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17 February 2013

Haym Benaroya

Department of Mechanical

& Aerospace Engineering

Space Show Webinar: Engineering Structures in Space

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Elements of the Whole 1. human physiology

2. human psychology

3. plant physiology

4. the lunar surface radiation environment

5. the lunar surface temperature cycles

6. lunar regolith mechanics

7. human factors studies

8. structural mechanics

9. thermal science in low gravity and vacuum

10. low gravity fluid mechanics

11. power systems

12. astronomy requirements on the Moon

13. geology requirements on the Moon

…

n-1. economic theory

n. lunar tourism.

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Arthur C. Clarke, 1951

Drawing: R.A. Smith

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A 1962 lunar base study by DeNike and Zahn for a

flat region on the Moon that included the Sea of

Tranquility (the Apollo 11 landing site).

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Lunar Environment

• gMoon = 1.62 m/s²

• internal air pressurization can range from 34.5

kPa (5 psi) to 101.3 kPa (14.7 psi)

• protection from radiation and micrometeoroids

• insulation (temperature differentials of 250°C)

•2.5 m - 3.0 m of regolith cover needed

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Additional Critical Environment Factors

• Regolith dust: very small particles that are

easily electrostatically charged, easily

suspended and displaced, are abrasive, and

attach to everything

• Moonquakes: Order of magnitude ~ 5 Richter,

can last 10 minutes vs. 2 min max on Earth

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Structural Concepts

• first generation:

pre-fabricated and pre-outfitted

modules like the ones for the

ISS

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Cylinder

Modules

Brand Griffin

9 Courtesy Orbital Sciences

Drawing: Carter Emmart 1996

Emmart

Carter Emmart

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Structural Analysis and

Design of the

RUTGERS

Lunar Base Structure 2002-Present

Structural Design of a Lunar Base

Lunar Design Reliability • What reliability is considered “acceptable”? • Should the Lunar outpost be designed to higher or lower

risk tolerances? • How does the designer consider reliability of a structure

that has never been built before and cannot be tested? • Can we afford to fail?

Considerations for a Detailed Structural Reliability Study

• Lunar temperature gradients and material fatigue (exposed structures)

• Structural sensitivity to high/low temperatures

• Outgassing for exposed steels/materials

• Factors of safety according to risk tolerance

• Dead loads, live loads under lunar gravity

• Buckling, stiffening, bracing requirements for lunar structures (internally pressurized)

• New failure modes (micrometeorite impacts)

Redundancy

Duplication or repetition of elements for alternative functional channels in case of failure

Parallelism

Multiple options in the face of unanticipated difficulties

Logistics • Replace or Repair

• Acquisition, Distribution, Maintenance, Replacement

Serviceability limit may lead to Ultimate limit quickly: Design for escape and rescue

Design Process

Prototyping

Conceptualization

*Evaluation

Manufacturing

Construction

Total Life Cycle

Conception

**Concurrent Engineering

Recycling of System & Components

Retirement & Disposition

System Design

Acceptable risk ?

Economic costs

*Reliability concepts are analysed at this point. **Move major items early in the cycle to anticipate potential problems.

Reliability

• Human Safety • Minimum Risk

Design Philosophy Limit States

Redundancy

Logistics

Parallelism

Ultimate Serviceability

Limit State Function <= 0

Failure

Design for Escape & Rescue

GOALS

use know

if not

NEED

Constructability

LINK to USERS’ LOSS of USE

PerformancePerformance--Based EngineeringBased Engineering

• Covers range of hazard levels

• Accounts for uncertainty in parameters, relationships

dIMEDPdGEDPDMdGDMDVG IMDV

Intensity

measure

Engineering

demand

parameter

Damage

measureDecision

variable

Cost of

repair Or

Loss of

Function

Structural

or non-

Structural

Damage

Forces, Displ,

Temp.Input

Spectra

After: Kramer, Mayfield and Mitchell, Ground Motions

and Liquefaction

Performance-based engineering methodology leads to decision variables.

Input/Intensity Spectrum

Fragility/ Damage

Cost/Decision Variable

Engineering Demand

Comparisons of Concepts

On a scale of 1-6, with 6 being the highest reflecting a very positive characteristic of the concept, the following ratings are given to various structural concepts:

17 4 4 1 2 6 Underground

23 6 4 6 4 3 Three-hinged arch

19 6 2 4 2 5 Crater base

21 6 5 1 3 6 Tuft-Pillow

14 2 3 1 3 5 Spherical inflatable

Total Excav. Found. Exper Constr Transp Structure

Three-hinged arch: •Transportation 3 •Easy of construction 4 •Experience with the structural system 6 •Foundations 6 •Excavation 4

Proposed Design:

A Tied-Arch Shell Structure

Concept and picture by F. Ruess and H. Benaroya

global safety factor applied: 5

Design Volume Habitat dimensions: • Volume: 120 m3 per person for

a lunar habitat has been recommended

• Floor height: 4.0 m seems most

suitable. Use of slightly magnetic boots could reduce the floor height (need metal floors) = 34.4 m2 floor area per person.

It will depend not only on the

crew size but also on the amount of equipment and stowage space needed.

415 320 250 Total area ~

69 55 41 20% for Equipment & Stowage

343 275 206 Habitable area

10 8 6 Crew size

A three-hinged arch

Loading and support conditions for the end walls

The static load cases: 1-internal pressure 2regolith cover 3partial regolith cover 4-floor loads 5installation loads

Tension force governs arch design

Structural Analysis

Structural Design of a Lunar Base

Additional calculation parameters:

• rise: 5 m

• regolith modulus of subgrade reaction: 1000 kPa / m

• global safety factor applied: 5

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Load Case 1: Internal Pressure

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Load Case 2: Regolith Cover

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Bending Moment: Parabolic Arch

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Bending Moment: Circular Arch

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Cross Section Types

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

The Tie / Floor

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Bending moment

distribution (BMD)

Floor shape similar to

BMD

Cross Sections: Summary

Structural Design of a Lunar Base

• cross section Type 4 is most efficient

• material: high-strength aluminum

• arch mass: 31 kg / m²

• average floor mass: 118 kg / m²

• max. deflections for operational loads are about 5 cm

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Dynamics

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

• simulated cam mechanism: f = 172 Hz; a = 4.6 cm

• no significant increase in forces and deflections was found

Modal shape 1

The End Walls: Bending Moments

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Bending moment In the x-direction. Blue represents Minimum bending moment of -90.4 kNm/m. Red represents Maximum bending Moment of 16.8 kNm/m.

Hinged Connections: Variant 1

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Hinged Connections: Variant 2 Concept: Jörg Schänzlin

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Wall Connections

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

The Construction Sequence

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

Base Layout

Structural Design of a Lunar Base

Contents – I. Introduction – II. Environment – III. Concepts – IV. Structural Analysis – V. Conclusion

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Drawing: Andre Malok, Newark Star Ledger

Base – Star Ledger

Conclusions

Lunar structures must:

• minimize mass

• show robustness (reliability)

• be expandable

• be easy to construct

• eventually use local materials (ISRU)

• be transferable to Mars with

minor redesign

PerformancePerformance--Based EngineeringBased Engineering

dIMEDPdGEDPDMdGDMDVG IMDV

Intensity

measure

Engineering

demand

parameter

Damage

measureDecision

variable

Cost of

repair Or

Loss of

Function

Structural

or non-

Structural

Damage

Forces, Displ,

Temp.Input

Spectra

The following slides are supplementary.