Comparison of Lunar and Martian Environments

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Comparison of Lunar and Martian Environments

• Presentation to 16.83
• 7 February, 2005
• _________________
• Jeff Hoffman

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Mars-Back TM

• Ultimate goal is sustainable human and robotic
  exploration of Mars
• Approach
• Define candidate Mars missions that produce high
  value
• Derive lunar missions to increase Mars
  Exploration Readiness Level
• Secondary objective maximizes lunar science and
  exploration goals
• Develop architectures in support of Mars and moon
  missions
• Refine architectures to deliver maximum value

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Summary of CER Study

• A sustainable exploration program must focus on
  delivering value throughout its lifetime to all
  stakeholders
• We must deliver value, and make all the
  stakeholders aware that we are delivering value
• A Mars-back focus should be maintained throughout
  the architecture and mission development process
• Increasing credible evidence that design of the
  system for Mars, and progressive development and
  deployment on the moon, will only cause minor to
  modest suboptimality for the moon

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Summary - Rationale for Mars via Moon

• Crew must arrive on Mars the first time with a
  wide variety of assets fully operational
  landers, rovers, habitats, power, etc.
• Using moon as development test bed has many
  systematic advantages
• Moon exploration will provide value to many
  external stakeholders, including scientific,
  security, commercial and public
• Can progressively deploy hardware classes to the
  moon, compatible with available funding,
  supporting affordability
• The long preparation time for Mars direct will
  not yield a sting of high visibility events - not
  policy robust
• In the event of significant malfunction, crew can
  be returned from the moon on flexible schedule
  and quickly, with significant impact on risk

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Gravity

• Moon has 16 of Earths gravity.
• Mars has 38 of Earths gravity.
• Large impact on landing/ascent!
• Impact on surface operations
• Power required for rovers
• Space suit weight

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Time Scales

• Lunar day Earth month 29.53 Earth days
• For most of lunar surface, daily variations are
  constant throughout the year
• Near the lunar poles, can get six months of
  nearly constant solar illumination and six months
  of dark, similar to the Earths polar regions
• Martian Day 24 hours 37 minutes
• Earth day, but with a phase shift that can
  cause physiological problems for crew and/or
  mission controllers
• Martian Year 686.98 Earth days 669.60 Martian
  days
• Earth-Mars close approach every 26 months
• (vs. continuous access to the Moon)

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Length of Daylight vs. Latitude
Axis Tilt 1.5 degrees
25.2 degrees
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Power - Mars/Moon Insolation

• Mars reference architecture is solar power near
  equator, reduced flux, Martian day cycle from day
  to night
• MERL considerations - two Lunar environments
  considered
• Lunar equator 14 earth day lunar night probably
  precludes solar as primary option
• Lunar pole high topography is permanently
  illuminated
• gt630 m at pole, but must also consider local
  topography.
• gt1700 m at 89o
• South pole has about 28 km2 which pass this test
  (shown above in red)
• North polar topography is everywhere too low to
  be illuminated in winter
• Use solar power plant in regions of eternal
  sunlight for lunar base

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Surface Mobility - Mars Back to Moon

• The moon may be considered to consist of four
  major units mare, highlands, craters, and
  shadowed regions that may contain ice
• An area of primary lunar science interest is the
  poles
• MERL considerations
• Crater slopes on moon and Mars have comparable
  inclinations
• Open rovers will give range to several craters of
  eternal darkness
• Pressurized rovers can be added later to explore
  nearby basins
• Pressurized rover will needed for Mars, and can
  be tested on moon
• Open rovers will be useful at both moon and Mars

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Solar Constant

• Moon 1368 w/m2 Earth
• (low orbital eccentricity .0167)
• Mars 1.5 AU from the Sun
• Orbital Eccentricity .0933
• Perihelion 718 w/m2
• Aphelion 493 w/m2

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Solar Array Area
Assumptions Mars Aphelion Regenerative Fuel
Cell Storage System Ga-As Solar Cells Arrays
track the Sun
DUST!!
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Thermal Environment
Mars has greater variation with latitude. Moon
has greater daily variation.
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Habitation - Mars/Moon Thermal

• Mars reference architecture is habitat near
  Martian equator, for up to 600 days large
  diurnal temperature range (100K), but small
  seasonal temperature changes
• MERL considerations - two Lunar environments
  considered
• Lunar pole (within the 1.5o of axis tilt) no
  diurnal temperature changes, but large seasonal
  changes
• Lunar equator huge diurnal temperature range
  (300 K), but virtually no seasonal change
• During summer of up to 150 earth days, lunar
  poles have temp within about 50 K, and range is
  about 100 K below that of Mars
• Run up to 150 day missions at lunar poles, and
  design for slightly harsher thermal conditions

100 K
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Atmosphere

• Lunar surface can be considered a vacuum.
• Mars surface atmospheric pressure 100,000 ft.
  on Earth
• Maximum heating during typical Earth reentry
  between 250,000 ft. to 200,000 ft.
• i.e. Mars-bound spacecraft can use
  aerocapture/aerobraking.
• Require heat shields.
• Parachutes work, but sensitive to surface
  altitude.
• Flash evaporator and sublimator cooling systems
  cease operation 100,000 ft.
• (serious implications for Space Suit thermal
  control)
• Martian atmospheric density is highly variable.

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Mars Atmospheric Composition
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Lunar Water

• Moon appears to be dry except possibly near poles

Lunar epithermal neutron count in the lunar north
(left) and south (right) polar regions. A low
epithermal neutron count indicates a high
hydrogen concentration.
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Martian Water

• Liquid water cannot exist on the Martian surface.
• Extensive evidence of past activity of flowing
  liquid on Martian surface.
• Location of current Martian water
• Atmosphere - small quantities
• Polar Caps - thickness unknown
• Northern Cap 1000 km. diameter
• Southern Cap 350 km. Diameter
• Seasonal CO2 ice cover extends size
• Soil
• Viking landers released 1 water by heating to
  5000 C
• Some types of soil (e.g. clays) may have up to
  15 water
• Permafrost layer - evidence for extensive
  permafrost at latitudes gt400. Water ice may exist
  within a few meters of the surface. Liquid water
  may exist at greater depths.

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Dust

• Fine-grained dust exists both on the Moon and
  Mars.
• Apollo astronaut EVA activity raised dust clouds
  that stuck to space suits. Finer particles became
  embedded in the fabric and could not be brushed
  off. Significant amounts of lunar dust entered
  the LEM.
• Analysis of rover tracks indicates typical
  Martian dust may be somewhat coarser than typical
  lunar dust.
• Viking landers measured 100 ppm of active
  oxidants. These oxidants may have dangerous
  effects on humans.

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Martian Dust Storms

• Two types of storms regional and global
• Regional Dust Storms
• Can be a few million km2
• Appear annual, probably in all seasons
• Tend to appear on the equator side of the
  seasonal polar ice caps also in the southern
  subtropical region
• Global Dust Storms
• Tend to start near perihelion (southern
  spring/summer)
• Do not occur every year
• Start as regional storms and spread over entire
  planet
• Can last for months
• Size, duration and opacity are variable

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Soil Resources - 1
Note Viking did not directly measure
concentration of elements with Zlt12.
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Soil Resources - 2
Note Carbon on the Martian surface is completely
oxidized.
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Radiation

• Lunar Surface is completely exposed to galactic
  cosmic radiation (GCR) and solar particle events
  (SPE). Exposure 50 of deep space due to
  geometry.
• Mars CO2 atmosphere provides significant
  shielding (highly dependent on altitude).

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Effect of Mars Atmosphere on Radiation
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Thats all, folks!
QUESTIONS?