Structural Reliability Considerations for Lunar Base Design

1
Structural Reliability Considerationsfor Lunar
Base Design
Florian RUESS Benjamin BRAUN
Rutgers Symposium onLunar Settlements3-8 June
2007New Brunswick, NJ
HE2 Habitats for Extreme Environments www.he-squar
ed.com
2
Contents
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design

• Motivation
• Structural Concepts
• Structural Reliability
• Example
• V. Conclusions

www.he-squared.com
3
I. Motivation
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
4
NASA Constellation Program
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
The Vision for Space Exploration
Photo NASA
Goals on the Moon Science, Exploration
Preparation, Eventual Settlement
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
5
Everybody wants to go to the Moon
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
The European Aurora program intends to sends
humans to the Moon by 2024 Chinas Change
program plans human missions to the Moon after
2020 Russia, India, Japan and many others also
have lunar ambitions
Photo ESA
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
6
II. Structural Concepts
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
7
Structure Classification
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
first generation pre-fabricated and
pre-outfitted modules like the ones for the
ISS second generation locally assembled
structures after a certain presence on the Moon
as been established third generation structures
exclusively made from local materials
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
8
Structural Concepts
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Focusing on second generation habitats, most
proposed concepts can be divided into

• inflatable structures
• cable structures
• rigid structures

Photo NASA
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
9
Rigid Structures
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Advantages

• experience
• robustness
• all-in-one concept possible

Disadvantage
Photo and concept Schroeder et al.

• relatively large volume mass

I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
10
A Tied-Arch Shell Structure
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Concept by HE2 and H. Benaroya
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
11
Structural Design on the Moon
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Scope of existing design standards exceeded
Many more uncertainties exist
? resistances, e.g. new materials ? loads, e.g.
micrometeoroid impacts
Global safety factor concept

• easy to apply
• uneconomic
• actual reliability unknown

I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
12
III. Structural Reliability
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
13
Classical vs. Structural Reliability
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
1000 hours / life
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
14
How to picture the reliability index ?
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Probabilistic models for the uncertain?
resistance R? load S
Probability of failure
In case of two N-distributed variables
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
15
Limit state functions
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
In the general case functions of several random
variables x
u2
safeg(u) gt 0
R S fR(x) fS(x) g(x)
Limit state function g(x) can be
u1
? linear
failureg(u) lt 0
? nonlinear
Normalisation of therandom variables x g(x) ?
g(u)
g(u) 0
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
16
Limit state functions
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
In the general case functions of several random
variables x
u2
safeg(u) gt 0
R S fR(x) fS(x) g(x)
Limit state function g(x) can be
u1
? linear
failureg(u) lt 0
? nonlinear
Normalisation of therandom variables x g(x) ?
g(u)
g(u) 0
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
17
How safe is safe enough ?
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Pf
b

• Level of safety depends on
• Societal acceptance
• Costs
• Failure consequences
• injuries
• loss of life
• economic loss

Structural codes on Earth
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
18
IV. Example
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
19
Example Calculation
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Internal pressure
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
20
Example Calculation
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Regolith cover
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
21
Assumptions for random variables
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
Coefficient of variation (COV) 0.07 0.30 0.12 0.
03 0.04
Random variable Yield strength fy (aluminium
fy,nom 50 kPa) Internal pressure sint Regolith
cover sreg Cross section A Section modulus W
Mean value 54.1 kPa 69.0 kPa 8.3 kPa nominal
value nominal value
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
22
Calculation results
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design

• Target reliability b 4.77

• Iteration result for a - values

? Determination of required cross - sectional
properties
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
23
Savings in Structural Mass
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
on Earth
100
40
73
30
Global safety factor
LRFD
Reliability-based
Pf 10-4, gglob ? 2.1
gglob 5.0
Pf 10-6, gglob ? 2.6
gglob 4.0
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
24
V. Conclusions
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
25
Conclusions
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design

• Reliability-based framework most appropriate
• Agreement on target reliabilities necessary

• Further steps should include
• Influence of system redundancy
• Consideration of maintenance strategies
• Collection and statistical evaluation of data

I. Motivation II. Structural Concepts
III. Structural Reliability IV. Example V.
Conclusions
26
Thank you for your attention
Ruess / Braun - Structural Reliability
Considerations for Lunar Base Design
www.he-squared.com