ASEN 5158 Space Habitat Design

9/23/2008

Chapter 4   Surface Environments

 

Learning Objectives

  1. Identify primary characteristics of moon and Mars surfaces that affect spacecraft design requirements
  2. Contrast planetary or lunar surface environmental drivers with Earth baseline (and orbital space flight)
  3. Describe engineering concerns and potential design solutions

 

The Moon

 

•         No atmosphere

•         Gravity = 1.62 m/s2

–        0.17 g

•         No magnetic field

–        No drag

–        No radiation protection

•         Water?

•         Ave Temp = 253 K (-4 F) (Earth is 275 K or 35 F)

–        Range 40 to 396 K

•         Day length ~30 days (diurnal cycle)

•         Escape Velocity = 2.37 km/s (Earth is 11.19)

 

Mars

 

•         Has an atmosphere ~1% as dense as Earth

–        Mainly CO2

–        Water?

•         Gravity = 3.71 m/s2 (0.38 g)

•         No global magnetic field, but has local magnetic anomalies

•         Ave Temp = 210 K (-82 F) (Earth is 275 K or 35 F)

•         Day length = 24.67 hours

•         Escape Velocity = 5.03 km/s (Earth is 11.19)

 

Low Lunar and Martian Orbits

 

•         Solar UV degradation around the moon is about the same as in LEO, Mars is ~40% of LEO

•         Drag, sputtering, AO erosion, glow are all negligible around the moon and Mars

•         Plasma charging is sporadic due to SPE’s

•         Radiation

–        No trapped belts around the moon or Mars

–        SPE’s worse around moon, ~60% less around Mars

–        GCR’s worse at both due to no magnetic shielding

•         MMOD

–        No OD (yet!), similar MM impacts

Surface Parameters

 

•         Soil

–        Bulk Properties

•         anchoring, radiation protection and MMOD shielding potential, dust/rock size/distribution, EM ground

–        Material Properties

•         Density, cohesion, friction angle, thermal inertia/conductivity, electrical conductivity, chemical reactivity

•         Radiation levels

–        Dose, type and dose rate

•         Thermal aspects

–        Solar Incident (angle dependent), reflected, absorbed

•         ISRU potential

 

Types of Material Properties

 

•         Grain size and Density

•         Cohesion ~ shear strength

•         Adhesion ~ molecular attraction

•         Angle of internal friction – normal stress to shear fracture ratio

•         Thermal inertia and conductivity

•         Specific heat

•         Electrical conductivity

 

Macrostructure Properties

 

•         Slope angle stability

•         Craters and major Geological Units

•         Seismic activity

•         EM environment (diaelectric permittivity)

 

Lunar Surface

 

•         Surface temperature

–        Function of incident solar, albedo, angle, diurnal cycle (and eclipses), thermal inertia

–        Daytime temperature reaches ~equilibrium of 387 K at equator (237 F)

–        Predawn temperature falls to ~90K (-298 F)

–        Apollo 15 experiment

•         Temperature dropped 216 K during eclipse

•         Reflectivity

–        Overall albedo ~13% (fresh snow up to 90%, Earth ave 37-39%)

–        Strong backscatter – whiteout

•         Bidirectional reflectance of 3 angles (Hapke function)

–        Maria – dark, basalt lava basins (Albedo ~6-9%)

–        Young craters albedo up to 20%

•         Lunar Dust

–        Size, distribution, composition, transport and mechanical properties

–        Issues from Apollo missions

•         ISRU potential

 

•         Lunar Exploration Chronology

–        http://nssdc.gsfc.nasa.gov/planetary/lunar/lunartimeline.html

 

Mars

 

•         Considered a ‘terrestrial’ planet

–        rocky, dense makeup

•         Orbit somewhat more eccentric than Earth’s

–        Greater perihelion and aphelion deltas

–        Larger season swings (length and severity)

•         Mean Solar Martian day

–        sol

–        24h 39.6 min

•         Martian Year ~2x Earth Year

•         Lower bulk density than Earth

–        3933 vs. 5520 kg/m3

–        Suggests different composition and core

•         Total surface area of Mars ~ same as Earth’s landmass area

•         Gravity ~0.38g

–        significant variation associated with topography

–        610 Pa baseline for 0 km contour

–        Hellas Basin at -4 km

–        Olympus Mons at +27km

•         Rocks

–        Solid mineral aggregates

•         Soil (or regolith)

–        Loose unconsolidated, surface material

–        Origin from chemically or physically weathered rocks

•         vs. from catastrophic impacts on the lunar surface

•         Drift material

–        Fine grained, transported by wind

–        covering surfaces and creating dunes

•         Chemical composition

–        ISRU

•         CO2, H2O?

–        Habitat shielding

•         Densities similar to moon regolith

•         SPEs less on Mars than the moon

•         Shielding required for GCRs and MMs about the same (0.5-3 m)

•         Reactivity?

–        Viking ‘biological’ data

•         Seismic activity?

•         Atmosphere and Pressure

–        Mainly CO2, ~1% as dense as Earth

•         Temperature

–        Viking sites

•         166 K (-161 F) winter to 255 K (0 F) summer

–        Winter pole 130 K

–        Summer tropics 300 K

•         Wind speed (ave 2-10 m/sec)

•         Dust storms (up to 30 m/sec)

–        Local and ~global phenomena

 

•         Mars exploration chronology

–        http://nssdc.gsfc.nasa.gov/planetary/chronology_mars.html

 

Summary

•         As a space habitat designer, you need to be aware of various environmental parameters that affect site selection, set up/fabrication, vehicle design, operations, launch mass & ISRU potential

 

 

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