ENVIRONMENTS
The Moon and Meteorites
A very large number of meteoroids enter the Earth's atmosphere each day,
amounting to more than a hundred tons of material.
But almost all are very small, just a few milligrams each. Only the largest ones ever
reach the surface to become meteorites.
The largest found meteorite (Hoba, in Namibia) weighs 60 tons.
There are probably at least 1000
asteroids larger than 1 km in
diameter that cross the orbit of
Earth. One of these hits the Earth
about once in a million years or so
on the average.
The average meteoroid
enters the atmosphere
at between 10 and 70
km/sec. But all but the
very largest are quickly
decelerated to a few
hundred km/hour by
atmospheric friction
and hit the Earth's
surface with very little
fanfare. However
meteoroids larger than
a few hundred tons are
slowed very little; only
these large (and
fortunately rare) ones
make craters.
Earth
Order from the Sun
Average distance from the sun
Orbital period
Orbital velocity
Rotation period
Equatorial Diameter
Surface Area
Mass
Density
Surface Gravity
Average temperature
Temperature range
Atmosphere
Atmospheric surface pressure
Atmosphere extent
3rd planet
149.6 million km
1 Astronomical unit
365.26 days
1 year
29.79 km/s
23.9 hrs
1 day
12756 km
5.11 x 108 km2
5974 x 1021 kg
5515 kg/m3
9.8 m/s2
1G
15o C
-89o C to 58o C
78% Nitrogen- 21% Oxyge
101.3 millibars (14.7 psi)
100 km (Karman line)
The only world on which life and intelligence are
confirmed.
Distinctive surface feature: water oceans
Geologically active
Earth‟s Atmosphere
http://en.wikipedia.org/wiki/Earth%27s_atmosphere
Mars Atmosphere
Viking Atmospheric
Measurements
Composition
95.32% carbon dioxide
2.7% nitrogen
1.6% argon
0.13% oxygen
0.07% carbon monoxide
0.03% water vapor
trace neon, krypton, xenon,
ozone, methane, ammonia
Surface pressure 1-9 millibars, depending
on altitude;
average 7 mb
http://www.daviddarling.info/encyclopedia/M/Marsatmos.html
http://www.daviddarling.info/encyclopedia/M/Marsatmos.html
Earth‟s Moon
days
1 month
24.1 km/s
Orbital velocity
24.6 hrs
Rotation period
1.025 earth days, 1 sol
6794 km
Equatorial Diameter
.53 earth diameters
1.45 x 108 km2
Surface Area
28% surface area of earth
657 x 1021 kg
Mass
.11 earth‟s mass
Density
3933 kg/m3
Surface Gravity
3.7 m/s2
.38 G
Average temperature
-65o C
Temperature range
-140o C to 20o C
Atmosphere
95% Carbon dioxide – 2.7% Nitrogen
Atmospheric surface pressure 7 millibars (.1 psi)
Atmosphere extent
60 km
Orbital period
A rocky planetary object, differentiated in the crust,
mantle and core
Heavily cratered surface; partly flooded by lava
flows over 3 billion years ago
Since then, only impacts by comets and asteroids,
grinding up surface into chaotic layer of debris
called the regolith
Unpressurized Traverses
On Apollo, astronauts explored the surface of the
moon in the vicinity of their landings using space
suits and unpressurized lunar roving vehicles. They
could tevel no further than about 10-20 km from
their landing craft during moonwalks of no more
than about 9 hours
Pressurized Traverses
A pressurized roving vehicle will allow exploration
more like undersea exploration using presurized
submersibles. Astronauts would live inside in a
shirt-sleeve environment.
A pressurized rover could be designed for traverses
of 100s of kilometers and weeks in length.
Many of the unfamiliar characteristics of the environment trace back to processes in our
galaxy or on our sun.
Some of these phenomena are not familiar to earthlings because of protection afforded by the
earth‟s geomagnetic field and because of the earth‟s dense atmosphere.
Aerospace engineers, medical doctors and physiologists who design space vehicles for deep
space missions or for mission to the moon and planets need to be familiar with these
environments.
Unlike the earth, the moon has no weather or geologic activity; the state of the surface
materials can provided unanticipated challenges.
The laws of nature still apply on the moon, and the materials there are not inherently
malicious.
Conditions inside the Apollo lunar module
were cramped and movement was limited
The Moon : Low Gravity
The acceleration due to gravity is 1/6 G on the
surface of the moon.
- the acceleration due to gravity is 1.62 m/sec2
- the escape velocity from the moon is 2.37
km/sec
Astronauts reported that working in lunar gravity
is easier than working in weightlessness.
Low gravity is a design environment for which
we have limited experience.
- how will people move around in the habitat?
- how high should ceilings be?
- How do earthmovers work when their weight is
reduced?
- how do bubbles move in fluids?
Lunar Atmosphere
• The lunar atmosphere is technically termed a surface-bounded exosphere,
meaning that individual molecules are so sparse that they rarely collide
• The number desity is one-thousandth the number density at the altitude of
the International Space Station above earth, 225 mi
• The entire lunar atmosphere would occupy a cube about 64m on a side at
Earth sea level pressure
• Each Apollo landing increased the volume of the lunar atmosphere by 30%
• The composition of the lunar atmosphere is not well known.
- there are various noble gases either of solar wind origin or from outgassing
from the moon itself
- sodium and potassium have been detected by astronomers in Houston
• Visual observations by one of the Apollo 17 astronauts have been interpreted
as a population of very small particles streaming from the moon presumably
driven by electric fields.
An „aura‟ caused by offgassing from the spacesuit
auring Apollo 12 and just the appropriate amount
and angle of sunlight
Lunar Surface Lighting
• The length of a lunation is the time of
successive zenith passage of the Sun, i.e. „noon‟,
is 29.53 Earth days or 707 hours, 44 minutes
• The obliquity of the moon, the tilt of its spin axis
from the ecliptic pole, is 1.5o. A person living near
either lunar pole, at a latitude higher than 88.5 o,
will have 6 months of daylight and
6 months of night, as you would on Earth above
the Arctic Circle.
Sun low on the eastern horizon during the
Apollo 14 mission
Reflected Sunlight
(Visible and Infrared)
• Lunar albedo (solar reflectance) is generally bimodal:
- dark in the marias or „seas‟, smooth plains
- not so dark in the highlands
• Lunar soils show increasing reflectance from the blue
to the red, further increasing in the near infrared
• The approx upper millimeter of the lunar surface has
very porous structure (described as a „fairy castle‟ that
causes high retroreflection of light (like highway
reflectors)
downsun
cross-sun
up-sun
Reflected Sunlight
(Visible and Infrared)
• Looking downsun, one sees a loss of detail
like a white out in snow
• The lunar photometric function is well
documented and modeled
• The lunar reflectance function is
characteristic of bodies without
• Substantial atmosphere and with a
regolith
panorama taken on Apollo 14
downsun
Gnomen used on several
Apollo missions provided a
color photographic chart for
comparison
up-sun
The disk of the earth in the sky as seen from the moon is about 4 times the solid angle
of the disk of the moon as seen from the earth.
The earth is a much more highly reflective object than the moon, particularly when it is
covered with clouds.
The light from earthshine is much brighter than the light of the moon on a clear night.
When the sky is clear on the earth, at new moon, you can see the „Old Moon in the
arms of the New‟. You are seeing the unlit portion of the moon illuminated by
earthshine.
Astronauts likely will be able to work on the lunar surface at night under the illumination
by the earth.
Apparent sizes of the moon when at apogee and perigee.
Generally the moon keeps the same face towards the earth, so there
is a lunar nearside and farside. But the moon actually wobbles so
sometimes we can see further over the north or south poles and
further over the eastern or western limbs. The wobble, as seen from
earth is called a libration:
http://apod.nasa.gov/apod/ap991108.html
Albedo photos of the lunar near and farside from the Clementine probe.
The nearside of the moon has many more smooth, dark areas called maria
(seas) than the lunar farside, which has now large smooth areas and which is
therefore much more rough. 0
nearside
Photograph of the moon as taken
from the earth
farside
Photograph of the moon as taken
from Apollo 16 showing mainly
the lunar farside.
Lunar Surface Thermal Regime
Lunar Challenges: Dust
Regolith: Surficial layer covering the entire lunar surface ranging in thickness from meters to tens of
meters formed by impact process – physical desegregation of larger fragments into smaller ones over
time. Particle size ranges from enormous boulders to micron-sized particles
Formation
Pulverization by bombardment – makes things smaller
Agglutinate formation – makes things bigger
Exposure of fresh bedrock
• The lunar surface was covered with loose, ground-up rock
that was very compacted below about 10 cm, but loose and
fluffy from the surface down to 10 cm
• This material would be both a bane and a boon - operational
a pain in the neck, but providing a record of lunar and solar
history that we are still unraveling
Mare
volcanic
basaltic
relatively few craters
relatively flat
Highlands
primary crust (magmatic)
anorthositic
heavily cratered
relatively rough
Size-Frequency Distribution
“Soil”: <1 mm size fraction (<1 cm also used)
“Coarse fines”: 1-10 mm and/or 4-10 mm size fraction
“Dust”: <50 micron size fraction (<20 micron also used)
Constellation definition: <10 microns (W. Mendell)
95% <1.37 mm by weight
~10-20% <20 μm
5% <3.3 μm
Dust (<50 μm) makes up 40-50%
Median particle size: 72 μm (40-130 μm)
Mean particle size: 70 μm
Half is silt size or smaller - can not be resolved with naked eye.
Highlands average: 50-60 μm
Some highlands >30% mass <20 μm size fraction
Mare average: 60-80 μm
Mare ~15-20% mass <20 μm size fraction
The amount of material disturbed by the LM descent engine is
a strong function of the approach trajectory and speed. Oblique
trajectory causes the least disturbance of the surface. Vertical
descent ( A15) caused the most disturbance.
Note deeper (10-15 cm) foot prints on
crater rim (below) compared to farther on.
AS11-40-5943
LRV wheel tracks
averaged about 1.25 cm, 0 – 5 cm
deepest on rims of small fresh craters
primarily surface shear
developed excellent floatation
50% chevron covered wheels developed
excellent traction well defined imprint of
chevron cohesion, minimal slip
Dust
Lunar Terrains
Craters
Impact Crater Frequency
Crater Frequencies
>10 cm
1000 / 100 m2
10 / m2
>100 cm
10 / 100 m2
0.1 / m2
>1000 cm 0.1 / 100 m2 000.1 / m2
Depth / Diameter Ratios
Diameter (cm) Depth* (cm)
10
2.3-2.5
50
11.5-12.5
100
23-25
500
115-125
1000
230-250