow-mode ventilation and water circulation, and PLSS 

rotation-translation, could be alleviated by exploration vehicle assets capabilities.” 

The following conclusions were reached that need additional assessment:

• Research and development of hardware and materials necessary to 

perform suitport-type operations in a planetary environment may 

significantly increase the overall Design, Development, Test and 

Evaluation (DDT&E) cost. 

• The assessed impacts of a suitport mission on an exploration EVA suit 

architecture might be mitigated or potentially eliminated by the maturation 

of a suitport mission design which, at this time, is still very much 

undefined.

• To design and develop an exploration EVA space suit against an 

undefined and incomplete requirement set poses cost, mass, and crew 
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time risks due to the potential re-design necessary to resolve interface, 

operational challenges and technical risks not yet known. 

There are trades from a vehicle perspective that may alleviate the burden on the 

suit which can help to reduce suit development risk. The following bullets indicate 

which challenges (as identified in Section 3) have been addressed to some extent 

in this study:

• Suit Architecture: Yes

• Unassisted Don/Doff: No

• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: No

• Minimal consumables usage with vehicle ingress/egress cycles: No

• Increased crew autonomy for airlock operations: No

• Increased quantity and access of EVAs: No

• Alternative atmospheres for reduced prebreathe time: No

• Volume for in-flight suit maintenance and spares: No

• Dust mitigation and Planetary Protection: No

5.6 EXPLORATION ATMOSPHERES

Exploration Atmospheres (defined as 8.2 psia / 34% O2) coupled with suitport-type 

operations is a major paradigm shift from the way operations are done today. 

Suitport, Suitport-Airlock, and exploration atmospheres are design challenges for 

the host vehicle. An alternative cabin atmosphere enables readily available EVA

by decreasing prebreathe duration (Abercromby, et al., 2015). NASA’s Exploration 

Atmosphere Working Group (EAWG) selected an atmosphere of 8.2 psi and 34% 

O2 as the best achievable balance of DCS risk, mild hypoxia, and materials 

flammability (Norcross, J., et al. 2013) after re-examining the 2006 8.0 psia/32% 

O2 recommendation. The final report from the 8.0 psia/32% O2 working group 

finding is highly recommended: Recommendations for Exploration Spacecraft 

Internal Atmospheres: The Final Report of the NASA Exploration Atmospheres 

Working Group”, NASA Technical Report NASA/TP-2010-216134, 2010. The use 

of a suitport technology system as the method of high frequency or readily 

available EVAs is dependent on the implementation of the alternate atmosphere; 

however, the use of an exploration atmosphere is not dependent on the use of 

suitports. The alternate atmosphere is a driving requirement for systems hardware 

located inside the pressurized cabin and presents technical challenges to the 

systems. The EAWG concluded with the following testing needs and 

recommendations:

• Recommended the Human Exploration and Operations Mission 

Directorate (HEOMD) formally adopt a development strategy to enable an 
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additional capability for 8.2 psia / 34% O2 for high frequency EVA phases 

of missions beyond LEO 

• Directed forward work by programs and projects to enable this new 

capability of 8.2 psia / 34% O2 in all future exploration Environmental 

Control and Life Support System (ECLSS) 

- Prebreathe protocol ground test (to validate prebreathe protocols in 

simulated microgravity & planetary environments & characterize the 

mild hypoxic environment) 

- Human health & performance at 8.2 psia/34% O2 with micro-g, 

elevated Carbon Dioxide (CO2), Visual Impairment / Intracranial 

Pressure (VIIP) Syndrome, etc. 

- Materials testing for flammability limits in O2 rich environments (test to 

ignition) 

- ISS does not test at oxygen concentrations above 24.1% (30% for the 

airlock)

- Orion does not test above 30% O2 except in special cases associated 

with avionics bays (where we have obtained threshold data)

- With a similar philosophy as above, the 34% O2 environment at 8.2 

psia is a nominal oxygen concentration and materials are required to 

meet flammability requirements at the maximum oxygen concentration 

– which is 34% plus some quantity based on sensor accuracy

uncertainty and control bands (this is expected to be about 1%, so 

35% total)

- Research increased fire risk in reduced gravity environment (early 

indications that risk is much higher in reduced gravity than micro‐g or 

1‐g)

- Large-scale microgravity fire tests (Saffire) on three Orbital ATK 

Cygnus re-supply vehicles scheduled for mid- to late-2016 will 

evaluate large-scale flame spread and the effect of low-gravity on 

material flammability limits

- Additional Saffire experiments being developed to investigate material 

flammability in exploration atmospheres, fire detection, and post-fire 

monitoring and cleanup

A memorandum from the HEOMD Associate Administrator for Human Exploration 

and Operations endorsed the EAWG recommendation that those habitable 

elements associated with enabling high frequency EVA phases of a mission should 

be capable of operating at 8.2 psia total pressure and 34 percent oxygen to 

conduct EVAs, while meeting the Agency’s health and safety requirements.

Work on the AES Suitport Project for suitport technology development and 

associated exploration atmospheres studies were deferred at the end of FY12. An 

initial assessment by JSC Engineering concluded that the impact to the ECLSS 

system is likely minimal. Prebreathe protocol ground test (to validate prebreathe 
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protocols in simulated microgravity & planetary environments & characterize the 

mild hypoxic environment) preliminary testing environments were to be defined

and engineering was to develop models for chamber testing. JSC Engineering 

(EA) was to work with NASA’s Human Research Program (HRP) and the JSC 

Human Health and Performance (HHP) directorate to prepare for appropriate 

ground testing with an 8.2 psi/34% O2 atmosphere with micro‐g, elevated CO2, 

VIIP Syndrome, etc. However, up to this point, limited additional activities were 

performed due to shifting priorities and funding availability. 

One of the main challenges associated with the combined effects mentioned above 

is that an 8.2 psia/34% O2 atmosphere has only been approved by HRP for a 1 

week duration early in a 30-day mission, but HRP cannot currently certify or 

approve humans to go to this atmosphere after 30 days. The Mars moons and 

Mars surface mission concepts include repeated 2 week durations in rovers or 

surface elements over a 500 day mission. 8.2 psia/34% O2 hypoxia is not a 

concern for astronauts at 1g, but due to lack of evidence is considered 

unacceptable today for long duration (> 1 week) exposure in space. No 

physiological showstopper is anticipated, but forward work is required to validate 

the new capability. Physiological concerns include vision changes, sleep quality 

changes, increased fatigue, exercise prescription changes, and sensorimotor and 

immune dysfunction. The health concern includes the synergistic or additive 

effects of an 8.2 psia/34% O2 atmosphere and the expected spaceflight 

environment, including weightlessness, elevated CO2, and radiation (reference 

Figure 5.6-1).

FIGURE 5.6-1 HEALTH CONCERN DIAGRAM

The following bullets indicate which challenges (as identified in Section 3) have 

been addressed to some extent in this study:
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• Suit Architecture: No

• Unassisted Don/Doff: No 

• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: No

• Minimal consumables usage with vehicle ingress/egress cycles: No

• Increased crew autonomy for airlock operations: No

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: Yes

• Volume for in-flight suit maintenance and spares: No

• Dust mitigation and Planetary Protection: No

5.7 VERTICAL AND HORIZONTAL HABITATS IN STRATEGIC PLANNING

Different habitat structures have been assessed over the years through projects 

such as the Deep Space Habitat, Habitat Demonstration Unit analog, and the EAM 

project. The vertical habitat concept is shown in Figure 5.7-1 (courtesy of Scott 

Howe), 

FIGURE 5.7-1 VERTICAL HABITAT CONCEPTS

Cylindrical horizontal habitats have also been studied (reference Figure 5.7-2, 

courtesy of Scott Howe).
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FIGURE 5.7-2 HORIZONTAL HABITAT 

Though these structures interface with EVA, habitat orientation is not expected to 

be a differentiator for EVA as a functional airlock will be needed either way.

5.8 SMALL HABITAT COMMONALITY

A Small Habitat Commonality assessment was performed under the auspices of 

the Evolvable Mars Campaign (EMC). For this assessment, small habitats were 

considered to be the Exploration Augmentation Module, the Mars Ascent Vehicle

(MAV), a Mars Moon Taxi, a Mars Moon Excursion Vehicle, a logistics module, 

and a Mars pressurized rover. The following are findings from an EVA perspective

in 2015.

While EVAs and suit maintenance will be performed from large habitats on the 

surface of Mars Moons and Mars surface, there are small habitats that also include 

EVA capability. In order to look at commonality from an EVA perspective, a high 

level assessment of EVA hardware and functionality per small habitat was 

performed to evaluate the number and types of suits in each, hardware, logistics, 

potential ingress/egress methods, and to gain a better understanding of the 

masses in each small habitat. 

In the current EMC operational concepts, EVA functionality exists on small habitats 

such as the Mars Moon Exploration Vehicle, the Mars Rover and the Exploration 

Augmentation Module. EVA operational drivers such as having readily available, 

high-frequency EVA capability with dust mitigation and shorter prebreathes drive 

cabin atmosphere to an alternative atmosphere of 8.2 psi, 34% O2 in conjunction 

with the suitport concept (Boyle et al. 2013). This alternative atmosphere in turn 
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impacts materials selection, suit mass, etc., while potentially saving on vehicle 

consumables and power. This is beneficial for the Mars Moon Exploration Vehicle 

and the Mars Rover. For other vehicles, such as the EAM, high-frequency EVAs 

are not necessary unless used for testing purposes to ensure the alternative 

atmosphere and suitport operations are vetted prior to use for the first time in the 

Mars vicinity. Forward work should assess cabin atmosphere commonality and 

ingress/egress commonality with a large habitat. 

Dust mitigation and planetary protection are also factors to consider, which can 

drive ingress/egress concept design. Dust could also be present near the EAM for 

potential asteroid missions. While not all small habitats should be common by 

including EVA functionality, those that do include EVA could all have common 

methods of ingress/egress. For example, the Mars Moon Exploration Vehicle, 

Mars Rover, EAM, and the Mars Taxi could all include suitports, suitport-airlocks, 

or suitlocks (possible commonality with the large habitat); however, past studies 

have shown that mobile elements (Mars Moon Exploration Vehicle and Mars 

Rover) should have an unpressurized enclosure (suitports) to cut down on mass 

and increase excursion range. The quantity of different ingress/egress 

architectures used across the EMC should be reduced as much as possible. 

Assuming the baseline for pressurized rovers is the suitport concept, and a large 

habitat includes the suitport-airlock (which has a pressurizable enclosure and is 

common with the suitport at a sub-system level), the rest of the ingress/egress 

methods throughout the campaign could be reduced to two. 

Suitports, suitport-airlocks, and suitlocks all include a different hatch size through 

which the crewmember dons/doffs their suits through a vestibule hatch on a 

bulkhead. In addition to the suitport vestibule hatch, a larger hatch size (potentially 

40” x 40”) must be utilized on any habitat with EVA capability to allow a suited, 

pressurized crewmember to pass through for EVAs and contingency cases. 
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FIGURE 5.8-1 SMALL HABITAT COMMONALITY EVA METHOD OPTIONS

The other small habitats in this study may include transfer of the EVA suits, but not 

the functionality to support EVAs. Stowage volume for EVA suits must also be 

considered during transfer between mission elements. EVA equipment is 

transferred in the Mars Moon Taxi, MAV, and logistics modules. The Mars Moon 

Taxi can be common with the MAV, or it can be common with the Mars Moon 

Exploration Vehicle. The EVA suits must be checked out on-orbit prior to descent. 

Discussion is taking place on how 4 EVA suits and 4 crewmembers can fit on a 

Mars Moon Taxi common with a MAV. If the Mars Moon Taxi is common with the 

Mars Moon Exploration Vehicle, which includes suitports, two suits can be stowed 

on the suitports during descent to the moons, thus saving volume and potentially 

addressing this issue. This would also drive the atmosphere to an alternative 

atmosphere common with the Mars Moon Exploration Vehicles and Mars Rover.

The following bullets indicate which challenges (as identified in Section 3) have been 

addressed to some extent in this study:

• Suit Architecture: No

• Unassisted Don/Doff: No
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• Recharge of all suit consumables (incl. high pressure O2): No

• Volume for donning/doffing and prebreathe: Yes

• Minimal consumables usage with vehicle ingress/egress cycles: No

• Increased crew autonomy for airlock operations: No

• Increased quantity and access of EVAs: Yes

• Alternative atmospheres for reduced prebreathe time: Yes

• Volume for in-flight suit maintenance and spares: Yes

• Dust mitigation and Planetary Protection: Yes

5.9 EXAMPLE INGRESS/EGRESS METHODS

After understanding the challenges and information discussed during past trades 

(potential impacts to a space suit, benefits for EVA prebreathe, potential impacts 

due to exploration atmospheres, benefits for pressurized rover traverses, 

commonality, etc.), the question remains for each new mission element that 

includes EVA capability – what is the right answer from a vehicle perspective for 

each new spaceflight project that forms? A preliminary chart from 2014 including 

ingress/egress methods was examined for a 4 person mission with EVA capability 

for Asteroid Rendezvous Crewed Mission (ARCM) (shown in the following figure).

FIGURE 5.9-1 EXAMPLE INGRESS/EGRESS METHODS
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5.10 DEEP SPACE GATEWAY AND TRANSPORT

The EAM evolved to the Future Capabilities Team (FCT) in 2015, which also 

studied capabilities needed for a cislunar habitat. The FCT formed a relationship 

under ISS which also included IP involvement. This led to the formal National 

Advisory Council presentation of phases (shown at the beginning of this document) 

and included both IPs and commercial partners. This laid the groundwork for the 

Deep Space Gateway and Transport (DSGT) team established in 2017. In order 

to prepare for the onramp of NASA studies, including International Partner (IP)

integration and evaluation of commercial mockups under Broad Area 

Announcements, the EVA community agreed upon a set of assumptions to prepare 

each with a beginning set of EVA assumptions. These will be highlighted in the 

next section.
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6.0 EVA ASSUMPTIONS FOR FUTURE VEHICLES

As new vehicles are developed to meet NASA’s exploration goals, interface 

requirements will be developed between the exploration vehicle and EVA System 

(space suit, support equipment, tools). These requirements will define values 

needed to support EVA Operations on and around the vehicle such as worksite 

envelopes, translation path dimensions, external vehicle touch temperatures, and 

sharp edges and burrs. While it is expected that program/project specific interface 

requirements and control documents will be created as each new project arises, 

the EVA Office has prepared a document in EVA-EXP-0035: Exploration EVA 

System Compatibility that provides a set of requirements to be tailored to and fed 

into any new project’s interface requirements with EVA. The intent of the guide is 

to act as a template for developing interface requirements between the EVA 

system and a program/project and will not be directly referred to or verified to by 

the program/project. Verifications for the project would flow up through that 

projects specific Interface Requirement Document (IRD) with the EVA Office. As 

the guide is based on the EVA Office’s prior operational experience it is an ideal 

source for understanding what the necessary interface requirements between an 

EVA system and vehicle would be. The following assumptions are given to 

feasibility study groups prior to the need for an IRD.

The EVA strategic planning community has identified a set of EVA interface needs

to provide all future vehicle architecture teams. The assumptions reflect the needs 

of NASA’s exploration EMU (xEMU) but not the design of the ingress/egress 

method. The needs describe the general utility functions in terms of quality, level, 

volume, amount, etc. NASA EVA is not specifying the detailed design solution for 

the Servicing and Performance Checkout Equipment (SPCE) until the PLSS 

detailed designs are complete, but it is important to derive the supporting vehicle 

systems utilities “up to the back of the SPCE”. As cislunar stack elements and the 

EVA Systems’ flight development plans mature, EVA SPCE will be developed that 

supports a common approach through cislunar and the follow-on destinations and 

spacecraft.

• NASA would plan for at least three EVA Suits on orbit to provide the 

resources and equipment to support US EVA capability for 2 crewmember 

EVAs. While this does not provide full redundancy for both crewmembers, 

it is an assumption to carry some redundancy until component R&Rs are 

better understood. This is also assuming no other commercial or IP suits 

on orbit, in which case it could be argued these other suits provide the 

redundancy needed reducing the number of US suits to two. 

• EVA logistics/ancillary needs are based upon the number of EVAs per 

mission.
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• NASA would provide any SPCE needed to go between the general airlock 

utility services and the exact, specific output needed by the NASA EVA 

suit. This enables maximum flexibility for the airlock developer while also 

allowing for the independent definition and detailed development of the 

US EVA SPCE hardware.

• Umbilical Interface Panels for International Partner-provided and NASAprovided EVA suits could be separate or combined. This allows each EVA 

Suit provider to manage and develop their detailed suit interfaces without 

over-complicating the design of each country’s SPCE hardware. A 

downside of separate UIPs allows for the potential of multiple different 

versions, which would be a significant problem when looking at stowage 

in any spacecraft.

• EVA translation assumes the use of double safety tethers vs. Simplified 

Aid for EVA Rescue (SAFER) pending a discussion with NASA Safety on 

fault tolerance for cislunar and Mars transit. 

• For an EVA crewmember to safely translate through a hatch in 

microgravity, the hatch must be sized such that the largest suited, 

pressurized crewmember will be able to fit through. The airlock would 

include primary and secondary hatches large enough (1000 mm.) to allow 

a pressurized suited crewmember to exit and enter the vehicle.

• Unpressurized EVA components can be transferred through an NASA 

Docking System (NDS) hatch (31.5 in.).

6.1 EVA CONTINGENCY SECONDARY INGRESS HATCH AND DUAL CHAMBER 

AIRLOCKS

While not all vehicle or ingress/egress designs require both a primary and a 

secondary EVA hatch, an analysis of failure modes could reveal the need when 

coupled with program-specific choices for human rating and redundancy/fault 

tolerance strategies. Fault tolerance should be included in the detailed mechanism 

designs; however, there are some failure modes that may not be able to be 

mitigated without adding a secondary hatch. Fundamental failures can be grouped

into the following categories:

• Failure of Extravehicular (EV) Hatch to close

o This could include binding/jamming of hinges, loss of alignment of 

hatch mating halves, or failure of locking mechanism (design details 

TBD)

• Failure to equalize airlock pressure with the vehicle
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o This could include external leakage through EV hatch/seals or failure 

of the equalization system that pressurizes the airlock

There are three conceptual options for conventional airlock volumes (this does not 

include the suitport concept):

• A stack with a “Single Chamber” airlock element

o This is operationally similar to “Capsule Based EVA” such as the 

ARCM baseline, though the size might allow for nominal Exploration 

EVA Suits

• A stack with a “Dual Chamber, Conjoined” airlock element

o This is operationally similar to the Joint Airlock on ISS, providing a 

separate crew and EVA equipment lock which can each function as 

an airlock in the event of a hatch or repress failure

• A stack with a “Dual Chamber, Separately Located” airlock element

o Airlock and Orion (this incurs other risks such as isolating the 

Intravehicular (IV) crew, Orion preparation, volume, translation paths, 

and umbilical transition interfaces; Orion may not travel with Mars 

transit habitat)

o Note that a full EVA suit cannot currently make it through the Orion 

side hatch without modifications to both hatch mechanisms, IVA 

translation aids, and the EVA system

o Airlock and Habitat element (this incurs other implications such as 

equipment designed to go to vacuum, umbilical interfaces, 

preparation, external hatch access, etc.) 

It is important to note that Orion can be used as an airlock to support EVA 

capability. Therefore, it would be possible to depend upon the docked presence 

of Orion for any contingency EVA needs. There are, however, a couple of safetyrelated, risk considerations with this approach. First, when Orion is docked to the 

spacecraft, it represents the life raft in the case of the need to escape the 

spacecraft in an emergency. If Orion is depressurized in order to support an EVA, 

then it is not immediately available to function as a life raft. In this state, several 

time-consuming steps would be required before Orion could be returned to a state 

sufficient to support evacuation of the cislunar, proving-ground spacecraft. Thus, 

using Orion as the contingency airlock represents a high-risk choice. Second, 

there may be planned periods where a crew will be present on the spacecraft and 

Orion will not be docked. These would be intentionally high-risk missions 

endeavoring to eventually evolve to Mars mission capabilities where abort 

possibilities will be limited or even nonexistent. In this situation, already high risk 

with Orion not present as the life raft, it is likely not appropriate to also be entirely 

without the capability for contingency EVAs. Thus, based upon these 

considerations, the requirement for the inclusion of contingency EVA capability on 

a cislunar stack is clarified further to state that it must be independent of this 
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capability existing on Orion. This kit-based approach is further documented in 

EVA-EXP-0042 Exploration EVA System Concept of Operations.

The EVA community assumes that a cislunar stack and surface habitats will 

include secondary ingress capability at the very least. A dual chamber airlock 

(equipment lock and crew lock) provides secondary ingress capability as well as 

the sufficient access and free volume necessary to perform all of the 

aforementioned activities to conduct EVAs. The crew lock can then be optimized 

for minimal consumables depletion.

6.2 EVA INTERFACES

General interfaces between an exploration EVA suit and exploration vehicle are 

outlined in Figure 6.2-1. A future ingress/egress method would incorporate 

interfaces associated with a new EVA suit, including consumables recharge such 

as high pressure O2, water, and power. Other utility style interfaces not 

conventionally used thus far in EVA may also be needed such as high throughput 

vacuum interfaces. General EVA interfaces between the vehicle and the EVA 

SPCE are summarized in the graphic below. This is used as a checklist for the 

summary of current NASA xEMU EVA to Airlock interface details. 
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FIGURE 6.2-1 GENERIC EVA INTERFACES DIAGRAM

6.2.1 EVA Interface Details

• Power 

– Umbilical Power (hardline during IV Suited Ops)

• Average power draw during EVA prep: 400 W; Peak 900 W 

– Battery Charger Power (EVA prep/post servicing)

• 40 W idling; Peak 110 W 

• Oxygen: For the purposes of this assessment, EVA O2 Demand is 

defined as any event that causes the EVA System to draw upon oxygen 

resources stored directly in a tank or through the transfer medium of the 

cabin atmosphere. The following line items are representative events 

that cause EVA O2 Demand:

– Suit Maintenance (such as EMU Airlock Cooling Loop Recovery Unit 

(ALCLR) Loop Scrub on ISS)

– On-Orbit Fit Verification (OFV)

• OFV’s only occur 1+ per crew for their time on orbit, NOT every EVA a 

given crew member conducts
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• The number of occurrences change per DRM (long duration, partial 

gravity, etc.)

– Prebreathe Protocol gas loss (changes per DRM)

– Cabin Atmosphere for Airlock repress (whatever is not reclaimed)

• Residual air after airlock depress (gas loss vented after air reclamation)

– EVA Consumables lost during the EVA itself

• xEMU Suit Leakage and Met Rate

• High Pressure O2 Recharge (EVA prep/post servicing)

– 3000 psia O2 @ 99.5% O2 (MIL-PRF-27210G Type I, 99.5% O2 with 

balance of N2/Argon + allowable contaminants in Table I of the milspec); a purity range may be moved from EVA-RD-001 Exploration 

EVA Suit Systems Requirements Document (now SSP 51073) to this 

document in a future update

– Cleanliness 200A

– Total O2 needed for 10 EVAs:

• 140 lbm (prebreathe, fit verification, recharge)

• Water

– For the purposes of architecture evaluation and consumables 

estimates EVA assumes beyond LEO Exploration EVA Systems use 

water as a utility consumable for cooling of the EVA Crewmember 

during the EVA (drinking water assumed to be included in everyday 

IVA water consumption)

• JSC-66695 EMU Water Quality Spec as reference

• Cooling water recharge volume of 1 lbm water/hour per EVA 

crewmember (160 lbm per mission assuming 10 EVAs)

– Biocide

• A trade is ongoing on preferred Biocide – Either Silver nitrate 0.3-1ppm 

in the feedwater supply or Iodine 0.5-6 ppm; Whichever is selected, a 

goal is to achieve a common Biocide

– Cooling Water (hardline during IV suited ops prep/post servicing)

• The temperature of the cooling water received from the Airlock for return 

to each xEMU will not be greater than eighty-eight (88) degrees 

Fahrenheit at a flow rate of 187 lbm/hr

• The temperature of the cooling water received from each Suit is not 

greater than ninety-eight (98) degrees Fahrenheit at a flow rate of 187 

lbm/hr

– Waste Water (EVA prep/post servicing)

• Many options are acceptable, including waste water drain to either a 

consumable bag or a vehicle receptacle. The rate needed is a maximum 

of 30 lbm per hour against a back pressure of up to 8 psig per suit
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For the purposes of feasibility studies, consumables for 10 two crewmember 

EVAs were computed based on both EMU calculations and xEMU estimates in 

Figure 6.3-1:

FIGURE 6.3-2 GENERIC EVA INTERFACES DIAGRAM

• Vacuum Access (support for CO2 Removal and Regeneration during IV 

Suited Ops)

– Vacuum source capable of providing a vacuum of <0.1 torr 

• Volumetric flow rate >1150 lpm (single flow rate addressing two suits) at 

1.6 torr

– Vacuum source capable of tolerating O2, CO2, H2O, and NH3

• Qmet = 400 BTU/hr (metabolic rate for each crew member)

– CO2 = 37 g/hr per suit => 74 g/hr total

– H2O = 44.3 g/hr per suit => 84 g/hr total

– Used for ~3 hours prior to EVA, 1 hour post (supports suited IV 

operations including EVA Prebreathe and post-EVA doffing)

• Communication Interfaces: EVA Assumes all stack elements are outfitted 

with infrastructure/utility that will support deployment of both IVA and EVA 

nodes for wireless and hardline communications. The vehicle will provide 

active radiation monitoring and an alerting function to signal the suit to 

alert the crewmember via high reliability transmission. The current 

exposure limits for deterministic effects (short-term exposure limits) are 
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specified in NASA-STD-3001, Volume 1, and to demonstrate compliance, 

radiation monitoring is required. Reference NASA-STD-3001, V2 

requirement V2 11010.

– Wireless Communication Interface

• High reliability UHF

• High rate 802.11 

– Hardline Data and Communication

• 2-Way Data Interface

• Hardline Communication Interface

• Consumables implications would need further discussion (air 

reclamation/airsave)

6.2.2 EVA Volumes

Volumes needed for EVA capability include volume for EVA stowage, volume to 

don/doff EVA suits (including prep/post servicing), volume for suit maintenance, 

volume for NASA-provided EVA SPCE, logistics, common vehicle tools and 

science tools, volume to egress/ingress the vehicle, and volume for large 

ORUs/equipment (if applicable) that need to be transferred via EVA from IVA 

stowage to outside of the vehicle. 

Volume for EVA stowage would include enough volume to stow three exploration 

EVA suits (cislunar) to four EVA surface suits plus any spares needed for the 

mission. The stowed volume for three EVA suits would be on the average of 1.75 

m3. Some of this volume can be combined with the volume the crew uses to 

don/doff the suits and perform maintenance. Trade-offs would be available to stow 

EVA hardware in locations other than the airlock, such as a logistics module; 

however, this would be a crew time/efficiency consideration. 

While thinking of minimizing volume to depress in order to conserve consumables, 

the volume cannot be limited too much, such that the prevention of entrapment 

and/or suit damage is not a concern. Mockups and testing should include all 

equipment needed in the airlock.

The EVA community assumes the capability for two crewmembers to self don/doff 

suits simultaneously with the ability to view each other. It is assumed the 

equipment lock portion of a dual chamber airlock would be used similar to ISS 

procedures. Currently on the ISS, a third IV crewmember assists the EV 

crewmembers during don/doff procedures. A minimum volume of 7 m3 is assumed 

to be necessary for simultaneous donning (this does not include a third IV 

crewmember). Further analysis is necessary to determine volumes. Serial 

donning could be considered for smaller airlock designs; however, this would be a 

hit to the crew timeline and efficiency on an already packed EVA day.
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Volume necessary for NASA-provided EVA SPCE, minimum logistics, common 

vehicle and the minimum necessary microgravity tools could be on the order of 1

m3. Extra volume may be needed for equipment to support both RS and US 

operations.

EVA tasks must be considered during airlock concept design in order to 

understand whether or not large ORUs or payload volumes will need to be 

accommodated for with two crewmembers in the crew lock. Heritage programs 

have to prioritize critical tasks due to the size of the ORUs/payloads.

For surface operations, volume would be needed for suit maintenance, as the 

luxury of sending suits back to Earth for refurbishment/certification gets less 

feasible the farther out humans explore. Additionally, for the design reference 

missions that include suitports, suits must be brought inside a habitable volume for 

most, if not all, maintenance tasks.

6.3 EVA NEEDS FOR TRANSLATION PATHS (μg)

Further refinement of cislunar stack concepts with commercial or international 

partners will lead to EVA translation path definition. Task definition, stack design 

layout, and robotic interface locations and reach envelopes are necessary to define 

translation paths along the elements of the stack. Translation paths are required 

on the airlock and should lead to the paths based on the tasks.

Task Definition includes:

• External vehicle maintenance: PDR-level vehicle design concepts should 

reveal if there are any stack failures EVA may be used to mitigate 

• External payload installation, removal or interaction: Architecture 

maturation should identify if there are any needs for EVA interaction with 

payloads

• Interaction with other spacecraft or docked objects: Mission scenarios will 

determine which docking interfaces EVA should be able to translate 

to/across

• Other contingency scenarios: Cislunar stack utilization/mission 

assurance analysis will determine if there are any other contingencies 

which require EVA for mitigation (examples may include failure of 

returning excursion vehicles to dock/seal)

Stack design layout:

• Some items may not be designed to withstand EVA induced loads 

because of their function and/or mission limitations. Translation paths will 

need to be located to avoid those areas. Further definition of these items 
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and their placement will help determine remaining locations for handrails 

and translation paths. Keeping track of what meets kick loads (or other 

limit loads) is practically a full time job on ISS. Many of these become "no 

touch" i.e. no kick or load sensitive and crew must be either trained or told 

by ground crew to manage each case. Since my understanding of future 

missions is delayed com/more autonomous crew, anything you do to 

make special cases that the crew has to be warned about or remember 

creates a potential hazard 

• Other external hardware which may pose hazards to EVA crew (such as 

sensitive instruments, comm antennas, moving solar arrays, ejection 

paths, etc.) may be categorized as keep-out zones which will also 

influence the placement of the EVA translation path hardware

Robotic interface locations and reach envelopes:

• How far robotics can reach, grapple, and interact with EVA Crew could 

alter EVA translation path design.
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7.0 FUTURE TRADES FOR VEHICLES

Moving forward, the EVA strategic planning community has recognized the need

to document the main trades and past discussions involved with ingress/egress 

methods as a primer for new vehicle concept teams trading EVA architectures. 

Some of these trades are very abstract and are not focused on any one vehicle 

architecture, but rather on common features such as hatches. Though abstract, 

these trades are listed here because they consistently emerge in all human 

spaceflight programs and studies under development such as ISS, CxP, and the 

HAT EMC strategic planning. While these trades are common across all of these 

programs and projects, there is not yet a communally agreeable solution because 

the FOMs change as the mission objectives change. Though there is not as yet a 

one-size-fits-all solution, it is thought that proactive studies can however trade 

options with the expectation of identifying families of vehicle architectures and 

corresponding families of ingress/egress solutions. Most of the future trades 

described in this section have direct influence on an exploration EVA suit or 

operations and may need to be very detailed. 

This section is organized in tiers based upon the scope of potential trades. The 

section begins with a very broad overall mission section, followed by habitable 

volume and associated ingress/egress method trades, and trades involving suit 

versus vehicle functions. 

7.1 OVERALL MISSION

The overall mission architecture will determine the FOMs by which each 

ingress/egress method is evaluated. While mission architecture design and 

campaign assessment are beyond the scope of this document, the merits and 

findings of individual concepts and trades can dramatically change when evaluated 

for different mission architectures. Thus, each detailed trade should consider the 

weighting of FOMs and how that would change across various DRMs. Such 

variable sensitivity should be included in future trades as a way of validating the 

findings. A general listing of the concerns and perspectives is included in the 

following subsections; for further understanding of the spectrum of trades under 

consideration for beyond LEO human exploration, please see the Global 

Exploration Roadmap (GER, International Space Exploration Coordination Group 

(ISECG), 2013). 

7.1.1 Overall Mission Asset Trades

Currently, missions being developed and evaluated are intended to be evolvable

campaigns and kept at a high enough level that certain assumptions may be 

interchangeable/adaptable to future policy directions. 
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Listed here are the fundamental questions that must be considered and addressed 

as any DRM is created. More than any other detailed trade, the answers to these 

questions will have greater influence on the EVA capability a given space flight 

architecture possesses: 

• What are the overall mission objectives?

• Is it assumed that EVA capability is contingency only, or are there nominal 

EVA tasks planned? 

• If there are contingency EVA tasks planned, what is their nature?

o Are there certain known failures that require an EVA crewmember to 

fix such as a failed ORU changeout?

o Does the architecture desire to attain any capability to address 

unknown or unplanned failure modes?

o Is a simple “fail to dock/hard seal” scenario requiring a hatch to hatch 

transfer a valid risk? 

• If there are nominal EVA tasks planned, what is their nature?

o Are there external experiments on the vehicle that may need an EVA 

crewmember to install/enable/fix? 

o Are there assembly or maintenance tasks? 

• How far from a habitat is the EVA crewmember capable of going for 

exploration and research?

• How often will EVAs be performed?

• How many EVAs will be performed?

• How long will each EVA be in duration?

• How long is the mission?

• How long is uncrewed portion of mission (quiescent mode)?

• What mass and volume is available for the entire EVA system, including 

the ingress/egress method? 

• What is the testing lead time for suit compatibility, partial g delta pressure 

don/doff and human research clinical trials to address any unknown

physiological risks by the 2030s?

• What are possible mitigations in lieu of this? 

• Is dust mitigation required?

• Is planetary protection required?

The architectures chosen will affect testing and each phase of the mission through 

launch, transit, landing/rendezvous, emplacement, daily operations,

ascent/departure and crew return. 

Once the EVA capability is determined, the following challenges should be 

considered when determining ingress/egress methods:

• Suit Architecture

• Unassisted Don/Doff 
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• Recharge of all suit consumables (incl. high pressure O2)

• Volume for in-flight suit maintenance and spares 

• Volume for donning/doffing and prebreathe

• Minimal consumables usage with vehicle ingress/egress cycles

• Increased crew autonomy for airlock operations

• Increased quantity and access of EVAs

• Alternative atmospheres for reduced prebreathe time

• Dust mitigation and Planetary Protection

These challenges are embedded in most, if not all of the trades listed below and 

the reader will recognize the list from the status summaries of previous/historic 

trades. Listing out the vehicle mission purpose first is important to closing an entire 

mission and campaign level operational concept. For instance, a mission with 

contingency-only EVAs should still address each of the challenges above to 

determine the method of ingress/egress, even though an exploration class mission 

may address them to a greater extent or in different ways. 

7.2 HABITAT AND INGRESS/EGRESS METHOD TRADES

A study of past airlocks and vehicles can show different perspectives on what they 

were used for, what worked well, and what should be considered going forward. 

See Appendix D for details. The following sections highlight a series of trades for 

habitats and ingress/egress methods. 

7.2.1 Ingress/Egress Method: Integral to vehicle or separate module?

Whether or not the ingress/egress method chosen for the vehicle is integral to the 

vehicle or is a separate module has been a topic for discussion throughout human 

spaceflight. An ingress/egress method in which the full bulkhead is being used as 

the pressure bearing end is considered integrated. Most legacy airlock hardware 

has either been as a separate module, like the ISS Joint A/L or an entire cabin 

depress using the cabin itself as the airlock like Gemini and Apollo (Figure 7.2.1-

1). 

Past and Current Airlock Architecture Integrated or Separate

Gemini Capsule Integrated

Apollo Lunar Module Integrated

Skylab Both (Internal)

MIR Voskhod (Inflatable) Separate

MIR Separate
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ISS Russian A/L: Pirs Docking Module 1 Separate (Dual use as A/L and 

docking port)

ISS Russian A/L: Poisk Mini-Research

Module 2

Separate (Dual use as A/L and 

docking port)

ISS Russian A/L: Zvezda Service Module 

Transfer

Integrated

Shuttle A/L Separate

ISS Joint Quest A/L Separate

FIGURE 7.2.1-1 INTEGRATED VS. SEPARATE AIRLOCK FUNCTIONS

When discussing the use of suitports on a small pressurized rover, the suitports 

are often depicted as integral to the vehicle itself (reference Figure 7.2.1-2). 

FIGURE 7.2.1-2 SUITPORTS INTEGRATED WITH PRESSURIZED ROVER

The rear-entry airlock and suitport-airlock have also been shown to be integral to 

horizontal habitats (reference Figure 7.2.1-3) or can be shown as a separate 

module (reference Figure 7.2.1-4):
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FIGURE 7.2.1-3 INTEGRATED HORIZONTAL HABITAT CONCEPTS

FIGURE 7.2.1-4 SEPARATE MODULE FOR REAR-ENTRY AIRLOCK OR SUITPORTAIRLOCK

Ingress/egress methods for habitats and other vehicles, such as test vehicles, 

transit vehicles, landers, and ascent vehicles are less certain with the possibility of 

either an integral ingress/egress method or a separate (add-on) ingress/egress 

method which includes additional volume (reference Figure 7.2.1-5). 
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OR 

FIGURE 7.2.1-5 INTEGRATED OR SEPARATE INGRESS/EGRESS CONCEPTS

Having the structure with additional volume as an “add-on” has pros and cons that 

need to be considered and weighed. The following sections include further detail 

on both the add-on concept and the integrated concept.

7.2.1.1 Ingress/Egress Method as a Separate Add-on Module

An add-on module could allow some amount of flexibility in the development and 

delivery schedule depending on when/where the module is to be flown. If 

considering near-term, and the estimated launch date of a vehicle precedes the 

completion date of the ingress/egress method being developed, it could be 

delivered separately at a later date when flight ready. For example, this would not 

be an issue for an ingress/egress method development project going to the ISS 

due to the already present EVA capability from both the Russian segment and the 

United States segment. If discussing a different vehicle at a location other than 

ISS, the capability to go EVA may not be available until the arrival of the “add-on” 

ingress/egress method, so the risk level would need to be discussed or the vehicle 

could be depressed for contingency EVA use until the add-on arrives (assuming it 

is designed and constructed to be EVA compatible). This could pose additional 

concerns, such as consumables for an entire cabin depress/repress, and the 

certification of all items in the cabin to sustain capability after exposure to vacuum. 

Many vehicles have found this to be an undesirable trade. 

As long as the host exploration vehicle and the add-on module fit within the shroud 

of the launch vehicle and the schedule allows (the ingress/egress method 

development is completed in parallel with the host vehicle) they could be launched 

connected. Depending on the launch vehicle used, an add-on module could mean 

an additional launch if the stack does not fit or if not launched attached to the

vehicle. Volume inside the Space Launch System (SLS) or other launch vehicles

would need to be analyzed. If the add-on module fits with the host vehicle inside

the launch vehicle shroud, it would most likely still be more mass than an integrated 

concept. 
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Depending on the design and layout of the vehicle, an add-on module could be 

berthed to other ports of the vehicle as opposed to being attached to the end of 

the vehicle (some vehicle concepts show propulsion modules or other vehicles on 

the ends). This decreases the chances that the add-on module could be flown 

with the host vehicle inside the launch vehicle shroud, which could lead to on-orbit

installation.

Installation of the add-on module should also be considered. Attachment could be 

performed with robotics, but depending on the complexity of the attachment 

mechanism, it may take EVA to install, so the vehicle/module that it is attached to 

would have to go to vacuum for installation, unless it has an additional airlock. For 

surface ops, an offloading technology (presumed necessary for surface ops) could 

be used to connect the add-on module to the habitat. One choice to make is 

whether or not the habitat remains on the lander or is offloaded to the surface. If

the habitat is left on the lander, discussion needs to take place on how the 

astronaut translates up and down from the surface to the ingress/egress method 

via stairs, ramps, etc.

An add-on module could potentially be common and used with any vehicle design 

concept (microgravity vehicle or surface horizontal or vertical habitats) depending 

on pressurizable volume, maintenance capability, and atmosphere. It also has the 

ability to be relocated or replaced.

An add-on module (assuming it is not a single volume or regular airlock) could 

provide enough volume to perform a prebreathe if such is necessary at a pressure 

different than the primary stack. Otherwise, the host vehicle or habitat would need 

to provide prebreathe capability at the EVA prebreathe or the crewmembers would 

have to endure significant prebreathe time using mask protocols. For example, 

this would be the case for a large habitat with a small Shuttle-sized airlock. In this 

case, the airlock volume is too small to don the suits and prebreathe, which places 

the burden of the prebreathe atmosphere on the habitat. See Figure 6.2.2-1 for 

further habitat atmosphere trades. 

7.2.1.2 Ingress/Egress Method Integrated with the Host Vehicle

Clearly, an integrated ingress/egress method with the host exploration vehicle 

would be schedule dependent on one another’s development. If the 

ingress/egress method design is to be integrated with the vehicle and the design 

of the method is delayed beyond the estimated delivery date of the vehicle, the 

schedule would have to be adjusted.

Having the structure integrated with the host vehicle is a permanent solution and 

would be launched with it (no EVAs for installation, no extra launch). 
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If used, an alternative atmosphere of 8.2 psia/34% O2 or similar prebreathe 

atmosphere would be created in the host vehicle cabin with a suitport or suitportairlock concept as there is not a separate chamber in which to perform a long 

prebreathe. 

On a vehicle/module that is not docked at ISS and/or is standalone and includes

the suitport concept, everything inside of at least one compartment must be 

vacuum compatible to allow for contingency entrance through a side hatch for 

contingency suit maintenance. This is not true for the rear-entry airlock or the 

suitport-airlock since the volume around the suits can be pressurized and an 

internal hatch is included in these concepts. 

As opposed to an add-on module, an integrated structure inside of a horizontal 

habitat on the forward or aft ends of the cylinder (horizontal habitat for microgravity 

or surface) would be a much lower mass since it is utilizing an end cone bulkhead

instead of adding on a completely separate module. The additional mass on an 

integrated structure would mainly be the internal bulkhead with the suitport/suit 

access hatches and an internal hatch (for rear-entry airlock and suitport-airlock). 

The mass of the outer end cone bulkhead is therefore shared between habitat and 

ingress/egress method.

7.2.2 Logistics Module Conversion to Airlock

In order to save upmass, a discussion on converting a logistics module to an 

airlock became a topic of discussion. Any airlock would need to be designed and 

constructed to be EVA compatible and would need to include EVA interfaces and 

assumptions listed in section 6 of this document. A quick look resulted in the 

following:

• What is the trade of cost of using the logistics carrier, cutting the primary 

structure, and outfitting with ECLSS/Thermal/hard mounted equipment 

vs. building an airlock element?

• Primary Structure changed for EVA hatch size TBD (2 axial)

• EVA Servicing Equipment Kit based vs Hard mounted: Hard mounted

– Assume hard mounted due to criticality of dust mitigation, planetary 

protection, etc. (assume ground tested)

– ECLSS and Thermal should be plumbed (would want to get their 

input) – has its own depress/repress pump and active coolant loop

– Include consumables tanks pre-connected: high pressure O2 lines 

and water lines, etc.

– Using In-Situ Resource Utilization (ISRU)? Include refill connections

– Secondary structure included for panels and plumbing
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• Question of how you would transfer O2, water, air, comm, data, etc. 

through the tunnel concept (connects directly to the modular habs)

• Assume it includes:

– Suit/general maintenance area

– Dust mitigation

– Secondary ingress capability (could use rover cabins as secondary 

ingress acceptable – operationally would have to be available)

• Dust Mitigation/Planetary Protection

– Dual chamber with internal bulkhead

• Hard bulkhead with Single hatch (don/doff stands in crew lock for 

layered engineering defense) vs suitlock (rear-entry airlock)

• External inflatable crew lock 

It was not discussed whether the logistics module is converted on orbit (i.e., 

repurposed after delivering cargo) or if it would be a module outfitted on the ground 

and flown as an airlock. Repurposing a used logistics module on orbit could be 

more upmass-intensive than simply building a dedicated airlock on the ground. It

could be that modifying one on the ground would be about as expensive as building 

from scratch. Building from scratch also would avoid many design compromises 

that would have to be considered when trying to convert a module to a purpose for 

which it was never designed. 

However, the ISS RS airlocks use modular suit supply hardware that could be 

integrated into an existing module. 

7.2.3 Host Vehicle Atmosphere

The dual chamber airlock, rear-entry airlock, suitport, and suitport-airlock concepts 

are dependent upon the vehicle’s ECLSS alternative atmosphere settings. An 

integrated ingress/egress method would rely on the vehicle’s ECLSS, therefore 

playing a role in how an EVA prebreathe protocol is determined. There are many 

variables that are included in determining an EVA prebreathe, including the 

duration the crewmembers are at a certain atmosphere/O2 level, gravity level, etc. 

An add-on module could be built to include alternative atmospheres allowing the 

host vehicle to avoid the alternative atmosphere by isolating the two with a hatch. 

The add-on module may have to include a minimal galley and waste control 

management (which adds mass) such that the crew can camp out for longer 

periods of time in order to adjust to the alternative atmosphere for prebreathe prior 

to going EVA. During the Near Term DRM Quick Study, it was found that having 

a separate module without a minimal galley and waste control management was 

unacceptable as the crewmembers would have to stay in Maximum Absorbent 

Garments (MAG) and take food and water into the chamber with them for an 

extended amount of time to adjust to the alternative atmosphere. The host vehicle 
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will have to be compatible with the alternative atmosphere if the add-on module is 

not large enough to include a galley and waste management system. 

There are quite a few trades to look at when considering bringing down a vehicle 

from a sea level atmosphere to any other atmosphere designed to decrease DCS 

risk and EVA prep time. Whether the air from the habitat or vehicle stack is vented, 

reclaimed into another part of the habitat, or pumped into other gas tanks could 

determine differences in overall mass and consumables necessary. The point at 

which the mass of the consumables/tanks equals the mass of an integrated or addon module should be considered to help inform architecture decisions. ISRU also 

has an influence on consumables and should be considered, but it is still a low 

Technology Readiness Level (TRL) technology in the context of relying upon it to 

provide high pressure and high purity O2 for use in EVA applications. EVA suit 

impacts have already been brought up in this document, but medical concerns 

should be understood further. Assuming that mission designers are trading stack 

architectures or have already chosen a vehicle ingress/egress method, one still 

has to trade the habitat saturation pressure the crew will live at long term or live at 

short term prior to determining a prebreathe protocol and the corresponding 

prebreathe duration that is acceptable for the frequency of EVA envisioned. 

Although it is significantly advantageous for EVA to utilize crewmembers saturated 

at ever lower habitat operating pressures because of the corresponding reduction 

in prebreathe time, as discovered in the previous Exploration Atmospheres trade 

(see Section 5.6 and Figure 7.2.3-1) many vehicle systems have not been 

conventionally designed to operate at such lower pressures and conversion of 

them to do so creates the appearance of delta cost. 
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FIGURE 7.2.3-1 A HISTORY OF HSF: HABITABLE ATMOSPHERES EMPLOYED IN 

THE PAST

The following table is an example of the different vehicle operating and prebreathe 

pressures that have been proposed for human spaceflight recently with a 4.3 psia 

pressure during EVA. It describes some of the trades that need to be conducted

going forward for habitat atmosphere, hardware, EVA prebreathe, and medical 

considerations (reference Figure 7.2.3-2). 
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Habitat 

Nominal 

Pressure

Pressure at 

prebreathe 

initialization

Duration at 

prebreathe 

pressure

μg EVA 

prebreathe 

duration 

estimation

Surface EVA

prebreathe 

duration 

estimation Hab A/L trades Hab System trades EVA trades Med trades

14.7 psia

21% O2

14.7 psia

21% O2

Constant 245 minutes ~420 minutes Trade to prebreathe on mask or include separate module 

with minimal galley and WCS (for surface)

• Prebreathe in integrated Next Gen A/L module with 

MAGs or separate w/o min. galley and WCS

• Prebreathe in Next Gen A/L in separate module with 

minimal galley and WCS 

• Vent Next Gen A/L chamber air

• Level of ISRU resupply vs logistics?

• Reclaim A/L chamber air

• Into Hab (like ISS)

• Additional O2 tanks

• Prebreathe protocol 

different from ISS

• N/A, but long EVA prep

• Crew injury, 

fatigue?

14.7 psia

21% O2

10.2 psia

26% O2

< 12 hours 210 minutes ~2-3 times worse Trade to go prebreathe on mask to separate module with 

minimal galley and WCS (for surface) or bring habitat

down to 10.2psia/26% O2

• Bring habitat down for prebreathe (Integrated Next 

Gen A/L module with MAGs or separate w/o min. 

galley and WCS)

• Prebreathe in integrated Next Gen A/L module with 

MAGs or separate w/o min. galley and Waste 

Collection System (WCS)

• Prebreathe in Next Gen A/L in separate module with 

minimal galley and WCS 

• Vent habitat air

• Level of ISRU resupply vs logistics?

• Reclaim habitat air

• Additional O2 tanks

• Vent A/L chamber air

• Reclaim A/L chamber air

• Into habitat (like ISS)

• Additional O2 tanks

• Similar to ISS ISLE 

prebreathe protocol

• N/A, but long EVA prep

• ?

14.7 psia

21% O2

10.2 psia

26% O2

24 to < 36 

hours

100 minutes ~2-3 times worse • Same options as < 12 hours at 10.2 psia, 26% O2 • Same trades as < 12 hours at 10.2 psia, 

26% O2

• Similar to Shuttle 

prebreathe flight rule

• ?

10.2 psia

26% O2

10.2 psia

26% O2

≥36 hours 40 minutes ~2-3 times worse • Integrated or separate module • Vent A/L chamber air

• Reclaim A/L chamber air

• Into habitat (like ISS)

• Additional O2 tanks

• Similar to Shuttle 

prebreathe flight rule

• VIIP, hypoxia 

issues?

14.7 psia

21% O2

8.2 psia

34% O6

≥36 hours 15 minutes ~2-3 times worse • Bring entire habitat down for prebreathe (Integrated 

Next Gen A/L or separate w/o min. galley and WCS)

• Prebreathe in separate Next Gen A/L module with 

MAGs

• Prebreathe in Next Gen A/L in separate module with 

minimal galley and WCS 

• Exploration Atmospheres vehicle trades:

• Consumables, thermal, materials, 

avionics, food preparation

• Vent habitat air

• Level of ISRU resupply vs logistics?

• Reclaim habitat air

• Additional O2 tanks

• Vent A/L chamber air

• Reclaim A/L chamber air

• Into habitat (like ISS)

• Additional O2 tanks

• Prebreathe protocol 

different from ISS

• PLSS packaging

• PLSS OML

• SIP

• 8.2 psid PGS

• Decreased MPT

• Equipment vacuum certified

• Short EVA prep

• Decreased crew 

injury 

• Decreased crew 

fatigue

• VIIP, hypoxia 

issues?

10.2 psia

26% O2

8.2 psia

34% O6

≥36 hours 15 minutes ~2-3 times worse • Same • Same • Same • Same

8.2 psia

34% O6

8.2 psia

34% O6

≥36 hours 15 minutes ~15 minutes • Integrated or separate module • Same • Same • same

FIGURE 7.2.3-2 HOST VEHICLE ATMOSHPHERE TRADES ASSUMING A 4.3 PSIA EVA PRESSURE
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Furthermore, discussion should include the impacts of whether or not vehicles 

planned to operate with different atmospheres should all have the ability to operate 

at any of the planned mission atmospheres for commonality, as well as 

contingency situations.

7.2.4 Inflatable Portions of the Ingress/Egress Method 

Inflatable structures technology utilizes high-strength fabric materials and internal 

pressure to create a stiffened structure that replaces traditional metallic primary 

structure. The flexibility of fabric structures allows them to be compact during 

launch and expanded in space, providing significant launch volume savings.

7.2.4.1 Inflatable Structures History

The use of inflatables in space has been worked since the 1960’s for both habitats 

and airlocks. The first ever EVA was conducted by the Union of Soviet Socialist 

Republics (USSR) in 1965 using an inflatable airlock known as the Volga. This 

airlock was attached to the Voskhod 2 spacecraft, was successfully deployed, 

used once, and jettisoned after a historic spacewalk (Portree, D., et al. 1997). 

Inflatable airlock development continued in the 1990’s when NASA-JSC led an 

effort to demonstrate inflatable structures as feasible long-term pressurized 

elements with the TransHab project. The technology developed and pioneered 

during this project led to multiple patents and feasibility that inflatables could be 

used for large habitable structures (delaFuente, H., et al. 2000).

7.2.4.2 Current Inflatable State of the Art

In the early 2000’s, Bigelow Aerospace used NASA support to continue 

development that eventually led to the successful flight certification, launch, 

attachment and deployment of the Bigelow Expandable Activities Module (BEAM) 

on the ISS in 2016 as shown in Figure 7.2.4.1-2 (Dasgupta, R., et al. 2014).
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FIGURE 7.2.4.1-2 – BEAM MODULE DEPLOYMENT SEQUENCE

BEAM completed a successful two year evaluation period on the ISS, advancing 

the technology readiness level of a habitable inflatable module to TRL 9. It is 

considered a flight proven system and is currently used as a logistics module on 

the ISS. 

Although BEAM is not an airlock system, the structural technology demonstrated 

could act as a baseline for the construction of an inflatable airlock system. Its 

current design poses limitations for EVA that would need to be addressed. The 

exterior of BEAM includes soft, fabric handrails meant for contingency EVAs, but 

can only be used for translation, does not allow for crew safety tethers, and does 

not include any worksites.

Inflatable and expandable airlock structures have undergone various detailed 

feasibility studies for over 15 years, most notably the Advanced Inflatable Airlock 

(AIA), Dual-Chamber Hybrid Inflatable Suitlock (DCIS), Minimalistic Advanced Soft 

Hatch (MASH), and Lightweight External Inflatable Airlock (LEIA). Through this 

time, full-scale articles have been built and pressure-tested, and mock-ups and 

demonstrators have been constructed and evaluated. The following sections are

high-level summaries of these projects, and additional references are included for 

more detail. 

7.2.4.3 Inflatable Development Work to Date

In 2001, the AIA concept was matured through requirements development, 

conceptual design, subscale and full scale engineering breadboards subjecting 

various test articles to deployment and pressure testing (Trevino, L., et al. 2002, 

2003). These tests proved the feasibility of successful deployment and structural 

integrity of an inflatable crew lock. Figure 7.2.4.3-1 shows the fully-inflated 

pressure test articles as well as details of the latching and deployment systems.
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FIGURE 7.2.4.3-1 – A) AIA FULL-SCALE PRESSURE TEST ARTICLE AND

B) LATCHING/DEPLOYMENT SYSTEM SHOWN IN PACKED CONFIGURATION

The 2017 LEIA effort advanced the design of an internal secondary structure and 

placement of handholds and foot restraints to enable hatch opening, closing and 

translation through the crew lock using a full scale mockup as shown in Figure 

7.2.4.3-3. The results of these tests inform the volume required, hatch size, 

configuration and location of translation aids for crewmembers in a microgravity

crew lock.

FIGURE 7.2.4.3-3 – LEIA SECONDARY STRUCTURE MOCKUP TESTING

7.2.4.4 Alternate Inflatable Concepts

In 2011, the DCIS was developed as a suitport-airlock with inflatable portions and 

meant as a planetary surface airlock concept. It utilizes three rigid bulkheads with 

dual chamber inflatables that are expanded to create additional volume as shown 

in Figure 7.2.4.4-1. The concept incorporates suitports into the middle bulkhead 

where one chamber is continuously pressurized and the second chamber is 

pressurized or at vacuum. A secondary structure is used to maintain structural 

capabilities in the depressurized chamber. This dual-chamber airlock allows for 
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suit maintenance, dust mitigation, and compact packaging for transportation 

(Howe, S., et al. 2011).

FIGURE 7.2.4.4-1 – DUAL CHAMBER INFLATABLE SUITLOCK CONCEPT

In 2014, the MASH project developed an ultra-lightweight airlock concept with a 

fabric hatch and airlock that utilized a unique pressure vessel shape to minimize 

structural load on the fabric material as shown in Figure 7.2.4.4-2 (Doggett, W., et 

al. 2016). The advanced concept uses a robotically controlled zipper-like latch and 

opening that is then peeled away to allow for crew egress/ingress.

FIGURE 7.2.4.4-2 – MASH AIRLOCK CONCEPT

Due to the novelty and uniqueness of this design, it offers a number of operational 

issues and concerns compared to traditional airlock systems. The hatch and 

sealing system would need to be redundant, reliable, and able to be controlled by 

a suited crewmember without extraneous force. A secondary structure would be 

necessary not only for structural stiffness, equipment mounting, and tethering, but 

to open and close the fabric hatch. Additional development is required to address 
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these and other outstanding issues related to this design, but the mass and weight 

savings that it offers could provide EVA capabilities to a variety of spacecrafts with 

minimal costs. 

Other concerns were noted during an EVA Office review of the Lightweight 

Materials & Structures Minimalistic Advanced Softgoods Hatch project in 2015:

• Overall comment - The idea of a soft hatch, although providing 

engineering optimization (lower mass, etc.) is worrisome from an 

operational standpoint since softgoods tend to have ‘memory’ in a 

weightless environment. It is unknown how this will be during 

pressurization/depressurization of air beams. 

o ‘Fighting’ this material memory, can quickly lead to fatigue, as has 

been seen when handling various large pieces of Multi-Layer 

Insulation (MLI) during EVAs on ISS

• Concerns with solution of using a zipper for sealing the soft-hatch

o It looks very labor intensive from a crew fatigue perspective 

(specifically hands and forearms), as the crew would have to 

continually adjust their body position and how they are reacting the 

forces that are required to pull the zipper during both egress and 

even worse on ingress when the crew is fatigued from the EVA

o Required forces that are easy to overcome in 1-g become 

exaggerated in 0-g, as the crew has to essentially double it to 

account for both the force to manipulate the hardware, as well as the 

reaction force to manipulation force

o From a hazards perspective it seems it would be more likely to fail to 

properly seal.

o Is every tooth required to properly connect?

o Is there any redundancy, such as would be with multiple seals?

• Time required for operating (opening & closing) – impacts to emergency 

repress ability

o How does pressurization/depressurization of the different air beams 

work? Does the crew control them?

• Recommend the open/closing motion be similar to ISS airlock, vs. a 

simple ‘door-hinge’ style motion

o Rationale for this: a ‘door-hinge’ style motion will require depth to be 

added to the airlock that is equivalent to the ‘sweep’ of the hatch into 

the airlock

o Rationale for this: a ‘door-hinge’ style motion requires crew to 

continually change their body position/location throughout the 

opening and closing motion, and if the hatch includes a fabric hinge, 

there will likely be ‘memory’ in the fabric that will have a neutral 

position that will need to be compensated for during manipulation 

(also need to consider the volume required for this manipulation and 

whether there will be enough to accommodate two crewmembers)
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o Benefit of a door-hinge like in the RS A/L is that it is a simpler design

• Performing regular EVAs from an inflatable would require the use of 

safety tethers (assuming no SAFER) to be able to withstand 220 lbf 

applied to the translation path used by the crewmember on the airlock 

and 200 lbf on all primary and secondary structure inside or near a 

translation path or worksite

• Worksites would be needed

• Hard internal structure would be necessary for hard mounting the UIA 

and interfaces to ECLSS recharge 

In 2018, concepts focus on an inflatable crew lock-type structure attached to a rigid

equipment-lock or habitat structure as shown in Figure 7.2.4.4-3. Since most of the 

SPCE items required are rigid components, a fabric structure cannot provide the 

capabilities of a full equipment-lock. The use of an inflatable as a crew lock, 

however, provides all the required capabilities for EVA operations. 

FIGURE 7.2.4.4-3 – INFLATABLE CREW LOCK CONCEPT

Since an inflatable module gets its stiffness from internal pressure, it needs a 

secondary structure to maintain the shape and stiffness of the fabric shell during 

depressurization. The secondary structure also provides support for handholds, 

tether points, workstations, cameras, etc. on both the interior and exterior of the 

crew lock. 

The inflatable crew lock components are shown in Figure 7.2.4.4-4 with rigid 

bulkheads at each end of the structure. The use of a traditional, rigid EVA bulkhead 

meets thermal heating requirements and allows for any hatch design to be used 

with an inflatable shell. A rigid IVA bulkhead includes utility passthroughs for fluids 

and power, and an integrated UIA that is installed and launched inside the 

inflatable crew lock.
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FIGURE 7.2.4.4-4 – INFLATABLE CREW LOCK CONCEPT

WITH CONCEPTUAL COMPONENT PLACEMENT

Based on the work completed to date, an inflatable crew lock has been 

demonstrated to be feasible and is currently included in the trade space for 

potential alternative ingress/egress methods for deep space or planetary 

exploration.

7.2.5 Diameter of Module

Note: this section is primarily for suitport and rear-entry airlock concepts and does 

not apply to dual chamber airlocks. For an ingress/egress method on an internal 

bulkhead on a horizontal habitat, it has been shown that the diameter of a module

can be driven by the ingress/egress method used and hatches needed. With 

suitport as the primary ingress/egress method on the Small Pressurized Rover 

(SPR), and based on older SIP assumptions, Figure 7.2.5-1 shows different 

diameter sizes with the two suitports on a bulkhead (Brand Griffin, Marshall Space 

Flight Center (MSFC), 2008, dimensions not to scale).
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FIGURE 7.2.5-1 SUITPORT BULKHEAD (SPR APPLICATION)

With the rear-entry airlock or suitport-airlock options on a habitat, the bulkhead 

diameter must be larger in order to accommodate the addition of the internal hatch 

between the two suitports (reference Figure 6.2.4-2). This allows the crewmember 

to walk into the pressurizable volume shirtsleeve to perform maintenance on the 

front of the suits or transfer items between the pressurized volume and the habitat 

cabin. 

FIGURE 7.2.5-2 REAR-ENTRY AIRLOCK BULKHEAD (HABITAT APPLICATION 

WITH INTERNAL HATCH)
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While a 3.5 meter diameter would help decrease consumables, first drafts of the 

concept have shown unacceptable interference between the opening of the 

vestibule hatch and the side wall. Two bulkhead designs were examined including 

a tri-planar and a planar bulkhead (Figure 7.2.5-3). Both were angled to facilitate

donning. The tri-planar bulkhead helped to decrease internal volume but made 

the interference constraint much worse and ingressing at an angle going 

backwards adds to the operational difficulty. It was recommended that further work 

be done to look at the right diameter, mass, and volume to find out if objectionable 

interference could be eliminated.

FIGURE 7.2.5-3 REAR-ENTRY AIRLOCK BULKHEAD (ANGLED 3.5 M DIAMETER 

TRI-PLANER AND PLANAR BULKHEADS)

Although it has not been sized yet and has trades of its own, the hatch within a 

hatch idea has been discussed as an option to allow the internal hatch access 

while keeping the diameter of the module down. 

7.2.6 Hatches

There is a large historical dataset available on hatches, and only a small portion is

described within the scope of this document. The following sections will focus on 

EVA-compatible hatches and what direction they open, what size they need to be 

to support suited pressurized crewmember ingress/egress for both microgravity 

and surface operations, primary and secondary hatch requirements, and 

discussion of having a “hatch within a hatch” for a specific architectural concept.

In addition to a suited crewmember being able to exit the hatch, depending on the

operational scenario and task, you may also need to move large ORUs or other 

equipment through the hatch, and may need to size the hatch accordingly.

7.2.6.1 Inward-opening vs. Outward-opening Hatches

Referencing Worldwide Spacecraft Crew History (NASA/TP–2010–216131, 2010):
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“The future design of human spacecraft crew hatches will require a trade study to 

weigh the risk of designing an inward-opening hatch as compared to an outwardopening hatch. A rigorous risk analysis of conditions or hazards that can 

potentially create a need for emergency crew egress or emergency ingress of 

ground personnel for the pre-launch and post-landing time periods must be 

performed. To mitigate the crew safety hazard, a single unified (pressure seal and 

thermal protection) hatch for quick outward opening is preferred; reference the 

Apollo Crew Module (CM) and shuttle orbiter crew ingress/egress hatch. This 

would be compared to a risk analysis of long mission time exposure to space 

vacuum in which the crew safety hazard is cabin depressurization/loss of cabin 

atmosphere due to crew hatch seal leakage or failure. To mitigate the crew safety 

hazard related to depressurization, an inward-opening and pressure-sealing hatch 

is preferred, as cabin pressure tends to seal the hatch vs. an outward opening 

where cabin pressure tends to open the hatch. This may result in an inwardopening pressure-sealing hatch and an outward- opening thermal protection hatch, 

as the Russians designed for the Buran. An earlier look at the performance history 

of spacecraft hatches has shown that when the crew hatch is also the EVA hatch, 

an inward-opening pressure-sealing hatch is preferred.” 

For safety purposes, those hatches within the cabin and the ingress/egress 

method that are not otherwise cycled on a launch pad for emergency egress would 

most likely be inward-opening. The size of the hatch will also be of concern as 

there is a minimum dimension that should be utilized on the vehicle for a 

crewmember to safely translate through during an EVA.

7.2.6.2 Hatch Size in Microgravity

Hatch sizes were evaluated by Computer Aided Design (CAD) models in 2015 

using the Z-2/PLSS 2.5 model showing static egress (does not take into account 

that the crewmember can change position to fit through an opening or soft goods 

shape change) through the U.S. crew lock, the Russian airlock Pirs, the ability to 

fit through the FGB bulkhead hatch, and IDA/NDS. The model used comes with 

the following caveats:

• SAFER, Display Control Unit (DCU), Modular Mini-Workstation (MMWS)

or tools are not attached

• Boots, a full arm assembly, and gloves are also not currently in the Z-2 

CAD model 

• The Hard Upper Torso (HUT) in the CAD model is not the largest size 

HUT expected for the Advanced Extravehicular Mobility Unit (AEMU).
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For current microgravity operations, the ISS A/L EVA hatch for ingress/egress of 

the crew is a 36 in. x 40 in. diameter “D” hatch. (reference Figure 7.2.6-1, courtesy 

NASA Imagery Online iss028e016325): 

FIGURE 7.2.6-1 ISS AIRLOCK EVA INGRESS/EGRESS HATCH WITH EMU 

(MICROGRAVITY EVA)

With the mini-workstation and tools attached, clearance is limited for the EVA 

crewmember to exit the ISS EVA hatch. When exiting the airlock, the PLSS should 

align with the D-flat to maximize clearance on the front of the suit for the MMWS 

and DCU. 

The Z-2/PLSS 2.5 assembly should fit through the U.S. and Russian airlocks (Pirs) 

even when a SAFER, DCU, and MMWS are installed as shown by CAD.

Pirs EVA hatch is 1m (39.37 inches) in diameter (not a D-flat style airlock hatch). 

Given the clearance seen for Z-2 in the U.S. airlock, the suit should have no trouble 

clearing the Pirs EVA hatches

However, the Functional Cargo Block (FGB) bulkhead to Pirs docking module is 

about 800mm (31.49”) in diameter. The Z-2/PLSS 2.5 will not fit through the FGB 

bulkhead once the SAFER, DCU, and Mini-workstation (MWS) are installed. 

Transfer through the FGB bulkhead may be possible if the MWS is not installed, 

but this needs to be demonstrated by a physical test as the CAD model is not 

dynamic and the clearances are too small to determine if it is possible. It may be 

difficult for the crew member to pull themselves through such a small passage way, 

especially if operating at a higher suit pressure. The legs will interfere if the 

position of the suit is not changed and the crew member will need to roll forward 

out of the hatch. The CAD shows there is less than an inch between the PLSS 

and the hatch (again, the suit model is not the largest size) in the following figure. 
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FIGURE 7.2.6-2 FGB 800MM HATCH INGRESS/EGRESS HATCH WITH Z2 CAD 

(MICROGRAVITY EVA)

Ideally, pressurized suited crew would be able to translate through spacecraft 

docking collars. This capability would also need to include transfer of an 

incapacitated crew through the docking collar. However, the International Docking 

System Adapter (IDA) Standard Pass-Through requirement is 31.5 inches inner 

diameter of the petals (similar in diameter to the FGB hatch) and is expected to be 

used for future Exploration-class vehicles (Reference SSP 50933, IDA to ISS and 

Visiting Vehicle IRD, Soft Capture Ring Dimensions). See figure 7.2.6-3 for the 

clearance through the IDA petals. While the crewmember can possibly maneuver 

through the petals, especially if one of the petals could be removed, the tunnel 

diameter would still be 800 mm when docked.

FIGURE 7.2.6-3 IDA INGRESS/EGRESS HATCH WITH Z2 CAD (MICROGRAVITY 

EVA)
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Again, if adding in the DCU and MMWS, this could be an issue. As shown by the 

FGB hatch CAD, there is not enough clearance through an 800 mm hatch. 

The current hatch assumption held by the EVA community is discussed in the EVA 

Assumptions for Future Vehicles section of this document. 

Orion side hatch operations have also been discussed and evaluated in the Neutral 

Buoyancy Lab (NBL) in 2011 (reference EVA Systems Project Office (ESPO) Test 

8: Joint EVA NBL Orion Mackup (JENOM) Neutral Buoyancy Laboratory Test 

Report). While it is possible to fit through the side hatch with an EMU, changes 

would need to be made both to Orion and the xEMU to enable EVA capability. 

Currently, Orion is not considered EVA compatible. 

7.2.6.3 Hatch Size for Surface Operations

For exploration vehicle assets that include surface operations with any significant 

quantity of EVA’s, the ingress/egress hatch size is assumed to be large enough to 

support the upright stature of a walking person. The hatch size recommended is 

40 in. x 40 in. (0.92 m. x 0.92 m.) minimum up to ~40 in. x 60 in. (0.92 m. x 1.52 

m.) depending on the frequency of the EVAs. Note that this assumption could be 

deferred on an architecture with very, very few EVAs per mission (such as Apollo), 

in which case it is likely acceptable that smaller size hatches may trade favorably 

even if they require somewhat less convenient postures such as crawling as did 

the Apollo Lunar Lander EVA hatch. In this case, the mobility to perform such 

tasks could impact the suit. 

7.2.6.4 Secondary Hatch Requirement

While not all vehicle or ingress/egress designs require both a primary and a 

secondary EVA hatch, an analysis of failure modes could reveal the need when 

coupled with program-specific choices for human rating and redundancy/fault 

tolerance strategies. Fault tolerance should be included in detailed mechanism 

designs; however, there are some failure modes (repress failure) that may not be 

able to be mitigated without adding a secondary hatch. 

Hatches must allow a pressurized suited crewmember to exit and enter the vehicle. 

Sufficient access and free volume will be needed to allow the crew to perform 

nominal EVAs, as well as contingency ingress operations such as a hatch failure 

or a failure to repress. For ISS, this is resolved by providing a separate crew and 

EVA equipment lock which can each function as an airlock in the event of a hatch

or repress failure. Other solutions might include having a secondary hatch and 

bringing the cabin down to vacuum to allow the crewmembers to transfer into the 

cabin and repress the cabin. Having an inner secondary hatch along with suitport 

hatches inside of a suitport-airlock allows the crewmember to either enter the cabin 

shirtsleeve as they doff their suits through the bulkhead, or could allow the 

crewmember to transfer through the secondary inner hatch. 
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7.2.6.5 Hatch within a Hatch

Note: this section is primarily for suitport and rear-entry airlock concepts and does 

not apply to dual chamber airlocks. For the hatch within a hatch concept, the 

potential benefits may be outpaced by the inherent complexities (see graphics 

below, courtesy of Brand Griffin 2008, notional dimensions) (reference Figure 

7.2.6-2 and Figure 7.2.6-3 in the blue box). Vehicle services described in Section 

3.1 have to be integrated with the bulkhead/hatches to reach the PLSS located in 

the inner vestibule hatch. This will allow for recharge of the suit between EVAs 

which could add to the complexity of the umbilicals and running lines around the 

hatch openings.

FIGURE 7.2.6-2 COMPLEXITY OF HATCH WITHIN A HATCH
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FIGURE 7.2.6-3 REAR-ENTRY AIRLOCK BULKHEAD (HABITAT APPLICATION 

WITH INTERNAL HATCH WITHIN A HATCH)

7.2.7 Dust Mitigation/Planetary Protection Differences between Ingress/Egress 

Concepts

Dust mitigation can refer to either the lunar surface or the Martian surface and is 

an important aspect for both. Planetary Protection is particularly important for the 

Martian surface and concerns both forward and backward contamination. Forward 

meaning contamination of humans on the Martian surface. Backward meaning 

bringing Martian microbes back to the Earth. So far, the Planetary Protection 

Office does not have specific requirements, but instead understands the 

operational control of defining special regions that the humans cannot enter. This 

will be better understood once a landing site is determined and the degree of 

particle transport on the Martian surface is further understood. While Planetary 

Protection is not necessary on the Earth’s moon, the lunar surface would be a good 

analog to demonstrate a “layered engineering defense”.

For the lunar surface, only dust mitigation is of moderate concern due to respirable 

complications. The following is an example standard derived from NASA-STD3001, Volume 2, V2 6053 in consideration for the entire system between the 

vehicle, ECLSS, and crewmembers: 
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• The system shall limit the levels of lunar dust particles less than 10 μm in 

size in the habitable atmosphere below a time-weighted average of 0.3 

mg/m3 during intermittent daily exposure periods that may persist up to 6 

months in duration. 

o Rationale: This limit was based on detailed peer-reviewed studies 

completed by the Lunar Atmosphere Dust Toxicity Assessment Group 

(LADTAG) and is specific to the conditions relevant to the lunar 

surface, i.e., this standard would not necessarily be applicable to other 

missions. The standard assumes that the exposure period is episodic 

and is limited to the time before ECLSS can remove the particles from 

the internal atmosphere (assumed as 8 hours post-introduction). 

Although the standard is being conservatively applied to all inhalable 

particles (all particles ≤10 μm), it is most applicable to dusts in the 

respirable range (≤2.5 μm) that can deposit more deeply into the lungs. 

Studies show that the particle size of lunar dust generally falls within a 

range of 0.02-5 μm.

An example of a system collaboration is discussed below.

Certain ingress/egress methods provide dust mitigation techniques by keeping 

EVA suits on the opposite side of the bulkhead from the habitable environment, 

while others may amplify dust contamination. For instance, a traditional airlock

allows the crewmember to doff their presumably dusty suit on the don/doff stand 

and then translate/walk through the dust that was just carried in on the suit. On a 

subsequent EVA, crewmembers must reverse this path and again translate/walk 

in their undergarments/Liquid Cooling Ventilation Garment (LCVG) through the 

dust prior to donning the suit on the don/doff stand. This architecture would 

fundamentally promote dust contamination issues. 

To address this concern, one possible solution utilizes a “Layered Engineering 

Defense” plan (Wagner, S. 2014) which utilizes “layers” to help mitigate the effect 

of dust on the suit materials, control the transfer of dust on the suits, reduce or 

eliminate forward and backward contamination to the crew and habitation, and 

minimize cleaning and protection (interior and exterior) and the use of air quality 

contamination zones. The space suits need to be brought inside a habitable 

volume for nominal and contingency maintenance, which will introduce some 

amount of dust into the habitable volume. The operations of the removal of dust 

from the suits will be a multi-phase operation to limit dust introduction into the suits 

and into the crew cabin. Tools and samples could also introduce dust into the 

airlock. Stowage/containment and cleaning of these items is important in 

addressing dust mitigation. Operational controls and air quality zones utilize

ingress/egress methods that will mitigate dust transfer into the cabin, (i.e. rearentry airlocks, suitport-airlocks, and suitports). An ingress/egress method can also

provide particulate mitigation and backward and forward planetary protection by 
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donning/doffing the rear-entry EVA suit through a bulkhead, such that the 

crewmember does not translate through the dust during vehicle ingress and 

don/doff. Cabin filtration is necessary on the assets/habitation for dust mitigation

and planetary protection. Ingress/egress methods such as rear-entry 

airlocks/suitlocks and suitport-airlocks could include a large enough chamber to 

perform the maintenance in or a secondary chamber or mud room to further 

contain contamination and increase air quality as the crewmember translates to 

the cleanest areas of the vehicles, such as habitats, pressurized rovers and ascent 

vehicles. 

With a suitport, suitport-airlock, or rear-entry (suitlock) the majority of dust 

remaining on the suit will be kept on the other side of the habitation zone. 

Depending on the design of the habitat, the ingress/egress method can add one 

or two zones to keep the contamination out of the crew quarters (reference Figure 

7.2.6-1). Below is an example of a layered engineering defense plan (tailored for 

EVA); other protocols can be followed. These details and operational concepts 

are in-work. 

• 1st Layer – Mission Architecture Design

o Avoidance of Special Regions (defined within X radius of 

lander/habitat prior to the mission)

• 2nd Layer – Hardware Design 

o EVA Suits will leak/vent – Engineering limits must be understood and 

intentionally accounted for

o Sample tool collection/containment

• 3rd Layer – Operational Design

o Suit ingress directly to habitable volumes should be eliminated to 

extent possible, examples of this include the ingress/egress method

(rear-entry suit don/doff through bulkhead)

o Sampling Protocols limit inadvertent contamination

o Leaving EVA suits on the surface prior to ascent to “break the chain” 

of contamination 

• 4th Layer – Contamination Control

o Conduct verifiable decontamination of EVA hardware on a regular 

interval

o Conduct Exterior and Interior Cleaning

o Utilize Air Quality Contamination Zones 

 
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FIGURE 7.2.7-1 LAYERED ENGINEERING CONTAMINATION ZONES

While suitports, suitport-airlocks, and rear-entry airlocks keep the suit outside of 

the crew cabin, the PLSS is still on the inside of the cabin vestibule door. Dust 

mitigation tools such as brushes attached to the vestibule door, sealing 

mechanisms around the PLSS on the vestibule door to keep the dust inside that 

inner volume, and vacuum/filtration for the vestibule volume need to be 

investigated. 

Ingress/egress methods may be the best option for minimizing dust inside of the 

cabin for the rover; however, exploration EVA suits must still be brought inside a 

pressurizable volume for suit maintenance on missions longer than 30 days in 

duration. It is assumed that a rear-entry airlock or suitport-airlock will be on the 

long duration habitat; however, it should be demonstrated how much this helps 

keep dust out of the habitable volume compared to the regular airlock (e.g. walking 

through the dust after every EVA). Dust modeling/testing should be performed to 

show the differences between using a concept that keeps suits on the opposite 

side of the bulkhead and heritage airlocks.

Multiple chambers such as the dual chamber airlock can also be utilized, but may 

require more cleaning and innovation to help keep the dust from getting inside the 

suits. 

7.2.8 Volume Studies and Suit Maintenance

Volume studies have been done in the past for both a surface airlock and don/doff 

volumes. New volume studies should be performed to further understand the 

amount of room needed inside of an ingress/egress method to facilitate suit 

maintenance, allow enough room for tools, and hatch swing. 
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The following is an overview of EVA tasks and volume:

• Internal task volumes are mission architecture dependent

– Purpose of EVA (contingency vs. nominal)

– Destination class (type of suit) – focus on μg first

– Contingency scenarios (secondary ingress, number of chambers)

• Ops Con, architecture and risk dependent

– EVA assumes a secondary ingress – this is usually dual chamber 

configuration (similar to ISS equipment lock and crew lock)

• Permanent Hardware:

– Volume for EVA support equipment (already have ISS SPCE)

• PLSS recharge equipment (power, communications, umbilical interface 

panel, etc.)

• ECLSS consumables and plumbing (not included in EVA System 

volumes)

• Some of the following tasks can be performed in the same volume:

– Volume for 2 crewmembers to don/doff 

• Assume unassisted (possibly third IVA crewmember support)

– Volume for prebreathe

• Duration dependent (assume shared location with don/doff)

– Volume for suits, tools, logistics and spares stowage

• Mission duration dependent (number of suits, how suits are stowed, 

amount of logistics needed based on usage exceeding limited life, sparing 

philosophy)

• Mission objectives dependent (science, suit maintenance tools, vehicle 

maintenance tools, dust mitigation tools)

– Volume for in-flight maintenance

• Mission duration dependent

• Planetary Protection needs (partition, chamber, etc.)

• Suit architecture dependent (ORU level)

In any airlock, the don/doff volume needs to be considered to accommodate selfdonning for two crewmembers. The volume in front of the suit needs to be large 

enough to accommodate a crewmember standing/kneeling in front of the suit to 

perform suit maintenance. The overall volume of the pressurizable area needs to 

be able to accommodate a crewmember and an incapacitated crewmember. The 

following is an overview of volumes needed based on a 10 EVA assumption:

• Interface/Volume to Don/Doff Suits (EVA prep/post servicing)

– It is assumed the Equipment Lock portion will be used to don/doff suits 

potentially with a third IV crewmember assisting (dual chamber airlock)

– Minimum ~3.5 m3 assuming serial donning (~7 m3 for simultaneous 

donning not including 3rd crewmember)
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• Volume for EVA Stowage

– Stowage volume for 3 suits (bundled similar to stowed EMU) = ~1.75 

m3

– Some of this volume can be combined with the Volume to Don/Doff 

Suits

– Trade available to stow EVA hardware in locations other than Airlock

• Volume for permanent support hardware = ~1.1 m3

– Most of this equipment would be located in the Equipment Lock

• Volume for logistics and tools = ~2.3 m3

• Vehicle Egress/Ingress (hatch size)

– 1000 mm clearance in projection (for microgravity)

• Volume for spares and additional logistics are TBD depending on mission 

duration and failure modes and component life

• Volume for ORUs and/or samples are TBD

7.2.8.1 Don/Doff Volume estimate

Estimates for a pressurized suit from CxP (not don/doff volume) was bookkept as

2.2 m (H) x 1.0 m (W) x 0.95 m (D). From past studies performed in a reduced 

gravity flight, a don/doff volume was estimated (reference Constellation Space Suit 

Element Engineering Memo EM-CX-Suit-09-0047); however, with the addition of 

including the head room of about 12 to 14 inches for rear-entry donning and room 

leg room, a new estimate has been formulated of 2.36 m (H) x 1.55 m (W) x 0.84 

m (D) (see Figure 7.2.8-1):

FIGURE 7.2.8-1 DON/DOFF VOLUME ESTIMATE
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7.2.8.2 Suit Maintenance

Suit maintenance is performed on SoA EMUs on the ISS. For instance, the Fan 

Pump Separator (FPS) Remove and Replace (R&R) takes place in the ISS 

equipment lock, but it has been reported that there is more room and better hand 

holds in another module. There is not a dedicated suit maintenance area on the 

ISS; however, maintenance can be performed to the suit while it is on the donning 

stand. Most suit maintenance (especially refurbishment and recertification) is 

performed in facilities on the ground with test fixtures, clean rooms, and a multitude 

of tools. Transitioning from the way things are done today to on-orbit, long-term 

suit maintenance in a dusty environment will be very challenging. Failure modes 

and end of life cycles/testing need to be well understood for a new exploration suit 

to compile a complete list of services, maintenance, logistics, and spares needed 

for each mission. Current operations concepts assume pressurized rovers and 

habitats; however, suit maintenance cannot be fully performed on a pressurized 

rover due to their current suitport configuration. Only maintenance on the PLSS 

and whatever may be within reach of the inside of the PGS can be performed from 

the inside of the cabin while the rest of the suit is on the other side of the bulkhead. 

A pressurizable volume is necessary to bring suits inside for nominal suit 

maintenance such as repairs, sizing, etc. 

Prior to entering the pressurizable volume, the suit is cleaned to the extent possible 

to bring in as little dust as possible. Basic inspection and cleaning operations are 

conducted within the pressurizable portion of the airlock and more extensive repair 

is conducted in the habitat general maintenance area if necessary. Umbilical 

interface panels should be located where suited crewmember operations occur. 

In order to have the volume to perform suit maintenance in front of the suit, an 

initial assumption was that 1.22 meters was needed between the bulkhead and the 

outer bulkhead. This number could be optimized and will need to be refined 

through testing.
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FIGURE 7.2.8-2 PLANAR BULKHEAD WITH 1.22 METER CLEARANCE

There has also been discussion of a mudroom. This adds volume, mass, and 

consumables; however, if the trade to go with a separate module for the habitat 

proves optimal, then the extra area could be used as a general maintenance area 

and an extra zone for dust mitigation assuming equipment is properly cleaned. See 

figure below. 
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FIGURE 7.2.8-3 “MUDROOM” EXAMPLE

7.2.9 Incapacitated Crewmember

It is required to protect for the scenario where a crewmember may become 

incapacitated during EVA operations (microgravity and surface) as outlined in 

NASA-STD-3001 Volume 2, NASA Space Flight Human-System Standard Volume 

2: Human Factors, Habitability, and Environmental Health. Incapacitated 

pressurized-suited crewmembers may be unable to ingress the vehicle on their 

own and may require assistance from a second crewmember. This may include 

ingress after an EVA, ingress/egress to/from the vehicle during an EVA, or any 

vehicle or module to which the vehicle is docked. The worst case scenario is 

always the pressurized suited crewmember as it involves the volume within the 

vehicle to perform the assisted task, hatch opening size and operation, as well as 

the external translation path and mobility/stabilization aids. Removing an 

incapacitated crewmember from a rear entry suit could be challenging and could 

require extra volume in the airlock, extra support structure, or possible tools to 

assist the crewmember inside as well as removal from the suit. The volume in any 

airlock option will need to take into account room for an IV crewmember to assist 

with rescue and suit doffing of an incapacitated crewmember.
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All ingress/egress methods will need to allow for incapacitated crewmember 

operations. Each mission will be evaluated as the architecture and ops cons are 

defined.

7.2.10 Add-on to ISS and Integration

The Near Term DRM study determined that adding a suitport demonstration onto 

a new habitat module project, whether as an add-on, or as integrated onto the 

module, could be beneficial on the ISS. Testing another module with exploration 

atmospheres on the ISS has increased safety due to the availability of the ISS 

Joint A/L as a backup in case of contingencies. The ISS also has berthing 

installation capability with the Space Station Remote Manipulator System 

(SSRMS). Testing on ISS would avoid the need to design a vehicle to be used in 

cislunar space that is suitport compatible. The idea of adding the demonstration 

to ISS has been viewed as significantly challenging due to incompatibilities with 

existing airlock hardware, as well as the pressure differential and flammability 

concerns of integrating the module with the ISS, for example: 

 

• Integration with ISS has not been formally assessed (ECLSS, power, 

communication/avionics, port availability, etc.)

• Materials testing at the maximum O2 concentration (~35%) as opposed 

to the 30% O2 (ISS A/L O2 compatibility, Flight Rule B17-3) would need 

to be looked into further

• Most of the same consumables used by the ISS EMU would be used by 

the EVA suit interfaces 

• The ISS A/L interfaces are currently being updated to enable 3000 psi O2 

capability

The need to determine what should be tested on the ISS is limited by schedule 

with current extension to 2024 and a potential extension to 2028.

As opposed to testing an alternative concept at ISS, it has been proposed to 

perform limited exploration atmospheres studies on ISS to determine alterations 

to physiological parameters, such as hematologic, immunologic, oxidative stress, 

visual impairment, and cognitive function, from reduced gravity exposure to mild 

hypoxia. Potential ISS issues were discussed along with draft test procedures and 

a list of impacted flight rules. 

7.3 SUIT vs. VEHICLE SUITPORT OPERATIONS

Note: this section is primarily for suitport concepts and does not apply to dual 

chamber airlocks. 
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With future assets currently undefined, a study of some of the functions that are 

currently a burden on the suit can be placed on the vehicle as opposed to adding

mass to suit (affects CG and mobility). For instance, suit access hatch open-close 

mechanism, PLSS rotation-translation, pressurization, ventilation, water 

circulation, dust mitigation, and environmental protection could be alleviated by 

exploration assets (TDS 1228 CSSS-T-010 RAC02 – Suitport Requirements 

Assessment). 

7.3.1 Pressurization, Suit Access Hatch Open-Close, PLSS RotationTranslation

Pressurization/depressurization of the suit and volume between the vestibule and 

the suit hatch/PLSS is a very important step in the procedures before the 

crewmember dons/doffs the suit. While the suit is unoccupied and stowed on the 

suitports, the suit is kept at 0.9 psid to keep it thermally conditioned. For the 

suitport concept, there may need to be extra thermal conditioning inside the 

cabana or environmental cover protecting the suits. 

When the crewmember is ready to prepare for an EVA, the suit is brought up to 

cabin pressure at 8.2 psi, such that the suit is at 8.2 psid to vacuum. While the suit 

access hatch/PLSS and the vestibule hatch are still closed, the volume between 

the vestibule hatch and the suit access hatch/PLSS is assumed to remain at cabin 

pressure to enable PLSS access while the crewmembers are on the inside of the 

cabin. Equalization valves must be in the architecture to equalize the pressure 

between the three volumes. The crewmembers are then ready to ingress their 

suits and close the hatches. There can be a mechanism on the vehicle allowing 

the crewmembers to close their suit access hatch and rotate/translate/latch the 

PLSS to the suit and close the vestibule hatch. Once the crewmembers have 

completed a short prebreathe while performing suit checkouts, the volume 

between the vestibule hatch and the suit access hatch/PLSS is brought down to 

vacuum. 

As discussed above, the suit is kept at 0.9 psid to keep the suit thermally 

conditioned while it is on the suitport and unoccupied. Previously, this implied that 

the suit primary regulator was constantly operational; however, there could be a 

regulator between the vehicle services and the suit which allows the burden to be 

transferred to the vehicle.

It is reasonable to assume that the higher the delta pressure across the suit, the 

higher the leakage rate. Keeping the suit at a delta pressure also causes suit 

leakage. In the past, suit leakage calculations were performed assuming the suit 

was kept at 8 psid, which was assumed to be the maximum delta pressure of the 

suit. This should be recalculated using the minimum delta pressure (this is 
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currently assumed to be 0.9 psid, which needs to be verified) to show the difference 

in consumables loss.

7.3.2 Ventilation and Water Circulation

While the suit is unoccupied and stowed on the suitports, it was assumed that the 

PLSS pump was operating continuously to prevent the water lines from freezing, 

but this could be performed by the vehicle. If the umbilicals are on the outside of 

the vehicle, they must also be thermally controlled or in operation continuously. 

There could be a pump on the vehicle side which circulates the water.

7.3.3 Thermal Heat Sync

The presence of an exposed metal plate on the suit upper torso constitutes a heat 

sink. Thermal analysis is necessary to characterize the impact of the SIP acting as 

a conductor to the spacecraft and its effects on adjacent suit components such as 

batteries. An examination into SIP materials could be done to alleviate this issue 

along with thermal control (passive and command controlled) of the suitport 

interface on the vehicle. Covers may need to be developed keeping the thermal 

heat sink in consideration.

7.3.4 Environmental Protection

The vehicle cabana or environmental cover is undefined at this point. The amount 

of environmental protection from dust, micrometeoroid debris, Ultra Violet (UV) and 

ionizing radiation, and thermal environments are assumed to be mostly provided 

by the vehicle. 

7.3.5 100% O2

Space Suits inherently have some amount of leakage. The suitport vestibule 

volume is small and suit leakage will enrich the vestibule environment during 

storage meaning that at startup, the external surfaces of the PLSS may be 

exposed to oxygen enriched environments of 100% O2. Additionally, if an offnominal leak develops inside the PLSS during an EVA, resulting in an EVA 

terminate or abort, a suitport ingress scenario would result in the PLSS being 

exposed to an elevated oxygen environment at the conclusion of the EVA. 

Therefore, the PLSS must be designed to operate with not only 100% O2 inside 

the vent loop but also with 100% O2 on all surfaces which would nominally be 

exposed to the cabin environment.

7.3.6 Don/Doff

2012 and 2013 suitport testing showed difficulties during pressurized don/doff for 

several different reasons already mentioned in this document. Reference CTSD-
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ADV-1014 Z-1 Suit and Pneumatic Flipper Suitport Chamber B Test Report for 

findings and suggestions for further ground testing and reduced gravity testing.

7.3.7 PGS Impacts and Suit Center of Gravity

The integration of the SIP with the suit causes the CG to move up (Y direction) and 

back (Z direction), potentially complicating ambulatory capability. Additional 

hardware, resulting from suitport compatibility will contribute to increasing suit onback mass. Tests and evaluations should be performed to assess the impacts and 

determine if the vehicle can decrease these impacts.

7.3.8 PLSS Impacts

Impacts to the PLSS include additional on-back mass (vacuum plumbing for the 

regulators, beefier pumps, etc.), PLSS outer mold line, environmental exposure, 

and suit center of gravity as listed above. Assessment should be performed to 

determine what the vehicle can do to decrease these impacts.
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8.0 SUMMARY

The EVA community is seeking innovative solutions to the challenge of transferring 

a pressurized suited crewmember from within the spacecraft to an external

environment and back. It is desired to find airlock solutions that make progress 

towards:

• Improved consumables usage

• Increased crew autonomy

• Increased quantity and access of EVAs

• Reduced prebreathe time

• Mitigation of dust intrusion

• Provision for a layered defense for planetary protection

However, while addressing these challenges the solution should also consider 

features that improve overall EVA architecture such as:

• Providing unassisted don/doff

• Providing suit consumables recharge

• Providing the volume for donning/doffing and prebreathe 

• Providing the volume for in-flight suit maintenance

This document surveys historical and currently suggested methods of solving

these issues either in whole or in part. However, the remaining challenges 

associated with each known concept requires crossing the boundary between the 

EVA System and the host spacecraft. Gaining the perspective of a vehicle provider 

can allow further understanding of impacts to the suit as well as overall mission 

capabilities through the intermediary interface of the airlock. 

Given the large number of interrelated variables associated with airlock design and 

operation, it can be easy to lose one’s way when considering the merits of various 

conceptual solutions. This review was created to organize the conversation and 

mark the intellectual progress of the strategic planning community and EVA. 

Ultimately, this document intends to capture all of the constraints, highlight known 

open trades, and provide organization and citation of the most influential 

references useful to advancing ingress/egress methods, design strategies, and 

architectures. 

Barring a revolution in propulsion technology, mass and volume will ultimately end 

up being the principal figures of merit for human spaceflight beyond LEO, once all 

other unique functional requirements are satisfied. Therefore, all trades must 

emphasize estimating these values in order to provide a useful comparison to 

contemporary and heritage solutions. Rigorously estimating mass and volume 
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across the entire spaceflight architecture a given airlock solution will be used on 

allows it to be compared to heritage solutions. As proposed concepts are traded

and taken beyond the conceptual graphics level, the language of mass and volume 

will facilitate the spaceflight community’s acceptance of design choices. 
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9.0 REFERENCE DOCUMENTS

Document 

Number

Document 

Revision Document Title

EVA-EXP-0035 Exploration EVA System Compatibility

EVA-EXP-0042 Exploration EVA Concepts of Operations

CTSD-ADV1014Ju, H., Rodriggs, L., Ross, A., “Z-1 Suit and Pneumatic 

Flipper Suitport Chamber B Test Report”, 2013

Abercromby, A., Conkin, J., and Gernhardt, M., 

“Modeling a 15-min Extravehicular Activity Prebreathe 

Protocol using NASA’s Exploration Atmosphere (56.5

kPa/34% O2),” Acta Astronautica, vol. 109, DOI: 

http://dx.doi.org/10.1016/j.actaastro.2014.11.039, 

2015.

Abercromby, A., Gernhardt, M., Jadwick, J., 

“Evaluation of Dual Multi-Mission Space Exploration 

Vehicle Operations during Simulated Planetary 

Surface Exploration”, Acta Astronautica, DOI: 

http://dx.doi.org/10.1016/j.actaastro.2012.02.022, 2013

Abercromby, A., Chappell, S., Gernhardt, M., “Desert 

RATS 2011: Human and Robotic Exploration of NearEarth Asteroids”, Acta Astronautica, vol. 91, DOI: 

http://dx.doi.org/10.1016/j.actaastro.2013.05.002, 2013

TP-2010-

216136

Abercromby, A., Gernhardt, M., Litaker, H., “Desert 

Research and Technology Studies (DRATS) 2008: 

Evaluation of Small Pressurized Rover and 

Unpressurized Rover Prototype Vehicles in a Lunar 

Analog Environment”, NASA Technical Report TP2010-216136, pp. 131, 2010

TP-2012-

217360

Abercromby, A., Gernhardt, M., Litaker, H., “Desert 

Research and Technology Studies (DRATS) 2009: A 

14-Day Evaluation of the Space Exploration Vehicle 

Prototype in a Lunar Analog Environment”, NASA 

Technical Report TP-2012-217360, pp. 144, 2012

Boyle, R., Mitchell, K., Alton, C., “Suitport Feasibility –

Development and Test of a Suitport and Space Suit for 

Human Pressurized Space Suit Donning Tests”, 42nd

International Conference on Environmental Systems, 

San Diego, CA, DOI” http://dx.doi.org/10.2514/6.2012-

3631, 2012

AIAA-E2013-

3399

Boyle, R., Rodriggs, L., Allton, C., Jennings, M., 

Aitchison, L., “Suitport Feasibility – Human Pressurized 

Space Suit Donning Tests with the Marman Clamp and 

Pneumatic Flipper Suitport Concepts”, AIAA-E2013-
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Document 

Number

Document 

Revision Document Title

3399 International Conference on Environmental 

Systems, Vail, CO, USA, 14-18 Jul 2013

NASA/TM2011-

217062/Volume 

I

Brady, T., Polk, J., “In-Suit Light Exercise (ISLE) 

Prebreathe Protocol Peer Review Assessment”, NASA 

Technical Memorandum, NASA/TM-2011-

217062/Volume I, NESC-RP-10-00659, Feb 2011

Cohen, M., Bussolari, S., “Human Factors in Space 

Station Architecture II; EVA Access Facility: A 

Comparative Analysis of Four Concepts for On-Orbit 

Space Suit Servicing”, NASA Technical Memorandum 

86856, Washington DC, 1987

AIAA-95-1062 Cohen, M., “The Suitport’s Progress”, AIAA-95-1062 

Life Sciences and Space Medicine Conference, 

Houston, TX, USA, 3-5 Apr 1995

SAE Technical 

Paper Series 

2000-01-2389

Cohen, M., “Pressurized Rover Airlocks”, SAE 

Technical Paper Series 2000-01-2389 30th

International Conference on Environmental Systems, 

Toulouse, France, 10-13 Jul 2000

Conkin, J., Norcross, J., Wessel, J., Abercromby, A., 

Klein, J., Dervay, J., Gernhardt, M., “Evidence Report: 

Risk of Decompression Sickness”, 

https://ntrs.nasa.gov/search.jsp?R=20140003729, 

2013

AIAA 2011-

5064

Howe, S., Kennedy, K., Guirgis, P., Boyle, R. A DualChamber Hybrid Inflatable Suitlock (DCIS) for 

Planetary Surfaces or Deep Space AIAA 2011-5064 

41st International Conference on Environmental 

Systems, Portland, Oregon, USA, 17-21 Jul 2011

NASA/TM2013-217377Norcross, J., Norsk, P., Law, J., Arias, D., Conkin, J., 

Perchonok, M., Menon, A., Huff, J., Fogarty, J., 

Wessel, J., Whitmire, S., “Effects of the 8 psia / 32% 

O2 Atmosphere on the Human in the Spaceflight 

Environment”, NASA Technical Report NASA/TM2013-217377, pp. 72, 2013

NASA/TP2014-217399Wagner, S., “Asteroid, Lunar and Planetary Regolith 

Management: A Layered Engineering Defense”, 

NASA/TP-2014-217399, 2014

Romig, B., Alton, C., Litaker, H., “1-g Suitport Concept 

Evaluator 2008 Test Results”, SAE International 

Journal of Aerospace, vol. 4(1): 557-566. DOI: 

http://dx.doi.org/10.4271/2009-01-2572, 2009
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Document 

Number

Document 

Revision Document Title

NASA/TP2010-216134“Recommendations for Exploration Spacecraft Internal 

Atmospheres: The Final Report of the NASA 

Exploration Atmospheres Working Group”, NASA 

Technical Report NASA/TP-2010-216134, pp. 178, 

2010

NASA/TP–

2010–216131

“Worldwide Spacecraft Crew History”, NASA Technical 

Report NASA/TP–2010–216131, 2010

The Global Exploration Roadmap”, NASA, ISECG,

http://www.globalspaceexploration.org, 2013

NAS15-10110 Depress Pump Assembly Micron-A Technical 

Description and Operation Manual, NAS15-10110

ISS Concern 

#6458

“Suit Port design implications to Exploration EVA Suit”, 

ISS Concern #6458, ISS Program’s Integrated Risk 

Management Application

Drawing 683-

51960

ISS Joint Airlock Drawing 683-51960

TDS #1228 Ronalds, A., “Constellation Space Suit System Suitport 

Requirements Assessment – TDS #1228, Oceaneering 

D-0588270, 2014

JSC-66182 EVA Systems Project Office Test 8: JENOM Neutral 

Buoyancy Laboratory Test Report, JSC-66182, 2011

NASA-STD3001, Volume 2

NASA Space Fight Human-System Standard, NASASTD-3001, Volume 2, [V2 6053], 2011

EM-CX-Suit09-0047

Constellation Space Suit Element Engineering Memo 

EM-CX-Suit-09-0047, 2009

AIAA 2000-

1822

delaFuente, H., Raboin, J., Spexarth, G., Valle, G., 

“TransHab: NASA's Large-Scale Inflatable Spacecraft”, 

AIAA 2000-1822, URL: 

http://hdl.handle.net/2060/20100042636, 2000

JSC-CN-32373 Dasgupta, R., Mundary, S., Valle, G., 

“Bigelow Expandable Activity Module (BEAM) - ISS 

Inflatable Module Technology Demonstration”, JSCCN-32373, URL: 

http://hdl.handle.net/2060/20140017027, 2014

NASA/TM2016-219331

Doggett, W., Jones, T., Kenner, W., et al., “NonAxisymmetric Inflatable Pressure Structure (NAIPS) 

Concept that Enables Mass Efficient Packageable 

Pressure Vessels with Sealable Openings”, NASA/TM-
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Document 

Number

Document 

Revision Document Title

2016-219331, URL: 

http://hdl.handle.net/2060/20160013336, 2016

IAA-2017-0854 Doggett, W., Jones, T., Warren, J., et al., “NonAxisymmetric Inflatable Pressure Structure (NAIPS) 

Full-Scale Pressure Test”, AIAA-2017-0854, URL: 

http://hdl.handle.net/2060/20170000733, 2017

AIAA 2011-

5064

Howe S., Kennedy. K, et al., “A Dual Chamber Hybrid 

Inflatable Suitlock (DCIS) for Planetary Surfaces or 

Deep Space”, AIAA 2011-5064, 

URI: http://hdl.handle.net/2014/43909, 2011

NASA/TM-97-

112941

Portree, D., Trevino, R., “Walking to Olympus: An EVA 

Chronology”, NASA/TM-97-112941, URL: 

http://hdl.handle.net/2060/19980004606, 1997

SAE 2002-01-

2314

Trevino, L., Raines, T., Barido, R., et al., “Advanced 

Inflatable Airlock System for EVA”, SAE 2002-01-2314, 

DOI: https://doi.org/10.4271/2002-01-2314, 2002

SAE 2003-01-

2449

Trevino, L., Kennedy, K., Barido, R., et al., 

“Breadboard Development of the Advanced Inflatable 

Airlock System for EVA”, SAE 2003-01-2449, DOI: 

https://doi.org/10.4271/2003-01-2449, 2003.
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APPENDIX A

ACRONYMS AND ABBREVIATIONS

AES Advanced Exploration Systems

AIA Advanced Inflatable Airlock

A/L Airlock

AEMU Advanced Extravehicular Mobility Unit

ALCLR Airlock Cooling Loop Recovery Unit??

ARCM Asteroid Rendezvous Crewed Mission

ASPAT Airlock Suitlock Suit Port Team

BCA Battery Charger Assembly

BEAM Bigelow Expandable Activity Module

BSA Battery Stowage Assembly

CAD Computer Aided Design

CCB Configuration Control Board

CG Center of Gravity

CO2 Carbon Dioxide

CR Change Request

CSSS Constellation Space Suit System

CTSD Crew and Thermal Systems Division

CxP Constellation Program

DCS Decompression Sickness

DCIS Dual-Chamber Hybrid Inflatable Suitlock

DCU Display Control Unit

DDT&E Design, Development, Test, and Evaluation

DOT Destination Operations Team

DRATS Desert Research and Technology Studies

DRM Design Reference Mission

EA JSC Engineering

EAM Exploration Augmentation Module

EAWG Exploration Atmosphere Working Group

ECLSS Environmental Control and Life Support System

EDDA EMU Don/Doff Assembly

EMC Evolvable Mars Campaign

EMU Extravehicular Mobility Unit

ESPO EVA Systems Project Office

EV Extravehicular

EVA Extravehicular Activity

FCT Future Capabilities Team

FGB Functional Cargo Block

FOM Figures of Merit

FPU Fluid Pump Unit

FY Fiscal Year
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g gravity

GER Global Exploration Roadmap

HAT Human Spaceflight Architecture Team

HEOMD Human Exploration and Operations Mission Directorate

HHP Human Health and Performance

HRP Human Research Program

HUT Hard Upper Torso

IDA International Docking Assembly

INFO Infomatics 

IP International Partner

IRD Interface Requirements Document

IRMA Integrated Risk Management Application

ISECG International Space Exploration Coordination Group

ISLE In Suit Light Exercise

ISRU In-Situ Resource Utilization

ISS International Space Station

IV Intravehicular

IVA Intravehicular Activity

JENOM Joint EVA NBL Orion Mockup

LADTAG Lunar Atmosphere Dust Toxicity Assessment Group

LCVG Liquid Cooling Ventilation Garment

LDRO Lunar Distant Retrograde Orbit

LEIA Lightweight External Inflatable Airlock

LEO Low Earth Orbit

MAG Maximum Absorbent Garments

MASH Minimalistic Advanced Soft Hatch

MAV Mars Ascent Vehicle

MLI Multi-Layer Insulation

MMD Micrometeroid Debris

MMSEV Multi-Mission Space Exploration Vehicles

MWS Mini-workstation

MMWS Modular Mini-Workstation

MTV Mars Transit Vehicle

NASA National Aeronautics and Space Administration

NBL Neutral Buoyancy Lab

NDS NASA Docking System

O2 Oxygen

OFV On-orbit Fit Verification

OPR Office of Primary Responsibility

ORU On-Orbit Replaceable Unit

PLSS Portable Life Support System

PPE Personal Protective Equipment

PSA Power Supply Assembly

psi pounds per square inch
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psia pounds per square inch absolute

psid pounds per square inch delta

PWR Payload Water Reservoir

RAC Requirement Analysis Cycle

R&R Remove and Replace

REM Rapid EVA Methods

RS Russian Segment

SAFER Simplified Aid for EVA Rescue

SMT System Maturation Team

SIP Suitport Interface Plate

SoA State of the Art

SLS Space Launch System

SPR Small Pressurized Rover

SPCE Servicing, Performance, and Checkout Equipment

SPTM Suitport Transfer Module

SSPCB Space Station Program Control Board

SSRMS Space Station Remote Manipulator System

TBD To Be Determined

TDS Task Description Sheet

TRL Technology Readiness Level

UIA Umbilical Interface Assembly

USSR Union of Soviet Socialist Republics

UV Ultra Violet

VIIP Visual Impairment / Intracranial Pressure

xEMU Exploration Extravehicular Mobility Unit
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APPENDIX B

SUITPORT TESTING OPTIONS

After the Near Term DRM Quick Study was performed, the team focused on 

coming up with a draft set of suitport testing options for the ground (B1.0) and onorbit (B2.0):

• B1.0 Ground Testing Thermal vacuum Suit testing

o Suit leakage (amount of leakage)

o SIP seal leakage 

o Impact of leak rates into vestibule

• 0.9 psid analysis (Analysis is needed for suit leakage as well as thermal)

• SIP Stiffness 

• Umbilical design for Vacuum access in a contingency case

• Suit Don/Doff

o Difficulty for comparison to microgravity

o Tightening gloves & boots after donning

• Radiation, Thermal (cabana assumptions for protection) analyses

• SIP Canted Dimensions (needed for vehicle bulkhead design – is this 

included in SIP Outer Dimensions?) 

• SIP Surface Finish (sealing & Thermal & regolith mitigation & abrasion 

resistance)

• Vehicle vestibule equalization

• Ingress/egress controls and location (interior and exterior)

• 8.2 psid mobility (suitport operations, hatch latch, operation switches and 

controls, mate/demate umbilicals) 

• Hardware suit to vehicle restraints/equipment for nominal testing

o Minimizing flail

o For ingress/egress from suit

• Suitport Random Vibration and Dynamic Loads

o Hardware and suit restraints/equipment for vibration testing

• Suit/Tether attachment

• Dust mitigation and dust testing with simulants (dust into vehicle)

• Volume studies

o Suit Maintenance capability

 Nominal suit maintenance in rear-entry airlock

 Contingency suit maintenance in pressurized rover cabin

• Prebreathe protocol

• Need hardware and materials testing for flammability 

o In cabin and in rear-entry airlock/cabana volume

 Amount of suit leakage into cabana volume when used as suitport 

can build up 

• ECLSS and thermal testing
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• Failure scenarios

o Incapacitated crewmember through suitport

• Post operations analyses of systems for suit and vehicle (corrosion, buildup, mechanical wear, chemical wear, etc.)

B2.0 CAPABILITIES TO TEST ON-ORBIT

• Validate activities that were previously demonstrated on the ground prior 

to flight

• Test end to end operations of Suitport

o Insert ops con including performing EVAs 

• Test end to end operations of Rear-Entry Airlock 

o Insert ops con including performing EVAs

• Initial case: unstow suit, attach to suitport shirtsleeve for first time

• Ingress/egress controls and location (interior and exterior)

• Don/doff in microgravity (based on feasibility testing)

• 8.2 psid mobility (hatch latch, operation switches and controls, 

mate/demate umbilicals) 

• Intermodule integration (pressurize control and partial pressure control, 

reclamation air kept on module or in an accumulator for absolute pressure 

control?)

o ISS or other module

• Hatch (vestibule) within Hatch (internal hatch) or Internal Hatch between 

two suitport hatches or crawl through suitport hatch

• Hypoxia/VIIP

• Met Rate

• Prebreathe protocol validation

• Dust Mitigation (using simulant? At LDRO?) and mud room

• Suit Maintenance capability (suit checkout, suit recharge, wipe-down, 

ORU R&Rs)

• Hardware suit to vehicle restraints/equipment for nominal testing

o Minimizing flail

o For ingress/egress from suit

• Translation aids for ingress/egress

• Translation aids, tethering, etc. compatible with ISS

• Suit/Tether locations

• Tools stowage/attachment to suit 

• Porch and cabana ops

• Alignment for suit to suitport 

• Failure scenarios

o Emergency ingress via suitport

o Emergency ingress via rear-entry airlock 

o Emergency ingress with incapacitated crewmember through suitport 
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 Suit Restraints to facilitate pulling crewmember through suitport

o Emergency ingress with incapacitated crewmember via internal hatch 

or hatch within a hatch (assuming suitport ops); do we need internal 

umbilicals and panels for this? Crew lock on ISS does not have it.

o Emergency ingress with incapacitated crewmember through the rearentry airlock

• Post operations analyses of systems for suit and vehicle (corrosion, buildup, mechanical wear, chemical wear, etc.)
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APPENDIX C

CONCEPTUAL SUITPORT INTERFACE DESCRIPTION

C1.0 DRAFT CONCEPTUAL SUITPORT INTERFACE DESCRIPTION 

The following lists the initial interface description set from both the suit perspective 

and the vehicle perspective. 

C1.1 Space Suit

Microgravity Mobility with SIP Installed

Space suits should allow suited subjects within the anthropometric ranges to perform 

repeated circuits of the functional tasks shown in the Simulated Micro-g Functional 

Tasks Table without assistance in a simulated microgravity environment at EVA suit 

pressure. [EX-1026] 

Rationale: All tasks will be performed with the SIP, a cover layer and 

display and control module (or volumetric mock-up thereof) installed.

TABLE C-1 SIMULATED MICRO-G FUNTIONAL TASKS AT EVA PRESSURE

Task Name Description of Tasks to be Performed with Suit 

Pressurized to EVA Pressure

Visor Reach Controlled operation of sun visor open/close. Perform two 

complete cycles.

Shoulder Touch While standing, touch fingers of right hand to outside of left 

shoulder; hold for 5 sec. While standing, touch fingers of 

the left hand to outside of right shoulder; hold for 5 sec.

Wide Reach 

Translation

Demonstrate translation or slider bar that pushes laterally 

for 24 in. left and 24 in. right.

Hand-Over-Hand 

Translation

Demonstrate translation or pull loaded rope through ceiling 

mounted pulley.

Foot Restraint 

Ingress/Egress

Ingress and Egress the foot restraints

Pistol Grip Tool 

(PGT) Retrieve and 

Stow

Using body restraint tether mounted to square boss, stow 

PGT mock-up, rotate PGT/BRT combo to side and behind 

body, rotate PGT/BRT back to front, unstow PGT

Tether Point Reach Using large-small retractable tether, place large hook on 

waist tether point, connect small tether hook to each other 

tether point (in series)

Small Object 

Transfer

Controlled motion to relocate object (minimum size 8” cube) 

from knee height on right side of body to knee height on left 

side of body with feet in a fixed position in the Articulating 

Portable Foot Restraint (APFR).
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1-g Mobility with SIP Installed

Space suits should allow suited subjects within the anthropometric ranges to 

perform repeated circuits of the functional tasks shown in the 1-g Functional Tasks 

Table without assistance in a 1-g ambient environment at EVA pressure suit 

pressure. [EX-1027] 

Rationale: All tasks will be performed with the SIP, a cover layer and display 

and control module (or volumetric mock-up thereof) installed.

TABLE C-2 1-G FUNTIONAL TASKS AT EVA PRESSURE

Task Success Criteria

Single knee/single 

hand object pick-up

Controlled motion to kneel, lift 1.0lb object (minimum 

size 3”x2”x4”) with one-hand, controlled motion to 

standing while maintaining hold of object

Single knee/two 

hand object pick-up

Controlled motion to kneel, lift 2.0lb object (minimum 

size 8” cube) with two hands, controlled motion to 

standing while maintaining hold of object

Standing Toe 

Touch

Controlled motion down, touch fingers to top of each 

boot and rotate adjustment device, if present (may touch 

boot with hand of choice), controlled motion back to 

standing

Cross-body Reach While standing, grasp handle (or 1.0lb object) from 

approximate subject eye-height with two hands on 

subject’s left side, controlled motion to bring 

handle/object to subject’s knee height on right hand side 

at a distance of 1 foot to the right of the subject, 

controlled return to start position.

Single hand object 

floor to shelf

Controlled lean to side, grab small suitcase (with a mass 

of 4 lbs and a volume of 4” x 6” x 8”) with one hand, 

keeping object in same hand place on shelf at subject 

eye-height on opposite side of the body without taking a 

step, return to start position. Repeat for both sides of 

the body.

Walking Walk 20ft across level floor with stride length no less 

than 20% of unsuited subject stride length while walking

Visor Reach Controlled two-handed operation of sun visor 

open/close. Perform two complete cycles.

DCS Treatment Pressure Mobility with SIP Installed

Space suits should allow suited subjects within the anthropometric ranges to 

perform repeated circuits of the functional tasks shown in the Functional Tasks 
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DCS Treatment Pressure Table without assistance in a 1-g ambient environment 

at DCS Treatment suit pressure. [EX-1025] 

Rationale: All tasks will be performed with the SIP, a cover layer and 

display and control module (or volumetric mock-up thereof) installed.

TABLE C-3 1-G FUNTIONAL TASKS AT DCS TREATMENT PRESSURE

Task Name Description of Tasks to be Performed with Suit 

Pressurized to DCS Treatment Pressure

Operate Switches 

and Controls

Demonstrate operation of all switches and controls

Mate & Demate 

Umbilical

Mate and Demate the Umbilical 

Suit Hatch 

Operation

Cycle the rear hatch controls which includes: close, lock, 

unlock, and open twice using either hand while attached to 

a suitport simulator

Suitport

Space suits should be compatible with the operations outlined in EVA-EXP-0042, 

Exploration EVA SystemConcept of Operations Document. [EX-1008] 

Rationale: This is an interface need for exploration with a suitport 

compatible vehicle. Contractor will provide the SIP as part of the design.

PLSS Ports

Space suits should be packaged so that vacuum access port(s), O2 recharge port, 

electrical connection, cooling water inlet and cooling water return are on the 

forward facing PLSS surface. [EX-1028] 

Rationale: To ensure future Suitport compatibility, services which must 

be routed through the umbilical must face the front of the PLSS. 

SIP Interface

Space suits should interface with a Suitport Interface Plate (SIP). [EX-1029] 

Rationale: The suit to SIP interface is intended to be developed by the 

contractor and provided as a part of the RIDable content at PDR. The interface 

is expected to be both physical and structural. At a minimum the SIP will be 

supporting the weight of a 250 lb crewmember, the weight of the suit, and the 

plug load of a vehicle which is pressurized to 8.2 psi. The SIP is considered to 

be an internal interface to the space suit.
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Operating in O2 Environment

Space suits should operate in a 100% O2 environment at 8.2 psia. [EX-1014]

Rationale: Space Suits inherently have some amount of leakage. The 

suitport vestibule volume is small and suit leakage will enrich the vestibule 

environment during storage meaning that at startup, the external surfaces of 

the PLSS may be exposed to oxygen enriched environments of 100% O2. 

Additionally, if an off nominal leak develops inside the PLSS during an EVA, 

resulting in an EVA terminate or abort, a suitport ingress scenario would result 

in the PLSS being exposed to an elevated oxygen environment at the 

conclusion of the EVA. Therefore, the PLSS must be designed to operate with 

not only 100% O2 inside the vent loop but also with 100% O2 on all surfaces 

which would nominally be exposed to the cabin environment.

Pressurized Suitport Donning 

Space suits should be donnable by an unassisted crewmember while mounted to 

a suitport and pressurized to 8.4 psid (maximum). [EX-1017]

Rationale: This is required to support utilization of a Suitport on 

Exploration Class Vehicles with a cabin environment of 8.2 psi / 34% O2. 

During donning the interior of the suit will be exposed to the vehicle cabin 

pressure and the exterior will be at vacuum. For the purposes of this rationale

donning starts with the occupant in IVA clothing and is considered to be 

complete when the hatch is closed and all suit functions necessary to establish 

pressure integrity have been completed.

Pressurized Suitport Doffing

Space suits should be doffable by an unassisted crewmember while mounted to a 

suitport and pressurized to 8.4 psid (maximum). [EX-1018]

Rationale: This is required to support utilization of a Suitport on 

Exploration Class Vehicles with a cabin environment of 8.2 psi / 34% O2. 

During doffing the interior of the suit will need be equalized to the vehicle cabin 

pressure and the exterior will be at vacuum. For the purposes of this rationale, 

doffing starts with the suit docked to the suitport and the hatch closed. Doffing 

is considered to be complete when the occupant has completely egressed the 

suit and all hardware worn by the occupant is physically detached. 
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Suitport Hatch Clearance

Space suits should contain adequate cable/line length for all hardware which 

crosses the suit hatch parting line to allow it to rotate open while translating a 

minimum of 4 inches. [EX-1019]

Rationale: This is required to support utilization of a Suitport on 

Exploration Class Vehicles. Interfacing with past prototype exploration vehicles 

indicates that the hatch will not only have to rotate open but will also have to 

translate a minimum of 4 inches to clear the vehicle bulkhead and nearby 

hardware. 

C1.2 Space Suit Interfaces

Suitport SIP Proximity Sensors

Space suits should contain proximity sensors at the corners of the SIP. [EX-1020]

Rationale: This is required to support utilization of a Suitport on 

Exploration Class Vehicles. In the current suitport concepts, the proximity 

sensors are utilized to allow the vehicle to sense when the suit is fully engaged 

in the Suitport. 

Suitport Interface Plate Dimensions

Space suits should employ the use of a Suitport Interface Plate (SIP) that 

implements the features and keep out zones defined on drawing number 

CA2B11900 rev B in SIP Dimensions Figure. [EX-1021] 

Rationale: The geometry of the SIP must be defined to ensure a working 

interface with the suitport. Note that the 0.005 flatness spec in drawing 

CA2B11900 Rev B is only required in the keep-out zone areas, and elsewhere 

a flatness of 0.065 is allowed.
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FIGURE C-4 SIP DIMENSIONS
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Suitport Interface Plate Differential Deflection

Space suits should have a SIP to suitport sealing interface differential deflection of 

less than 0.020 inches when integrated with the suitport and pressurized to a 

maximum of 8.4 psid. [EX-1022] 

Rationale: Various loads are induced by the suitport, suit, PLSS, and 

crewmember that could impair an optimal SIP/suitport interface or suit 

function. SIP flatness, for example, must be maintained to ensure an adequate 

seal and function of suitport and hatch locking mechanisms. This, in 

conjunction with maintaining proper hatch latch function at 8.4 psid, may drive 

aspects of the SIP, hatch, or hatch locking mechanism design such as 

thickness and material selection, among others.

C1.3 Vehicle Interfaces

EVA Suit Protection on Suitport

The vehicle will provide protection (TBD) for suits stowed external to the vehicle. 

[VI-1029] 

Rationale: Suits stowed externally to the vehicle, e.g., Suitport, will be 

exposed to the EVA environment for periods of time far in excess of 624 

hours. Protection from the thermal, ionizing, and non-ionizing environment 

will contribute significantly to the life of the suit. Resolution of the 

environmental protection (TBD) will provide the degree of protection afforded. 

C2.0 FORWARD WORK ITEMS 

The table Forward Work Items lists the specific items in the document that are 

not yet known, need to be discussed, or added to the document.

TABLE C2-1 FORWARD WORK ITEMS

Item Section Description

Reference 

Documents

Documents or studies referred to in the 

document need to be listed at the front of 

this document.

Suitport Ops 

Con

Update operational concepts in EVA-REF004, Exploration EVA Capabilities and 

Operational Concepts Document.

Additional Suit 

Related 

Interfaces

Forward work could include the following:

Umbilical design for Vacuum access in a 

contingency case
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Tightening gloves & boots after donning

Leakage (SIP to suit)

SIP Mass support of crew and suit weight 

SIP thermal insulation from rest of suit 

SIP seal at suit/SIP interface 

SIP hatch lock/unlock mechanism operation 

Additional 

Suitport 

Interfaces

Forward work could include the following:

Radiation, Thermal (cabana assumptions for 

protection)

SIP Canted Dimensions (needed for vehicle 

bulkhead design – is this included in SIP 

Outer Dimensions?)

SIP Surface Finish (sealing & Thermal & 

regolith mitigation & abrasion resistance) 

Dust into the vehicle 

Vehicle vestibule equalization

Suitport Random Vibration and Dynamic 

Loads

SIP seal leakage

Long Duration Pressurized Materials Creep

Particulate 

Control in 

Suitport, 

Planetary 

Protection, 

Crew Health, 

and Sample 

Contamination

Dust infiltration/contaminant control/cleaning 

techniques/venting.

Space suits should limit the concentration in 

the suitport vestibule atmosphere of 

particulate matter ranging from 0.5 μm to 10 

μm (respirable fraction) in aerodynamic 

diameter to <1 mg/m3 and 10 μm to 100 μm 

to <3 mg/m3.

Rationale: Inhalation of particulates can 

cause irritation of the respiratory system. 

Limits for particulates are based on 

Occupational Safety and Health 

Administration (OSHA) standards for 

nuisance dusts, which is the best analog for 

the ordinary dust present in spacecraft. This 

does not include reactive dust (e.g., LiOH). 

Reference CCT-REQ-1130 ISS Crew 

Transportation and Services Requirements 

Document Revision A.
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APPENDIX D

HATCH AND AIRLOCK HISTORY

Vehicle;

Yrs of service Visual Shape # of Hatches Dimensions Type of EVA Life Support Source

Voskhod 2 

Volga Airlock 

(USSR);

1965

2 small hatches EVA hatch: 26 in 

diameter

Umbilical; TBD 

open or closed 

loop

See Appendix C 

of EVA-EXP-0031

Gemini 

(USA);

1962-1966

2 (Docking and 

EVA)

EVA hatch: 1ft 3 in 

deep x 4ft 3 in long 

x 3 ft 1 in wide

Umbilical; closed 

loop, unganged

See Appendix C 

of EVA-EXP-0031

Apollo Crew 

Module 

(USA);

1963-1972

2 (Docking and 

EVA)

EVA Unified Hatch 

@ 23.2 in x 29 in x 

34 in

Umbilical; open 

loop, unganged

See Appendix C 

of EVA-EXP-0031

Apollo Lunar 

Module 

(USA);

1969-1972

2 (Docking and 

EVA)

EVA hatch: 32 in 

square

PLSS See Appendix C 

of EVA-EXP-0031

Skylab A/L - 

used Gemini 

hatch (USA);

1973-1974

2 (Docking and 

EVA)

EVA hatch: 1ft 3 in 

deep x 4ft 3 in long 

x 3 ft 1 in wide

Umbilical; open 

loop

See Appendix C 

of EVA-EXP-0031

Shuttle A/L 

(USA);

1983-2011

2 EVA hatches

40 in diameter, 

(one flat side 

minimum 

dimension of 36 in)

PLSS See Appendix C 

of EVA-EXP-0031

Mir – 

Transfer 

Compartment 

Node Module 

(USSR/RS)

1986-2001

5 Docking/ 

Berthing Ports 

(Prior to Kvant 2, 

no EVA hatches, 

but they could 

egress through 

any of the 5 

ports)

TBD Assuming 

hatch is similar to 

Docking hatches: 

31.49 in (800 mm)

PLSS See Appendix C 

of EVA-EXP-0031

Mir Airlock – 

Kvant 2 

(USSR/RS)

1989-2001

2+ EVA hatch: 39.37 

in (1m) PLSS See Appendix C of EVA-EXP-0031

~29.0”

~34.0”

~23.2”

~Ø39” 

36” straight

Ø40” diameter 

~Ø26” (only 

used once then 

disposed)

32.0”

32.0”

~51.0”

~37"

~15”

~51.0”

~37"

~15”

~Ø31.5” 
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Vehicle;

Yrs of service Visual Shape # of Hatches Dimensions Type of EVA Life Support Source

ISS CBM 

(USA)

1998-present

Common 

Berthing 

Mechanism 

hatches (many)

50 in x 50 in None SSP 41004 Part 1 

Rev H

ISS USOS 

Quest A/L 

(USA)

2001-present

1 Nominal EVA 

hatch; 1 

Contingency EVA 

hatch

Nominal EVA 

Hatch: 40 in 

diameter, (one flat 

side minimum 

dimension of 36 in)

PLSS See Appendix C 

of EVA-EXP-0031

ISS RSOS 

Docking 

Compartment 

DC1 - Pirs 

(RS)

2001-~2017

4

2 EVA hatches: 

39.47 in (1m)

Docking hatch: 

31.49 in (800 mm)

Module hatch: 43.3 

in (1100mm) 

PLSS See Appendix C 

of EVA-EXP-0031

ISS RSOS 

Zvezda 

Transfer 

Compartment

(RS)

2001-present

3

To Functional 

Cargo Block 

(FGB): 31.49 in 

(800mm) 

To Pirs: 43.3 in 

(1100mm) 

To Poisk: 43.3 in 

(1100mm) 

Contingency Only See Appendix C 

of EVA-EXP-0031

ISS RSOS 

MRM2 - Poisk 

(RS) 

2009-present

4

2 EVA hatches: 

39.47 in (1m)

Docking hatch: 

31.49 in (800 mm)

Module hatch: 43.3 

in (1100mm) 

PLSS See Appendix C 

of EVA-EXP-0031

Orion and 

TBD NDS/IDA 

Docking 

hatches

1 Docking

Docking hatches: 

31.49 in (800 mm) 

transfer 

passageway inside 

petals

None planned as 

of 2015; future ops 

may change

IDSS 

(International 

Docking System 

Standard) IDD 

Rev D Final 

043015

Node Module 

UM (Docking 

Ball) - (RS)

6 (5 module 

hatches and 1 

vehicle hatch)

5 module hatches: 

43.3 in (1100mm)

1 vehicle hatch: 

31.49 in (800 mm), 

Nadir position 

None planned as 

of 2015; future ops 

may change

TBD

Orion Side 

Hatch (USA)

1 (possible 

contingency EVA)

24.9 in x 32.1 in 

height x 32.6 in

None planned as 

of 2015; future ops 

may change

MPCV 72000 

SRD Rev C

36” straight

Ø40” diameter 

~Ø31 
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National Aeronautics and Space Administration

Historical Airlock and EVA Hatches

September 17, 2015
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Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Voskhod

• Voskhod Airlock (1965)

– Inflatable airlock (24 min tethered 

spacewalk; airlock jettisoned after 

use)

– 1st EVA in history, by Alexei Leonov

(only EVA)

– Double-walled fabric airlock tube 

(name – Volga)

• Length: 2.50 m (8.2 ft)

• 1.2 m (3.9 ft) wide metal upper ring 

that fit over Voskhod’s inwardopening airlock hatch 65 cm (26 in) 

wide

• Inward opening EVA hatch

– Internal volume 2.50 m3 (88 ft3) 

3

Alexi Leonov first EVA on 3/18/65

NASA

Source/References:

1. NASA RP 1357 Mir Hardware Heritage

2. Walking to Olympus: An EVA Chronology

Image from museum
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Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Gemini Capsule

• Gemini Capsule – (comprised of three 

modules: reentry, retro, and equipment)

– Enlargement of the Mercury capsule

– Length: 5.8 m (19 ft)

– Diameter: 3 m (10 ft)

– Weight: 3851 kg (8490 lb)

– Habitable Volume: 2.55 m3 (90 ft3)

– Two hatches (crew of 2) (outward opening hatch)

• EVA hatch dimensions

– 1ft 3 in deep x 4ft 3 in long x 3.1 ft 1 in wide

• Reentry Module

– Length: 3.4 m

– Maximum diameter: 2.3 m

– Habitable Volume: 2.55 m3 (90 ft3)

– Total Mass: 1982 kg (4370 lb)

• Total EVAs performed

– 9 EVAs

4

EVA Hatch – from Gemini IV

http://airandspace.si.edu/collections/artifact.cfm?object=nasm_A19680035000

Ed White: 

1st US EVA on 6/3/65, NASA

Sources/References: 

1. http://science.ksc.nasa.gov/history/gemini/geminispacecraft.txt

2. http://www.nasa.gov/audience/forstudents/k4/stories/what-was-gemini-program-k4_prt.htm

3. http://www.braeunig.us/space/specs/gemini.htm

4. Walking to Olympus: An EVA Chronology
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Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Apollo Lunar Module

• Dimensions

– Overall height: 7 m (22 ft 

11 in), legs extended

– Width: 9.4 m (31 ft), 

diagonally across extended 

landing gear

– Maximum diameter: 4.3 m 

(14.1 ft)

– Habitable volume: 4.5 m3

(160 ft)

– Crew compartment: 2.35 m 

diameter x 1.07m long

– Total mass: 15,200 kg 

(33,510 lb) for H-series 

[16,440 kg (36,244 lb) for 

J-series], with crew and 

propellant

• Ascent Stage

– Height: 3.76 m (12 ft 4 in)

– Diameter: 4.29 m (14ft 1 

in)

• Descent Stage (unmanned 

portion)

– Height: 3.23 m (10 ft 7 in)

– Diameter: 4.22 m (13 ft 10 

in)

5

Sources/References:

1. SNA-8-D-027(III) Rev 2, CSM\LM Spacecraft Operational Data Book Volume III Mass 

Properties

2. NASA/TP-2010-216131: Worldwide Spacecraft Crew Hatch History

3. https://airandspace.si.edu/exhibitions/apollo-to-the-moon/online/apollo-11/about-thespacecraft.cfm

4. http://www.braeunig.us/space/specs/lm.htm

5. Apollo News reference – Lunar Module Quick Reference Guide published by Grumman

6. http://www.hq.nasa.gov/office/pao/History/alsj/frame.html
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 130 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

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Extravehicular

Activity 

Management 

Office

Apollo Lunar Module 

(cont.)

• Flight History

– First flight: 22-Jan-1968; first manned 

flight 3-Mar-1969 (Apollo 9) 

– Last flight: 7-Dec-1972 (Apollo 17) 

– Number of manned flights: 9 

– Crew size: 2 

– Hatch: 32 in (square), required 

complete depress of cabin for EVA

• Total EVAs performed

– 20 EVAs

• On Lunar surface: 15

• From Command Module: 5

6

Apollo 11 – Buzz Aldrin egress LM (AS11-40-5863), NASA

http://spaceflight.nasa.gov/gallery/images/apollo/apollo11/h

tml/as11-40-5863.html

Apollo 9 – David Scott egress CM (AS09-20-3064), 

NASA

http://spaceflight.nasa.gov/gallery/images/apollo/apollo9/

html/as09-20-3064.html

Source/Reference:

1. http://www.nasa.gov/directorates/s

omd/reports/eva.html
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 131 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

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Extravehicular

Activity 

Management 

Office

Skylab

• Airlock Module (comprised of STS and 

radiators, Tunnel Assembly, Flexible Tunnel 

Extension, and Support Truss Assembly)

– Gross wt: 15,166 lb (launch weight)

– Working volume: 610 ft3

– Overall length: 5.4 m (211.54 in)

– Diameter: 3 m (10 ft)

• Structural Transition Section (STS)

– Length: 47 in

– Diameter: 120 in (provided transition from 120-in 

diameter to 65-in diameter to mate with tunnel 

assembly)

– Enclosed volume: 288 ft3

• Tunnel Assembly

– Length: 153 in

• Forward compartment -31 in (support for stowage 

containers, tape recorders, and misc. equipment)

• Center (lock) compartment – 80 in (included a 

modified Gemini crew hatch for ingress/egress 

during EVA). Hatch was outward opening

• Aft compartment – 42 in (housing to OWS 

environmental control system)

– Diameter: 65 in

– Volume: 322 ft3

• Center (lock) compartment – 170 ft3

7

Sources/References:

1. MSFC Airlock Final Technical Report (MDC E0899 

Volume 1/NASA TM X-64810)

2. SP-400 Skylab, Our First Space Station -

http://history.nasa.gov/SP-400/contents.htm

3. http://www.astronautix.com/craft/skylab.htm

4. Walking to Olympus: An EVA Chronology

Skylab artist’s concept illustrating cutaway view 

of Skylab Airlock Module: NASA
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 132 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 133 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 134 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

MIR

10

• EVA hatch was outward opening (for Kvant 2) 

• Mir base block 

– Gross Mass: 21,000 kg (46,000 lb)

– Height: 13.13 m (43.07 ft)

– Span: 29.73 m (97.53 ft) – solar arrays

– Maximum diameter: 4.15 m

– Habitable Volume: 90 m3

• Mir complex (Mir base block – Kvant, Kvant 2, 

and Kristall) with docked Soyuz-TM and 

Progress –M spacecraft (as of 11/15/94)

– Weight: 93, 649 kg (206,461 lb) 

– Length: 33m

– Height: 13.13 m (43.07 ft)

– Maximum diameter: 4.35 m (habitable modules)

– Habitable Volume: 372 m3

Sources/References:

1. NASA RP 1357 Mir Hardware Heritage

2. http://www.astronautix.com/craft/mir.htm
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 135 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

MIR (Cont.)

• Mir Airlock – Kvant

– Weight: 9,600 kg

– Length: 5.8 m

– Maximum diameter: 4.15 m

– Habitable volume: 40 m3

• Mir Airlock – Kvant 2 (top of stack)

– Launch weight – 19, 565 kg

– Length: 13.73 m

– Diameter: 4.35 m

– Habitable volume: 61.3m3

– EVA Hatch size: 1m (39.37 in)

• EVAs

– Total performed: 75

• Outside Mir: 72

• Inside Spektr Module (IVA): 3

Source/Reference:

1. http://www.nasa.gov/directorates/somd/reports/eva.html

• Mir was gone by early 2001 as ISS 

was growing in orbit. Mir was 

deorbited on March 23, 2001.

11

Mike Foale: Mir-23 & Mir 24 (5/97), view of Mir space station airlock 

including Orlan suits

http://spaceflight.nasa.gov/history/shuttle-mir/multimedia/mphoto.htm

Linenger: Mir-22 & Mir 23 (1/97), exit hatch in Kvant-2 primary airlock

http://spaceflight.nasa.gov/history/shuttle-mir/multimedia/linengerphotos/linenger-p-008.htm
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 136 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

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ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

ISS Airlock

12

• ISS Airlock

– Equipment lock stores spacesuits and 

equipment, the Crew Lock is 

depressed for ingress/egress (design 

based on Shuttle airlock)

– Length: 5.5 m (18 ft)

– Diameter: 4m (13.1 ft)

– Volume – 34m3

– EVA Hatch size: 40 in diameter (one 

flat side minimum dimension of 36 in)

• Inward opening EVA hatch

– Total mass: 9932 kg (21,877 lb)

• Total EVAs performed to 

construct/maintain ISS

– 188 EVAs (as of Expedition 44, 

8/10/15)

• From docked Space Shuttle: 28

• From ISS Airlock: 112

• Russian EVAs: 48 

View from Shuttle Atlantis on STS-110, NASA

Sources/References:

1. https://www.nasa.gov/mission_pages/station/structure/elements/q

uest.html

2. http://www.nasa.gov/directorates/somd/reports/eva.html

3. Reference Guide to the International Space Station, Utilization 

Edition July 2015
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 137 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 138 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

ISS Russian Airlocks

• Russian Docking Compartment (DC) 

and Airlock Pirs (Pier)

– Provide the capability for EVA using 

Russian Orlan suits. 

– Provide contingency capability for 

ingress for US EMU EVAs. 

– It also has a docking system with a port 

for docking of Soyuz and Progress 

logistics vehicles. 

– Launched in and docked to ISS in 2001. 

– Plan is for it to be detached and 

jettisoned and replaced with a Russian 

Multi-Purpose Logistics Module (current 

timeline is 2017).

• Pirs

– Length: 4.9 m (16 ft)

– Maximum diameter: 2.55 m (8.4 ft)

– Mass: 3,838 kg (8,461 lb)

– Volume 13 m3 (459 ft3)

– Two identical EVA hatches 1m (39.37 

in) diameter – Inward opening EVA 

hatches

• Total EVAs performed from Pirs (as 

of Expedition 44, 8/10/15)

‒ Total: 46

14

NASA ISS017e011287:

Pirs Airlock

Sources/References:

1. https://www.nasa.gov/extern

alflash/ISSRG/pdfs/russiand

ocking.pdf

2. http://www.nasa.gov/director

ates/somd/reports/eva.html

3. Reference Guide to the 

International Space Station, 

Utilization Edition July 2015

NASA ISS009-E-17168:

Pirs Docking Compartment with Orlan 

Spacesuits
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 139 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

ISS Russian Airlocks

• Russian Mini-Research Module 

(MRM) 2 and Airlock Poisk (Explore)

– Is almost identical to Pirs Docking 

Compartment

– Additionally provides systems for 

servicing and refurbishing of the Orlan 

suits

– Allows extra space for scientific 

experiments including power supply 

outlets and data transmission interfaces 

for two science payloads

– Launched in 2009

• Poisk

– Length: 4.9 m (16 ft)

– Maximum diameter: 2.55 m (8.4 ft)

– Mass: 3,795 kg (8,367 lb)

– Volume 14.8 m3 (523 ft3)

– Two identical EVA hatches 1m (39.37 

in) diameter – Inward opening EVA 

hatches

15

Poisk Airlock

Source/References:

1. https://www.nasa.gov/externalflas

h/ISSRG/pdfs/MRM2.pdf

2. Reference Guide to the 

International Space Station, 

Utilization Edition July 2015

Poisk Airlock: after arriving at ISS 

(November 2009)

• No EVAs have been 

performed out of 

Poisk

‒ Current plan is for 

Russian EVAs to be 

performed from 

Poisk once the 

Russian MPLM is 

integrated with ISS
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 140 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

ISS Russian Airlocks

• Transfer Compartment

– Located on the forward port of the service 

module Zvezda (integrated with service module)

– Serves as the location for docking to other 

modules/spacecraft

– Used as an airlock for Russian EVAs 

(contingency)

• Hatches (at the three docking ports) –

inward opening

– To Functional Cargo Block (FGB): 1100mm (43.3 

in)

– To Pirs (1100mm) 43.3 in

– To Poisk (1100mm) 43.3 in

16

Source/References:

1. Zvezda Press Kit, 

July 7, 2000

2. Reference Guide 

to the International 

Space Station, 

Utilization Edition 

July 2015

NASA ISS032e020830: Interior of 

Zvezda Transfer Compartment

NASA ISS020e007223: Zvezda

Transfer Compartment with no 

airlocks attached

NASA ISS017e11097: Zvezda

Transfer Compartment with Pirs

airlock and Soyuz attached

• Transfer Compartment as 

Airlock

‒ Only EVA was 19 min 

on Expedition 2 (never 

left module)

‒ Internal spacewalk prep 

for arrival of Poisk on 

Expedition 20
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 141 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

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Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Vehicle Consumables

• The following slides address the question of “Per a single ISS EVA, what is the 

total consumables impact?”

• The methodology used to determine this is as follows:

– The following numbers are calculated per EMU, per EVA

– Since ISS uses a 2-Crew for any US EVA as a rule, we would double these values in order to 

determine the total Program impact of a given EVA

– These values are based upon Certification Specs and then compared to Actuals using JSCMOD’s On-Orbit Tracker (OOT) record of actual flight notes

• The EVA Console team (JSC-CX) records EVA Consumable Actuals as a matter of course during pre-post 

EVA servicing events

• These “Internal Notes” were mined from OOT by JSC-XX as a data reference

– Though Loop Scrubs are typically Calendar Driven (due every 90 days) they must also be 

conducted within at least two weeks of a given EVA

• Thus, for this data set, we assume that at least 1 Loop Scrub can be attributed to a given EVA on average.

• It is known that in some cases it is higher, in some lower (depends on how regularly EVA’s are being done 

which changes through time based upon the “health” of ISS and other operational variations such as 

External Payloads utilization. 

• This is a working assumption that is analytically inserted into the bottom line summary and could be easily 

changed in the calculations spreadsheet given superior rationale

– Battery recharges include EMU Battery, REBA Battery, Helmet Light Battery, PGT Battery

• It is known that the L-REBA battery displaces the need for stand-alone Helmet Light Batteries, but the total 

amount of energy used is the same

17
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 142 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Vehicle Consumables

• Per a single ISS EVA, what is the total consumables impact?”

– _58.25_ hrs. of Crew Time is required on average to prep the EVA System (pre EVA)

• Beginning prior to the EVA itself, Tools Logistics, Procedure Review, etc (everything up to EVA prep on 

EVA day)

– _12.25_ hrs. of Crew Time is required on average for OFV

– _12.42_ hrs. of Crew Time is required on average for EVA prep

• On EVA day minus time out EVA – includes 2 EV and 1 IV)

– _0.9_ lbm O2 per suit per IV Activity - ALCLR (Loop Scrub)

– _0.15_ lbm O2 per suit per IV Activity – On-Orbit Fit Verification (OFV)*

– _5.13_ lbm O2 ISLE Prebreath Protocol gas loss per suit/crewmember

– _1.0_ lbm Air residual Airlock depress gas loss

– _0.80_ lbm O2 per suit for post EVA recharge

– EVA Consumables lost during the EVA itself

• _0.89_ lbm O2 per suit per EVA (lost to EMU Suit Leaks and Met Rate)

• _4-6_ lbm H20 assumed per suit per EVA (Sublimator Cooling Water recharge, ullage)

• _2_ lbm (32 oz) H20 drinking water per Crew per EVA**

• _____ W*h Battery Recharge (post EVA)

• _____ W*h MetOx Regen Oven (post EVA)

• _6:39_ h Crew Time of the EVA itself (time not spent doing other things)

– _15.83_ hrs. of Crew Time is required on average for post EVA servicing

• After the EVA itself, cleaning the EMU, re-stowing all components and tools, recharge/refill operations, etc

*OFV’s only occur once per crew for their time on orbit, NOT every EVA a given crew member conducts

** Drinking water is not actually tallied in the bottom line summary b/c it would have otherwise been consumed with or without the 

EVA by the human

18
Revision: Baseline Document No: EVA-EXP-0031

Release Date: 04/18/2018 Page: 143 of 143

Title: EVA Airlocks and Alternative Ingress Egress Methods Document

The electronic version is the official approved document.

ECCN Notice: This document does not contain export controlled technical data.

Pre-decisional, For Internal Use Only

Extravehicular

Activity 

Management 

Office

Vehicle Consumables

• Representative screenshot (portion)from excel file on O2 consumables

19