A Review Of Technical Requirements For Lunar

Structures – Present Status

September 22, 2005Alexander M. Jablonski1a, Kelly A. Ogden1b,2

1aResearch Manager, 1bSummer Student, Canadian Space Agency, 6767 route de l'Aéroport

Saint-Hubert, Québec J3Y 8Y92Student, University of Waterloo, 200 University Avenue West, Waterloo,

Ontario, N2L 3G1

Moon

Scientifically important

Natural first step in human exploration beyond earth

Currently not fully understood

Uses

Science (low gravity experiments, platform for astronomy, knowledge of creation of earth-moon system)

Resource utilization (3He, regolith)

Exploration

Scientifically important

Resource utilization (3He, regolith)

Natural first step in human exploration beyond earth

Recent interest in moon indicates need for future structures

Technical requirements due to environmental conditions, shape, location, and materials for each phase are reviewed

One – equipment support and shelter structures

Two – inhabitable shelters for science

Three – long term habitats for in-situ resource utilization

New classification based on purpose is presented with three phases of construction:

Lunar Construction Code should be developed

Introduction

First Russian missions (Luna, Zond), first American missions (Ranger) 1959 to 1965

Earth-based mapping of moon by telescope

Samples returned from crewed Apollo missions (1969 – 1972), and Luna 16 (1970)

Future structures –permanent use of moon for science, resources, and further exploration

First Russian missions (Luna, Zond), first American missions (Ranger) 1959 to 1965

Earth-based mapping of moon by telescope

Samples returned from crewed Apollo missions (1969 – 1972), and Luna missions (1970)

Future structures –permanent use of moon for science, resources, and further exploration

Moon: The Nearest Important Destination

Phase One

Support and shelter to scientific equipment, (e.g. LLMT)

Constructed entirely on earth, transported to moon

Automatically deployed, or set up by robots or humans (late in phase)

Protect equipment from dust, meteoroids, radiation, and provide structural support

Other important factors: temperature and fluctuation

Phase Two

First structures inhabited by humans

Allow scientists to stay on moon to conduct experiments, preparation for phase three

Inflatable structures, constructed on earth, few lunar resources used (regolith)

Up to ten people, several months

Additional conditions affecting design: gravity, pressure

Phases of Construction

Phases of Construction Continued

Phase Three

Semi-permanent lunar bases, constructed mainly from lunar resources, building on phase two structures

Continue science, develop ISRU, little dependence on earth

Same conditions as phase two, radiation more important

Phase One Phase Two Phase Three

Primary cause of unique lunar technical requirements is the environment

Conditions that affect lunar structural design are:

Temperature

Radiation

Atmosphere and Pressure

Meteoroids

Gravity

Length of the lunar day

Dust

Seismicity

Environmental Conditions

Temperature

Maximum temperature range is 280 K, temperatures are generally very cold

Importance is high

Affects all phases of construction

Technical Requirements: material must not be brittle above -233°C in permanently shadowed craters, -188°C at the equator, -85.5°C at mid-latitudes, and -63°C around the poles (all phases, at least during set up); insulation/shielding must be provided in phases two and three

Average Temperature 40 K -233°C 220 K -53°C 255 K -18°C 237.5 K -35.5°C

Thickness of Regolith Cover (m)

Variation Range Variation Range Variation Range Variation Range0.0 0 -233 +/- 10 -63 to -43 +/- 140 -158 to 122 +/- 50 -85.5 to 14.50.5 0 -233 +/- 3.9 -56.9 to -49.1 +/- 55.8 -73.8 to 37.8 +/- 19.6 -55.1 to -15.91.0 0 -233 +/- 1.2 -54.2 to -51.8 +/- 16.6 -34.6 to -1.4 +/- 5.8 -41.3 to -29.71.5 0 -233 +/- 0.5 -53.5 to -52.5 +/- 7.5 -25.5 to -10.5 +/- 2.7 -38.2 to -32.82.0 0 -233 +/- 0.3 -53.3 to -52.7 +/- 4.3 -22.3 to -13.7 +/- 1.5 -37.0 to -34.02.5 0 -233 +/- 0.2 -53.2 to -52.8 +/- 2.8 -20.8 to -15.2 +/- 1.0 -36.5 to -34.5

Monthly Variation and Range (°C)

Permanently Shadowed polar

craters Other Polar areas Equatorial zone Mid-latitudes

Radiation

Radiation Limits

Average dose on earth (all radiation) is 0.0036 Sv/yr; on moon (GCR only) 0.25 Sv/yr minimum (up to 0.9)

SEP events on moon, additionally up to 1000 Sv/event

No definitive limit; recommended limits are 0.5 Sv/yr (Space Studies Board 1996; NCRP 1989) or 0.05 Sv/yr (International Commission of Radiological Protection, for nuclear power plant workers)

Sources: Galactic Cosmic Rays (GCR) and Solar Energetic Particle (SEP) events

Degrades equipment (all phases); threat to human life (phases two and three)

Phase One: ion induced charge (electronics), extra noise (sensors), vacancies (materials), reduced output of solar panels; solution – redundancy, some shielding in materials of structure (radiation hardened materials), few cases may use regolith

Blood Forming Organs Eye Skin

Depth (cm) 5 0.3 0.0130 Days (Sv) 0.25 1.0 1.5Annual (Sv) 0.50 2.0 3.0Career (Sv) 1.0 to 4.0 4.0 6.0

Table from NCRP No. 98, 1989Recommended Ionizing Radiation Exposure

Limits For Flight Crews

Radiation Continued – Phases Two and Three

Significant shielding required: minimum 700 g/cm2

Regolith shielding (in-situ): thickness depends on density of regolith; ρ = 1.3 g/cm3 (min), regolith thickness = 5.4 m

Thin layer of shielding causes brehmsstrahlung radiation (initial collisions create high energy particles); more dangerous

Radiation Dose vs. Protection

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 100 200 300 400 500 600

Protection (g/cm2)

Do

se (

Sv)

GCR

1956 Solarflare

1960 SolarFlare

1972 SolarFlare

Phase Three

Dose should be as low as possible: minimum 1000 g/cm2, equal to the protection of the earth's atmosphere

Other possible methods include electromagnetic radiation shielding, use of lavatubes

Atmosphere and Pressure

Thin (almost non-existent) atmosphere contributes to severity of other conditions

No thermal insulation –increases temperature range

No radiation shielding provided

Does not burn up meteoroids

Structural requirements in phases two and three

Structure must be pressure vessel to sustain life (min 26 kPa, realistically much higher, inside)Increased tensile loads; somewhat countered by regolith but not entirely; also horizontal loads

Pressure caused by 5.4 m of regolith (ρ=1.3 g/cm3 to 1.75 g/cm3) is 11.4 to 15.9 kPa

Atmosphere and Pressure

Meteoroids

Hit with full velocity (no atmosphere) 13 – 18 km/s

Phase One: threat accepted due to low probability of impact, relatively insignificant consequences, lack of feasible solutions

Meteoroid Flux vs. Diameter

1.00E-121.00E-111.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+001.00E+011.00E+021.00E+031.00E+041.00E+051.00E+061.00E+071.00E+081.00E+09

1.00

E-0

4

1.00

E-0

3

1.00

E-0

2

1.00

E-0

1

1.00

E+

00

1.00

E+

01

1.00

E+

02

8.00

E+

02Particle Diameter (cm)

Flu

x (i

mp

acts

/ km

^2/y

r)

(Lindsey,2003)(p.148, Eckart)

(p.256, Apollo16, Hawkins)(p.256, Apollo16, McCrosky)

Meteoroids - Phases Two and Three

Phases two and three: any puncture has significant consequences, so shielding must be provided

Fish-Summers Penetration Equation used to approximate effectiveness of regolith (equation not tested for this use; approximation must be further tested before results used)

Thickness assumed to be 5.4 m (minimum for radiation protection)

Will prevent penetration through spallation of particles of mass 37 kg or diameter 52 cm, reducing flux of particles that will penetrate to between 10-8 and 10-7

impacts/km2/yr (Lindsey, 2003; p. 148, Eckart, 1999)

6/1875.0352.0mmmtt vmkt ρ×××=

kAl = 0.57vm = 18 km/s (max v)ρm = 0.5 g/cm3

ρAl = 2.7 g/cm3

ρre = 1.3 g/cm3 (min ρ)kre = 1.18 (using tAl ρAl/ ρre= tre)

t = thickness of target (cm)k= constant for target materialm= mass (g)v= velocity (km/s)ρ= density (g/cm3)The subscript t stands for target, Al for aluminum, m for meteoroid, and re for regolith.

g = 1.62 m/s2 (1/6 g on earth)

Self-weight of structure relatively small compared to earth

Benefit in phase one

Phases two and three; will not greatly reduce net vertical tensile loads caused by internal pressure

Gravity

Lunar day is 29.53059 earth days

Contributes to thermal extremes, allowing more time to heat up and cool down

Structures must be able to withstand cold temperatures, at least during set-up (if covered with shielding later)

Missions can be timed to arrive before lunar noon, giving maximum time in warmest temperatures to set up

Length of Lunar Day

Dust

Materials must be abrasion resistant

Mechanical parts able to operate with grit

50% of particles between 20 and 100 µm

Photoelectric change in conductivity at sunrise and sunset cause particles to float in air, adhere to surfaces

Seismic energy released on moon much less than on earth: moon E = 1011 to 1015

ergs; earth E = 5*1024 ergs

Moonquakes usually of magnitude 1 to 2 on Richter scale

Maximum magnitude recorded on moon was 3 to 4 on Richter scale

Loads created are very small

Largest recorded seismic activity from meteoroid impacts rather than moonquakes

Seismic Activity

Materials

Must retain mechanical properties in lunar environment

Phase One

Resistant to radiation, abrasion, and temperature

Solid collapsible structures, inflatable structures, rigidizable inflatable structures

Rigidizable structures: low weight and volume when compact; do not depend on maintaining internal pressure

Phase Two

Same conditions, also must contain internal pressure

Inflatable to minimize weight and volume; must maintain internal pressure to sustain life

Multi-layered membrane including lining, bladder, restraint layer, insulation, and some meteoroid protection (Example TransHab)

Further testing must be done (vacuum, temperature)

Material Continued

Phase Three

In-situ resources to construct habitat, used further than just regolith shielding

Lunar concrete, sulphur-based concrete, cast basalt

Problems with concrete: must obtain water; water evaporates too quickly, weakens concrete

Solutions: build under construction dome or set concrete in other pressurized environment

Sulphur concrete: does not require water; uses less energy to manufacture; can be produced in cold environments

Cast basalt: basalt widely available on moon; also does not needs water; requires heat (directed sunlight)

All materials must be tested before use: one common drawback is lack of strength under tension

ShapePhase One: shape determined by instrument

Phase Two

Must allow practical use of space; maximize internal volume for minimal weight and volume when compact

Eliminate corners to avoid concentration of stresses

Most effective options are sphere, cylinder, and toroid shells

Phase Three: dome

Location

Phase One

Location determined by scientific goals of mission (e.g. South Pole Aitken Basin, far side astronomy)

Phase Two

Location still determined by scientific interests, also influenced by location of resources

Phase Three

Location determined by ideal base conditions; environmental conditions (radiation, temperature, meteoroids) minimized

Peaks of eternal light at the south pole

Lavatubes

Phase One

Determined by scientific goals of mission (e.g. South Pole Aitken Basin, far side astronomy)

Phase Two

Determined by scientific interests, also influenced by location of resources

Phase Three

May minimize some environmental conditions

Location

Peaks of Eternal Light

Almost constant sunlight results in smaller temperature range, almost constant solar power

Lavatubes

Ceiling would provide radiation, temperature, and meteoroid shielding (more than required 5.4 m), also during construction and maintenance

Five recent lunar missions (since 1976)

Hiten (ISAS, 1990)

Clementine (NASA, 1994)

AsiaSat 3/HGS 1 (China, 1997)

Lunar Prospector (NASA, 1998)

SMART 1 (ESA, 2003)

Recent Findings

Top: SMART 1

Left: Clementine

Clementine (NASA, 1994)

Mapping of lunar surface; showed variation of topography at poles, especially South Pole Aitken Basin and permanent dark areas that may contain ice water

Found mascons and irregularities in gravity

Small Missions for Advanced Research in Technology

Continue search for water, after Lunar Prospector's crash to the lunar surface did not find traces

Advances in geology, morphology, topography, mineralogy, and geochemistry of lunar surface

Mission extended by one year, from original six months (Now planned to finish Aug. 2006)

SMART 1 (ESA, 2003)

Planned missions include Lunar Reconnaissance Orbiter (LRO) (NASA), Trailblazer (US private mission), Lunar-A and SELENE (JAXA), Chang'e 1 (CAST), Chandrayaan-1 (ISRO), Baden-Württemberg 1 (Technical University of Stuttgart)

Planned missions include:

Trailblazer (US private mission, end of 2005)

Lunar-A and SELENE (JAXA, 2006) – SELENE will investigate chemical and mineralogical composition of the moon and tectonicsand geological history, helping to determine areas for in-situ investigation

Chang'e 1 (CAST, late 2007)

Chandrayaan-1 (ISRO, 2007-2008) – will study 3D topography of the moon and distribution of chemicals and elements, and produce chemical imaging of poles and chemical stratigraphy of the lunar crust; it is important in determining the location of structures in phases two and three

Lunar Reconnaissance Orbiter (LRO) (NASA, end of 2008)

Baden-Württemberg 1 (Technical University of Stuttgart, after 2008/09)

Planned Missions

Primary Objective: identify landing sites for future missions

Will also study radiation environment, topography, and resources in polar regions

Continue composition mapping

Relevant to all phases, particularly with respect to shielding

Lunar Reconnaissance Orbiter(LRO) (NASA, end of 2008)

Although further planning by the Lunar Strategic Roadmap Committee has been cancelled, the recommendations already produced will still be considered. Two of the four lunar exploration plans from the Lunar Strategic Roadmap Status Report from April, 2005, are of particular relevance to the proposed phases of construction, and the NASA plans from these are shown here.

from

Briefing to the ISS Strategic Roadmap CommitteeMike HawesSpace Operations Mission DirectorateApril, 2005

Technical Requirements and Importance

Condition Quantification Phase One Importance

Phase Two Importance

Phase Three Importance

Temperature Temperature range = 280 K High High HighRadiation Average dose = 0.25 Sv/yr Medium High HighAtmosphere/ Pressure

3 nPa (p.15, ISU, 2000) Medium High High

Meteoroids Micrometeoroids v = 13 to 18 km/s; for particle diameter = 1 cm or less (mass =

0.262 g), flux = 0.405 impacts/km2/yr

Low High High

Dust More than 50% of particles between 20 and 100 µm, (Toklu, 2000)

Medium Medium Medium

Length of Lunar Day Lunar day = 29.53059 earth days Low Medium Low

Gravity g =1.62 m/s2 - Low Low

Seismicity Maximum quake recorded 4 on Richter Scale, average 1-2

- - -

Recommendations

Strategic Recommendations

Develop Lunar Construction Code, to be updated annually

RecommendationsStrategic Recommendations

Develop Lunar Construction Code

Included in the code will be:

Mapping of the lunar surface and environmental conditions

A description of the technical requirements for lunar construction for each phase

Quantification of these requirements

Guidelines for lunar construction

The code should be updated annually with the findings from recent missions

Specific Recommendations

Phase One

Temperature and abrasion resistant, radiation hardened materials

Redundant electronics and solar panels

Phase Two

700 g/cm2 regolith for radiation shielding, also sufficient for temperature and meteoroids

Pressure vessel with minimum 26 kPa internal pressure, therefore no corners; shaped as sphere, cylinder, toroid

Multi-layered, including bladder, restraint layer, and inner liner

Phase Three

Provide more radiation protection, ideally 100 g/cm2

Alternative materials such as concrete and cast basalt, other possible shapes (dome) and other methods of radiation shielding (electromagnetic)

Phase One

Temperature and abrasion resistant, radiation hardened materials

Redundant electronics and solar panels

Phase Two

700 g/cm2 regolith for radiation shielding, also sufficient for temperature and meteoroids

Pressure vessel with minimum 26 kPa internal pressure, therefore no corners; shaped as sphere, cylinder, toroid

Specific Recommendations for Each Phase

Multi-layered, including bladder, restraint layer, and inner liner

Phase Three

Provide more radiation protection, ideally 1000 g/cm2

Alternative materials such as concrete and cast basalt, other possible shapes (dome) and other methods of radiation shielding (electromagnetic)

Additional Recommendations

Develop rigidizable pneumatic structures; resistant to temperature, radiation, and abrasion

Develop materials that are temperature and radiation resistant

Research vacuum multi-layered pressure vessels

Develop in-situ structural experiments with regolith shielding (first robotic missions)

Develop in-situ investigations of lunar soil (civil engineering applications) (first robotic, later manned missions)

Develop radiation shielding

Develop ground based experiments simulating lunar conditions (analogues)

Develop rigidizable pneumatic structures; resistant to temperature, radiation, and abrasion

Develop materials that are temperature and radiation resistant

Research vacuum multi-layered pressure vessels

Develop in-situ structural experiments with regolith shielding (first robotic missions)

Develop in-situ investigations of lunar soil (civil engineering applications) (first robotic, later manned missions)

Develop radiation shielding

Develop ground based experiments simulating lunar conditions

Additional Recommendations for Future Research