Minimum Functionality Lunar Habitation Element

Home , First Lunar Outpost, Peary (crater), Sodium tail of the Moon, Space habitat (facility)

The University of Maryland Space Systems Laboratory

Dr. David L. Akin Massimiliano Di Capua Adam D. Mirvis Omar W. Medina William Cannan Kevin Davis

July 2009 ABSTRACT

Title: MINIMUM FUNCTIONALITY LUNAR HABITATION ELEMENT

Dr. David L. Akin, Massimiliano Di Capua, Adam D. Mirvis, Omar W. Medina, William Cannan, Kevin Davis

University of Maryland - Space Systems Laboratory February 2009

NASA’s vision for the future of space exploration includes the establishment of a permanent human presence on the Moon through the Constellation program. Under the auspices of the NASA Exploration Systems Mission Directorate, the University of Mary- land Space Systems Laboratory has investigated, through literature reviews, a survey, and rigorous statistical methods, the definition of Minimal Functionality Habitation Element for medium duration lunar missions. By deploying a survey and making use of the Analyt- ical Hierarchy Process (AHP) and the Quality Function Deployment (QFD) methods, the study team determined a list of functions and their relative importance, as well as their impact on systems design/implementation. Based on the past literature and the survey results, four habitat concepts were proposed, focusing on interior space layout and preliminary systems sizing. Those concepts were then evaluated for habitability through virtual reality (VR) techniques and merged into a single design. Trade studies were conducted and the final design was defined. A full-scale functional mockup of the final concept was also implemented to enable more realistic human factors studies and to validate the VR techniques used previously. This study was funded by the NASA Exploration Systems Mission Directorate (ESMD). BAA: NNJ08ZBT002, Topic 2. This is the final report for NASA Grant NNJ08TA89C. Acknowledgments

The University of Maryland Space Systems Laboratory wishes to thank all who participated in our survey, especially the American and Italian Navies, whose extensive cooperation allowed us to acquire important data for our study. We also wish to thank Heather Bradshaw for all her help in setting up and conducting the data acquisition session at the Mars Society - Mars Desert Research Station (MDRS). We also wish to thank MDRS Crew 73 for participating in our study. Finally, special thanks go to the all the SSL personnel whose help, particularly in creating a full-scale habitat mockup outdoors in the coldest January in recent memory, was priceless. This study was funded by the NASA Exploration Systems Mission Directorate (ESMD), under BAA NNJ08ZBT002, Topic 2. We would like to acknowledge and thank Larry Toups, NASA COTR, supported by Marianne Rudisill and Kriss Kennedy, along with Chris Culbert (ESMD Surface Systems lead) and his deputy, Matt Leonard, for all of their help and support. Finally, we would also like to express our appreciation for all of the NASA and contractor personnel who participated in design reviews and the ﬁnal brieﬁng, for their excellent questions and even better advice and support.

ii Contents

List of Abbreviations xiii

1 Introduction 1 1.1 Background ...... 1 1.2 Research Approach ...... 2 1.3 Milestones and Deliverables ...... 3

2 Review of Relevant Literature and Research 4 2.1 Regions for Possible Landings ...... 4 2.2 Lunar Temperature Range ...... 7 2.3 Ionizing Radiation ...... 8 2.4 Micrometeoroid Impact ...... 8 2.5 Habitability in Conﬁned and Austere Environments ...... 9 2.6 Past Designs ...... 15

3 Data Acquisition 18 3.1 Use of the Analytical Hierarchy Process ...... 18 3.2 AHP Implementation ...... 19 3.3 AHP Data ...... 22 3.4 AHP Analysis and Conclusions ...... 22 3.4.1 AHP Data Analysis ...... 22 3.4.2 Importance Value Conclusions ...... 28 3.5 Statistical Analysis ...... 28 3.5.1 Fidelity of Analogue Environments ...... 30 3.6 Quality Function Deployment ...... 30 3.7 Lessons Learned ...... 33

4 Preliminary Concepts 35 4.1 General Requirements from BAA ...... 35 4.1.1 General Requirements List ...... 35 4.1.2 Contract Deliverables ...... 36 4.2 Concept Development Approach ...... 36 4.3 Initial Concept ...... 37 4.3.1 EVA Support ...... 37 4.3.2 Structure ...... 38 4.3.3 Radiation Shielding ...... 38 4.3.4 Life Support ...... 38 4.4 Concept 1 : The Lunar Pup-Tent ...... 42 4.4.1 Operational Scenario ...... 42

iii 4.4.2 System Concept ...... 42 4.4.3 Interior Layout ...... 43 4.4.4 Life Support ...... 43 4.4.5 Avionics, Power, Thermal, and Communications ...... 44 4.4.6 Structure and Storage ...... 45 4.5 Concept 2 : The Winnebago ...... 46 4.5.1 Operational Scenario ...... 46 4.5.2 Design Concept ...... 46 4.5.3 Pressurization and Furnishing ...... 46 4.5.4 Interior Layout and SPE Shelter ...... 47 4.5.5 Life Support ...... 48 4.5.6 Avionics, Power and Thermal ...... 49 4.5.7 Exterior Layout and EVA ...... 49 4.6 Concept 3 : The Igloo ...... 50 4.6.1 Operational Scenario ...... 50 4.6.2 System Concept ...... 50 4.6.3 Habitat Layout ...... 51 4.6.4 Structure ...... 52 4.6.5 Life Support ...... 52 4.6.6 Power ...... 53 4.6.7 Avionics ...... 53 4.6.8 Additional Equipment ...... 53 4.6.9 Summary ...... 53 4.7 Virtual Reality Testing and Evaluation ...... 54 4.7.1 Equipment ...... 54 4.7.2 Lessons Learned ...... 55

5 Conﬁguration Trade Studies 57 5.1 Analytical Modeling ...... 57 5.2 Trade Studies ...... 60

6 Mockup Design Construction and Testing 65 6.1 Design and Construction ...... 65 6.2 ECLIPSE Crew I: Mission Report ...... 70 6.3 Lessons Learned ...... 72

7 Final Design: ECLIPSE 77 7.1 Configuration ...... 77 7.1.1 Exterior Configuration ...... 77 7.1.2 Interior Layouts ...... 82 7.1.3 Configuration Growth Options ...... 83 7.2 Life Support Systems ...... 84 7.2.1 Basic Assumptions ...... 84 7.2.2 EVA Support Requirements ...... 85 7.2.3 Air Circulation ...... 86 7.2.4 CO2 Capture ...... 87 7.2.5 Air Revitalization ...... 89 7.2.6 Air Replenishment ...... 90 7.2.7 Water Reclamation ...... 90

iv 7.2.8 Food Storage and Preparation ...... 91 7.2.9 Waste Management ...... 91 7.2.10 Logistics and Storage ...... 91 7.2.11 Lighting ...... 92 7.3 Power Budgets ...... 93 7.4 Thermal Control ...... 93 7.5 Mass Budgets ...... 95

8 Conclusions and Future Work 99 8.1 Conclusions ...... 99 8.2 Future Work ...... 99 8.2.1 Mars Society Crew 73 Data Acquisition Preview ...... 99 8.2.2 Potential Future Analytical Studies ...... 100 8.2.3 Future Mockup Development and Testing ...... 100

A Web Survey Screenshots 104

B ANOVA tables 114

C Renovated ECLIPSE Interior Conﬁguration 126 C.1 Lower Level ...... 126 C.2 Upper Level ...... 127 C.3 Exterior Views ...... 128

D Partial Gravity Simulations of Habitat Habitability Issues 129 D.1 Underwater Simulation of Partial Gravity ...... 129 D.2 Upper Berth Ingress/Egress Study ...... 129 D.3 Intralevel Motion Study ...... 130

E Alternative ECLIPSE Interior Conﬁgurations - Academic Leverage of ESMD Study 133 E.1 Team Alpha ...... 133 E.2 Team Beta ...... 134 E.3 Team Gamma ...... 134 E.4 Team Delta ...... 135 E.5 Final Discussion ...... 136

v List of Tables

2.1 Lunar Regolith Composition ...... 4

2.2 In-Situ Resource Utilization ...... 6

2.3 NASA Radiation Limits ...... 10

2.4 Habitat Space Allocation as a Function of Time Spent in that Area . . . . . 12

2.5 Characteristics of Past Lunar Habitat Designs ...... 16

3.1 Example AHP matrix ...... 19

3.2 AHP survey data page 1 ...... 23

3.3 AHP survey data page 2 ...... 24

3.4 Subjective assessment weights ...... 24

3.5 Importance values ...... 25

3.6 Consistencies ...... 27

3.7 Demographics of Survey Respondents ...... 28

3.8 Statistically Signiﬁcant Variances to 95% Conﬁdence ...... 29

3.9 QFD Matrix ...... 31

3.10 QFD Top Twenty Design Feature Importance Values ...... 32

4.1 Concept 1: Mass and Power Budget ...... 43

4.2 Concept 2: Mass Budget ...... 47

4.3 Concept 3: Mass and Power Budget ...... 51

7.1 Lighting Allocations for ECLIPSE Habitat ...... 92

7.2 Power Usage Summary ...... 93

vi 7.3 Summary of Habitat Thermal Cases ...... 95

7.4 Structural Mass Estimates ...... 96

7.5 Crew Accommodations Mass Estimates ...... 96

7.6 Fixed Life Support Mass Estimates ...... 97

7.7 Consumables Mass Estimates ...... 97

7.8 Top-Level Mass Estimates ...... 97

B.1 Arctic/Antarctic base ANOVA - Table 1 ...... 114

B.2 Arctic/Antarctic base ANOVA - Table 2 ...... 115

B.3 Ship Crew ANOVA - Table 1 ...... 116

B.4 Ship Crew ANOVA - Table 2 ...... 117

B.5 Submariner ANOVA - Table 1 ...... 118

B.6 Submariner ANOVA - Table 2 ...... 119

B.7 American ANOVA - Table 1 ...... 120

B.8 American ANOVA - Table 2 ...... 121

B.9 Italian ANOVA - Table 1 ...... 122

B.10 Italian ANOVA - Table 2 ...... 123

B.11 French ANOVA - Table 1 ...... 124

B.12 French ANOVA - Table 2 ...... 125

vii List of Figures

2.1 Past Landing Sites ...... 5

2.2 Lunar Surface Temperature ...... 7

2.3 Micrometeoroid Impact Flux on the Lunar Surface ...... 8

2.4 Micrometeoroid Impact Mass on the Lunar Surface ...... 9

2.5 Temperature Zones for Man in an Enclosed Environments [11] ...... 10

2.6 Functional Areas by Noise Level and Privacy Level [1] ...... 11

2.7 Interactions Between Diﬀerent Activities [14] [15] ...... 13

2.8 Combined Habitability Approach: Zoning, Unit and Flow [15] ...... 13

2.9 Morale during Mission [16] ...... 14

2.10 Habitat Volume vs Mission Duration ...... 15

2.11 Habitat Volume vs Mission Duration ...... 17

3.1 Example multi-level AHP hierarchy ...... 20

3.2 Final survey hierarchy ...... 21

3.3 Cumulative importance values ...... 26

3.4 QFD Notional Diagram ...... 30

3.5 Design Feature Importance Values ...... 33

4.1 Initial Concept Section ...... 37

4.2 Comparison of Open and Closed Loop Water Systems ...... 39

4.3 Comparison of Expendable and Reusable CO2 Collection Systems . . . . . 39

4.4 Comparison of CO2 Disposal and Reuse ...... 40

viii 4.5 Comparison of ESM Performance of 28- and 180-day Optimal Systems . . . 41

4.6 Pup-Tent Dimensions ...... 42

4.7 Pup-Tent Interior ...... 44

4.8 Pup-Tent Folding ...... 45

4.9 Winnebago Dimensions ...... 46

4.10 Winnebago Interior...... 48

4.11 NASA’s incremental build strategy (Source: NASA ESAS [5]) ...... 50

4.12 Igloo Dimensions ...... 51

4.13 Igloo Interior ...... 52

4.14 VR Equipment ...... 54

4.15 Concept 1 VR ...... 55

4.16 Concept 2 VR ...... 55

4.17 Concept 3 VR ...... 56

5.1 Concept of "Habitable Space" Internal to a Horizontal Cylinder of Varying Diameters ...... 58

5.2 Deﬁnition of Parameters for Habitable Volume/Area Analysis ...... 60

5.3 Total Habitat Volume vs. Cylindrical Diameter (η=0.25) ...... 61

5.4 Habitatable Volume vs. Cylindrical Diameter (η=0.25) ...... 61

5.5 Habitatable Volume vs. Cylindrical Diameter with Multiple Floors (η=0.25) 62

5.6 Structural Mass vs. Cylindrical Diameter (η=0.25) ...... 62

5.7 Structural Mass vs. Available Habitable Area ...... 63

5.8 Structural Mass vs. Available Habitable Volume ...... 63

5.9 Structural Mass vs. Total Volume ...... 64

6.1 SSL Outdoor Mockup Storage Facility ...... 66

6.2 Porthole Ingress/Egress ...... 67

6.3 Day 1 - Power Washer ...... 68

6.4 Day 1 - Chipping/Melting Ice ...... 69

ix 6.5 Day 1 - Big Chunks of Ice ...... 69

6.6 Day 3 - Ground Floor Structure ...... 69

6.7 Day 3 - Floor Construction ...... 70

6.8 Day 4 - First Floor Structure and Support Columns ...... 71

6.9 Day 5 - Hatch ...... 71

6.10 Day 6 - Dome Center ...... 72

6.11 Day 6 - Dome First Layer ...... 72

6.12 Day 6 - Dome Assembly ...... 72

6.13 Day 6 - Dome Frame ...... 72

6.14 Day 7 - Upper Floor with Bunks ...... 73

6.15 Day 7 - Toilet ...... 74

6.16 Roof Padding and Upper Floor Lighting ...... 74

6.17 Vertical Ladder with Fire Extinguisher ...... 75

6.18 Crew 1: Massimiliano Di Capua, Adam Mirvis ...... 75

6.19 Crew 1: William Cannan, Kevin Davis ...... 75

6.20 Crew 1: Work Area ...... 75

6.21 ECLIPSE at Dusk ...... 76

7.1 ECLIPSE Logo ...... 77

7.2 Habitat Pressure Vessel without External Structure ...... 78

7.3 External Support Structure for Habitat ...... 79

7.4 Detail of Habitat Support Leg Conﬁguration ...... 81

7.5 Front View ...... 81

7.6 Left View ...... 81

7.7 Right View ...... 82

7.8 Top View ...... 82

7.9 Notional Image of Habitat on Altair Deck ...... 83

7.10 Interior Layout of Lower Deck ...... 84

x 7.11 Cutaway of Individual Berth ...... 85

7.12 Interior Layout of Upper Deck ...... 86

7.13 Dual Habitat Conﬁguration ...... 87

7.14 Triple Habitat Conﬁguration ...... 88

8.1 Moonyard Team: Eclipse, Airlock and the sandbox containment perimeter. . 101

8.2 Public Outreach Activity Featuring ECLIPSE Habitat Mockup and UMd Moonyard ...... 103

A.1 Survey page 1 ...... 105

A.2 Survey page 2 ...... 106

A.3 Survey page 3 ...... 107

A.4 Survey page 4 ...... 108

A.5 Survey page 5 ...... 108

A.6 Survey page 6 ...... 109

A.7 Survey page 7 ...... 110

A.8 Survey page 8 ...... 111

A.9 Survey page 9 ...... 112

A.10 Survey page 10 ...... 112

A.11 Survey page 11 ...... 113

C.1 Lower Level - Airlock Side ...... 126

C.2 Lower Level - Suitport Side ...... 126

C.3 View from Galley Wall ...... 127

C.4 Lower Berth ...... 127

C.5 View from Ladder Entrance ...... 127

C.6 Waste Management Compartment ...... 127

C.7 Airlock Egress ...... 128

C.8 Exterior View of Habitat Mockup ...... 128

xi C.9 UMd Moonyard - ECLIPSE Habitat and TURTLE Pressurized Rover Mock- ups ...... 128

D.1 Ballasted Underwater Simulation of Berth Ingress ...... 131

D.2 Setup for Testing Motion between Levels in Lunar Gravity ...... 132

D.3 Stepping Down from Upper Level ...... 132

D.4 Climbing Up from Lower Level ...... 132

E.1 Team Alpha Lower Deck Concept ...... 134

E.2 Upper Deck Concept ...... 134

E.3 Team Beta Lower Deck Concept ...... 134

E.4 Upper Deck Concept ...... 134

E.5 Lower Deck Concept ...... 135

E.6 Upper Deck Concept ...... 135

E.7 Team Gamma Overall Interior Layout ...... 135

E.8 Lower Deck Plan View ...... 136

E.9 Lower Deck Concept ...... 136

E.10 Upper Deck Plan View ...... 136

E.11 Upper Deck Concept ...... 136

xii List of Acronyms

2BMS Two Bed Molecular Sieve 4BMS Four Bed Molecular Sieve ACH Air Changes per Hour AHP Analytic Hierarchy Process BAA Broad Agency Announcement CFM Cubic Feet per Minute ECLIPSE Extensible Concept for Live-In Pressurized Sortie Elements ECLSS Environmental Control and Life Support System ESM Equivalent Systems Mass ESMD Exploration Systems Mission Directorate EVA Extra-Vehicular Activity FEA Finite Element Analysis GFCI Ground Fault Circuit Interruptor HMD Head Mounted Display ISRU In-Situ Resource Utilization LiOH Lithium Hydroxide LOX Liquid Oxygen LPT Lunar Pup-Tent LSS Life Support System MDRS Mars Desert Research Station MF Multi Filtration MFH Minimum Functionality Habitat MLI Multilayer Insulation NASA National Aeronautics and Space Administration NBRF Neutral Buoyancy Research Facility PISCES Paciﬁc International Space Center for Exploration Systems PLM Pressurized Logistics Module PMAD Power Management and Distribution QFD Quality Function Deployment RASC-AL Revolutionary Aerospace Systems Concepts – Academic Linkage RO Reverse Osmosis SCFM Standard Cubic Feet per Minute SPA South Pole/Aitken Basin on Moon SSL Space Systems Laboratory TRL Technology Readiness Level TURTLE Terrapin Undergraduate Rover for Terrestrial Lunar Exploration UMd University of Maryland VCD Vacuum Compression Distillation VR Virtual Reality

xiii Chapter 1

Introduction

The University of Maryland (UMd) Space Systems Laboratory (SSL) is pleased to submit this ﬁnal report to the NASA Exploration Systems Mission Directorate (ESMD) in completion of its obligations under award NNJ08TA89C, as part of the NASA Broad Agency Announcement NNJ08ZBT002, Exploration Systems Mission Directorate Lunar Surface Systems Concepts Study, Topic 2: Minimum Functionality Habitation Element. This report is the comprehensive documentation of the work performed by the SSL in fulﬁllment of award NNJ08TA89C.

1.1 Background

In August 2008, NASA awarded the University of Maryland Space Systems Labora- tory a contract to design a minimum functional habitat (MFH) for the Constellation lunar exploration program. One of three similar contracts awarded in parallel, the purpose of this study was to define the minimum requirements for an extended-stay lunar habitat, to be used as a “jumping-off” point for informed decisions on the marginal costs and increased benefits of adding capabilities over and above those required for the minimal system. This approach paralleled that taken by the NASA Exploration Systems Architecture Study (ESAS), which decided on the basic transportation architecture and spacecraft configurations for the Constellation program. Rather than design an “all-up” vehicle, which could easily wind up overweight and require expensive downscoping, the approach taken was to define the minimum lunar habitat element which could meet the most basic requirements of the program. Given this minimum as a baseline, subsequent trade studies could be performed to evaluate enhanced capabilities by adding systems beyond the minimum set, quantified by the marginal costs and complexities of the added components. This would allow for logical decisions on which augmentations are worth their additional costs. The basic minimum function set, as presented by the sponsor, included:

• a crew of four, drawn from the anthropometric data base of current US astronauts

• a 28 (Earth) day nominal mission duration, with a 30 day contingency

• access for extravehicular operations, with mitigation of dust hazards in and around the habitat

• suﬃcient radiation protection to meet NASA’s overall loss of crew probability limit of 0.001 per mission

1 • assumption of the availability of the rest of the current planned Constellation architecture for the outpost which includes the habitat

• the capability for augmentation and extension to more demanding mission goals

• a total habitat mass limited to no more than 7000 kg

Beyond this simple list, it was the responsibility of the study contractors to decide what constituted the detailed form of a "minimum functional habitat", and to produce a design concept which could be used as a development baseline while assessing additional capabilities. To extend this list of requirements, the University of Maryland created a rudimentary concept of operations and used that to evolve additional design constraints. Critical habitat design issues are predicated on the level of extravehicular operations, particularly in the number of ingresses and egresses and the mode adopted. Since this habitat is to be used for exploration activities, the UMd team assumed that there would be a two-person EVA every day throughout the 28-day nominal mission. Due to the severe problems of controlling dust intrusion at this level of EVA operations, a further decision was made to baseline the use of suitports for nominal operations. Although currently at a low technology readiness level (TRL), suitports offer the advantages of negligible atmosphere loss with each cycle and no dust infiltration to the habitat with normal use. Since there will be the necessity to bring items into and out of the pressurized volume, including suits for maintenance and repair, the design team also established a requirement for a conventional airlock, which was assumed to be inflatable. Nominal mission operations assumed an airlock cycle on a weekly basis. Since the 30-day contingency requirement was assumed to be “waiting out” the time to another launch window back to Earth, no allocation of resources was made for EVA operations during this period.

1.2 Research Approach

The University of Maryland team decided to attempt a formal assessment of habitat functions and capabilities, and to obtain the best practices from those experienced in remote habitation to guide the selection of which items are part of the minimum functionality set. As detailed in succeeding sections, this took the form of an online survey, sent to personnel with experience in submarines, scientiﬁc shipboard habitation, Antarctic operations, and space design. The survey was designed to provide rigorous pairwise evaluations of the relative importance of each of 34 diﬀerent habitation issues, which would be prioritized by mapping the results into an Analytical Hierarchy Process to get a quan- titative evaluation of the relative importance of the design issues, with a further mapping via Quality Function Deployment into understanding the interactions between the design features and the operational capabilities of the habitat. In parallel with this, an extensive literature search and review was performed on lunar habitat and rover design, with many of the candidate papers dating back to the 1960’s, when a number of detailed lunar habitation systems were designed in anticipation of continued post-Apollo lunar exploration. While some of the sources found were designs for extensive surface infrastructure, the approach taken was to focus on the small end of the range of habitat designs, which would maximize applicability to this project. Following a down-select to a set of “most applicable” design documents, regression analysis was used to look for meaningful trends in both habitat design and concept of operations. At this point, a preliminary design was developed for a truly "minimum" habitat, termed the "lunar pup tent". Assumed to be a contingency shelter for emergency use

2 only, the pup tent design was not predicated on the availability of Constellation surface architecture elements, but was self-sufficient for 28 days. This design exercise provided valuable experience into the details of lunar habitat design, and was a “jumping-off” point for further detailed point designs. A major focus of the study was the creation of three independent teams, tasked with developing specific habitat designs for three different operating cases. As detailed later in this report, these ranged from a further development of the contingency shelter, to a habitat as small as could be designed while still meeting minimal habitability criteria for the nominal mission, to a more expansive habitat taking maximum advantage of the surface system infrastructure. Each of these designs involved the development of detailed solid models, which were adapted as environments for a virtual reality system. This system was used for qualitative assessment of interior layout and habitability, which were assessed comparatively between designs. This process provided valuable data on the effects of size and complexity on system parameters, and offered an opportunity to explore various corners of the design space. All of these point designs are archived in Chapter 4. In parallel with the point design exercise, a set of trade studies were undertaken to quantify critical design parameters and better understand the constraints of the top-level requirements, particularly the 7000 kg mass limit. These trades, presented in Chapter 5, looked at the overall habitat size and configuration, as well as system-level choices such as life support components and thermal control approach. At this point an overall configuration was established for the UMd habitat design, and an effort undertaken to create a full-scale mockup for habitability testing and layout assessment. Despite the difficulties of outdoor construction in the depth of winter, as described in Chapter 6, the mockup was completed in two weeks and used for verification of the basic configuration chosen. With all of the above as preliminaries, the final habitat design was developed in detail, including interior and exterior layout, selection and emplacement of support systems, and accommodations for future growth options. All of this is documented in Chapter 7.

1.3 Milestones and Deliverables

The University of Maryland design team had a number of reporting milestones throughout the six month term of this study. These included:

• an initial progress report, conducted via telecon on October 20, 2008

• a midterm progress brieﬁng in Houston on November 11, 2008

• the ﬁnal brieﬁng in Houston on February 9, 2009

• a public brieﬁng at the U.S. Chamber of Commerce in Washington, DC on Feb. 25, 2009.

All of the brieﬁng packages for these presentations are publicly available through the "Publications" link at http://spacecraft.ssl.umd.edu, and at various NASA sites.

3 Chapter 2

Review of Relevant Literature and Research

2.1 Regions for Possible Landings

The lunar surface is divided up into highlands, maria, and craters. The highlands are the oldest features on the Moon and account for 83% of the lunar surface. They have an average height of 5 km above the nominal lunar radius. The maria, or seas, were formed by large lava ﬂows and are the smoothest areas on the surface. They are about 2 to 5 km below the nominal lunar radius and account for 17% of the lunar surface. Craters speckle the surface and are formed by two methods, meteor impact and volcanic activity. They are located on both the highlands and mare regions [1]. The lunar surface, or regolith, is made up of agglutinates, igneous rock, breccias, mineral fragments, and glass [2]. Its density varies, but on average is about 1.75 g/cm3. The elemental composition of the regolith is listed in table 2.1 below.

Table 2.1: Lunar Regolith Composition Element Average Abundance Average Abundance Sites [atom %] [mass %] Oxygen 60 % 45 % Maria / Highlands Silicon 16.5 % 21 % Maria / Highlands 10 % 13 % Highlands Aluminum 5 % 5 % Maria 5 % 10 % Highlands Calcium 4.5 % 8 % Maria Magnesium 5 % 5.5 % Maria / Highlands 2.5 % 6 % Highlands Iron 6 % 15 % Maria Titanium < 1 % < 1 % Maria / Highlands Sodium < 1 % < 1 % Maria / Highlands Source data from [1]

4 Additionally, the solar wind imparts additional elements on the lunar surface, including hydrogen, carbon, nitrogen, helium, and others [1]. The lunar regolith can be utilized to provide atomic oxygen for propulsion systems, silicon for solar cell development, and concrete, metal, glass, insulation, and shielding for future building materials. The ability to conduct in-situ resource utilization (ISRU) is of signiﬁcant importance for permanent lunar base site development, sustainment, and expansion [2]. Figure 2.1 shows the past landing sites and future potential exploration sites.

Figure 2.1: Past Landing Sites Source: [3]

The crosses in Figure 2.1 indicate the top ten sites for future exploration. As table 2.2 below indicates, most of these sites are rich in materials that can be used for ISRU.

5 Table 2.2: In-Situ Resource Utilization Name Location Rationale South Pole 89.9oS, 180oW This area of near-permanent sunlight on the rim provides access to (Rim of Shak- power and proximity to a cold trap (crater interior) that may contain leton) water ice. The site is on the floor of the South Pole-Aitken (SPA) Basin, the oldest and biggest impact feature on the Moon. The south- ern celestial hemisphere is continuously visible. SPA Basin 54oS, 162oW This site is on the floor of the SPA basin, which possibly exposes the floor (near lower crust or upper mantle of the Moon. The site is on the far side Bose) of the Moon, out of Earth view, and would require a communications relay system for Earth contact. Observation of the low-frequency radio sky would be possible here. Aristarchus 26oN, 49oW This is a diverse site containing unusual rock types, ancient crust, Im- Plateau (north brium Basin ejecta, non-mare volcanism, and extensive dark mantling of Cobra Head) (pyroclastic) deposits. The dark mantle may be good feedstock for ISRU processing (e.g., solar wind hydrogen). There is easy and routine access to this near-equatorial, near-side site. Rima Bode 13oN, 3.9oW There are extensive regional high-Ti dark mantle deposits at this site. (near Vent) The vent system for these ash deposits may contain xenoliths (exotic chunks) of rock from the deep mantle of the Moon. Existing data suggest high-Ti pyroclastic glass may be excellent feedstock for ISRU processing. There is easy and routine access to this near-equatorial, near-side site. Mare Tranquil- 8oN, 21oE High-Ti maria near the landing site for the Apollo 11 mission in 1969. litatis (north of High-Ti basalts are excellent feedstock for ISRU processing. Smooth Arago) maria is physically well-characterized and already covered by extensive, high-resolution photography (from the lunar orbiter). There is easy and routine access to this near-equatorial, near-side site. North Pole 89.5oN, 91oE This area of near-permanent sunlight on the rim provides access to (rim of Peary power and proximity to a cold trap (crater interior) that may contain B) water ice. The site is on the distal edges of the Imbrium Basin ejecta blanket. The northern celestial hemisphere is continuously visible. Oceanus Pro- 3oS, 43oW This mare site is on the western near side. Basalts here appear to cellarum (in- be some of the youngest lavas on the Moon, possibly as young as side Flamsteed one billion years. High-Ti lavas provide excellent feedstock for ISRU P) processing. There is easy and routine access to this near-equatorial, near-side site. Central far side 26oN, 178oE This highland site is on the central far side of the Moon. The site highlands (near appears to be on the most ancient, primordial crust of the Moon the Dante) original magma ocean anorthosites. There is Al and Ca rich regolith available for ISRU processing. Observation of the low-frequency radio sky would be possible here. This site would require relay satellites for Earth communications. Orientale basin 19oS, 88oW This is a combination highland/mare site on the floor of the youngest floor (near major basin on the Moon. Crater Kopff has unusual morphology and Kopff) may be an endogenically modified impact crater. This site contains both mare and highland regolith feedstock for ISRU processing. The limb site is sometimes out of view of Earth and would require a relay for continuous communications. Smythii Basin 2.5oN, 86.5oE This mare site is on the floor of the ancient Smythii basin on the floor (near eastern limb of the Moon. Mare basalts here are very young (approx- Peek) imately 1 to 2 billion years) and could be used to study lunar thermal history. This site contains high-Fe mare regolith feedstock for ISRU processing. The limb site is sometimes out of view of Earth and would require a relay for continuous communications.

Source: [3]

6 The main limitation for ISRU will be establishing infrastructure capable of supporting the equipment and power requirements for excavation and processing. Certain regolith processing may not be economically feasible in the early phases of lunar exploration [4] [5]. One region, however, where missions may beneﬁt from early ISRU will be the lunar poles. It is believed that the lunar poles have water trapped in permanently dark impact craters [5]. If water is conﬁrmed to exist in large and accessible quantities, an early outpost on the poles may be a very attractive opportunity.

2.2 Lunar Temperature Range

The lunar day is 29.5 Earth days. Therefore, most of the Moon, except the poles, experiences a 14 day-night and 14 day-light cycle. The solar ﬂux on the lunar surface is about 1360 W/m2 and its radiation back out to free space is 360 W/m2. This extended diurnal cycle is responsible for a temperature variation between 120-380 K at the equator and between 120 and 160 K at the poles [1]. Figure 2.2 below shows the lunar temperature based on latitude and sun angle.

Figure 2.2: Lunar Surface Temperature

Note from the ﬁgure that the Apollo missions were never subjected to the full range of temperature variation. This will not be the case for lunar bases where the mission duration can exceed a full lunar day-night cycle. Due to the low conductivity of the lunar regolith and the lack of an atmosphere, radiation is the prime mechanism by which heat is transferred [1]. The thermal conductivity is 1.5 × 10−5 W/cm2 for the top soil and ﬁve to seven times greater at lower depths [1] [6]. Because of this low thermal conductivity, the temperature gradient experienced at the surface is neglible at 50 cm below the surface and virtually nonexistent at depths greater than 100 cm below the surface [2]. At these depths, the regolith temperature stays a constant 230 K [7]. Base location, as well as other

7 design considerations such as mission duration and surface material properties, impacts the thermal design of a lunar base. For example, at mid-latitude regions, low thermal heat rejection becomes diﬃcult during the lunar day. This is because the temperature of the surroundings is greater than the temperature of the radiators. In these situations, the use of a more complex thermal control system is required.

2.3 Ionizing Radiation

The lunar environment receives ionizing radiation due to the solar wind and from solar and galactic cosmic events. Due to the lack of an atmosphere or a significant magnetic field, all of this radiation makes its way to the surface [6]. The solar wind flux density is between 1010 and 1012 particles/cm2/sec. Its energy is about 1 KeV per atomic mass unit, and it has a regolith penetration depth of 10 cm. Solar flares and other solar events are on the order of 1-100 MeV, but due to a lower flux density of around 102 particles/cm2/sec, its effects are only significant to about 1 cm of regolith. Galactic cosmic radiation (GCR) is the most severe form of ionizing radiation. GCR energy is on the order of 102-104 MeV per atomic mass unit, and it can penetrate the regolith up to a depth of 300 cm. Galactic radiation is a significant hazard for missions longer than six months [8]. To protect against these hazards, passive shielding can be accomplished with the use of regolith, structural material, and consumables like food and water. For example, a 50 cm shield made up of lunar regolith would provide adequate cover for most types of ionizing events [6].

2.4 Micrometeoroid Impact

Reference [7] presents a mathematical model for micrometeoroid ﬂux on the lunar surface. Figure 2.3 below shows the ﬂux as a function of the mass of the particles.

Figure 2.3: Micrometeoroid Impact Flux on the Lunar Surface Graph created using Matlab source code from Josh Johnson, University of Maryland

Using this data, an appropriate estimate of the number and mass of particles was developed. Figure 2.4 below shows the number of particles and their respective masses for various lunar base surface areas. It is important to note that the number of particles to impact a lunar base is dependent on the planar surface area of the structure and its duration on the surface.

8 Figure 2.4: Micrometeoroid Impact Mass on the Lunar Surface Graph created using Matlab source code from Josh Johnson, University of Maryland

From Figure 2.4, a particle mass between 3 and 40 micrograms is expected to strike a lunar base with a surface area between 20 and 500 m2 and operating on the surface for 60 Earth days. The particles will have an impact velocity of 20 km/sec and impart energies between 0.6 to 8 Joules. Micrometeoroids of these sizes can produce craters half a millimeter wide or larger in metals, where the depth of the crater is similar to its diameter. It is important to note that external structural shielding used to protect against radiation would be of suﬃcient thickness for these classes of micrometeoroid impacts [2].

2.5 Habitability in Conﬁned and Austere Environments

The study of habitability crosses engineering, physiological, and psychological dis- ciplines. Habitability does not have a universally agreed-upon definition, but in general terms it is the relationship between humans and their environment, or more precisely, the “suitability of an environment” for the acceptable performance of humans [9] [10]. Perfor- mance can be defined as three hierarchical levels: (1) health and safety, (2) function and efficiency, and (3) psychological well-being [10]. The first level of performance is achieved simply through the habitat’s structural and life support systems. The second level of performance requires an optimization of the human-machine interfaces within the habitat, where special attention is given to habitat layout and automated mission support systems. The third level of performance is affected by crew selection, mission duration, available area/volume per person, habitat layout, stress levels, and other psychological factors. Al- though a minimum functional habitat is sparse compared to an outpost design, it should, nevertheless, provide features that help to achieve the highest levels of human performance for the duration of the mission. Providing for health and safety is accomplished by the structural and life support systems in a habitat. The requirements for maintaining the health and safety of the crew are detailed in NASA’s man-system integration standard [11]. The recommended temperature range for humans is 18oC to 26oC, with a humidity range corresponding to dew points between 4oC to 16oC [12]. This atmosphere corresponds to a tolerable airflow range between 0.1 and 1 m/sec within the space and a CO2 partial pressure level no greater than 667 Pa (0.1 psi). Figure 2.5 shows the preferred temperature zone for humans in an

9 enclosed environment.

Figure 2.5: Temperature Zones for Man in an Enclosed Environments [11]

Acceptable acoustic levels are dependent on the functionality of the space and the sensitivity of the inhabitants. At 30-40 dB, normal voice communication is possible. At 50 dB, irritation of the crew is observed. At 75 dB crew performance is degraded for missions greater than 10 days. At 85 dB, noise levels are considered hazardous and require hearing protection. Finally, the habitat shall not have any element which exposes the crew to continuous noise levels above 120 dB. The habitat must be designed to prevent ionizing radiation from sickening or killing the crew, as detailed in Table 2.3. For a 30 day mission, a dosage of 25 rems is the upper acceptable limit.

Table 2.3: NASA Radiation Limits

Career Exposure by Age and Sex (rem) Sex Age 25 35 45 55 Male 150 250 325 400 Female 100 175 250 300 Ionizing Radiation Exposure Limits (rem) Exposure interval Dept (5 cm) Eye (0.3 Skin (0.01 cm) cm) 30 days 25 100 150 Annual 50 200 300 Career 100 to 400 400 600

10 Satisfying only these requirements creates a habitat whose function is simply to support life. This habitat can only provide the crew with the ﬁrst level of habitability. To achieve higher levels of habitability and performance, consideration should be given to the functional layout and psychological aspects of the habitat and the crew. Reference [13] notes that the “environment in which the crew works and lives has been a primary issue since [ISS] Expedition 1” and has been rated as one of the top ﬁve issues to rectify. Based on the literature, this issue can be ascribed to poor zoning of functional areas. Figure 2.6 below provides a zoning of functional areas based on their individual or group use and their respective noise levels.

Figure 2.6: Functional Areas by Noise Level and Privacy Level [1]

Although this zoning provides a good rule of thumb for arranging the spaces within the habitat, it is but one aspect of a proper design. Other factors that should be addressed are the total size of the space, the percentage of total time within the space, and the crew ﬂow or interaction between the spaces. Parker [14] divides the habitat into four functional areas and provides volumes for each space. Additionally, Schowalter and Malone [15] provide a breakdown of time per activity. Table 2.4 combines their work to reveal how a habitat space should be allocated based on function and the time spent within the area.

It is evident from the table that there is a direct relationship between the relative size of the space and the amount of time spent in the space. Schowalter and Malone go one step further and present a ﬂow diagram for crew activities. Figure 2.7 below reveals the interactions between diﬀerent activities.

As shown in this figure, a crew in a lunar habitat would operate on the following rough schedule. They would awaken from their sleep, proceed to a waste elimination and hygiene activity, eat, and head out to an EVA or IVA activity. After the EVA or IVA is complete, they could complete a housekeeping function or rest. The activity flow continues until the crew is ready for bed. Figure 2.8 below combines the three different habitability approaches. The color scheme groups the activities based on functional space. The sizes of the activities denote the relative size of the space and the time spent on the activity. The zoning of the activity is also shown.

11 Table 2.4: Habitat Space Allocation as a Function of Time Spent in that Area

Unit Description Unit Activity Percent Percent of Total of Total Time doing Habitable activity Volume Work Operational or Mission Work 44 % 40 % Mission Related Tasks Nourishment 9 % Public Dining, Food Rest & Relax- 8 % 25 % Management, ation Recreation, and Exercise Spaces Total 17 % Personal Sleeping, Privacy, Sleep 33 % 20 % and Personal Storage Waste Elimina- 1 % tion Hygiene 3 % Service Hygiene, waste Housekeeping & 1 % 15 % management, and Personal Equip- public storage ment Care Locomotion 1 % Total 6 % Table 2.4: Sources Combined from data in [14] and [15]

12 Figure 2.7: Interactions Between Diﬀerent Activities [14] [15]

Figure 2.8: Combined Habitability Approach: Zoning, Unit and Flow [15]

From this view, certain design traits become evident. First, it may be useful to group the waste elimination and hygiene activities into one area and place them near where the sleeping activity occurs. This area should be acoustically isolated from noises above 40 dB. Second, the mission, nourishment, and housekeeping activities can be grouped into a common functional area. Acoustic dampening of noises above 50 dB within this area will help facilitate team communication and cohesion, resulting in improved performance and morale. Finally, because of the varied nature of the rest and relaxation activity, it should not take up its own dedicated area, but should be allocated within the two primary functional spaces. Addressing the functional layout, relative size, and crew ﬂow of the habitat contributes to the second level of crew performance/habitability. The last performance level, psychological wellbeing, requires the engineers to consider crew morale in the design of the habitat. Analogous environments like Antarctic stations provide insights into the variation of crew morale throughout the year-long stay. As seen from Figure 2.9 below, morale dips in the arriving months because of the overlap of outgoing and incoming personnel, which contributes to an overcrowded situation. Once the outgoing personnel leave the station

13 and the doors close for the winter-over period, morale increases[16].

Figure 2.9: Morale during Mission [16]

Morale begins to dip as the winter-over period sets in. Inhabitants mentioned that the “lack of different stimuli,” such as sunlight and fresh food, and the sterility of the environment contributed to the dip in morale. At the end of the winter-over period, morale increases as the inhabitants begin to head home [16]. In this graph, the lunar habitat analogue period begins in January when the station closes for the winter. For a two month period, morale is high. From the middle of March until the middle of July, the morale decreases sharply. It can be inferred from this heuristic curve that mission durations longer than two months would require design with special attention to crew morale. For the MFH study, crew morale would only come into play for an extended 180-day mission. One indirect contributor to increased morale is the amount of space per person, in order to provide an increased level of privacy. The amount of required space, however, is subjective and varies for each crew member [14]. Privacy stems from an individual’s perception of territorial space. Cabin sizing for habitats is largely done heuristically, with little physical or psychological justification, and a notable lack of consensus in the literature. Cabin layout and crew size, as drivers of psychological well-being, are likely at least as important as total cabin volume [17]. For some missions, a sense of personal space can be achieved with nothing more than a personal storage locker. However, because of the mission duration, it is expected that a minimum functional habitat would require more space for privacy. At a minimum, these private spaces could be provided by a combination of individual sleeping quarters and the personal hygiene facility. Another contributor to morale is personal hygiene and habitat cleanliness. These two functions directly impact the psychological performance of the crew and the habitability of their living spaces. The personal hygiene facility should be equipped for personal grooming, and for collecting, processing, and disposing of body and other waste. At minimum, it can be nothing more than a private area where a crew member can clean themselves with water and a cloth [14]. Similarly, it is equally important from a psychological and physiological perspective to keep the living spaces clear of equipment and debris. Mealtime is another area where crew morale increases. For the crew, mealtime is a major social activity where experiences are shared and problems resolved. Communication with family and friends also provides a morale boost and contributes to mental stability [14]. Clearly, to provide a habitable environment, designers must consider the crew health and safety, efficient use of space for mission operations, and the crew’s mental state. All of these factors contribute to high crew performance and should be required considerations in a minimal functional habitat.

14 2.6 Past Designs

Even before the Apollo Missions, NASA and the aerospace industry were designing lunar habitats. The purpose of these lunar habitats ranged from strategic deterrence of Soviet nuclear aggression, to lunar excavation for exotic elements, to establishing a premier scientific outpost for local and celestial research. The designs varied in size, volume, and mission duration. Table 2.5 is a compilation of characteristics of some proposed lunar habitat designs. Figure 2.10 plots the data from Table 2.5 in the form of specific volume (volume per crew member) versus mission duration. As can be readily seen, the allocated volumes vary widely across all categories of missions. Since the basic plot would provide no insight into the mass estimates corresponding to the specific designs, the data points are separated into two sets, based on whether the design mass of the habitat is above or below 10,000 kg. Although it would be supposed that the dividing line would be set by the 7000 kg limit of this study, only two of the historical precedents had a mass below that level. By arbitrarily raising the cut-off to 10,000 kg, the curve separates "small" habitats from large. Also superimposed on this figure are the three "classic" curves for habitability from Celentano, as referenced in numerous textbooks since the original publication. These curves are of the form volume − duration = A 1 − e B (2.1) crew member where A represents the asymptotic value of volume/crew for an extended duration mission and B represents the "rise time" of the curve. The Celentano curves were adequately represented by this heuristic equation by using a value of 20 days for B, and asymptotic A values of 5, 10, and 20 m3/crew for the "tolerable", "performance", and "optimum" limit values, respectively.

Figure 2.10: Habitat Volume vs Mission Duration

This graph also incorporates a new trend line, based on the assumed form of equation (2.1) but with values of A and B chosen by a least squares fit to the data of Table 2.5. This curve shows some surface similarities to the Celentano "optimal" curve, with a slower exponential time constant of 35 days and an asymptotic value of 62 m3/crew member. Some caveats on this regression analysis: with a coefficient of determination (R2) of 0.32, the fit is too poor to make any sweeping conclusions as to the universal applicability of this curve. Also, this curve is based exclusively on lunar surface habitats, so while it might

15 Table 2.5: Characteristics of Past Lunar Habitat Designs Name of Habitat Source Document Overall Overall Crew Mission Mass Volume Size Dura- (kg) (m3) tion (days)

Lunar Surface Emergency Shelter NASA-CR-195551 10,000 8.56 4 5

Concept 1 AIAA 2009-823: Lunar Surface 7,596 15.53 3 14 Base Architecture Mass and Cost Comparison Results

Pressured Lunar Rover NASA-CR-192034 6,197 49.5 4 14

Pressured Lunar Rover NASA-CR-192033 7,015 125.7 4 14

Scaled Apollo Scaled Apollo Command Module 14,965 25 4 21 Mass Estimate

Orion Zero Base Vehicle Scaled Apollo Command Module 17,535 40 4 21 Mass Estimate

MOLAB http://www.astronautix.com/ 3810 12.8 2 21 craftfam/lunbases.htm

Concept 2 AIAA 2009-823: Lunar Surface 11,790 26.13 3 30 Base Architecture Mass and Cost Comparison Results

Concept 1 (NASA-TM-104114) Concepts for 17,060 162.07 4 30 Manned Lunar Habitats

Concept 2 (NASA-TM-104114) Concepts for 24,510 273.68 4 30 Manned Lunar Habitats

Concept 3 (NASA-TM-104114) Concepts for 8,608 131.31 4 30 Manned Lunar Habitats

First Lunar Outpost First Lunar Outpost Report No Data 446.6 4 45 (Puerto Rico Doc)

First Lunar Outpost AIAA 93-4134: A System Overview 29,986 337.5 4 45 of the First Lunar Outpost

LESA http://www.astronautix.com/ 9,700 80 6 90 craftfam/lunbases.htm

Habot Mobile Lunar and Planetary Bases 10,000 98 4 100

Concept 3 AIAA 2009-823: Lunar Surface 22,313 38.07 3 180 Base Architecture Mass and Cost Comparison Results

Horizontal Hard Shell Habitat Constellation Architecture Team- 14,376 234 4 180 Lunar Habitation Concepts

Inﬂatable Habitat Concept Constellation Architecture Team- 13,867 426 4 180 Lunar Habitation Concepts

Hard Shell "Core Habitat" Constellation Architecture Team- 13,332 220 4 180 Lunar Habitation Concepts

Concept 4 AIAA 2009-823: Lunar Surface 34,974 90.56 3 365 Base Architecture Mass and Cost Comparison Results

DLB Lunar Base http://www.astronautix.com/ 52,000 662 9 365 craftfam/lunbases.htm

Habitat Module Project LEAP No Data 445 6 Indef

Lunar Surface Base Shelter Lunar Base Synthesis Study (Vol- 59,460 1,200 12 Indef ume III)

Standard Habitat Unit A Habitat Concept for the 60,000 1,965 24 Indef MOONBASE-2015, H.H.Koelle

Lunex: Lunar Expedition http://www.astronautix.com/ 61,000 No Data 3 No Data craftfam/lunbases.htm

Horizon Lunar Outpost http://www.astronautix.com/ 22,000 No Data 21 No Data craftfam/lunbases.htm

16 be more applicable to that category of habitat, it should not be particularly relevant to microgravity habitats. Figure 2.11 zooms in on the data from Figure 2.10, dropping the set of habitat data for masses above 10,000 kg. This reduces the size of the historical data set to six points, which include one outlier of particularly low volume/crew for a 90 day mission; the other five points are all for missions below 30 days. This graph repeats the Celentano predictive curves, along with the curve of the same form fitted to the entire historical data set. By eye, the Celentano curves do a better job of fitting the disparate data points than the larger population curve fit at this low end of the spectrum. To further investigate this, Figure 2.11 also includes a similar curve fit to equation (2.1) for only the six points of this reduced data set. The resultant plot has a very similar asymptote to the Celentano "optimum" curve, but a much faster time constant (8 days as opposed to 20 for Celentano). With such as small and disparate data set, there is little reasonable expectation of a numerically meaningful curve fit; with an R2 value of 0.02, this final curve fit is presented as a curiosity, since no meaningful argument may be made for its actual relevance.

Figure 2.11: Habitat Volume vs Mission Duration

As a "bottom line" to the historical database activities, the analysis provides an interesting perspective on the "traditional" Celentano curves matching volume/crew member to the duration of the mission, but is probably of primary significance in verifying the existence of prior studies in the mass range specified for the minimum functional habitat study. Eight of the 24 data points fall below the "optimum" asymptote of 20 m3/crew; five are at or below the "performance limit" of 10 m3/person. The four 30-day missions from the data set have specific volumes of 8.7, 32.8, 40.5, and 68.4 m3/person, for an average of 37.8. However, these same design examples have habitat mass estimates of 11,790, 9700, 17,060, and 25,410 kg (respectively), for an average mass estimate of 15,720 kg – more than a factor of two higher than the MFH mass limit. The real "bottom line" to this study is that while there are existence proofs of habitat systems in the MFH mission duration and mass ranges, they are the low-end exception rather than the rule, and clearly meeting the MFH design requirements will be a significant challenge.

17 Chapter 3

Data Acquisition

The methodology used to acquire data on habitability and apply it to habitat design started by generating a list of habitat features considered important to habitability from the literature review. This list of features was then ranked in importance using an Analytic Hierarchy Process. The results of that process were used as inputs to a Quality Function Deployment matrix, in which relationships were established between habitat features (as they impact the crew), and design features/systems. This process resulted in a vector of relative importance values for various design features/systems, intended for use within the trade space to assist in determining the impact of system alternatives on overall habitability. In this way, a minimum habitat design was achieved which provides an acceptable level of habitability for its crew.

3.1 Use of the Analytical Hierarchy Process

In order to determine the relative importance of the habitability functions, an Ana- lytic Hierarchy Process (AHP) was used. The Analytic Hierarchy Process, originally developed by Thomas L. Saaty in the 1970s, is a method of determining the relative importance of a set of parameters, based on a series of subjective pairwise rankings. Redundant information generated by the AHP improves the reliability of the results, and can be used to check the consistency of the subjective rankings[18]. To perform an AHP on a given set of n parameters, an n × n matrix is created, with the value of each element (i, j ) corresponding to the relative importance of parameter i with respect to parameter j. By definition, the diagonal elements are equal to one, and the value of each element (j, i) is equal to the reciprocal of the value of its conjugate element n2−n (i, j ). Thus, only 2 elements must be known in order to fully populate the matrix. The values of these elements may be determined through survey responses of relevant subjects, in which subjective statements of the form “parameter A is [some degree more or less] important than parameter B” are converted to numerical values. An example of an AHP matrix is illustrated in table 3.1. Only the upper right half of the matrix must be filled in; the remaining elements are defined as described above. For a fully populated AHP matrix, the importance values of the parameters are contained in the normalized principal eigenvector of the matrix, such that the importance of parameter i is the ith element of the eigenvector. A consistency value for the matrix can be determined by dividing the matrix size n by the principal eigenvalue. Consistency can be expressed as a percentage, with a consistency of 100% indicating a totally consistent matrix.

18 Table 3.1: Example AHP matrix Parameter 1 Parameter 2 Parameter 3 Parameter 4 Parameter 1 1 0.20 3.0 2.0 Parameter 2 5.0 1 4.0 0.25 Parameter 3 0.333 0.25 1 6.0 Parameter 4 0.5 4.0 0.167 1

Consistency indicates the extent to which the pairwise comparisons populating the matrix are in agreement with one another. Consider, for example, a three-parameter AHP matrix. Given the statements “Parameter A is twice as important as parameter B” and “Parameter B is three times as important as parameter C ”, one can generate the statement “Parameter A is six times as important as parameter C ”. If this is in fact the third statement, then the matrix is entirely consistent. If the third statement disagrees with the expected statement, then the matrix will have a consistency less than one, depending on the magnitude of the disagreement between the statements. In an AHP matrix, some inconsistency is to be expected. However, a high inconsistency (a consistency less than 90%) can indicate that the subject was confused or unclear about the definitions of the parameters or the instructions for completing the pairwise comparisons, or made a mistake in responding to one or more pairwise comparisons. Thus, consistency can be a valuable tool in obtaining the most reliable data possible from a sample of subjects. By weighting the means of importance values by the consistencies of the matrices from which the values were generated, less reliable data can still be used, while emphasizing the most reliable data in the final average. Multi-level AHPs can also be constructed, in which the parameters of a given matrix are identifiers of sub-matrices, each of which is populated with a group of related parameters. In such a hierarchy, the importance values of parameters in a sub-matrix are multiplied by the importance value of that matrix as a whole, to arrive at a global importance value for the parameter in question. Because the principal eigenvector is normalized for each matrix in the hierarchy, the sum of the parameter values across any level of the hierarchy will be 1. Figure 3.1 illustrates a sample multi-level AHP. Numbers in red indicate the importance of each parameter within its sub-matrix; the black numbers indicate the importance of each parameter globally.

3.2 AHP Implementation

To implement the Analytic Hierarchy Process and determine which features are most crucial to habitability, an online survey was generated, which consisted of ninety pair-wise ranking questions on thirty-four habitat features/functions. (The terms “feature” and “function” are used interchangeably in this report.) Several of the features considered had binary values, in that subjects were asked to consider the importance of the feature being either present or absent. Among features with a range of possible values, the ideal value for many features was assumed to be as great (or in some cases as little) as possible; these features were assumed to fall under the heading of “more is always better”. For features where the ideal value could not be assumed to be at one extreme of the range, the survey included a series of “preferred-value” questions, by which the ideal value could be gauged.

19 Figure 3.1: Example multi-level AHP hierarchy

The list of desirable habitat features/functions was generated from the literature review. It was assumed that Preiser’s first level of habitability, health and safety, would be provided, as discussed in section 2.5, in the form of minimum life support as defined in NASA’s Manned Systems Integration Standards and the existing research. Thus, the habitat features considered in the survey focus on Preiser’s second and third levels of habitability: function and efficiency, and psychological wellbeing. In order to reduce the overall size of the survey and the time required to complete it, while maintaining a high information value, it was decided to use a two-level AHP with a total of eight matrices, as illustrated in figure 3.2. It was also decided that, to maximize the design value of the data generated, features which were assumed to have a negligible impact on habitat design would be excluded from the survey. After initial feedback on a preliminary survey, it was discovered that the AHP results were significantly weighted toward parameters in smaller matrices. Thus, it was determined that good design of a multi-level AHP requires that all the ultimate parameters (the habitat features, in this case) be on the same level of the hierarchy, and that all the matrices in a given level of the hierarchy be of approximately the same size. The survey hierarchy was redesigned to meet this requirement before the final version of the survey was implemented. The final survey hierarchy consisted of one top-level matrix and eight sub-matrices. The top level matrix ranked the relative importance of the following areas: health and hygiene, communications, general environmental quality, non-physical recreaction space, exercise space, work space, and sleeping/resting space. Within health and hygiene, the parameters considered were: cleanliness of the habitat, level of personal hygiene, physical comfort of the bathroom facility, quality of medical facilities, and cleanliness of clothing. Within communications, the parameters were: functionality of communications (e.g., data only, voice only, voice plus video, etc.), amount of communications time per crew member per day, privacy of personal communications, and quality of connection (e.g., what portion of data is recieved, are radio alphabets required, etc.). Within general environmental quality, the features considered were: lighting quality, noise control, the presence and size/location of windows, odor control, temperature control granularity, standing clearance within the habitat, and food quality. Within recreation space, the features were: recre-

20 Figure 3.2: Final survey hierarchy

ation time per crew member per day, recreation area and volume, variety of recreational activities, ratio of recreation time spent alone, and amount of time per crew member per day spent outside the habitat, on EVA. Within exercise space, the features were: exercise time per crew member per day, exercise area and volume, variety of exercise activities, and ratio of exercise time spent alone. Within work space, the features were: work time per crew member per day (defined as mission- and survival-related tasks, but otherwise unspecified), work area and volume, preparation time required per EVA, and fraction of work time spent alone. Finally, within sleep/resting space, the features considered were: sleep time per crew member per day, sleep area and volume, sleep privacy, physical comfort of the sleeping space, and no hot racking (i.e., no trading beds between crew members and sleeping in shifts). The target populations for the survey were populations with experience in remote and/or confined environments believed to be analogous to the lunar surface habitat environment. These populations included astronauts, submariners, ship crew, Arctic/Antarctic research scientists, and engineers and designers of space habitats. Based on the literature review, it was found that Arctic/Antarctic bases and submarines have in the past been considered reasonably analogous to space habitat environments. According to reference [19], “the South Pole is the closest place to space on Earth where a permanent, manned U.S. presence exists, and represents a good scientific/logistics/operations analogue for future Moon/Mars missions.” From reference [20], “submarines [have been] found to be the most similar overall to the space ship situation.” Because a large portion of the targeted population were members of the Italian Navy, two versions of the survey were produced, one in English, and one in Italian. Survey respondents were asked to envision a scenario in which they were one of four crew members in an unspecified isolated, confined environment for a period of one month, with a limited ability to leave the habitat for brief periods of time, in accordance with the reference mission for this study. Respondents were told that their habitat would, at a bare minimum, support

21 life, and that the goal of ranking the specified features was to maximize crew productivity and psychological wellbeing. Figures A.1–A.11 in Appendix A show screenshots of each page of the English version of the survey. The web survey included hover-over pop-up windows with additional clarification of the feature definitions.

3.3 AHP Data

Tables 3.2 and 3.3 show the raw data from all survey respondents. For questions labeled “AHP [#]”, the digits 1-7 correspond to pairwise ranking responses as follows: 1 = “Feature 1 is much more important than feature 2.” 2 = “Feature 1 is moderately more important than feature 2.” 3 = “Feature 1 is slightly more important than feature 2.” 4 = “Feature 1 is about as important as feature 2.” 5 = “Feature 1 is slightly less important than feature 2.” 6 = “Feature 1 is moderately less important than feature 2.” 7 = “Feature 1 is much less important than feature 2.” Other questions, such as ideal numbers of work hours/day or ideal fraction of time spent alone, were answered directly with numerical values.

3.4 AHP Analysis and Conclusions

3.4.1 AHP Data Analysis In converting the survey data to AHP matrices, numerical weights were applied to the subjective pairwise comparisons as described in Table 3.4. For each respondent, and for each matrix within the response, a vector of importance values and a consistency value were generated using the method described in section 3.1.

Importance Values The importance values of features within each of the seven submatrices were multiplied by the importance value of the submatrix itself, as determined by analyzing the top-level matrix. The importance value of each habitat feature was then averaged across all survey respondents, weighted by matrix consistency, to generate cumulative importance values for the habitat features. The vector of cumulative importance values was normalized, so that the total importance of all features was equal to one. The respondent values and cumulative values are presented in Table 3.5. The cumulative values are graphically presented in Figure 3.3. Weighting feature importance values by consistency had a small but noticable effect on the resulting cumulative values. Among all habitat features, the average difference between weighted and unweighted means was 1.7% of the unweighted mean. The feature which differed the most between means was “recreation alone-time ratio”, for which the importance value was 3.9% higher in the weighted mean than in the unweighted mean.

Consistencies In addition to the consistencies calculated for individual matrices, an overall consistency was computed for each respondent, by taking an average of that respondent’s matrix n2−n consistencies, weighted by the number of pairwise comparisons in each matrix ( 2 for a matrix with n parameters). For each matrix and for the average consistencies, a mean was

22 Table 3.2: AHP survey data page 1

23 Table 3.3: AHP survey data page 2

Table 3.4: Subjective assessment weights feature 2 Subjective assessment Weight = feature 1 “Feature 1 is much more important than feature 2 ” 2−3.0 = 0.125 “Feature 1 is moderately more important than feature 2 ” 2−1.5 = 0.354 “Feature 1 is slightly more important than feature 2 ” 2−0.5 = 0.707 “Feature 1 is about as important as feature 2 ” 20.0 = 1.000 “Feature 1 is slightly less important than feature 2 ” 20.5 = 1.414 “Feature 1 is moderately less important than feature 2 ” 21.5 = 2.828 “Feature 1 is much less important than feature 2 ” 23.0 = 8.000

24 Table 3.5: Importance values

25 Figure 3.3: Cumulative importance values taken across all survey respondents. These consistencies are presented in Table 3.6. Con- sistencies less than 0.9 are highlighted. As the table makes apparent, consistency varied greatly between respondents, although each of the six top-level matrices had a consistency value above 90%. The average consistency over all respondents and matrices was 92.5%. The most consistent matrix was “work space” at 96.6%. The least consistent matrix was “general environmental quality” at 90.3%.

Variation Standard deviations and coefficients of variation were computed for each habitat feature, across all survey respondents. The average coefficient of variation for all features was 73.4%. The feature with the greatest standard deviation was “no hot racking”, with a standard deviation of 0.0645, and a coefficient of variation of 97.4%. The feature with the greatest coefficient of variation was “quality of communications connection”, with a standard deviation of 0.0637, and a coefficient of variation of 112.5%. The feature with the smallest standard deviation and coefficient of variation was “recreation time per day”, with a standard deviation of 0.0066, and a coefficient of variation of 45.5%. Although interpretations of coefficient of variation vary with application, these numbers imply that there is a great deal of variation from person to person in how important the considered habitat features are. It should thus be noted that a habitat design based on general results may not be optimal for all crew members, and the preferences of individual crews should be taken into account in selecting a habitat configuration for a particular mission.

26 Table 3.6: Consistencies

27 Table 3.7: Demographics of Survey Respondents By Nationality By Environment By age group American (15) Submarine (19) ≤ 40 years Italian (11) Ship (11) >40 years French (2) Arctic/Antarctic base (3) Romanian (1) Other (2)

3.4.2 Importance Value Conclusions As the data illustrates, “no hot racking” was the most important habitat feature, at 2.3 times the importance of the average feature, and 6.5 times the importance of the least important feature. Quality of medical facilities, communications connection quality, and personal hygiene round out the highest ranked functions. Work time and work space were also highly ranked, with desired work time per day having an average value of 9.4 hours. This indicates that providing an ability for the crew to perform useful work is especially impactful on the overall habitability of an environment. At the opposite extreme, the data indicate that non-physical recreation features were considered especially unimportant. Lighting quality and windows were the least important features, with windows ranked at 0.35 the importance of the average feature. The top seven features account for more than one third of the total importance; in other words, combined, they are more than half as important as the remaining twenty- seven features combined. The top twelve features account for more than half of the total importance. The data can be heuristically ﬁt by a logarithmic function with an R2-value of 0.975:

Ifeat = −0.0156 ln rfeat + 0.0699

in which Ifeat is the importance value of a given feature, and rfeat is the ordinal rank of that feature (i.e., for most important feature, rfeat = 1). This conforms with the expected outcome, in which importance values are more widely spaced among the most important features than among the least important.

3.5 Statistical Analysis

Based on the demographic data included in the survey responses, an analysis of variance (ANOVA) was performed. The breakdown of demographics among the survey respondents is listed in table 3.7. Table 3.8 lists the statistically significant variances between specific demographics and their complementary sets (the set of all respondents who do not belong to the specified demographic), as well as the difference in weighted mean between the demographic and complementary sets. As table 3.8 shows, the statistically significant variances mostly represent small variations in the mean importance of the respective features. This indicates that demographic variation is not likely to play a significant role in determining design, at least among the populations which responded to the survey. Performing ANOVA between astronauts and analogue populations could be used to justify the statistical relevance of analogue populations. Unfortunately, there were no astronaut respondents to the survey.

28 Table 3.8: Statistically Significant Variances to 95% Confidence Demographic Feature Difference in unweighted mean from complimentary set French EVA time/day +26.3% French Exercise alone ratio -11.9% American Quality of communica- -5.3% tions connection Ship crew mem- Quality of personal hy- +0.9% bers giene Ship crew mem- Quality of medical facil- +1.3% bers ities Ship crew mem- Recreation alone-time -0.8% bers ratio Ship crew mem- Sleep privacy +0.3% bers Submariners Bathroom comfort -0.6% Age 40+ Communications pri- -1.4% vacy Age 40+ Temperature control -0.8%

29 3.5.1 Fidelity of Analogue Environments The analogue environments considered in the survey may be of limited ﬁdelity, due to several factors:

• Windows may be less important in environments with a static view or no view at all, such as submarines and ships.

• Any eﬀects that reduced gravity may have on the importance of habitat features is not accounted for in Earth analogue environments.

• The ability to leave the habitat environment during EVA may impact the importance of some habitat features. This eﬀect is not accounted for in all analogue environments.

These potential failures of fidelity were not evident in the collected survey data. However, more data would be needed to identify any effects that these and other factors may have on respondents with experience in analogue environments. In particular, larger samples of analogue populations would be required, in addition to samples of the astronaut population, in order to identify and correct for all statistically significant variations between analogue and space/planetary surface environments.

3.6 Quality Function Deployment

Quality Function Deployment (QFD), developed by quality assurance engineer Yoji Akao in Japan in 1966 [21], is a technique for mapping the demands of system users (in this case, AHP-ranked habitat functions) to design features, based on subjective assessments of the strength of the relationships between demands and design features. Figure 3.4 presents a notional diagram of a QFD matrix. QFD can be useful in determining the beneﬁt of adding an extra unit of mass, volume, or other resource to a given system or subsystem, beyond that required for basic operation of the system. In the case of a minimum functional habitat, basic operation is deﬁned as supporting life for the duration of the reference mission (see section 2.5).

Figure 3.4: QFD Notional Diagram

In determining the most important design features for a minimum functional habitat, twenty-eight AHP-ranked habitat functions were mapped to ﬁfty-three design features, as shown in table 3.9. (Six AHP functions were assumed to have little design impact, and were excluded from the QFD.) Each intersection of an AHP function and a design feature was given a strength of relationship between zero and nine, indicating the level of eﬀect

30 Table 3.9: QFD Matrix

that the design feature had on the habitat function, with all other design features assumed constant. A value of one indicated a weak positive correlation, a value of three indicated a moderately strong relationship, and a value of nine indicated a strong relationship. The subjective assessments of the researchers were averaged; the relationship strengths were then multiplied by the importance values of the respective habitat features, as determined in the AHP. These importance-weighted strengths were summed for each design feature, to yield an importance value for that design feature. The vector of design feature importance values was then normalized. The normalized importance values of the most important twenty design features are presented in table 3.10. All the importance values are presented in ﬁgure 3.5. Total habitable volume was found to be the most important design feature among those considered. This reﬂects the versatility of habitable volume; an extra unit of volume within the habitat could potentially be used to help achieve any of several AHP functions. The same is true of electrical power, which ranked second. In determining QFD relationship strengths, it was assumed that the value of each design feature could vary, while the other design features were held constant. Obviously, intercorrelation exists between design features which is not addressed by this method. For example, a number of the design features considered are dependent in turn on the level of electrical power available. To supplement the value of a QFD, the degree of correlation between pairs of design features are often recorded in a correlation matrix, which can be useful in quantifying relationships between design features and identifying independent underlying design variables. Creating such a correlation matrix would be a logical extension of the work performed in this study.

31 Table 3.10: QFD Top Twenty Design Feature Importance Values Rank Design Feature Importance Rank Design Feature Importance Value Value 1 Total habitable 0.0632 11 Number of con- 0.0257 volume trollable lighting zones 2 Electrical power 0.0602 12 Heat removal rate 0.0229 3 Running water 0.0555 13 Communication 0.0217 features 4 Particle/odor 0.0499 14 Ventilation rate 0.0217 /micro-organism ﬁltration 5 Earth downlink 0.0491 15 Accoustic iso- 0.0204 data-rate lation of sleep space 6 Closed-loop water 0.0406 16 Volume re- 0.0203 allocatable for medical use 7 Humidity 0.0395 17 Complexity of 0.0203 ﬁrst aid facility 8 Frequency of 0.0349 18 Medical sen- 0.0203 clothing changes sors/diagnostic equipment 9 Accessible storage 0.0304 19 Sponge bath vs. 0.0195 volume shower 10 Total noise pro- 0.0280 20 Communications 0.0195 duced by all sys- connection qual- tems ity

32 Figure 3.5: Design Feature Importance Values

3.7 Lessons Learned

Implementing this data acquisition methodology led to several lessons. With regard to AHP, it was found that multi-level AHPs can be valuable in maximizing the number of features which can be examined, while keeping the overall size of the AHP matrices within reason for a survey. The drawback to this approach is that it reduces redundancy of information. However, for any AHP matrix with at least four parameters, there exists at least twice as much information as is strictly necessary to populate the matrix. (For n2−n four parameters, 2 = 6, whereas only three pair-wise rankings are strictly necessary to generate importance values.) This level of redundancy is probably sufficient. Thus, the trade-off is between superfluous redundancy in a single-level AHP, and extending the survey to cover more features with a multi-level approach.

33 In designing a multi-level AHP, it was determined that matrices on the same level should all be approximately the same size, and that the ultimate parameters should all be on the same level, in order to avoid weighting bias. Functions which are expected to have little impact on the ultimate design should be excluded from the AHP, in order to maximize the eﬀectiveness of an AHP survey at generating knowledge which will inform the ultimate hardware design. Finally, in the implementation of an AHP survey, awkward and confusing function descriptions, such as “recreation alone-time ratio”, should be avoided, and all functions should be well-deﬁned and explained to survey respondents.

34 Chapter 4

Preliminary Concepts

4.1 General Requirements from BAA

The primary objective of this study is to produce a conceptual design for a minimum functionality habitation element based on a minimum set of functions that are required to perform the reference mission. The minimum functionality habitation element includes basic required safety features, but does not protect against contingency situations. This element may never realistically ﬂy, but the minimum set of functions identiﬁed would provide the backbone for crew accommodations on the surface, as well as provided growth options for Lunar Surface Systems. Minimum Functionality as a design philosophy begins with an element that delib- erately meets only the minimum set of functions required to perform the mission, and no more than that. Such an element

• does not consider contingencies, nor does it have added redundancy (i.e., it is a single string implementation);

• enables a process that can add safety, reliability and other functionality to the element with informed cost, risk and performance deltas;

• does not need to meet full operational standards: it is for concept development only.

4.1.1 General Requirements List The following requirements were speciﬁed by NASA ESMD for the minimum functionality habitat element:

• The element shall demonstrate the ability to support 4 crew for 28 days, and even- tually (with growth options) support continuous 4-crew, 180-day surface stays with surge (two 4-person crews = 8 total) during a crew handover

• The element will support a 30-day contingency stay beyond the scheduled mission

• The element will operate at a pressure of 8.0 psia at an O2 concentration of 30% • The element will protect the crew from the radiation environment

• The element will accommodate logistics required for the designated crew complement during both nominal and contingency stay times

35 • The element will be able to verify (back to Earth) initial safe operational mode after descent to the lunar surface and prior to the ﬁrst crew Earth departure

• The element will accommodate dormancy by providing health status prior to any crew Earth departure

• The element is constrained to a total mass not to exceed 7,000 kg

• The element will provide all human habitability accommodations required for the lunar surface crews, including: - Human waste management - Trash management (including food waste) - Surface EVA support - Life support - Air revitalization - Thermal control - Humidity control - Pressurization

4.1.2 Contract Deliverables Contract deliverables must speciﬁcally address the following:

• Identify and deﬁne the proposed minimum required functions

• Provide rationale for the proposed minimum required functions

• Provide a conceptual design (topology, layout, sections, 3D) that accommodates the minimum required functions

• Provide mass, power and volume estimates of the concept

• Provide potential growth options utilizing the concept

4.2 Concept Development Approach

The University of Maryland study team approached the issue of habitat concept development through the adoption of an evolutionary series of design studies. A truly minimal design approach (contingency inflatable shelter with no external support infrastructure) was developed, and used as the basis for a series of trade studies. Following this effort, three parallel independent designs were developed by separate members of the team. These are presented in this report as synopses only, focusing on the habitat configuration and internal layout options. Systems trades were performed on these preliminary studies to differing levels of detail, and no effort was made to ensure cross-design commonality in approaches or underlying assumptions. The principal impact of these parallel design efforts was to bound the design space in terms of habitat sizing, configuration, and assumed levels of external infrastructure. The lessons learned were applied in the selection of parametric design exercises and the detailed final habitat design, documented in following sections of this report.

36 4.3 Initial Concept

The proposed habitat reﬂects the initial assumptions and requirements that it must provide life support, radiation shielding and EVA support. The habitat consists of a main cylinder containing all the necessary supplies (food, O2, water, etc.). The following concept was created only to develop a methodology to follow during trade studies and future design concepts, and to gain experience from an initial design exercise.

Figure 4.1: Initial Concept Section

4.3.1 EVA Support The crew is considered to arrive on the Moon separately from the habitat, and one suitport is provided for entry and exiting the habitat. The suitport will be used as follows: • The ﬁrst astronaut locks in, exits the suit and seals the suitport. The astronaut then enters the crew compartment and reseals the backpack interface.

• The second astronaut (still outside the habitat) disengages the ﬁrst astronaut’s suit from the suitport and places it in an unpressurized enclosure located on the side of the habitat, hooking it into a suit recharge connector.

• The second and third astronauts repeat the operation until the last astronaut is the only one outside. The last astronaut then closes the external suit enclosure and locks into the suitport. The suitport is also equipped with a soft protective enclosure that the astronaut will have to close before exiting the suit.

• Once the last astronaut is out of their suit, that suit is attached to an internal recharge station. Once the operation is complete, the habitat is fully populated, with one suit attached to the suit port, and the remaining three in the external enclosure. All four suits are charging at this point and can be monitored from the inside. While this is a truly minimal

37 approach to EVA access, it does require a "last in, ﬁrst out" approach, unless multiple crew members ﬁt the suit in the suitport.

4.3.2 Structure The habitat will consist of a hybrid hard-soft structure. The crew quarters will only provide resting and minimal activity space. The volume allocated for the crew in this concept is designed to be the minimum possible and will be used as a lower limit in the later designs. All other activities such as recreation, eating, sleeping, etc. are assumed to take place in the resting position.

4.3.3 Radiation Shielding In order to reduce the habitat mass, radiation shielding will be provided by covering the inflatable part of the habitat with lunar regolith. Additional studies have to be performed in order to validate design issues, such as how much time will be required to cover the inflatable section of the structure, how much effort this will require from the astronauts in EVA, and whether this reduces the mechanical loads on the inflatable structure by applying a constant load opposing the pressurizing loads. Additional radiation shielding will be provided by locating the water tanks on the walls of the habitat.

4.3.4 Life Support A brief trade study was performed for the life support system in this design concept. The basic trades examined were

• expendable lithium hydroxide (LiOH) canisters for CO2 collection versus a regenerable two bed molecular sieve (2BMS)

• open loop oxygen replenishment versus a Sabatier reactor to obtain oxygen from captured CO2 • open loop water recycling versus recovery of water from atmospheric condensate versus recovery of condensate and urine water All system parameters were taken from Eckart [22]. Since the contingency shelter was required to be totally independent of other support systems, life support system trades were performed on equivalent system mass, in which it was assumed that the required power for each system added a mass allotment of 1.04 kg/W for power generation, energy storage, power management and distribution, and thermal control systems. Water is traditionally the consumable which requires the greatest mass allocations, and is therefore the first loop to consider closing. As shown in Figure 4.2, the breakeven point between open loop water and condensate recycling using ultrafiltration and reverse osmosis is less than 20 days. Although the more difficult task of recycling urine to potable water requires some form of distillation (assumed to be vacuum condensation distillation, or VCD, as the system with the current highest TRL), the breakeven point for this technology is still less than the maximum mission length specified for the habitat, with is a 28 day nominal mission with a 30 day contingency. For this reason, the full urine recycling system as adapted as the baseline water remediation system. Figure 4.3 shows the equivalent trade-off between the use of expendable LiOH canisters for CO2 scrubbing and a renewable 2BMS system. In this case, it takes a mission duration of approximately 100 days to reach equivalence between the LiOH and 2BMS

38 Figure 4.2: Comparison of Open and Closed Loop Water Systems

systems, driven largely by the ESM of the 2BMS power supply. The decision was therefore made to baseline an expendable LiOH system for CO2 capture.

Figure 4.3: Comparison of Expendable and Reusable CO2 Collection Systems

If carbon dioxide is captured in a releasable form, there is the potential for disso- ciating it to return the oxygen to the cabin environment. This is not an option for this design following the selection of a LiOH based scrubbing system, as the CO2 adsorbed by the LiOH granules is not conveniently releasable. However, for completeness, Figure 4.4 shows that at approximately 120 days mission duration the recovery of oxygen from CO2 becomes the mass-optimal approach.

39 Figure 4.4: Comparison of CO2 Disposal and Reuse

Figure 4.5 explores the sensitivity of the final life support system selected to operation in off-nominal conditions. In this chart, the choice of life support components was made based on the optimal selections for 28 day and 180 day mission durations. These choices were compared for mission durations up to 180 days. As can be seen in the figure, the 28- day optimal system produces the minimum equivalent system mass for mission durations up to 120 days. Above that limit, the use of the 180-day optimal system configuration is mass optimal. This clearly shows that the same life support configuration is ideal, whether the ESMD minimal habitat design is based on the 28-day nominal mission or the 58-day worst case contingency scenario. It also shows that, even designing for short durations, the overall mass of this concept is strongly dependent on the mass of the life support system and associated consumables and power supplies.

40 Figure 4.5: Comparison of ESM Performance of 28- and 180-day Optimal Systems

41 4.4 Concept 1 : The Lunar Pup-Tent

This is the ﬁrst of three parallel design exercises to explore the design space for minimum functional habitats. As discussed above, these three designs are presented in an abbreviated form.

4.4.1 Operational Scenario The Lunar Pup-Tent (LPT) preliminary concept ﬁnds its operational application in those contingency scenarios where crew survival is the only objective. After a critical failure in a primary system, such as a main habitat or a lunar rover, the LPT is designed to buy time for either an outpost-based or an Earth-based rescue mission. As a consequence of those initial assumptions, the LPT was designed to be as simple (and hence reliable), as light, and as small as possible while still guaranteeing crew survival. The LPT was required to provide for crew survival for a maximum duration of 28 days for a crew of four. From the top-level requirements, the life support system was sized to operate at a nominal pressure of 8.0 psi at an O2 concentration of 30%. Due to the nature of this concept, it must be capable of operating in a very wide range of locations on the lunar surface, and must be easily deployed and independent of external infrastructure.

4.4.2 System Concept

Figure 4.6: Pup-Tent Dimensions

As previously stated, the only objective of the LPT is to ensure crew survival. From a habitability perspective, this system will provide the basic needs such as the ability to rest, eat, communicate with mission control, exercise and take care of one’s personal hygiene. The shelter is divided into three separate areas: the cabin, the airlock, and the restroom. The cabin and the airlock are the biggest functional areas, at 25 and 5 cubic meters in volume, respectively. The restroom is an integral part of the cabin, from which it is separated by a thin fabric curtain. The entire habitat when deployed is a horizontal cylinder, 6.8 m long, varying in width from 1.6 to 2.2 m, and 2.6 m tall. From an initial budget exercise, its total mass is below 3000 kg and it has an average power consumption is approximately 400 W.

42 Table 4.1: Concept 1: Mass and Power Budget Mass (kg) Volume (m3) Power (W) Life Support 1318 2.3 77 Power 706 0.04 N/A Comm 35 0.02 100 Structure 164 0.3 0 EVA 30 N/A 20 Thermal 120 N/A 50 Avionics 30 0.2 50 Miscellaneous 400 5 100 Totals 2804 7.88 397

4.4.3 Interior Layout The cabin, as previously stated, is a single space separated from the restroom by a thin curtain, allowing for some privacy during use. The cabin is 4.5 m long and 2.2 m tall overall. The central passageway is 1.5 m wide, except in the mid-section where it is reduced to 0.75 m wide. This structural element is composed of three 1.5 m square platforms that allow for isogrid flooring and access points to lower storage spaces and systems for maintenance. The cabin also contains four beds, two of which are stowable (Figure 4.7 depicts the two bunks in the two possible configurations). Below the lower bunks, which are also used for seating during nominal daytime operations, there is extra storage space and food preparation equipment, such as a microwave and a small refrigerator. In the aft section of the cabin is the privacy curtain for the restroom, which contains a single toilet and a small sink as well as a small personal hygiene equipment storage space. The mid-section is the core of the LPT, since it will probably be the location where the crew will spend most of their time. During daily ops, the two upper beds are stowed in the vertical position and, if necessary, one of the two can be dismounted from its rack and mounted between the two lower bunks, making a table. In the forward section of the cabin there is exercise equipment (two treadmills and two multi-functional fitness bars), as well as the main control station for the LPT. This very simple and compact station will allow the crew to monitor the status of the habitat, communicate with Earth, and possibly allow for some recreational features such as music and videos. The LPT internal livable volume is 25 m3; it also allows for 2.5 m3 of storage space distributed under the flooring, under the two central bunks, and in the toilet space.

4.4.4 Life Support The LSS for the LPT was designed with simplicity paramount, followed by mass and power eﬃciency. Given the 28-day mission duration, it is easy to assume that a closed- loop LSS is necessary, at least with regard to water recycling. However, for this speciﬁc application where a quick deployment of the habitat and radiation shielding are necessary, there is clearly a dual use for the LSS water; the necessary water for the mission (720 kg) will be used for both life support and radiation shielding. Due to the cabin dimensions, it was found to be unnecessary to close the water loop. This solution allows for a much simpler and more reliable water system, composed of a number of small water sacks that

43 Figure 4.7: Pup-Tent Interior

make up an interior layer of the skin of the habitat. The system is automatically managed by the onboard avionics, and works in such a way that all sacks are always full of either potable or waste water. This function is achieved by the use of two small holding tanks (one for potable water and one for waste water) located under the restroom section. At launch, all the water sacks and the potable water holding tank are full. Once the waste water holding tank fills up, a full potable water sack is emptied in the fresh water tank and the empty sack is refilled with waste water. The environmental control for the LPT relies on pressurized gas tanks for oxygen and nitrogen, as well as two 2-bed molecular sieves for CO2 removal and particulate filters for dust and other contaminant mitigation. The CO2 removal system, which is more complex and less reliable than the other systems, was selected due to its advantages in mass and volume; it was therefore the only redundant system selected for this concept.

4.4.5 Avionics, Power, Thermal, and Communications In this preliminary concept, avionics, power, thermal management, and communications systems were not analyzed in detail. Avionics will rely on a single management computer which will acquire data from the various systems and relay data to the crew via an LCD screen. The data will also be transmitted back to mission control. The onboard avionics will also allow the crew to communicate through both text and voice (when necessary) with mission control, but with severe bandwidth limitations, and noticeable delays on the order of several seconds. This is the result of a low power transceiver equipped with a simple omnidirectional antenna. This setup allows for required communications with Earth at limited bandwidths. If one or more relay satellites are used, efficiency and bandwith will be improved. Thermal management of the habitat was the least explored system, since the dimen- sioning and design are highly dependent on location on the lunar surface. In order to allow for flexibility, it is very likely that an active dual phase system will be necessary in order to exchange heat from the interior to the exterior. Thermal management inside the habitat will be easier to implement, due to the relatively high pressure of the internal atmosphere, which makes convection exchange feasible. Power will be provided by a combination of lithium-polymer rechargeable batteries and a fixed solar array used to recharge them. Due to the mission duration and the unknown site location, the power system is designed to withstand a maximum of 14 days of darkness.

44 4.4.6 Structure and Storage The LPT, due to its nature as a contingency system, was designed to be easily stored and transported. In order to do so, the LPT was designed to be collapsible and to take up as little volume as possible. The main structure defines the shape of the LPT both when inflated and deflated. It is divided into three main square sections, each 1.5 m long. These three sections fold inwards, and the two end support hoops can also be rotated inwards, allowing for a high compaction ratio when the LPT is stored. The total volume of the LPT when stored is 7 m3, allowing for storage of the interior systems and the external skin, including the water walls and the airlock (not shown in Figure 4.8).

Figure 4.8: Pup-Tent Folding

The main structure is composed of aluminum, while the skin will be mainly Kevlar fabric. No finite element analysis (FEA) was done. As a derived requirement, the structure when stored must be capable of sustaining launch loads. While inflated, it must sustain all the loads induced by the pressurization of the habitat, and also all the loads created by the crew. The LPT will rely on six adjustable legs, positioned on the four edges of the structure and the center of the central section, for leveling on the lunar surface, as well as for separating the soft inflatable goods from sharp rocks that could cause damage to the shell. The airlock will rely on its own legs for the same purpose. Due to the dimensions of the stowed LPT and its mass, it can easily be launched with a conventional medium or large class ELV. Descent and landing operations and procedures have not been considered for this concept.

45 4.5 Concept 2 : The Winnebago

4.5.1 Operational Scenario The second preliminary concept design, dubbed the “Winnebago”, is based on a nominal sortie mission profile, in which the habitat element is supported by an Altair lander. The habitat element is designed to operate independently of the Constellation outpost architecture, but can be adapted and expanded to fill a role as part of an outpost. Because the mission profile of this concept is not a contingency scenario, the concept design can require more involved in-situ preparation before it is habitable. The Winnebago takes advantage of this, allowing for a more compact element to be delivered to the lunar surface, which is then expanded and furnished by the sortie crew.

4.5.2 Design Concept

Figure 4.9: Winnebago Dimensions

The design concept for the Winnebago is a habitat element which provides for crew functionality for the 28-day nominal reference mission with a minimum of resources. The selected habitat arrangement is a horizontal cylinder, mated to an airlock via a universal hatch that can dock to other elements in a possible outpost role. The habitat pressure shell is a mid-expandable hybrid rigid/inﬂatable design that addresses the need for low delivery volume, high habitable volume, low mass, and protection of the crew from solar particle events.

4.5.3 Pressurization and Furnishing The Winnebago habitat element is delivered unpressurized to the lunar surface. Interior systems are not hooked up, and are arranged compactly within the habitat. The habitat cylinder has a fixed diameter of 2.3 m, and expands axially upon pressurization to a length of 6.5 m. Mid-expandable geometry has been examined previously in NASA’s Rigid Expandable Module concept. The airlock expands to a length of 1.5 m. Mass estimation for inflatables was determined heuristically from existing examples of inflatable pressurized habitats. The combined mass of the pressure shell, SPE shelter (excluding water), and multi-layer insulation is 189 kg. Upon entering the habitat, the sortie crew must re-arrange

46 Table 4.2: Concept 2: Mass Budget System Item Mass (kg) Structures Shell 189 Life Support N2 Tanks 49 KO2 616 Nitrogen 19 Hygiene/ Medical Equipment 21 Food 473 Water 977 Avionics All 48 Power All 3203 Thermal All 140 Total Mass 5730 +30% Margin 7450

and install the internal systems, including aluminum isogrid ﬂoor pieces, hygiene facilities, stowage lockers, galley, mission/comms console, and wardroom table.

4.5.4 Interior Layout and SPE Shelter The interior of the Winnebago habitat element is arranged by functional grouping, with related or concurrent activities located near one another. At one end of the habitat is the crew quarters, which provide for sleeping, recreation, privacy, and communications. Each crew member has a bed, arranged in paired bunks, aﬀording approximately 0.58 m3 of habitable volume per crew member. Beds were chosen over hammocks for crew comfort, which, given the moderate-length mission duration, may be a factor in productivity. Each bunk space also includes a personal stowage area and a drop-down video monitor, which can be used for entertainment and communication. The crew quarters also serve as a solar particle event shelter, with a combined water and aluminum shield providing up to 7 g/cm3 of protection at the start of the mission. In a historically major SPE, this level of protection will keep radiation dosage to around the annual limit. Lunar regolith was not considered for SPE shielding, and galactic cosmic radiation protection was not considered in this concept design. The physical isolation of the SPE shelter also provides noise reduction and a sense of private space. Just outside the crew quarters/SPE shelter is the hygiene facility (including toilet, sink, hygiene equipment cabinet, and privacy curtain), and the exercise space. Ex- ercise activities include resistance training and potentially a treadmill or stationary bike. The exercise space can potentially have visual access to a window. Past the exercise space is the mission/comms console, from which crew members can monitor habitat and medical sensors, communicate with Earth, and perform mission- related tasks. The position of the console allows multiple crew members to share visual access, providing for easy information sharing, a feature which was found to be important based on survey comments (see section 3.02). The wardroom/eating area is located at the opposite end of the habitat from the crew quarters and hygiene facilities. Food preparation (heating) is done adjacent to the wardroom table, which is a foldable/stowable tray-table similar to that used on Skylab.

47 Figure 4.10: Winnebago Interior.

The stowing table allows easy access to the airlock hatch at the end of the habitat. The total pressurized volume per crew member is approximately 30 m3. This is at the low end for most heuristic models of the amount of space required for productivity, and may subsequently have an impact on crew morale. Regular extra-vehicular activity can help to reduce the stress of a cramped environment.

4.5.5 Life Support Life support requirements for the Winnebago are largely derived from NASA’s Man- System Integration Standards 90-day degraded limits. The cabin atmosphere is 30% O2/70% N2, at a total pressure of 67 kPa. This atmosphere allows for the lowest mass of diluent gas while staying within flammability limits. Oxygen generation and CO2 removal are provided by a KO2 superoxide/ozonide reaction, which was found to require the lowest mass for the mission duration out of the various systems considered, including gaseous O2 storage and LiO2 reaction for oxygen provision, and LiOH filtration, electrochemical depolarization concentration, and 2-bed molecular sieves for CO2 removal. The estimated mass of the superoxide system is 616 kg. Cabin air is circulated to generate a flow velocity of 1.4 m/s, the average of the operational guideline, in open cross-section portions of the habitat. The cabin air temperature is maintained at 22oC. 0.5 micron filtration, moisture removal, and activated charcoal odor adsorption complete the atmosphere treatment cycle. An ISS-legacy Evolved Water Recovery System (EWRS) was considered for water recycling. However, it was found that for the mission duration, the EWRS would incur a mass penalty rather than provide a mass savings. The 28 day reference mission is, however, just shy of the break-even point for the EWRS. The mass of water consumed during the mission is 977 kg. An estimated food mass of 473 kg, including packaging, is consumed during the mission. Flushed waste is stored in a tank underneath the habitat floor.

48 4.5.6 Avionics, Power and Thermal Continuously powered systems include: a heat pump compressor, computers, moni- tors, S-band radio, cabin lighting, air circulation fan, and personal entertainment centers. An estimated 1.5 kW of power is provided by 14.6 m2 of ultra-lightweight solar cells during the lunar day, which charge 3200 kg of lithium ion batteries for use during the lunar night. Given the length of the mission, fuel cells were considered for energy storage, but with a charge/discharge eﬃciency of around 50% compared to 99.9% for lithium ion batteries, they were not a practical option for multiple charging cycles. The active thermal control system is based on similar habitats, and weighs an estimated 150 kg. Avionics mass and power estimates were entirely heuristic.

4.5.7 Exterior Layout and EVA Nitrogen tanks, batteries, solar cells, radio antennae, and a radiator with a sun shade are mounted external to the habitat. The airlock exit features an open aluminum isogrid dust porch and stairs. The habitat will be as close to ground level as possible for ease of access to the surface. Jacks and foot pads at the corners of the habitat provide leveling.

49 4.6 Concept 3 : The Igloo

4.6.1 Operational Scenario The third preliminary concept looked at a minimum functional habitat which leverages systems provided by NASA’s permanent lunar outpost. NASA’s Exploration Systems Mission Directorate has plans for an initial outpost by 2022. Due to benign environmental conditions, continuous line of sight to Earth, and potential access to trapped water ice, NASA’s outpost is currently planned to be located near the Lunar South Pole. It will be developed as part of an incremental build strategy using a combination of crewed landers and dedicated cargo missions. Figure 4.11 depicts NASA’s incremental build strategy. Once operational, the outpost will house four crew members for four to six month intervals. This station will take advantage of in-situ resource utilization. Concept 3, named Igloo, leverages on the already established infrastructure by tapping into the power and communication equipment already present. The Igloo would be used as an emergency or expansion shelter. This ﬁgure also shows a NASA outpost layout with the additional habitat. Its placement within an excavated trench provides added protection against ionizing radiation and micrometeoroid impacts.

Figure 4.11: NASA’s incremental build strategy (Source: NASA ESAS [5])

4.6.2 System Concept The idea behind the Igloo is to provide a habitat with minimum functionality without sacrificing the ability to extend personnel or mission duration. Its functions include 24- hour power back-up for emergency operations, inner and outer airlocks, and two expansion nodes that double as emergency exits. It is initially equipped with enough consumables for an extended stay of 58 days. Figure 4.12 shows the overall design. The lower half is made up of an aluminum lithium shell and support longerons. The upper half is an inflatable Kevlar structure. The total mass of the habitat is 6,819 kg, with an overall volume of 184.3 m3. During transit, the inflatable structure is stowed. Once on the surface, the outpost crew moves the habitat to the ISRU excavation area, and connects the power and communication lines to the main outpost. Once connected, the habitat inflates the Kevlar dome and initiates an automated

50 system checkout process. After this process is complete, the crew can enter and begin setting up the habitat for operations. The overall mass breakdown of the habitat is shown in Table 4.3.

Figure 4.12: Igloo Dimensions

Table 4.3: Concept 3: Mass and Power Budget Subsystem Mass (kg) System Power (W) Structure 2207 Power (34 hrs of contingency) 600 ECLSS 2005 Thermal 300 PMAD 100 Avionics 250 Thermal 30 Life Support 2444 Avionics 100 Airlock with Pumps 631 Internal Systems 500 Internal Equipment & Supplies 567 Total 2735 Total 6999

4.6.3 Habitat Layout The first floor houses the main work space. Here, the crew can perform intravehic- ular activities (IVAs), prepare meals, exercise, and even perform a limited set of medical procedures. In addition, the first floor houses the internal and external airlocks. The internal airlock is used for EVA equipment and suit storage. This area reduces the potential for lunar dust entering into the main living areas. The upper floor is used for sleep, personal relaxation and hygiene. Here, the crew can relax and be visually and physically isolated from the main workspace. Dust mitigation is further accomplished through the vertical separation of the floors. The hole in the floor is used to transfer the beds and hygiene facilities from the first to the second floor during initial setup. This space can be closed by a hatch to provide acoustic isolation, or opened to provide a greater sense of total habitable volume. The total habitable surface area of the lower and upper floors is

51 Figure 4.13: Igloo Interior

58.2 m2, or 14.6 m2/person for a crew of four and 7.3 m2/person for a crew of eight. Below the ﬁrst ﬂoor but still within the pressurized shell is the housing for the environmental, life support, thermal, and power systems. Outside of the enclosure are the liquid nitrogen and liquid oxygen tanks.

4.6.4 Structure A hybrid rigid-inﬂatable structure was chosen to provide a compact transit structure without comprising overall habitable volume. The drivers for determining the thickness of the habitat’s structure were launch stresses, micrometeoroid impacts, ionizing radiation, and internal atmospheric pressure. The lower structure is comprised of an aluminum- lithium 8090-alloy shell. It has a tensile strength of 480 MPa and a calculated thickness of 0.3 cm. The upper structure is comprised of a Kevlar-49 double wall inﬂatable structure. It has a tensile strength of 690 MPa and a single wall thickness of 0.25 cm. The total mass of the structure including support longerons, internal decking, and external structure is 2,207 kg. Table 4.3 provides a mass breakdown of the structural elements of the habitat.

4.6.5 Life Support This habitat must support life for 28 days with a 30 day contingency stay. The atmospheric pressure is 8.0 psi with a 30% oxygen composition. In addition, an option to expand to a 180-day mission was considered in the design. To accomodate this option, a closed water system and a partially closed CO2 system was chosen. The water puriﬁcation system consists of a supercritical wet oxidation system to purify all types of waste water, and an initial potable water supply of 1,000 kg. The CO2 removal system consists of a

52 two-bed molecular sieve for CO2 reduction, and a trace contamination control system for removal of additional airborne hazards. Nitrogen and oxygen are housed in a cryogenic state outside of the habitat. The mass of the life support system including the mass of the water required for a crew of four for 58 days, external LN2 and LOX tanks, and other related equipment is 2,316 kg. Table 4.3 also details the mass break down of the life support system.

4.6.6 Power Main power is provided by the outpost nuclear power generation system. The habitat contains a power management and distribution system and a lithium-ion (100 W-hr/kg) energy storage system for use as an emergency back-up. The lithium-ion batteries were sized to provide 24 hours of emergency power. The system mass including the PMAD and wiring is 550 kg. Table 4.3 also shows the power budget used for sizing of the back-up power.

4.6.7 Avionics There is no independent avionics package in the habitat. The communication lines that link back to the main outpost create a local area network. This network allows the crew to connect their laptop computers and gain virtual access to the outpost communications capabilities. The habitat, however, does contain a small computer system that is used to initiate and monitor the life support, thermal, power, and emergency systems. It is estimated that the internal computer monitoring systems will have a mass of about 50 kg.

4.6.8 Additional Equipment The habitat also contains a freezer, microwave, food, hygiene and medical supplies. The total mass of these items comes to 567 kg.

4.6.9 Summary The third preliminary habitat concept is a minimal functional habitat that has volume and capacity for expansion to support a 180 day mission or crew expansion to eight. These drivers resulted in a larger environment, or habitat shell, to allow for expansion capability.

53 4.7 Virtual Reality Testing and Evaluation

In order to evaluate the three preliminary concepts, a quick and ﬂexible infrastucture was required that could give a feel for the concepts dimensions and internal space allocation. Through a simple implementation of virtual reality (VR), the team was able to use the previously developed CAD models to evaluate the concepts. This rapid testing of the concepts allowed a greater level of insight and a much better understanding of the layout environment. It also allowed the implementation of a more rigorous down-select process, and highlighted several aspects of the proposed concepts with regard to habitability that might otherwise have passed unobserved.

4.7.1 Equipment For this evaluation an eMagin Z800 3D Visor was used. The visor projects a 40o diagonal ﬁeld of view for the user with a resolution of 800×600 and a refresh rate of 60 Hz. The display is capable of displaying stereoscopic images by using page ﬂipping, commanded by proprietary Nvidia Drivers (Forceware 3D Stereo Driver 91.31). This system, along with Dassault Systems Virtools V4.1 Student Edition, allowed the importation of almost any CAD model into a virtual environment.

Figure 4.14: VR Equipment

The Head Mounted Display (HMD) is also equipped with three built-in accelerom- eters that allow tracking of the user’s head rotations, and maps those rotations into the virtual environment. Since translation tracking has not yet been implemented, a traditional joypad was used to allow the user to navigate in the environment. The combination of head rotation tracking, stereoscopic image display, and relatively high resolution and field of view allowed for significant user presence, and therefore gave an intuitive "feel" for the preliminary concepts. The first model to be evaluated was the Lunar Pup-Tent. This is the smallest of the three, and the first thing that was noticed in VR was a tunnel vision effect induced by the horizontal cylinder layout. The diameter of the cylinder is large enough to allow

54 for unconstrained range of motion in some areas, but still does not allow for any physical separation between functional areas. All the systems are very close together, and there is not a signiﬁcant amount of space to allow crew movement within the habitat. Storage and systems are located under the ﬂooring; therefore, it is most likely that equipment and personal belongings must be relocated in order to allow servicing or access to stored equipment. All crew areas are multipurpose, so little or no equipment can be permanently stored in sight.

Figure 4.15: Concept 1 VR

The second concept, the Winnebago, was similar to the Pup-Tent concept, in that it adopted the horizontal cylinder approach, and also showed tunnel vision eﬀects. On the other hand, the increased internal volume and internal space allocation allowed for some physical separation of the functional spaces, and reduced constraints in crew movement and temporary storage location.

Figure 4.16: Concept 2 VR

The last concept differed significantly from the first two, being a vertical cylinder. The tunnel vision effect was not present at all, and the two floor layout allowed for extensive separation between functional areas. This concept is very spacious, although it was found that the access hole for the second floor, if located in the center, reduces the usable floor area on the second floor and constrains area utilization.

4.7.2 Lessons Learned VR is a useful tool for rapid evaluation of concepts if one keeps in mind and ap- propriately implements the following system features. Accurate registration in the head

55 Figure 4.17: Concept 3 VR tracking is fundamental to allow for a realistic sensation of user presence, and must not be constrained to just rotations. It is highly recomended to also implement motion parallax through translational tracking of the user’s head. Future implementations of this system will use Flock of BirdsTM as the primary tracking system, providing 6 degrees of freedom tracking with 1:1 registration. Relative position information is a very eﬀective cue for determining the dimensions and placement of virtual objects, as well as for determining reach envelopes. Implementing properly-registered tracking and VR visualization of the user’s hand is a higly desirable feature. This will also be implemented in the future through Flock of BirdsTM by using a second sensor positioned on the user’s palm. Lastly, HMD properties such as wide ﬁeld of view and high resolution are key for a proper and immersive evaluation. Other considerations for the VR setup include:

• Models must be very detailed in order to give a feel for the environment. This doesn’t necessarily require the models to be photorealistic, although it would be desirable. However, this does require all the functional elements to be implemented in 3D, and to possibly allow for user interaction (e.g., if foldable tables are used, the user should be able to fold and deploy them in VR to gain a better feel for the diﬀerent possible conﬁgurations.)

• A future implementation of the VR system should take into account crew size and model the remaining crew members in the habitat in order to provide a better feel for the environment when fully populated. Artiﬁcial intelligence (AI) is a desirable feature for realistically interacting with the remaining crew members, but it can be bypassed by using static additional crew members, and by allowing the user to swap perspective between them and gain control of each of them in real time. This feature will allow for a better understanding of crew movements during routine operations.

• Horizontal cylinders give a sense of tunnel vision, if the view down the length of the cylinder is uninterrupted.

• Vertical cylinders allow for better ﬂoor space usage, but provide less wall area.

• In vertical cylinders, vertical ladders should not be located in the center of the ﬂoor space, but on the side to allow for better usage of the upper ﬂoor space.

56 Chapter 5

Conﬁguration Trade Studies

5.1 Analytical Modeling

The results of the multiple point design process yielded a strong knowledge base for the final design, but did not provide sufficient data to definitively choose between a horizontal or vertical habitat configuration. As it turned out, the sole vertical habitat design was targeted at a design point so much larger than the other two that none of the differences in the design could be clearly identified as a result of the orientation decision. The literature search offered some clues, but no definitive answers to the orientation question. By far, the majority of small habitats are horizontal cylinders, and some space architecture papers have concluded that the horizontal orientation is preferred up to a diameter of 3.5-4 meters, where split levels become feasible. Once the individual habitat becomes large enough for multiple levels, there seems to be a consensus transition to a vertical configuration, frequently inflatable with a completed diameter of 7-8 meters or more. However, few of these studies address the constraints NASA has placed on the minimum functional habitat. The maximum mass limit of 7000 kg (equipped) is much smaller than most of the studies from literature. Indeed, part of the bias for horizontal orientation in smaller systems may be traceable to the fact that many of these designs are pressurized rovers, and the horizontal configuration is mandated by center of gravity and rolling stability concerns. To address the orientation issue directly, the University of Maryland team under- took a geometry-based analysis to better understand the internal design efficiency of both configurations. For this trade study, the assumption was made that the habitat would be cylindrical with symmetrical ellipsoidal end caps. The goal of the analysis was to identify the habitable floor area and volume in each habitat, based on an assumed minimum ceiling height for standing headroom. Since much of the design functionality is driven by wall area in proximity to the ground (for access hatches, berthing ports, and suitports), the analysis also considered the length of available wall length at external ground level. As shown in Figure 5.1, the definition of “habitable space” is fixed by the assumption of a constant value for desired standing headroom. As the cylindrical diameter grows, the width of the available floor space increases based on the inscribed rectangle of constant height. A standard 7.5 ft headroom corresponds to a floor-ceiling height of 2.25 m. Using this value, the horizontal orientation cannot become a multifloor arrangement until some point after the diameter exceeds 4.5 m, which will be shown to be well above the feasible range for a habitat below 7000 kg. It is assumed for either orientation that the pressure hull is a right circular cylinder

57 Figure 5.1: Concept of "Habitable Space" Internal to a Horizontal Cylinder of Varying Diameters of diameter d and length `, with ellipsoidal endcaps of maximum height k. Simple analytic geometry provides the equations for volume and surface area of the cylindrical component as π V = d2` (5.1) cyl 4

Acyl = πd` (5.2) For the axisymmetric oblate ellipsoidal endcaps, the internal volume of both endcaps is defined as 4 V = πr2k (5.3) end 3 which, it should be noted, produces the traditional equation for the volume of a sphere when k = r. Given a desire to define the nature of the ellipsoidal endcap in terms of the ratio between radius r and height k, where a “4:1” ellipsoid has a value of r equal to 4 times k, we can define the reciprocal ratio

k 2k ≡ = (5.4) r d and rewrite equation 5.3 in terms of and d to find π V = d3 (5.5) end 6 The surface area of an ellipsoid is complicated to compute exactly; in this analysis, the approximation of 1 apbp + bpcp + cpap p A = 4π (5.6) end 3 is used; a, b, and c are the semi-principal axes of the ellipsoid, and an accurate estimate is generally obtained for p=1.6. Since this is an axisymmetric oblate ellipsoid, we can substitute d d a = b = r = and c = k = (5.7) 2 2 to find the final estimate of the surface area for the two ellipsoidal endcaps

1 1 + 2p p A = πd2 (5.8) end 3

58 As a check, substituting = 1 correctly produces 4πr2 as the area of a sphere. We can now write explicit relations for the total volume and surface area of the habitat pressure hulls: π π V = d2` + d3 (5.9) tot 4 6 1 1 + 2p p A = πd` + πd2 (5.10) tot 3 A further parametric enhancement of this can be obtained by deﬁning the length/diameter ratio for the cylindrical section of the habitat ` λ ≡ (5.11) d The total volume and area equations can now be written in nondimensional form V λ ν ≡ tot = π + (5.12) tot d3 4 6

" 1 # A 1 + 2p p α ≡ tot = π λ + (5.13) tot d2 3 The habitable area of a vertical configuration pressure hull is the cross-sectional area π A = d2 (5.14) xsec 4 multiplied times the number of floors, defined as η. The habitable volume is then simply the habitable area times the floor height h. Since there is little reason to extend the cylinder length beyond that required for the number of living levels, an assumption is made for vertical orientation habitats that the cylindrical length is fixed by ` = ηh. The final parameter of interest, surface contact length Lsurf , is the circumference of the cylinder regardless of the number of living levels. Formally, the equations for a vertical geometry habitat are π π V = d2hη + d3 (5.15) tot,V 4 6 1 1 + 2p p A = πdhη + πd2 (5.16) tot,V 3 π V = d2hη (5.17) hab,V 4 π A = d2η (5.18) hab,V 4

Lsurf,V = πd (5.19) The internal parameters for the horizontal orientation are deﬁned in Figure 5.2. From the Pythagorean theorem, p w = d2 − h2 (5.20) which produces a habitable ﬂoor area of w` and habitable volume of wh`. The surface contact length is approximately 2(` + d), which is a reasonable estimate for the baseline assumption of a 4:1 ellipsoidal end cap. The summary equations for a horizontal habitat orientation are listed below. π π V = d3λ + d3 (5.21) tot,H 4 6

59 Figure 5.2: Deﬁnition of Parameters for Habitable Volume/Area Analysis

1 1 + 2p p A = πd2λ + πd2 (5.22) tot,H 3 r p h2 V = h` d2 − h2 = d2hλ 1 − (5.23) hab,H d2 r p h2 A = ` d2 − h2 = d2λ 1 − (5.24) hab,H d2

Lsurf,H = 2(d + `) = 2d(λ + 1) (5.25)

5.2 Trade Studies

With the underlying equations derived, direct numerical comparisons can be made between the horizontal and vertical habitat orientations. For example, Figure 5.3 shows the trend of total internal volume for habitats with 4:1 ellipsoidal endcaps. The two vertical orientation lines correspond to single and double internal floors, which set the cylindrical length of the habitats at 2.25 m and 4.5 m, respectively. The cylindrical lengths of the horizontal pressure hulls were set somewhat arbitrarily at 3 m, 5.5 m, and 8 m. All of these cases follow identical trends; indeed, if the horizontal cases used the same values for length as the vertical cylinders use for height, there would be perfect alignment of the area vs. diameter lines for these cases, as these are identical geometries deployed in each orientation. The trends become less obvious when plotting habitable volume versus hull diameter. As shown in Figure 5.4, there is a significant advantage for the vertical versus the horizontal orientation, which becomes more pronounced with increasing diameter. In this case, the horizontal cylindrical lengths have been altered to 2.25 m and 4.5 m, to achieve exact correlation between the external configurations with the 1-floor and 2-floor vertical configurations, respectively. However, it is not a fair comparison – past a radius of 5 meters, the horizontal habitat has sufficient interior headroom for two living levels. Similarly, at a diameter of 8 meters, the preferred interior layout has three levels. Modifying equation (5.23) to account for various internal levels, a more accurate comparison of the available interior habitable volumes is presented in Figure 5.5. However, these charts do not convey all of the necessary information for decision- making. While it would be easy to calculate, for example, the volumetric efficiency of the

60 Figure 5.3: Total Habitat Volume vs. Cylindrical Diameter (η=0.25)

Figure 5.4: Habitatable Volume vs. Cylindrical Diameter (η=0.25)

various design options, the critical factor is to maximize habitable volume and area while meeting the stringent mass limits for this study. To study the mass implications of design conﬁgurations, the mass estimating relation (MER) for pressurized habitats was adapted from NASA JSC-26098, which provides a mass estimation based on external area [23]

2 1.15 mhull < lbs >= 2.00(A < ft >) (5.26)

A little judicious algebra produces the equivalent expression in metric units:

2 1.15 mhull < kg >= 13.94(A < m >) (5.27)

Using this result, we can replot Figure 5.3 in terms of habitat structural mass, as shown in Figure 5.6. Given the hard mass limit for the overall habitat of 7000 kg, it is unlikely that more than 3000-3500 kg would be available for the primary structure, considering the required masses for internal accommodations and crew consumables. As can be seen in Figure 5.6, this corresponds to a maximum cylinder diameter in the 3.5-5 m range, depending on exact

61 Figure 5.5: Habitatable Volume vs. Cylindrical Diameter with Multiple Floors (η=0.25)

Figure 5.6: Structural Mass vs. Cylindrical Diameter (η=0.25)

configuration. Use of this MER will also allow direct comparison of design parameters in terms of the real objective function, which is to minimize system mass. Based on the derived relations, we can now express for any habitat configuration the resultant mass, given desired parameter values for volume, area, or available wall length. These relations are shown in Figures 5.7 through 5.9 for habitats with a diameter of 3.65 m and a variety of lengths for horizontal orientations, and for one and two floor configurations for vertical orientations. It should be noted that in addition to the parametric sizing based on the mass estimation relation, these charts also show the design point based on the detailed analysis on the final design as presented in Section 7. This provides a “reality check” for the quality of the top-level estimating process, which in this instance is typically within 5-10% of the detailed analysis. Figure 5.7 shows that both of the vertical orientation cases provide greater habitable floor area per unit mass than any of the horizontal configurations. While even longer horizontal habitats would probably become lighter than the single-floor vertical habitat at the high end of the spectrum, this is in a range which exceeds the structural mass

62 allocation for this project. In addition, at any floor area above approximately 8 m2, the two-floor vertical habitat has a significant mass advantage over all other configurations on the basis of area per unit mass, despite giving up one square meter per floor for the ladder and pass-through areas.

Figure 5.7: Structural Mass vs. Available Habitable Area

Figure 5.8 shows that the mass advantage of the two-floor vertical habitat is equally pronounced when considering habitable volumes. All of these habitats are similar configuration structures, so the favorable effect for two-floor vertical orientations is entirely due to volumetric efficiencies in utilizing as much of the interior volume as possible for habitable volume.

Figure 5.8: Structural Mass vs. Available Habitable Volume

The other parameter of design interest is the linear extent of wall area accessible to the surface. Figure 5.9 shows the trend for this parameter. This is the only case where the horizontal habitat configuration is preferred over the vertical habitats. In fact, since the two-floor habitat offers no additional surface-accessible wall over the one-floor vertical configuration, but does have a higher mass, it is the least favorable system for this design parameter. This is not a deciding criteria in and of itself; the key is to ensure that the

63 habitat will have sufficient surface-accessible area to meet all of the design requirements (for such elements as airlocks and suitports) while maintaining the area and mass advantages of the vertical two-floor configuration.

Figure 5.9: Structural Mass vs. Total Volume

Based on all of this information, the decision was made to baseline a two-floor vertically-oriented habitat configuration for the University of Maryland final design. This decision was verified through the development and testing of a full-scale mockup (described in Chapter 6), and in the detailed final designs presented in Chapter 7. Based on the results presented in this section and the desire to keep the structural mass at or below 3000 kg to meet the overall habitat mass limits, the final habitable volume will be 3.65 m in diameter with two floors, each with 2.25 m standing head room.

64 Chapter 6

Mockup Design Construction and Testing

6.1 Design and Construction

VR and system trade analyses are excellent tools for a preliminary evaluation of concepts involving humans, but the only way to truly gain reliable information for validating a design is to physically test it. In order to do so, a full scale functional mockup of the final habitat design was built. Given time constraints and manpower limitations, existing hardware was utilized as much as possible. The SSL facilities on the University of Maryland College Park campus include an outdoor storage space secured by a chain-link fence (Figure 6.1). Located in this area was a 12-foot diameter fiberglass tank used for underwater testing while the Neutral Buoyancy Research Facility was being built in 1991-92, and unused since that time. Since there was originally no plan to reuse the tank, it was not covered or maintained during the 17 years in storage. As the final habitat design was being conceived, the SSL design team realized that the tank would be ideal for the external structure of a mockup. Although it was not exactly the right dimensions (the tank is 3.3 m tall, while the cylindrical section of the design habitat is 4.5 m in height), it was determined that a fairly high fidelity representation could still be achieved using this tank. After an initial inspection of the tank in late January 2009, it was evident that extensive preparation work would be required. As the tank had sat outside and uncovered throughout the winter, a solid sheet of ice 8-10 cm thick had to be removed from the bottom. Washing and coating of the interior walls was also required before conversion to a habitat mockup could begin. Although initial inspections were performed by climbing up a ladder to the top rail and then down a ladder mounted inside the tank to the bottom, the plexiglas was removed from the tank’s ground-level porthole to allow easier access into and out of the tank (Figure 6.2). Once the preliminary inspection was over, the decision was made to proceed with the mockup development, and the team was assembled. Four students had ten days in which to build and deliver a functional mockup, all to be done outdoors and in the coldest Maryland winter weather in recent years. Tank preparation work began on the 26th of January 2009. The first step was to remove the layer of ice that covered the bottom of the tank. Several methods were tried, including rock salt, hot water, and using a power washer (Figure 6.3) to melt divisions

65 Figure 6.1: SSL Outdoor Mockup Storage Facility

in the ice. Ultimately, it was concluded that brute force would be the fastest method of removing the ice, and the ice sheet was attacked with crow bars and claw hammers (Figure 6.4) and scooped into trash cans for removal (Figure 6.5). Beneath the ice, the floor of the tank was covered with a 1 cm thick rubber mat, which was cut and removed in sections. The tank was then covered with a tarp until the roof was completed. The first floor was designed in CAD as a series of 2”×6” joists with 23/32” plywood sheets on top. The entire structure was designed to be built of wood in order to limit costs and to allow for easy and fast shaping of the required pieces. The main beams are spaced 16” on centerline and joined together by 2”×6” segments (Figure 6.6). The frame is oriented to avoid interference with the three metal attachment rings that were once used to lift the tank. Once the main frame was assembled, four 4”×4”×7.5’ beams, that would later serve as support columns for the second floor, were mounted to the tank walls with screws. The feet of the pillars also had to be trimmed to conform to the curved bottom edge of the tank. Once the pillars were in position, the lower-level floor was prefabricated by laying out three plywood sheets on the ground and marking the circular interior diameter of the tank for cutting (Figure 6.7). The 4’×8’ sheets had to be further cut in sections no wider than 2 ft. to allow them to be passed through the porthole. Once the pieces were brought inside, the flooring was assembled with 2 in. screws and positioned perpendicular to the lower frame. The second floor, like the first floor, was designed in CAD, which was used to obtain the dimensions of the spiderweb-pattern floor joists. The main frame was designed to have a central reinforced beam made out of two 2”×6”s screwed together, and a central cross beam made from a single 2”×6” beam that was cut in half. The cross was positioned on the top of the four 4”×4” pillars and fixed in place with steel L-brackets (Figure 6.8). The remaining pieces of the second floor frame consisted of 45o angled beams, 16

66 Figure 6.2: Porthole Ingress/Egress

in. apart at their centerlines and reinforced with 2”×6” stiffeners. For the flooring of the upper level, it was not convenient to pass the plywood segments through the porthole. Therefore, a different arrangement for the upper flooring pattern was chosen which allowed the sheets to be passed over the top of the tank. The same procedure for marking and cutting the sheets was used for the second floor. In order to pass the shaped sheets over the top of the tank, the tarp was removed. Fortunately, the weather allowed the tank to be left uncovered overnight. Based on the final design, a hatch had to be positioned in the same wall quadrant as the internal vertical ladder. In order to cut the hatch from the tank walls, the hatch shape was drawn on the internal wall, and holes were drilled for the hinges. The cut-out section of tank was re-used as the door. Once the hatch was cut, a locking mechanism was prepared. The locking mechanism is a four link lock similar to the ones used on submarines. Handles were installed on both sides of the hatch, allowing for it to be opened and closed from both the interior and the exterior (Figure 6.9). The hatch opens towards the interior, as would an ideal pressurized hatch. Once the hatch was complete, the interior walls of the habitat were coated with white latex-based paint, for the purpose of improving the lighting of the habitat and preventing fiberglass fragments from falling and rubbing off of the interior walls. Once the second floor was ready, a geodesic dome frame was prepared for the roof of the habitat, constructed from lengths of 2”×3” wooden studs and assembled in a pentagonal-hexagonal pattern (Figure 6.10). The pieces of wood were joined with small metal strips that were screwed in place. The dome was assembled in layers (Figure 6.11); installing the cumbersome top layer (Figure 6.12) required the assistance of nearly all the SSL personnel (Figure 6.13). After the dome was in place, it was covered again with the tarp. Both floors of the habitat were covered with carpet, to reduce flammability and

67 Figure 6.3: Day 1 - Power Washer

improve comfort and safety. In the following days, attention shifted to the interior of the habitat. The main goal of constructing the mock-up was to produce a fully functional habitat that, in the future, would allow for human testing in a high fidelity analogue environment. The intrinsic difficulty was in producing an environment that not only resembled the final design as much as possible, but which also contained the fundamental working habitat systems. The upper floor living quarters were tackled first. Four bunks were built with 2”x4” wood frames. The primary problem with the bunks was that the final design doesn’t include a geodesic dome, but straight vertical walls that reach to the top of each bunk. In the mockup, the dome induces serious position constraints on the bunks, and therefore, in the first fabrication iteration, the upper level was the lowest fidelity functional area of the mock-up. The bunk concept consisted of two lower beds that could also be used as sitting space for group activities such as dining and recreation. The top bunks were higher than usual, since they were designed to allow people to sit comfortably on the lower beds without hitting the upper bed frame. The lower beds were raised above the floor level 16 in., allowing for storage space below them and improved comfort when the beds were used as seating areas (Figure 6.14). The restroom, originally positioned on the lower floor, consisted of a stand-alone camping toilet. The toilet itself contained two tanks, one for fresh water and one for waste water. The waste water tank, the lower of the two tanks, was normally sealed to contain odors, but could be opened with a handle on the front of the apparatus to allow wastes to flow into it. Chemical additives in the waste tank prevented decay and reduced odors from the solid wastes (Figure 6.15). In order to insulate the roof, medium density styrofoam was used to fill the trian-

68 Figure 6.4: Day 1 - Chipping/Melting Ice Figure 6.5: Day 1 - Big Chunks of Ice

Figure 6.6: Day 3 - Ground Floor Structure

gular sections of the dome, and was kept in place with screws and expanding foam. The triangular foam elements were cut to fit inside the dome structure, and once the expansion foam cured, they also added stiffness to the dome itself (Figure 6.16). Initially, heating of both levels was to be provided, in order to make the habitat livable despite the low external temperatures. However, once the insulation was complete, it was found to be so effective that both electric heaters were placed on the lower floor to prevent the upper floor from becoming too hot. The lower floor didn’t have any insulation, and was therefore more difficult to keep at a constant temperature. Due to convection, pleasant temperatures could be obtained on both floors by positioning the two ceramic heaters on the lower level. Finally, an electrical system needed to be implemented. Three power outlets and fluorescent lamps were wired on the lower floor and two on the upper. The lower and upper level circuits are separate, with each incorporating a 15 A ground fault circuit interrupter (GFCI). On both floors there were secondary 15 A circuits with GFCIs that served the two heaters. In total, the habitat was served by four independent power lines, each allowing 15 Amps of draw. The power was obtained temporarily through four independent extension cords that run from the NBRF building to the habitat. All the extension cords were connected to separate power outlets in the NBRF building, each including a 15 A ground

69 Figure 6.7: Day 3 - Floor Construction

interrupter. For safety purposes, a fire extinguisher and a smoke/fire detector were included on each floor (Figure 6.17). Although this project began as the "Minimum Functional Habitat Element Study" (drawn from the name of this section of the NASA Broad Agency Announcement), the physical reality of the habitat mockup motivated the team to come up with a more useful and interesting name for the study and the habitat itself. Drawing from the NASA tradi- tion for acronyms, the final choice was “Extensible Concept for Live-in Pressurized Sortie Elements”, or ECLIPSE.

6.2 ECLIPSE Crew I: Mission Report

In order to validate the functionality of the habitat, it was decided that a short duration technical mission should be carried out in the habitat. Four of the investigators of this study (Figures 6.18 and 6.19) agreed to spend 48 hours in the habitat to test its habitability, using their time to modify the habitat and record assessments. Before the test, habitation systems and supplies for two days were placed inside the habitat. Keeping in mind that no refrigeration would be available, the choices of food were limited to dehydrated or canned foods. A microwave was placed in the habitat, along with a water cooler that supplied both hot and cold water. A small supply of running water was installed, flowing from a 30-gallon tank positioned under the bunks to a small sink on the lower floor close to the toilet. However, small leaks in the plumbing precluded the use of this system during the test. The crew was allowed to bring some personal belongings, such as personal computers, changes of clothing, and sleeping bags. The bunks were outfitted with inflatable air matresses. The mission began on the 29th of January, 2009, and ended on the 31st. In the intervening 48 hours, a series of evaluations of the system were carried out, such as electrical load evaluation, storage space allocation, and observation of space usage. The simulation was not meant to be hyper-realistic, therefore “EVA’s” were allowed. Two crew members had classes to attend during the test, and several excursions were also required to gather tools for minor fixes to the system. A computer was also brought into

70 Figure 6.8: Day 4 - First Floor Structure and Support Columns

Figure 6.9: Day 5 - Hatch

the habitat to allow VR testing to be conducted. Observations during the test showed that the crew spent most of the time in the lower floor doing cooperative work, mainly preparing material for the final outbrief of this study. The lower floor was the main operations area of the habitat (Figure 6.20); most common activities took place there, although some social activities occurred on the upper level. Although food preparation was done on the upper level, the crew preferred to eat together on the lower level, highlighting the fact that a multi-level habitat must provide a means for convenient transfer of food and equipment between the two levels, which the mock-up did not have. It is hypothesized that the habit of eating on the lower level was due to the lack of a table on the upper level, an effect of the space constraints of this version of the mock-up. It was also observed that private time in the habitat was obtained primarily through the use of headphones, which allowed acoustic isolation. It is possible that, due to the very short duration of the test, the crew didn’t feel the need for more physical isolation. Private communications were mostly observed to occur on the upper level, indicating that it was desirable to have a provision for physical isolation during private communications. The upper level was also used for group recreation. It was observed that all activities tended to be done as a group; the crew members felt that this degree of interaction was key to crew morale. On the 31st of January 2009, the ECLIPSE Crew 1 ended the first mission in the

71 Figure 6.10: Day 6 - Dome Center Figure 6.11: Day 6 - Dome First Layer

Figure 6.12: Day 6 - Dome Assembly Figure 6.13: Day 6 - Dome Frame preliminary mock-up of the ECLIPSE habitat, having gained signiﬁcant insight into habitability issues, and many ideas for the future development of the mock-up. The observations gathered during this mission were crucial for the team’s understanding of group dynamics in such a small environment, and allowed the investigators to conceive of several future tests for studying space usage and systems location and performance (Figure 6.21).

6.3 Lessons Learned

During the intensive two-week habitat mockup development eﬀort, the team concluded that the ﬁnal habitat design must:

• accommodate easy equipment/logistics transportation between ﬂoors;

• avoid using beds/bunks for seating space; instead, implement folding seats in the bunk area;

• include a table in the living quarters; otherwise, move food preparation to the operations area where a table exists;

• have a source of potable water on each ﬂoor;

• provide sealed containers for the collection of trash, which accumulates fast and requires air tight storage or disposal space;

• provide bathroom privacy and comfort, which is not easy to obtain in such a tight environment.

72 Figure 6.14: Day 7 - Upper Floor with Bunks

The primary specific issue with the mockup habitat was the need to redesign the bunks in order to better interface with the dome and regain central floor space on the upper level. This is due to the limitations of the readily available tank structure used to build the habitat mockup; a better funded long-term simulation effort would involve the procurement of a tank more closely adhering to the final design to eliminate the inaccuracies of the geodesic dome close-out structure. Although the fabrication and initial testing of the full-scale habitat placed a tremen- dous demand on the human resources of the University of Maryland team, it is the unan- imous opinion of the participants that the effort was pivotal to the final success of the project. The fact that a full-scale operating mockup could be created in two weeks at a total materials cost of less than $5000 illustrates the advantages of performing this type of research in an academic environment.

73 Figure 6.15: Day 7 - Toilet

Figure 6.16: Roof Padding and Upper Floor Lighting

74 Figure 6.17: Vertical Ladder with Fire Extinguisher

Figure 6.18: Crew 1: Massimiliano Di Capua, Figure 6.19: Crew 1: William Cannan, Kevin Adam Mirvis Davis

Figure 6.20: Crew 1: Work Area

75 Figure 6.21: ECLIPSE at Dusk

76 Chapter 7

Final Design: ECLIPSE

Figure 7.1: ECLIPSE Logo

7.1 Conﬁguration

7.1.1 Exterior Configuration With the completion of the preliminary design and three parallel independent designs, the analysis of the results of the surveys and literature searches, the bounding of the problem through trade studies, and the initial stages of development of a full-scale mockup, the stage was set for the design and analysis of the final minimum functional habitat design. Based on the trade studies, it was apparent that a two-level vertically- oriented cylindrical configuration would provide the maximum internal volume per unit mass. The cylindrical diameter would be limited to 3.5-4 meters, in order to keep the structure below 50% of the allowable system mass. A back-of-the-envelope calculation of walking gaits in lunar gravity showed that crew will come off the floor at walking speeds above 1.1 m/sec, which would easily be achieved in moving about the habitat. However,

77 given the lack of experimental or careful analytical studies of partial gravity movements interior to a habitat, it was decided to keep the interior ﬂoors at a tight but acceptable headroom of 2.25 m (7.5 ft) in each level. Although the assumed habitat pressure of 55 kPa (8 psi) is low compared to most pressure vessels, the large diameter means that there is a longitudinal force in the cylinder of 572 kN (128,000 lb). This led to the adoption of ellipsoidal endcaps to prevent pressure concentrations in the cylinder/endcap transitions. Using the classical deﬁnition of longitudinal stress equilibrium in a cylinder to solve for minimum thickness gives

(FOS)P d t = (7.1) 2σ Using a conservative factor of safety (FOS) of 2 and a typical tensile yield stress of 37 ksi for aluminum gives a hull thickness of 0.031 in, or 0.79 mm. This is too thin for reliable manufacturing, and an alternate minimum thickness of 0.06 in (1.5 mm) was adopted for the pressure hull skin. This provides a margin of safety of 1 with a safety factor of 2. The external conﬁguration of the hull is shown in Figure 7.2.

Figure 7.2: Habitat Pressure Vessel without External Structure

Although a monocoque structure was assumed for simplicity of analysis, there will be a number of point loads which far exceed the pressure limits. Critical loads include launch and landing, and point load sources include the interface to the Altair lander and inertial loads of the internal accommodations of the habitat. Rather than attempt to take all of these loads through the pressure hull, an external cage structure was designed to carry these point loads, isolating the pressure hull to primarily pressure forces. As shown

78 in Figure 7.3, three circumferential rings carry the loads of the internal ﬂoors and ﬁttings, with inter-ring loads carried by six vertical struts. This structure is used for physical attachment to the landing vehicle, as well as for mounting the three stabilizer legs for supporting the habitat on the lunar surface.

Figure 7.3: External Support Structure for Habitat

The requirements of the BAA called for docking interfaces suitable for pressurized logistics carriers from the Constellation reference surface architecture. There was no specific size listed for this interface, but it had to circumscribe a pressure door listed as 1.5 m × 1 m. The berthing interface derived from this requirement is a rigid cylindrical extension to the pressure hull with a diameter of 1.74 m, a primary thickness of 6.4 mm, and a mating interface flange 7.6 cm wide. Jumping ahead to the requirement for growth options, it seemed clear that the berthing interfaces were also the obvious interface for mating multiple habitats to build up larger complexes. There was also a requirement for an EVA airlock, which was determined to best be implemented as an inflatable structure mounted externally to a berthing port. Studies examined the number of berthing interfaces to provide, ranging from two (the minimum number which provides both an airlock and a pressurized logistics module (PLM) at the same time) to six. The limit of six was based on the requirement that the longitudinal support struts of the external framework have to be located next to the cylindrical wall section; six berthing ports provide only enough space between the cylindrical bething extensions for the struts to pass by, and more than six means there is no contiguous cylindrical wall section at all. A further complication was the decision made to require four suitport access ports in the lower level wall structure. The suitport concept was viewed as the best operational solution to simplified EVA access with a high level of assurance that regolith would not

79 be routinely carried into the habitat environment. While an airlock was still considered necessary for bringing instruments, samples, and suits in and out for study or repair, the suitports were baselined for everyday surface access. However, in a cylinder with an external circumference of 452 in (11.48 m), each suitport would require 36 in (0.914 m) of horizontal wall space, including the overall width of the port docking interface and enough internal room to swing the backpack hatch open to the side for ingress and egress. The six sectors between the external vertical support struts each have a surface arc width of 72 inches (1.83 m), which is minimally adequate for two suitports. A berthing port, or two suitports, will fully occupy the width of an interstrut sector. Two sectors must be kept clear of ports for internal accommodations: the ladder to move between levels and the air handling and revitalization system need to be mounted against the wall, and will not fit in the same sector. If there are only two berthing ports, the module will be saturated with an external airlock and a pressurized logistics module; no further expansion would be possible, so the conclusion reached is that a minumum of three berthing ports are required. Three berthing ports, two sectors devoted to suitports, and two reserved for internal accommodations adds up to seven sectors. The feasible solutions to the problem of insufficient circumferential room (predicted by the trade studies of Chapter 5) include dropping back to two berthing ports or two total suitports. The former would severely limit eventual growth options for the Constellation surface architecture; the latter would markedly increase the number of airlock cycles, with corresponding increases in consumables usage and dust infiltration into the habitat. Rather than accept either of these restrictions, the UMd design team came up with a design for a suitport incorporated into an intermodule hatch in the berthing port. For early habitat operations, only one berthing port would be used for the airlock, and the other two berthing ports would be usable for suitport operations. When, in later years, additional habitat modules or logistics modules are attached to a berthing port, that suitport location is lost, but additional suitports could be integrated into the additional modules. Since one berthing port will be dedicated to the inflatable airlock, only two berthing ports will have the suitport fixture mounted in the hatch. Due to the long-term nature of the habitat, it will be important to ensure that the interior floors are level for crew comfort and safety. There will have to be some accommodation for standing on the lunar surface, as the lower dome shape is not a stable support base. Due to the six-fold symmetry of the external structure, it was decided to incorporate three support gear on the habitat for surface emplacement. Since the habitat will be fixed to the lander through a support truss mounted to the lower circumferential hoop of the external truss, there is no requirement for the support gear to take transitory loads on landing, or to resist lateral forces on touchdown. The key is to ensure that the habitat is statically stable on the lunar surface, and that it has some means of adjustment to remain level despite unevenness in the local topography. The basic support gear concept (Figure 7.4) is a simple tripod arrangement, with the lateral shear struts attached to the lower support hoop and the vertical strut connected to the longeron. An articulated connection allows the vertical strut to be moved up and down to adjust the relative lengths of the three support struts, and thereby allow fine adjustment of the habitat level. The interactions of the support gear and the hatch-mounted suitport cause an interesting design challenge. Since the suit is larger than the cylindrical berthing hatch extension (Figure 7.5), the length of the berthing port extension is limited so as to not impact the utility of the suit port. This short (1.2 cm) berthing port interface brings two mated habitat modules so close together that the support gear interfere with the module structure. In order to have a feasible docking interface, a 0.5 m berthing extension element

80 Figure 7.4: Detail of Habitat Support Leg Conﬁguration

has to be inserted between the modules to allow clearance for the support gear on each module. Insufficient design detail exists on the pressurized logistics modules to know if the extension would be required for use of the berthing port interface with that unit; either the PLM would be designed to accommodate the short habitat berthing ring, or the extension ring could be predeployed to the lunar surface or flown already connected to the PLM. The following figures show the baseline exterior of the habitat in four orthogonal views. As can be seen in Figures 7.5-7.8, much of the circumference of the habitat at the lower level is taken up by suits and suitports. berthing ports, and the airlock. The only two free segments are those adjacent to the inflatable airlock, which are internally reserved for life support equipment, wall-mounted stowage, and the access ladder between levels.

Figure 7.5: Front View Figure 7.6: Left View

One of the requirements of this study was to ensure that the habitat could operate while still mounted on the payload deck of an Altair lander. Although exact details of the Altair payload interface were unavailable to the University of Maryland study team, Figure 7.9 shows a notional sketch of the ECLIPSE habitat installed on an Altair lander. Other than moving the airlock exit hatch to be orthogonal to the entry, rather than diametrically opposed, there are no constraints to extended operations of the habitat on Altair.

81 Figure 7.7: Right View Figure 7.8: Top View

7.1.2 Interior Layouts As in the mockup, the functional division between the two decks was defined as operations in the lower level, and habitation in the upper. The design of the lower level is driven by emplaced life support system hardware, required stowage, and wall mounts for berthing ports and suitports. As shown in Figure 7.10, the two wall-mounted suitports are flanked by the berthing port hatch-mounted suitports. Opposite the suitports, which take up half the circumference of the habitat, is the berthing port to the inflatable airlock, flanked by the access ladder on one side and the air reclamation and stowage systems on the other side. A notional table and chairs are shown as the group working area in the center of the floor; while it would be preferable to have some fixed work stations for purposes such as monitoring and commanding habitat system operations, it was felt that these functions could be more than adequately performed via the crew’s personal laptop computers. The upper deck represents a far more difficult design challenge, as it incorporates the following functions:

• Food preparation and cleanup

• Eating

• Sleeping

• Socializing

• Waste management

• Personal hygiene

• Personal storage

• Radiation protection

• Oﬀ-duty activities

The critical element in this design process is the personal berth. The number one priority from the survey process was the desire of the respondents to have a berth space that supported and enforced personal space. In addition, the lowest-mass option for radiation protection against solar particle events turned out to be the design of the dual berth structures to incorporate a “water wall” for radiation protection. As shown in Figure 7.11,

82 Figure 7.9: Notional Image of Habitat on Altair Deck an individual berth incorporates sufficient volume for sleeping and sitting up to read or work on a laptop, while surrounding the individual with 5 cm of water and carbon-fiber composite for radiation protection. The four berths will require 860 kg of water to fill the interstitial spaces and provide 5 gm/cm2 bulk radiation shielding to the crew; this water is not accounted for in the habitat mass budgets, and it is assumed it can be added after the start of operations via a resupply module. A polyethylene door, also 5 cm thick, slides to cover the berth opening during radiation events. The circular arc area between the actual bunk and the habitat wall is also within the radiation shielding, and provides personal stowage for the crew. This includes all clothing for the mission, as well as food, water, and contingency waste management for periods of confinement during radiation events. The overall configuration of the upper deck is shown in Figure 7.12. Two berths are located on each side of a central table, mounted above a set of standard stowage lockers. Table wings and bench seats are folded down to provide transit room during most activities, but fold up for seating and table space for meals or group work. Berths are accessible in either configuration. At one end of the bunks is a “galley wall” for food storage and preparation, including a sink, small refrigerator, and hybrid microwave/infrared oven; at the other end of the starboard-side berths is a waste management compartment with toilet, sink, and shower, on an air circulation loop isolated from the rest of the habitat. The corresponding end of the port-side berths is the access way in the floor for the vertical ladder to the lower deck.

7.1.3 Conﬁguration Growth Options The requirements for the habitat design stated that the design teams should consider growth options; via the three berthing ports, a number of options based on modularity

83 Figure 7.10: Interior Layout of Lower Deck

are available. The baseline design is clearly extremely “tight” for four crew, and would be particularly confining in the event of a contingency situation without opportunities for EVAs or pressurized rover excursions. A second ECLIPSE habitat docked to the first (Figure 7.13) would provide significantly greater room, as well as eliminating the need for berthing hatch-mounted suitports and providing a redundant inflatable air lock. This would double operational area on the lower levels and provide a number of options for habitability, including a dedicated sleeping floor in one module and eating/socializing space on the upper floor of the second habitat. Due to the mass limitation of the ECLIPSE habitat, two of them could be transported to the Moon by a single Altair landing vehicle in cargo mode. This would allow the creation of a triple-module habitat, as shown in Figure 7.14. This configuration could easily support crew sizes of 6-8 for extended missions, or provide much less constricted space for a crew of four.

7.2 Life Support Systems

7.2.1 Basic Assumptions According to the terms of the study, the habitat is speciﬁed to support a crew of four for a nominal mission length of 28 (Earth) days, with a continued mission of an additional 30 days in the event of a contingency. The habitat should support extensive exploration and outpost development activities during the nominal mission. It is also desirable for the habitat to support a total crew of eight during a crew rotation “handover”, assumed to last no more than 48 hours. Taking these conditions together, the life support system should support a crew of four 95th percentile American males (worst case) for a nominal mission length of 30 days (including handover), and a supplemental contingency period of an additional 30 days. Simplistically, the requirement is for a 60-day life support capacity. It should be

84 Figure 7.11: Cutaway of Individual Berth

emphasized that, as a "minimum functional habitat", all optimizations were performed for this 60-day capability for four crew. In reality, the habitat as part of an outpost would host a number of sorties of varying sizes, and an optimization would incorporate this fact for minimum total life cycle costs; however, this study was directed to approach the analysis as if the habitat was to be occupied by only a single crew. Diﬀerent design decisions would be appropriate if the analysis considered the potential for a longer functional habitat lifetime. The basic assumptions for life support system design include:

1. Daily two-person EVAs during nominal operations

2. One two-person airlock cycle per week and two two-person cycles in support of crew rotation for 12 suit transits/six airlock pressurize/depress cycles (all other EVAs performed using suitports)

3. No appreciable atmosphere loss with a suitport cycle

4. No EVAs during the contingency support period

5. One four-person EVA at the end of the mission for the crew to return to the ascent vehicle

6. 64 EVA suit operations during a nominal mission, based on the preceding assumptions

7. Power supplied by a Constellation program Mobile Power Unit (MPU) and not charged against habitat mass

8. Systems to be considered should have the maximum TRL of the possible candidates (proven systems should be used for simplicity and mission assurance)

7.2.2 EVA Support Requirements Based on the assumptions above, there are 64 EVA suit operations during a habitat mission. The habitat must supply either replacement LiOH canisters or facilities for recharging METOX canisters for CO2 scrubbing in the suits. An EMU LiOH canister has a mass of 6.4 kg [24], whereas a METOX canister has a mass of 14.5 kg. The module to

85 Figure 7.12: Interior Layout of Upper Deck

regenerate two METOX canisters over 14 hours has a mass of 48 kg and an average power draw of 1000 W [25]. Each EVA consumes 0.72 kg of O2 and 2.1 kg of H2O [26]. Given this information, the total mass for disposable LiOH canisters for 64 EVAs would be 410 kg, while the mass for the METOX system (oven plus four modules) is 106 kg. Clearly, looking at the suits as a solitary system would strongly favor the adoption of the METOX system for CO2 scrubbing. This assumption will be revisited in looking for synergies between suit and habitat life support systems. In addition to CO2 system support, the habitat will have to supply 46.1 kg of O2 and 135 kg of water for the suit operations. As specified in [26], the airlock has a volume of 6.5 m3, with a 90% scavenging rate of air during a depress cycle. The atmospheric density at 8 psi can be calculated to be 0.667 kg/m3, so the total airlock atmosphere mass is 4.33 kg, and 0.43 kg is lost in every airlock cycle. With six airlock uses over the mission, the total air replacement mass for the airlock (including the initial complete fill) is 6.93 kg. With the specified 30% O2 atmosphere, this corresponds to 2.1 kg of O2 and 4.9 kg of N2.

7.2.3 Air Circulation The internal habitable volume of the habitat is 47.1 m3, which corresponds to a total atmosphere mass of 31.4 kg. Reference [26] speciﬁes an atmospheric leakage rate of 0.05%/day, or 0.016 kg/day, or 0.9 kg over the 58 days of the full contingency mission. This breaks down into 0.3 kg of O2 and 0.6 kg of N2. The atmosphere in the habitat must be circulated to ensure clean breathing air with acceptable parameters in terms of oxygen, CO2, particulates, odors, and temperature. Although circulation rates in terms of air changes per hour (ACH) are common in building

86 Figure 7.13: Dual Habitat Conﬁguration

codes on Earth, a fairly careful search of the publicly available NASA standards does not show any criteria in this area other than minimum and maximum flow rates of 0.076-0.347 m/sec [27] for air streams, based primarily on noise and crew comfort. One source on life support systems for International Space Station [28] seems to imply that air revitalization is primarily accomplished through an intermodule flow rate of 140 cubic feet per minute (CFM); converting to metric (3.97 m3/min) and applying it to the U.S. Laboratory module at 4.4 m diameter by 8.4 m long (128 m3) produces a calculated turnover of the total air volume every 32 minutes. This works out to an ACH for ISS of 2. By comparison, the design ACH for public spaces in buildings is 6, and commercial kitchen areas may be designed to values as high as 20 or more. On the other hand, a report of homes in Denmark cited a minimum ACH for bedrooms of 0.5, and found that a number of homes fell well short of even this minimal air circulation value [29]. The habitable volume of ECLIPSE is 47.1 m3; harkening back to the "minimum" aspect of this design, the lower limit of ACH in the habitat will be set at 0.5, which corresponds to a volumetric flow rate of 13.8 CFM. Air circulation in the habitat will consist of four parallel ventilation loops: one for the lower level, one for the common areas of the upper level, one split four ways for ventilation of sleeping berths, and one isolated loop for ventilation of the hygiene and waste control compartment.

7.2.4 CO2 Capture

Three systems were considered for CO2 scrubbing: lithium hydroxide canisters, metal oxide (METOX) canisters using EMU-standard components, and a four bed molecular sieve (4BMS). All of these systems are currently at a technology readiness level (TRL) of 9; the 4BMS system was preferred over the lighter-weight 2BMS due to its ﬂight-proven status, as well as superior performance at atmospheric moisture reclamation. At a speciﬁc mass of 1.75 kg/crew day and a total load of 240 crew days, an expendable LiOH system would require 420 kg of consumables (not counting system packaging). Alternatively, a

87 Figure 7.14: Triple Habitat Conﬁguration

4BMS system would perform the same air scrubbing at an installed mass of 120 kg and a power consumption of 680 W. (It should be noted that this budgeting does not take into account the decreased habitat consumables utilization due to EVAs. While nominal lunar operations would no doubt have a heavy schedule of surface operations, it was felt necessary to size the habitat systems without requiring separate EVA consumables to meet the system life goals.) In order to take advantage of commonality with the suit systems, the use of suit METOX canisters for CO2 scrubbing was also considered. Using the current EMU METOX system as the design standard, each 14.5 kg canister is designed for 6-7 standard cubic feet per minute (SCFM) of air flow, and can scrub 1.48 kg of CO2 before regenerating in an 47.5 kg oven for ten hours with a four-hour cool-down cycle. Since a 95th percentile male can generate 1.1 kg of CO2 per day, three METOX canisters would be required for one day of CO2 collection for four crew members. To maintain commonality with the EVA portable life support systems, two METOX canisters will be operated in parallel to meet the minimum habitat ACH within the air flow rate limits of the existing canister design; each canister pair will have to be changed out at 16-hour intervals. The current METOX oven can regenerate two canisters in parallel. The nominal regeneration cycle is 14 hours with cool-down, so one METOX regeneration oven would support all habitat life support requirements. A second METOX system would be required to support EVA operations. In the event of a system failure, the habitat can be supported indefinitely on a single regeneration oven if EVA operations are curtailed. Four METOX cartridges would be needed for the habitat. Following this 16-hr alternation pattern, each METOX canister goes through three recharges in four days, or 45 recharges over the total 60-day mission. This is well within the 50-55 recharge lifetime currently quoted on METOX canisters. The total system mass for a dedicated habitat METOX oven and four habitat canisters would be 106 kg, and would be in fact be identical to the components needed to support suit EVA operations. No accommodation has been made for pressurized rover operations in this design. There is significant discussion about pressurized rovers, and a general assumption is made that the rover life support systems will maximize commonality with (or will even directly use) the portable life support systems from the pressure suits. As an entry-level estimate, each day of detached rover operations will saturate three METOX canisters (one each for

88 two crew with a full day of EVAs, and one for the remaining 16-17 hours of reduced activity inside the rover cabin.) Mass and power restrictions will preclude the ability to regenerate METOX canisters on the rover, so a six-day sortie will result in 18 saturated canisters returned to the habitat for regeneration. A dedicated oven would require 9 cycles, or 126 hours (or 5.25 days) to renew these canisters for another rover sortie. Repetitive rover operations would require a third METOX oven dedicated to regenerating rover METOX canisters, which would alone add 47.5 kg to the habitat; two 18-canister sets of METOX canisters for repeated rover sorties would have a mass of 522 kg, which would have to charged against either the rover or the habitat.1 The 4BMS system has the advantages of automatic cycling (transitioning from adsorption to desorption without crew intervention) and a lower power requirement of 680 W. The METOX system saves 14 kg, but uses 320 more watts on average and requires a manual switching of both cartridges every 16 hours. This could be problematic in the event of a severe solar particle event, as the crew would be restricted to their radiation-shielded berths during the duration of the event for their health and safety. The life support system should be designed with emergency LiOH canisters which can be automatically activated if the METOX canisters reach saturation during a time when the crew cannot load the used canisters into the regeneration ovens and put fresh canisters in the air ducts. 72 hours of emergency standby LiOH canisters would add 22.5 kg to this component of the life support system. While the additional power requirement of the METOX system is a concern, particularly in the context of additional thermal load to the habitat, the safety advantages of commonality of suit and habitat METOX systems are felt to be too great to neglect. For this reason, the METOX CO2 scubbing system was adopted for the baseline habitat system.

7.2.5 Air Revitalization Each crew will consume, on average, 0.85 kg of oxygen per day. If no oxygen recovery is incorporated, the habitat will require 204 kg of O2 for the four crew over the 60 equivalent days of the maximum contingency mission. A Sabatier reactor could be incorporated to convert the CO2 collected in the METOX system to oxygen and methane, with about a 95% recovery rate. To convert the 4.4 kg of CO2 generated per day to oxygen would require a Sabatier reactor with a mass of 400 kg and a power demand of 1140 W. Since this mass is signiﬁcantly greater than the replenishment mass of oxygen, the minimum habitat design will not attempt to recycle the oxygen contained in captured CO2. It should be noted, however, that the Sabatier solution would be lower in mass than the open-loop oxygen system if the habitat mission were expanded to 180 days, and the ability to retroﬁt the habitat with a Sabatier oxygen recovery system would be important for growth applications of the habitat.

1As an aside, a single 6-day rover sortie using expendable LiOH canisters for both EVA and IVA life support would require 115 kg of canisters. There is suﬃcient time for four 6-day rover sorties (with some turn-around time) over the course of a 28-day nominal habitat mission, so an all-LiOH rover would require a total of 461 kg of LiOH canisters, as compared to a total system mass of 570 kg for two sets of METOX canisters and a dedicated regeneration oven. The interesting conclusion to be drawn here is that the mass-optimal solution is to use METOX for habitat and habitat-based EVA operations, and expendable LiOH canisters for rover and rover-based EVA operations.

89 7.2.6 Air Replenishment At this point, it is possible to total all of the contributions to air loss, and calculate the best replenishment method for this mass. Over the 60-day maximum contingency mission, the habitat will require 252.5 kg of oxygen (almost entirely for breathing O2 replacement in habitat and EVA) and 5.5 kg of nitrogen for cabin air leakage and airlock replenishment. For simplicity and to avoid boil-off problems in the lunar surface environment, it will be assumed that both elements will be supplied as high pressure gases. At a modest design pressure of 200 atm (20.2 MPa), the nitrogen tank would require an internal volume of 22.5 liters, and the oxygen tank(s) would require a total internal volume of 1.03 m3. Since the nitrogen tank is quite small, it may be assumed from standard mass estimating relations that the mass of the pressure tank will be approximately the same as the contained gases, for a total full N2 tank mass of 11 kg, with a lunar surface weight of 1.8 kg. The corresponding MER for larger oxygen bottles is for a tank mass of 0.4 times the contained oxygen. This corresponds to a total oxygen replenishment mass of 353.5 kg, or a lunar surface weight of 58.9 kg. Rather than worry about high-pressure hoses and topping pumps, the design assumption is that the habitat crew will manually attach new pressure bottles in EVA to the outside of the habitat when the time comes to replenish consumables between missions. While the 1.8 kg lunar weight of the nitrogen bottle is negligible, it is desirable to keep hand loads limited to below 15 kg to prevent fatigue and allow fine alignment tasks. For this reason, it is assumed that the oxygen will be replenished by the external attachment of four oxygen bottles, each with 63.1 kg of oxygen and a lunar carrying weight of 14.7 kg. For a typical high pressure configuration of a cylinder with hemispherical end caps, this corresponds to tanks with a diameter of 0.5 m and an overall length of 1.5 m.

7.2.7 Water Reclamation NASA’s Exploration guidelines for human missions call for 5.16 kg/crew-day of potable water and 23.4 kg of hygiene water per person day under nominal circumstances. These numbers drop to 2.84 and 5.45 kg, respectively, for contingency operations[30]. An open-loop water system would then require 3427 kg of water for the 30 equivalent days of the nominal mission (28 days plus crew turnover) and an additional 995 kg of water for the contingency operations, for a total of 4422 kg of water. This is prohibitively large when charged against the total habitat mass limit of 7000 kg. Clearly, some degree of water loop closure will be required. Condensate recycling using multiﬁltration and reverse osmosis would require an installed mass of 92 kg, 0.42 m3 in volume, 310 W of electrical power, and would need 28.5 kg of consumables for the maximum contingency mission [31]. This approach would result in a production shortfall of 2.1 kg/crew-day, as the urine (1.5 kg), ﬂush water (0.5 kg), and feces water (0.1 kg) would not be recycled. This produces an additional consumables requirement of 504 kg of water per mission. (Note: this is a conservative estimate, as additional water is continually entering the system via metabolic conversion of food and oxygen to water and CO2.) With an emergency 7-day drinking supply of 145 kg and 135 kg allocated to EVA replenishment, the overall system mass for a condensate-only water reclamation system would then be 905 kg, of which 668 kg must be replenished between missions. With the addition of a distillation system for urine recycling, the 504 kg of consumable water will not be required. This will require the addition of a vacuum condensation distillation (VCD) system, with a mass of 75 kg, volume requirement of 0.2 m2, power requirement of 90 W, and a consumables mass of 141 kg over the extended mission. This

90 version of the water reclamation system will have an installed mass of 167 kg, mission resupply mass of 304 kg (including EVA), power requirement of 400 W, and a total system mass (with emergency drinking water and EVA replenishment) of 616 kg. Due to the clear advantages of this system, the approach of condensate and urine recycling will be adopted for the ECLIPSE habitat.

7.2.8 Food Storage and Preparation Food details were subsumed in the speciﬁed stowage requirement of 1200 kg, packaged in 92 ISS cargo transfer bags (CTBs). The galley wall in the upper level of the habitat includes a food preparation area, including an oven for heating prepackaged foods and a sink for hygiene and meal clean-up.

7.2.9 Waste Management The Waste Management Compartment (WMC) on the upper level contains a toilet, sink, and handheld shower. Urine and flush water is collected and sent to the water reclamation system for reuse; feces and other flushed wastes travel down a septic line to a holding tank in the lower ellipsoidal endcap. Chemical treatments will be used to break down the solids and ensure that no bacterial growth will occur in the holding tank. A 60- day mission at 0.6 kg of feces and flush water per crew-day would require a tank volume of 0.144 m3, or a spherical tank with a diameter of 0.65 m. Physical wastes will be collected in plastic trash bags as per ISS and stored in the lower (and, if necessary, upper) ellipsoidal end caps for the habitat. Each end cap has approximately 10 m3 available for trash stowage, allowing a maximum disposal rate for the extended mission of 0.083 m3 (3 ft3) per crew per day. Alternatively, trash can be transfered to an expendable resupply module for long-term disposal on the lunar surface.

7.2.10 Logistics and Storage The sponsor specified a requirement for 1200 kg of total stowage, packaged in 92 CTBs. A search of the publicly available literature produced a reference which indicated that CTB dimensions were 9×9×16 inches (23×23×41 cm), and that value was used throughout this study. At the end of the study, it was discovered that a single CTB is 19.75×16.75×9.75 in (50.2×42.5×24.8 cm); the value used previously actually corre- sponded to a half-sized CTB [32]. The figures throughout this report correspond to the correct full-sized CTB, although the CTB storage rack spacers in the internal layout draw- ings still reflect the use of half-bags. A great deal of attention was given to stowage in the interior layout process, to ensure that the ECLIPSE habitat met or exceeded the requirement. The final stowage space allocations were

1. 24 CTBs in two stowage racks on the lower level

2. 25 CTBs in underberth stowage racks on the upper level

3. 8 CTBs in stowage racks in the galley wall

4. 12 CTBs in berth stowage (6 per berth)

5. 0.72 m3 of open stowage in the galley wall (17 CTB equivalents)

91 6. 0.96 m3 of open stowage in berths (22 CTB equivalents)

The overall stowage capability of this habitat design is 4.6 m3 or 108 CTB equivalents, of which there are sufficient stowage slots for 69 filled CTBs. The mass allocations provided for clothing are for 13.1 kg/crew if a clothes-washing capability is provided, and 0.046 kg/crew/day if no laundry is available. This corresponds to 28.5 days of expendable clothing per crew member for the basic allotment of clothing mass. Reference [33] gives details of a space-qualified laundry unit with a mass of 78 kg, volume of 0.8 m3, and a power requirement of 300 W. Even ignoring the marginal costs of additional power, water, and increased capacity required for the water reclamation system, this would correspond to equivalent masses between the laundered and expendable clothing options at 283 days, well beyond the 60 day limit for the minimum functional habitat including the full 30-day contingency extension. Reference [34] looked at a range of cases for total clothing mass with and without washing, and found breakeven times ranging between 144 and 850 days. Based on this data, the decision for the minimum function habitat is to forego laundry facilities and use expendable clothing throughout the mission. The clothing allocation for MFH is therefore 107 kg, which at a specific density of 0.00285 m3/crew/day [34] requires 0.66 m3 of stowage volume. This corresponds to 4 CTBs per person, which will be stowed in the individual berth stowage volumes. This detail was also subsumed in the assumption of 1200 kg of total mission stowage.

7.2.11 Lighting Artiﬁcial lighting is ubiquitous in human habitats, but often little-considered in the initial phases of system design. To assess power and thermal implications of lighting systems, the habitat was divided into functional areas, and lighting estimates made for each. In areas where the crew is active, there was generally a further discrimination between area and task lighting. The result of this process is documented in Table 7.1. Although the exact details of the lighting systems were beyond the scope of this study, the power estimates reﬂect the assumed use of similar technologies to CFL or LED lighting, with listed power requirements approximately 25% those of the corresponding incandescent bulbs.

Table 7.1: Lighting Allocations for ECLIPSE Habitat

Area Instances Lighting (W) Duty Cycle (%) Average Power (W) General Area 2 80 75 60 General Task 4 100 30 30 Galley Task 1 20 50 10 Exterior Flood 4 200 30 60 Totals 400 160

Lighting requirements for the four crew berths are based on data from the Inter- national Space Station crew quarters, and are subsumed in a single set of peak/average power requirements drawn from ﬂight experience with that program. It is anticipated that each berth would have both area and task lighting, as they would be required to support prolonged crew occupation during solar particle events.

92 7.3 Power Budgets

Speciﬁc electrical power requirements were addressed in the preceding design dis- cussions; this section will focus on summarizing overall power usage. Table 7.2 represents the collected power requirements of the individual systems. Where practical, a distinction was drawn between peak power requirements and average power draw. In some instances, such as the METOX regeneration ovens, both sets of data are available from the published literature. In other cases, such as the vehicle lighting, reasonable estimates were made of overall duty cycle for each instance of the system or subsystem.

Table 7.2: Power Usage Summary

Component Peak Power (W) Average Power (W) Air Circulation 205 205 Berth Systems 800 225 Lighting 400 160 MF/RO 310 310 VCD 90 90 METOX Ovens 3000 2000 Food Preparation 1000 50 Thermal Control Systems 150 150 Avionics 1000 500 Science Systems 2000 500 Totals 8955 4190

The speciﬁcations for this study declared that the power would be supplied by the Constellation surface infrastructure, so no design accommodation for power generation or energy storage is required. It should be noted that the Constellation Power Support Unit is currently speciﬁed to deliver a maximum power level of 8.8 kW [35], slightly below the peak power requirement calculated for ECLIPSE. It is assumed that the 1.8% variance is acceptable due to the low probability of every habitat system reaching peak demand simultaneously. The calculated average habitat power requirement of 4190 W is 48% of the nominal power system output, providing adequate margin for peak requirements and the power demands of other infrastructure elements.

7.4 Thermal Control

Thermal design and analysis is an intricate and complex process, and a full thermal design of the habitat was not practical within the scope of this study. The goal of the University of Maryland study team was instead to perform a top-level analysis which bounds the scope of the thermal control system, and indicates feasibility of an assumed thermal control system which could be studied in more detail in future follow-on activities. The Stefan-Boltzmann equation governs radiative heat transfer, and in this instance takes the form 4 4 IsαAilluminated + Qinternal = Aradiatingσ(Tradiator − Tenvironment) (7.2) where

93 σ = Stefan-Boltzmann constant 5.67×10−8 W m2K4

Qinternal = heat generated inside the habitat W Is = solar insolation 1.366 m2 α = habitat absorptivity

= habitat emissivity and the relevant areas (A) and temperatures (T) are identified by the descriptive subscripts. Modeling the habitat as a right circular cylinder, the area illuminated by the sun can be found based on the solar angle β from the vertical 1 A = `d sin β + πd2 cos β (7.3) illuminated 4 To simplify the analysis, we assume that non-radiator areas are the lower half of the habitat vertical wall and the lower ellipsoidal dome. These areas are assumed to be covered with sufficient layers of multi-layer insulation to be effectively adiabatic. We further assume that the support legs are designed to minimize conductive heat transfer from the lunar surface into the habitat. This reduces the thermal problem to radiative equilibrium on the radiator surfaces, which are assumed to be the upper half of the vertical walls and the upper elliptical dome. The upper dome is assumed to “see” only deep space, and thus radiates to an environmental temperature of 4 K. Vertical radiator surfaces are assumed to radiate half to deep space, and half to the local ambient surface temperature of the Moon. As a conservative estimate, the lunar surface is further assumed to radiate as a black body. The total heat generated internally is driven by crew and electrical power loads, and is parameterized as Qinternal. An average 2400 kcal daily diet corresponds to an individual metabolic heat load of 116 W; added to the mean power requirements from Table 7.2, the total internal heat load is thereby 4655 W. The heat load due to solar insolation can be found using Equation 7.3 as

Qsolar = AilluminatedαIs (7.4) The sum of the internal and solar heat sources is the total habitat heat load, which must be rejected by radiative equilibrium with the radiator surfaces. The upper ellipsoidal dome is 2 a radiator surface of Adome=10.5 m . The six interstitial surfaces between the longitudinal stringers on the upper deck are independently-selectable radiator panels which each have 2 an area of Apanel=5.3 m . The Stefan-Boltzmann equation for radiative equilibrium of the habitat thermal control system can be expressed as 1 Q + Q = σ A T 4 + n A T 4 − T 4 (7.5) internal solar dome rad rad panel rad 2 moon where nrad is the number of wall-mounted radiator panels active in the cooling loop. The vertical radiators are enabled and disabled to maintain the equilibrium radiator temperature in the range of 280-290 K. With some algebra, this equation can be solved for radiator temperature Trad

1 4 1 Qinternal + Qsolar 1 4 Trad = + nradAwallTmoon (7.6) Adome + nradApanel σ 2

94 Any sort of refrigeration cycle would involve additional heat generation due to the fundamental limit of Carnot efficiency. For that reason, it is strongly desirable to adopt a simple heat exchanger between cabin air and a fluid (mostly likely a glycol mixture) which circulates through the external radiator surfaces. This limits the radiator temperature to approximately cabin temperature, designed to be 295 K (22oC/72oF). At this point, there is sufficient analytical modeling to permit the calculation of thermal control system operations in standard lunar conditions, adapted from reference [36]. This analysis is summarized in Table 7.3. The notional thermal system provides nominal cooling in all cases except for the worst case of equatorial noon. Due to the extreme ambient surface temperature of 380 K (225oF), even with all six wall-mounted radiator panels active, the equilibrium habitat temperature would climb to 324 K (124oF). In order to reach a viable habitat temperature, the wall radiator panels need to be shielded from the local surface radiation to a greater degree. This could be accomplished by an "awning" of MLI stretched horizontally below the panels, reducing the amount of hot lunar landscape visible to the radiators. Alternatively, the wall-mounted panels could be hinged at the upper edge and deployed outward to increase the amount of deep space visible to the radiator surface. The case cited in Table 7.3 corresponds to mounting the lower ends of the panels outward at a 72o angle to provide a better radiative environment at local noon. This modification would only be required for a habitat located close to the equator; the table shows that the nominal wall-mounted panels are adequate with substantial margins at all other lunar locations and solar angles.

Table 7.3: Summary of Habitat Thermal Cases

Solar Angle Lunar Surface Active Wall Radiator Temp Case (deg) Temp (K) Panels (K) Polar Outpost 88 180 3 283 Day Local Midnight N/A 120 1 285 Typical Mid- 45 215 4 287 latitude Equatorial 0 380 6† 290 Noon †Radiator geometry modiﬁed to reduce total lunar surface exposure

While a more detailed thermal analysis will be necessary to reﬁne this estimate, the conclusion of this ﬁrst-order thermal system design is that a conventional heat exchanger and surface-mounted radiators are adequate for operational use of the habitat at almost any location on the Moon, including mid-latitudes. If there is a requirement for the use of this habitat in equatorial regions, some articulation of the radiator panels or innovative use of MLI shields would be required to maintain habitat temperatures near solar noon.

7.5 Mass Budgets

Individual mass estimates and their justiﬁcations have been embedded throughout the discussion of the ﬁnal design and constituent systems and subsystems. This section will be limited to summarizing the overall mass budgets for the minimum functional habitat

95 ﬁnal design. Mass estimates for major structural components are shown in Table 7.4. It should be emphasized that these are rough estimates made on simple structural sizing techniques. These numbers are conservative, and should be capable of signiﬁcant reduction given a focused study incorporating computational methods.

Table 7.4: Structural Mass Estimates

Element Mass (kg) Upper Dome 404 Upper Cylinder 934 Lower Cylinder 957 Lower Dome 404 External Structure 118 Floor Structures 207 Stabilizer Legs 272 Hatches 91 Inﬂatable Airlock 68 Totals 3455

Table 7.5 documents the mass estimates for items associated with crew accommodations, separated in the table into lower and upper deck items. These items are major furnishings, such as tables, chairs, and cabinets; smaller elements such as food service items or hand tools are assumed to be subsumed in the 1200 kg allocation for stowed equipment as speciﬁed by NASA.

Table 7.5: Crew Accommodations Mass Estimates

Element Mass (kg) CTB Storage Racks 36 Equipment Enclosures 27 Furniture 23 Lower Level Total 86 Waste Collection Module 68 Berths 278 Radiation Shielding Water 861† Table 14 Galley Wall 91 Upper Level Total 451 Overall Total 537 †Water for radiation shielding around berths is not charged against habitat mass budget and not summed into table totals.

Details of the ﬁnal selections for life support systems were presented in Section 7.2.

96 The masses of the ﬁxed life support equipment are listed in Table 7.6. Note that this includes the mass for the water and waste tanks, which are built into the habitat, but does not include the mass of the pressure bottles for atmospheric oxygen and nitrogen, with are replaced with the gases between missions.

Table 7.6: Fixed Life Support Mass Estimates

Element Mass (kg) Air Handling 23 CO2 Scrubbing (METOX) 212 Water Recycling (VCD/MF/RO) 167 Water and Waste Tanks 60 Thermal Systems 146 Totals 608

Life support consumable masses for the full design mission (240 crew-days including handover and contingency extension) are presented in Table 7.7. This table also includes the 1200 kg bulk storage in 92 CTBs as speciﬁed by NASA for this study.

Table 7.7: Consumables Mass Estimates

Element Mass (kg) Consumable Air & Tanks 365 Consumable Water 450 Bulk Storage (NASA speciﬁed) 1200 Totals 2015

Collating all of the data from Tables 7.4 to 7.7, Table 7.8 provided the overall mass summary for the ECLIPSE minimum functionality habitat design. As a reminder, the upper system mass limit set by NASA for this study was 7000 kg.

Table 7.8: Top-Level Mass Estimates

Element Mass (kg) Structures 3455 Crew Accommodations 537 Fixed Life Support 608 Consumables 2015 Totals 6615

The overall habitat mass estimate of 6615 kg is 5.5% below the mass limits, which is less margin than would be appropriate at this level of design detail. An alternate budgeting

97 approach would be to assume that the 2015 kg of consumables would be delivered separately to prepare the habitat for a habitation, and compare the 4600 kg habitat "dry" mass to the allocated 7000 kg system mass for a current mass margin of 34%. While all of these mass estimates must be considered tentative at this stage of design, the mass budgets clearly indicate that this design does result in a functional habitat design that is within feasible reach of the designated mass limit.

98 Chapter 8

Conclusions and Future Work

8.1 Conclusions

This paper has documented the six-month design process for the ECLIPSE habitat, developed under the NASA ESMD minimal functionality habitat program. This intensive exercise has demonstrated that relatively small and lightweight habitats can be created to fulfill the NASA program objectives for extended missions on the lunar surface. The ECLIPSE habitat configuration was based on an iterative design approach, along with rigorous collection of data from people experienced in restricted habitat environments on Earth and an extensive survey of prior publications. The selection of a two-floor vertically- oriented habitat structure, while outside the mainstream of recent thought in habitat design, was supported by analytical modeling of internal floor areas and volumes, correlated against NASA mass estimating relations for pressurized spacecraft cabins. The development of a full-scale mockup provided the design team with an greater level of assurance on their design choices, and will serve as an excellent testbed for further research in this area.

8.2 Future Work

8.2.1 Mars Society Crew 73 Data Acquisition Preview Heather Bradshaw, an undergraduate student at the SSL, independently arranged to spend her winter break at the Mars Society’s Desert Research Station (MDRS). Given the interest of this study in human factors in conﬁned environments and terrestrial analogues, her participation in this MDRS crew was a target of opportunity for data acquisition on habitat use patterns to supplement the literature review and survey data. It was decided that it would be of great interest to gather pictures of the habitat and, through post-processing of the data, to determine:

• where people spent their time

• how much time they spent in each functional area

• any patterns of space usage

In order to obtain basic data, two compact digital cameras were modified and programmed to shoot a low resolution picture whenever they detected a change in the content of their field of view. The two cameras were then positioned, one on each floor of the habitat, and

99 acquired data for one week. This resulted in approximately 100,000 images to be processed during data reduction. Since this activity was ancillary to the ESMD MFHE study, there was no attempt to compete this analysis before the end of this study; the analysis will be completed in the next few months and included in future publications arising from this study.

8.2.2 Potential Future Analytical Studies A number of interesting potential analytical studies could be performed as an out- growth of the ESMD MFHE development effort. Due to time constraints, approximately 30 past studies of small lunar surface habitats were examined in detail for regression analysis in Chapter 3; however, more than 200 such papers were located and collected in the process of literature review. It is hoped that the regression approach to initial habitat sizing could be better validated if the much larger data base could be applied en masse to the problem. Similarly, many of the unknowns about habitat interior design for planetary surfaces involve modification of human gait and motion in partial gravity environments. While this can and should be examined experimentally, the critical first step is to extend existing biomechanics models of human motion on Earth to account for changing dynamics in different gravity fields. This could serve to better focus the experimental design for the next phase of testing, while providing valuable insight into critical questions such as required standing headroom in partial gravity or more optimal designs for ladders and other translation aids between floors of a multilevel habitat. A great many benefits could accrue from further refinement of the ECLIPSE design. As mentioned in the previous section, the structural analysis was by necessity rudimentary; further analysis of the structural loads and design details would well yield significant mass reduction in the overall design. Alternative approaches to interior layout could be examined, and prioritized for experimental evaluation through virtual reality and mockup development. Operational aspects of the habitat design should be examined, such as separation from the lander vehicle and emplacement on the lunar surface. Perhaps one of the most significant analytical studies to be pursued in the near term are the optimal configurations and operational roles for a combined habitat/pressurized rover architecture. As detailed in the life support analysis, a pressurized rover which relies intermittently on habitat support can significantly affect habitat systems, and can lead to interesting results such as the presented analysis of the interaction of habitat and rover CO2 collection systems. The restriction to a minimum habitat scenario precluded the accommodation of pressurized rovers, but the design experience has highlighted that a wealth of opportunity exists to explore potential synergy between these systems.

8.2.3 Future Mockup Development and Testing The Constellation lunar surface systems vision is for an area with high activity for the habitat, pressurized, unpressurized, and autonomous rovers, and extravehicular astronauts. Since the UMd Space Systems Laboratory has decades of research and teaching experience in each of these areas, it made sense to use ECLIPSE as the “anchor tenant” for a state-of- the-art research testbed for planetary surface operations. To this end, one end of the fenced enclosure holding the ECLIPSE mockup has been modiﬁed under UMd funding to create the “Moonyard”. A 150 m2 region was framed with a 25 cm high border and ﬁlled with 11 m3 of sand, which covers the asphalt to a depth of 15 cm. Eclipse has been raised from the ground onto two 45 cm aluminum structures which simulate the height of the habitat

100 deployed on its legs. An airlock module was mocked up and mated to ECLIPSE’s hatch. The initial interior accommodations of ECLIPSE were removed, and it was completely updated to increase ﬁdelity and functionality to more closely represent the proposed ﬁnal design of Chapter 7 for advanced habitability and operations assessments.

Figure 8.1: Moonyard Team: Eclipse, Airlock and the sandbox containment perimeter.

Now completed, the UMd Moonyard will incorporate the ECLIPSE habitat mockup, a functional small pressurized rover system (TURTLE), numerous small autonomous robots and dexterous manipulator systems from past SSL research, and a fully pressurized space suit for surface operations. Currently under independent development by the SSL, the MX-3 pressure suit will be the next-generation successor to the MX-2, which has been used operationally in the UMd Neutral Buoyancy Research Facility (NBRF) for five years. Human simulation operations in the Moonyard will be supplemented by partial gravity simulations, performed both in the laboratories of the SSL via counterweighted suspension systems and via ballasted partial gravity simulation underwater in the NBRF. This will give the SSL unprecedented capabilities in undertaking short to medium duration simulations of human missions on the lunar surface, including EVA operations, EVA interface design and assessment, human-robot interactions, rover/habitat operations, etc. Photos of the completed Moonyard, as well as of the revised ECLIPSE habitat interior, are shown in Appendix C. A number of interesting challenges remain in the design, development, and operations concepts of lunar habitats. As has been demonstrated in proof-of-concept ballasted underwater simulation, partial gravity impacts every aspect of interior design, but is poorly un- derstood and is difficult to adequately model analytically. Further part-task experiments, using both ballasted underwater simulation and laboratory counterweighted approaches, would allow the careful validation of the design assumptions and final architecture, and would minimize unexpected design consequences when the actual habitat arrives on the

101 Moon. It would be a straightforward process to design and develop a mockup which is compatible, in terms of both materials and subject safety, with underwater simulation of partial gravity habitat design for further studies. Proof-of-concept tests were performed in the UMd NBRF to examine the feasibility for ECLIPSE upper berth ingress and egress in lunar gravity, as well as examining alternative approaches to interdeck transfer beyond a conventional ladder arrangement. A brief overview of these experiments is included as Appendix D. A great deal of work remains to be done in studying the complexities of mixed-fleet operations, in which an ECLIPSE-type habitat would serve as the base camp for one or more pressurized rovers, local unpressurized rovers, support vehicles such as ATHLETE systems, and remotely-supervised exploration robots of every size. Even given the small scope of the UMd Moonyard, many of these tests could well be initiated economically in this environment, and migrated to much larger (and more expensive) environments such as Desert RATS testing in future years. Indeed, given NASA’s focus on Desert RATS as the annual milestone for lunar surface operational simulations, it would be greatly advantageous to strive to immediately incorporate a functional habitat system in the analogue architecture. One of the advantages of the two-level design of ECLIPSE is that a transportable habitat could be created in a form that is easily trucked to and from the Desert RATS test sites, and erected on site for operational testing. Given the highly modular nature of the internal systems designed for ECLIPSE by the SSL, the crew accommodations would be easily portable to other advanced designs, such as a fully inflated habitat shell. Over and above the technical contributions of the UMd design team, the NASA ESMD study and development of the ECLIPSE design and mockup have served as a focal point for undergraduates and graduate students throughout the engineering school. During the Spring, 2009 semester, the ENAE 697 graduate class in Space Life Support and Human Factors performed team design projects on a "blank sheet" approach to the interior layout and life support systems for an ECLIPSE-type lunar habitat; examples of the teams’ outputs are presented in Appendix E. In the coming Fall 2009 semester, the Moonyard and ECLIPSE habitat will be the focus for interdisciplinary design activities being performed collaboratively by the University of Maryland and Arizona State University, as well as the inspiration and testbed for term projects in ENAE100 (a freshman-year introduction to Aerospace Engineering) and ENAE 398H (honors research projects). A long-term stable university program in lunar surface architecture technology would provide valuable technology to NASA in preparation for the return to the Moon around 2020; perhaps more importantly, it would provide a steady stream of highly competent, experienced, and enthusiastic new engineers as NASA starts to face the implications of an aging work force dominated by engineers who entered the agency in the late days of Apollo or development stages of the Space Shuttle program. Programs such as this one in universities also stimulates interest in science, technology, engineering, and mathematics (STEM) areas in K-12 education throughout the local region, as news of the university activities and developments serves to inspire local school children to consider exciting careers in STEM fields (Figure 8.2).

102 Figure 8.2: Public Outreach Activity Featuring ECLIPSE Habitat Mockup and UMd Moonyard

103 Appendix A

Web Survey Screenshots

104 Figure A.1: Survey page 1

105 Figure A.2: Survey page 2

106 Figure A.3: Survey page 3

107 Figure A.4: Survey page 4

Figure A.5: Survey page 5

108 Figure A.6: Survey page 6

109 Figure A.7: Survey page 7

110 Figure A.8: Survey page 8

111 Figure A.9: Survey page 9

Figure A.10: Survey page 10

112 Figure A.11: Survey page 11

113 Appendix B

ANOVA tables

Table B.1: Arctic/Antarctic base ANOVA - Table 1

114 Table B.2: Arctic/Antarctic base ANOVA - Table 2

115 Table B.3: Ship Crew ANOVA - Table 1

116 Table B.4: Ship Crew ANOVA - Table 2

117 Table B.5: Submariner ANOVA - Table 1

118 Table B.6: Submariner ANOVA - Table 2

119 Table B.7: American ANOVA - Table 1

120 Table B.8: American ANOVA - Table 2

121 Table B.9: Italian ANOVA - Table 1

122 Table B.10: Italian ANOVA - Table 2

123 Table B.11: French ANOVA - Table 1

124 Table B.12: French ANOVA - Table 2

125 Appendix C

Renovated ECLIPSE Interior Conﬁguration

Although accomplished after the completion of the ESMD Minimum Habitat Functional Element contract under discretionary funds of the Space Systems Laboratory, the following activity is included in this document with the goal of fully documenting the initial impact of this research project.

The interior layout of the ECLIPSE habitat mockup, as documented in Section 6 of this document, was an initial candidate configuration used to refine the final design, as presented in Section 7. As a result, the interior layout of the mockup did not accurately reflect the final design at the end of the ESMD contract. Using discretionary funds within the Space Systems Laboratory, the ECLIPSE development team stripped and rebuilt the interior of the habitat to more accurately reflect the final interior layout for future testing. As shown in the following photographs, the major discrepancy between the mockup and the flight design is the use of a geodesic dome to close out the mockup exterior structure, which intrudes into the planned living volume of the habitat’s upper floor. While much more work could be done to increase the fidelity of the current mockup, the configuration represented below is close enough to the flight design to allow human factors testing and longer-duration habitation experiments.

C.1 Lower Level

Figure C.1: Lower Level - Airlock Side Figure C.2: Lower Level - Suitport Side

126 C.2 Upper Level

Figure C.3: View from Galley Wall Figure C.4: Lower Berth

Figure C.6: Waste Management Compart- Figure C.5: View from Ladder Entrance ment

127 C.3 Exterior Views

Figure C.7: Airlock Egress Figure C.8: Exterior View of Habitat Mockup

Figure C.9: UMd Moonyard - ECLIPSE Habitat and TURTLE Pressurized Rover Mockups

128 Appendix D

Partial Gravity Simulations of Habitat Habitability Issues

D.1 Underwater Simulation of Partial Gravity

Given the limited human experience with life at lunar gravity levels, much of the interior design process for a lunar habitat must proceed on a “best estimate” (or, more accurately, “best guess”) basis. While the presence of discernible gravity allows the use of many Earth-normal architectural details, some issues could well change markedly in reduced gravity environments. Foremost among these are the issues of vertical access and transition, such as moving between ﬂoor levels or accessing upper bunks. The University of Maryland has extensive prior experience in the use of ballasted underwater simulation to replicate a partial gravity environment [37]. By applying appro- priately scaled ballast weights to major body segments, human test subjects can experience a realistic simulation of lunar, Martian, or other reduced gravity environment. While this simulation mode does have to deal with the damping eﬀects of hydrodynamic drag, it improves on counterweighted approaches in that each of the body segments is in simulated reduced gravity, and in the lack of wires or other external interfaces which would limit motion in restricted spaces or prevent the use of realistic mockups. Ballasted underwater partial gravity studies were performed following the formal completion of the ECLIPSE study to investigate some of these design questions for lunar habitats.

D.2 Upper Berth Ingress/Egress Study

As an initial proof-of-concept for the use of ballasted underwater simulation for habitat studies, the Space Systems Laboratory conducted a simulation of the process of getting into the upper bunk in the habitat design. An adjustable metal frame, representing the opening to the berth design, was constructed and added to an existing test structure. A

129 test subject, breathing off of an extended line to a remote air tank, was affixed with ballast weights on the front and back of the torso and on both upper leg segments to provide the appropriate apparent gravitation for a shirtsleeve environment in a lunar habitat. The revised interior layout in the habitat mockup, described in Section 7, was used to assess 1-G functionality of the stacked berth arrangement. It was found that ingress and egress from the upper berths was safe and relatively easy, as long as the bench seats are erected to provide a place to step up. If the bench seats are retracted for more floor space, reaching the upper bunk is still easily feasible if the subject steps on the edge of the lower berth first. The lunar gravity simulation performed underwater, as shown in Figure D.1, showed that the partial gravity environment greatly simplifies the complication and stress of reaching the upper berth. The test subject was easily able to hop high enough to grasp the upper edge of the entryway, and use a number of viable methods to bring his body inside the berth, including head first and butt first entries. This test also showed that there was more than adequate room to maneuver the subject’s body inside the berth volume, to allow repositioning of body posture. This test further demonstrated that a simple egress of "hopping" down off of the upper bunk directly to the floor is perfectly acceptable; basic physics shows that the resultant impact energy is comparable to dropping from a 1-ft. height on Earth.

D.3 Intralevel Motion Study

Given the ease of vertical motion found in the preceding tests, underwater ballasted partial gravity was used to more closely model the case of moving between levels in the lunar habitat. The same structure used in the ingress/eress study of the preceding section was moved adjacent to the fixed ladder on the wall of the UMd neutral buoyancy tank (Figure D.2), and used to represent the upper deck of the habitat in relation to the floor of the tank, which served as the lower deck. The test subjects experimented with a variety of methods to travel from the upper level to the lower (Figure D.3) and return (Figure D.4). Approaches tested including conventional rung-by-rung ladder mobility, alternate ladder mobility (such as hands-only and multiple rung intervals), and “brute-force” approaches such as jumping. These tests clearly indicated that traveling between levels in a multi-floor lunar habitat will be much easier than a one-g background would indicate. While directly jumping down from the upper level is equivalent to only an 18-inch drop on Earth, the landing impact is such that some intermediate deceleration would be welcome. Conversely, a standard rung-by-rung approach to the ladder was unnecessarily slow, and the test subjects found that the ability to use only one or two ladder rungs produced an entirely acceptable interdeck transition. One approach meriting further study and testing would be to provide a fairly wide (0.5 m square) step approximately a meter off the ground, to be used by crew in jumping up between levels and to reduce landing impact while coming down.

130 Figure D.1: Ballasted Underwater Simulation of Berth Ingress

131 Figure D.2: Setup for Testing Motion between Levels in Lunar Gravity

Figure D.3: Stepping Down from Upper Level Figure D.4: Climbing Up from Lower Level

132 Appendix E

Alternative ECLIPSE Interior Conﬁgurations - Academic Leverage of ESMD Study

During the University of Maryland Spring 2009 semester, the ENAE 697 Aerospace Engineering graduate class in Space Human Factors and Life Support was given a term project involving the detailed design of the interior layout and life support systems for the ECLIPSE minimum functionality habitat, as well as the TURTLE small pressurized rover originally designed and mocked up by the Spring 2008 ENAE 484 senior capstone design class. The primary focus of this exercise was to explore the human factors design space in both systems, and look for synergies when developing a habitat that interfaces closely with a pressurized rover system. The students had knowledge of the design solutions developed by the SSL study team under the NASA ESMD contract, but were encouraged to "think outside the box" and come up with alternative design approaches. This resulted in a number of interesting concepts for both systems and across systems; for the sake of conciseness, this brief summary will focus only on alternate takes on ECLIPSE interior layout.

E.1 Team Alpha

Andy Dykes, Leslie Eurice, Craig Nickel, John O’Donnell, Alejandro Rivera Team Alpha adhered closely to the baseline ECLIPSE interior design. Figure E.1 shows the lower deck essentially unchanged, but the image does illustrate the loss of a hatch-mounted suitport and the additional wall space dedicated to rover docking. Figure E.2 is also similar to the baseline design, but a greater concern for long-term health effects in lunar gravity led to the incorporation of a flush-mounted exercise treadmill in the upper level floor.

133 Figure E.1: Team Alpha Lower Deck Concept Figure E.2: Upper Deck Concept

E.2 Team Beta

Andrew Becnel, Heather Bradshaw, Nicholas D’Amore, Andrew Ellsberry, Madeline Kirk, Scott Weinberg Team Beta rethought the top-level space allocations, moving the food preparation and eating areas to the lower level (Figure E.3), and some work functions to the upper level. Changing the bunks to a three-high configuration (Figure E.4) allowed the incorporation of a fixed desk-type work station under the fourth berth; waste management compartments were provided on both levels. Although incorporating four suitports, this design did not provide a dedicated docking port for the rover; instead, a separate flexible tunnel assembly was proposed to allow suitport-suitport shirtsleeve transfer between the rover and the habitat. This team also proposed the use of a high-angle inclined ladder for moving between the upper and lower levels, rather than the vertical ladder in the baseline design.

Figure E.3: Team Beta Lower Deck Concept Figure E.4: Upper Deck Concept

E.3 Team Gamma

Mark Arend, Liz Billman, Sam Christen, Gretchen England, Theresa Lazar, Cory Ridge Team Gamma worked to incorporate a more traditional staircase into the design for moving between levels, formed out of stacked CTB storage bins (Figure E.5). This necessitated moving the food preparation downstairs, although the communal table was still situated upstairs, requiring carrying food between levels twice for preparation and

134 eating. The staircase also restricted wall space which could be used for suitports and berthing ports. The upper level (Figure E.6) maintained the 2×2 berthing arrangement of the baseline design, although the berths were moved closer together since they joined via the waste management compartment, rather than a galley wall. As shown in the overall interior view (Figure E.7), the berths moved the lower occupant to ﬂoor level and placed CTB racks between the berths; while this reduced noise coupling between berths, it also increased the mass required for radiation shielding the berths.

Figure E.5: Lower Deck Concept Figure E.6: Upper Deck Concept

Figure E.7: Team Gamma Overall Interior Layout

E.4 Team Delta

Syed-Ali Husain, Mark Infante, Sohit Karol, James Licata, Adam Mirvis Team Delta also moved the waste management compartment to the lower level, and further developed the concept of the general work table to include swing-out extensions to turn the lower deck table into an emergency medical station (Figures E.8 and E.9). All of the life support systems were consolidated in a single wall-mounted compartment between two berthing ports, and a single wall segment is available for locating suitports.

135 Figure E.8: Lower Deck Plan View Figure E.9: Lower Deck Concept

Moving the waste management compartment to the lower level freed up critical space in the upper level to provide a more open and useful food preparation area. One of the clever innovations of this team was to mount two sets of tapered berth compartments next to each other, providing a highly compact arrangement for all four crew to have private berths in one integrated stack (Figures E.10 and E.11). This opens up more upper deck area, reduces traﬃc constrictions around the baseline food service table, and reduces overall water required for crew shielding.

Figure E.10: Upper Deck Plan View Figure E.11: Upper Deck Concept

E.5 Final Discussion

This brief overview highlights that fact that projects such as the minimum functionality habitat can form the basis for a series of student projects, which in turn yield innovative design concepts which may improve the overall concept. Of the designs shown here, one future objective for the ECLIPSE team is to examine the single-block berth

136 design of Team Delta for possible incorporation into the next design revision for the upper level layout. It should also be noted that Team Beta was judged best overall of the four teams in the course, and was entered into the NASA Revolutionary Aerospace Systems Concepts–Academic Linkage (RASC-AL) design competition in June, 2009. Their summary paper, oral presentation, and poster earned them the prize for second place in the graduate category for that year. Student project outgrowths of ECLIPSE have also been entered into the Paciﬁc International Space Center for Exploration Systems (PISCES) lunar analog design competition for 2009, and will be incorporated into freshman design team projects and Aerospace Engineering senior honors research projects. This illustrates the fact that a singular activity such as the ESMD study eﬀort, awarded to a university, produces not only the direct results to NASA, but serves as inspiration and focal point across the academic curriculum for multiple generations of students long after the formal project ends.

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