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http://4.bp.blogspot.com/_ro4M93mVo6c/TJp8FHxfThI/AAAAAAAAAAM/POOg_3CfAc/s1600/070801_EX_astronautEX.jpg
Learning Targets
 I can define a perfect vacuum environment and a “hard” or “near”
vacuum environment.
 I can identify and explain the factors that contribute to a “near”
vacuum environment..
 I can explain the hazards of a vacuum environment.
 I can explain prevention strategies for designing a satellite to
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survive in a vacuum environment.
 Watch the following video about testing a space suit.
Write down 3 to 5 observations about a vacuum
environment.
 http://www.youtube.com/watch?v=KO8L9tKR4CY
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Designing spacecraft to survive in the
hazardous space environment is a
challenge.
All it took to punch this
0.025-cm hole in a U.S.
satellite was a paint
chip moving at
hypervelocity. When
the shuttle brought
back the sat, scientists
found six holes per
square foot.
NASA
Cold welding
Space junk
outgassing
Just a few of many
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What do you Know about a
vacuum?
 What is it?
 Where is it?
 What causes it?
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Vacuum environments
 A pure vacuum, by the strictest definition of the word, is
a volume of space completely devoid of all material.
With gas
molecules
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Without gas
molecules
In practice, however a pure
vacuum is nearly unattainable.
 Even at an altitude of 960 km (596 mi), we still find
about 1,000,000 particles per cubic centimeter.
So when we talk about the vacuum of
space, we’re talking about a “near” or
“hard” vacuum.
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Atmospheric Density
decreases with height.
Atmospheric
pressure
represents the
amount of force
per unit area
exerted by the
weight of the
atmosphere
pushing on us.
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Under standard
atmospheric pressure
at sea level, air exerts
more than 101,325
N/m2 (14.7 lb/in2) of
force on everything it
touches.
Predict what
happens to the
pressure as the
altitude increases.
Atmospheric pressure decreases
exponentially with altitude.
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What causes most of the atmosphere’s
molecules to be close to the earths
surface?
Force of gravity!!!
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So where does space begin?
The atmosphere gradually
thins with increasing
altitude so there is no
tangible boundary between
Earth's upper atmosphere
and Space.
The most widely accepted
altitude where Space
begins is 100 kilometers,
which is about 62 miles.
Link to altitude
chart:
http://www.spacetoda
y.org/SolSys/Earth/Al
titudesChart.html
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Rate
which
orbit
would
have the
greatest
to least
density.
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Oh no what a Drag!
 Although it meets the definition of outer space, the
atmospheric density within the first few hundred
kilometers is still sufficient to produce significant drag
on satellites.
 Drag is the force on an object that resists its motion
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Satellites in Low
Earth Orbit would
experience the
most atmospheric
drag
The following video link is a link
to “This Week @ NASA” news
show. The fourth segment “Ride
the Wind” (4:22) shows a wind
tunnel demonstrating drag.
http://www.youtube.com/watch?
v=xMvl3z8qFnQ
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The effect of drag on a spacecraft
depends on several variables:
 Spacecraft speed
 Shape
 Size
 Orientation to the airflow
DANDE (Drag and Atmospheric
Neutral Density Explorer)
http://events.eoportal.org/presentatio
ns/5/10002120.html
 Read through the articles provided to you by your
teacher about spacecrafts that have specific designs to
compensate for to much drag or not enough
How to get through the density of the
atmosphere?
Euro ion-rocket sat
Designed to skim through the extreme upper
atmosphere using ion drives to compensate for air
drag
http://www.theregister.co.uk/2009/03/17/goce_get
s_up_there/
Maintaining satellite attitude or orientation in
space is a challenge in space (near vacuum)
Gravity Probe B (GP-B) mission spacecraft
For the GP-B experiment, an unprecedented
amount of on-orbit control was required for
the vehicle to maintain its drag-free flight in orbit.
This was accomplished by harnessing the helium
gas that continually evaporates from the
dewar’s porous plug and venting it as a propellant
through eight pairs of opposing or balanced
proportional micro thrusters.
http://einstein.stanford.edu/TECH/tech
nology2.html
Atmospheric Drag in orbit can
cause orbital decay.
 Orbital Decay (loss of altitude
due to reduced speed)
 In 1979, the Skylab space
station succumbed to the longterm effects of drag and
plunged back to
earth.http://www.videojug.com/fi
lm/the-skylab-space-station
Video is 1:55 long
Beyond the thin skin of Earth’s atmosphere is
the vacuum of space that challenge space craft
engineers.
 Three potential problems
for spacecraft are:
 Out-gassing = (release of
gases from spacecraft
materials)
 Cold-welding = (fusing
together of metal
components)
 Heat transfer = (limited to
radiation)
Out-gassing also known as
“off-gassing”
 Out-gassing is the release of a gas that was dissolved,
trapped, frozen, or absorbed in some material.
 When you get into your car and it has that “new car
smell” is a common real world example
In a low pressure environment the
problem of out-gassing is increased.
In space-based equipment, released gas can
condense on such materials as camera lenses,
rendering them inoperative.
 Solutions:
 Laboratory testing to select materials
that have low out-gassing properties
in a “near” vacuum environment.
 Moisture sealants, lubricants, and
adhesives are the most common
sources, but even metals and glasses
can release gases from cracks or
impurities.
The industry standard test for
measuring outgassing in
adhesives and other
materials is ASTM E595.
Developed by NASA to
screen low-outgassing
materials for use in space,
the test determines the
volatile content of material
samples placed in a heated
vacuum chamber.
http://www.masterbond.com/certifications/n
asa-low-outgassing
Before being put into orbit, spacecraft are placed
into a thermal-vacuum chamber for a process
called “bake-out”. Why would they do this?
Thermal Vacuum
Chamber at NASA
Goddard
By Corrie Davidson |
Published October
27, 2010
What is cold-welding?
 Cold welding occurs between mechanical parts that
have very little separation between them.
 Or cold welding will occur when the lubricant between
moving mechanical parts outgas or evaporate.
Possible solution for cold-welding.
 Ground controllers must try different
strategies to “unstick” the two parts.
 One strategy is to expose one part to
the Sun and the other to shade so
that differential heating causes the
parts to expand and contract.
 Lubricants that don’t evaporate or
outgas must be used. For example
solid molybdenum-disulphide is an
example of lubricant that will not
evaporate or outgas.
How is heat managed in a
“near vacuum”?
 Heat transfer in and out of a satellite is a unique
problem in a near vacuum.
 Mechanical systems create heat that can degrade
spacecraft systems.
 In a laptop, fans are used to transfer heat out of the
system. That is not possible in a vacuum.
Methods of heat transfer.
Convection takes place when gravity, wind,
or some other force moves a liquid or gas
over a hot surface.
Conduction is heat flow directly from
one point to another through a
medium.
Radiation is the transfer of heat
through space by electromagnetic
waves without a medium.
Based upon the three definitions, which
method is the best way for a spacecraft to
transfer heat into a vacuum?
Solutions for heat transfer.
 ..
Thermacore loop heat pipes are at work in
aerospace and satellite thermal management
applications, helping designers meet the
strictest specifications and deal with the most
rugged operating environments.
http://www.thermacore.com/products/loopheat-pipes-and-loop-devices.aspx
http://www.ecnmag.com/Articles/
2010/11/Main-Circuit/PassiveHeat-Transfer-Devices/
Staying Cool on the ISS (International Space Station)
http://science.nasa.gov/science-news/science-at-nasa/2001/ast21mar_1/
In a strange new world where hot air doesn't rise and heat
doesn't conduct, the International Space Station's thermal
control systems maintain a delicate balance between the deepfreeze of space and the Sun's blazing heat.
 Read the Article “Staying
Cool on the ISS”
 Consider the following questions:
 1. What would it be like without
thermal control on the ISS.
 2. List and describe the specific
design considerations for thermal
control.
Radiation and charged
particles from the Sun and the
rest of the universe can
severely damage unprotected
spacecraft.
 Read the following article from Scientific American about
“Solar Storms: Effects on Satellites”
 http://www.scientificamerican.com/article.cfm?id=solarstorms-effects-on-satellites