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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 survive in a vacuum environment.

2

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

3

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.NASASpace junk

Cold welding

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?

6

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

Without gas molecules

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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.

7

Atmospheric Density decreases with height.

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.

Atmospheric pressure represents the amount of force per unit area exerted by the weight of the atmosphere pushing on us.

Predict what happens to the pressure as the altitude increases.

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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.

http://www.spacetoday.org/SolSys/Earth/AltitudesChart.html

Link to altitude chart:

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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

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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

The effect of drag on a spacecraft depends on several variables:

Spacecraft speed

Shape

Size

Orientation to the airflow

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

DANDE (Drag and Atmospheric Neutral Density Explorer)http://events.eoportal.org/presentations/5/10002120.html

Euro ion-rocket sat Designed to skim through the extreme upper atmosphere using ion drives to compensate for air draghttp://www.theregister.co.uk/2009/03/17/goce_gets_up_there/

Gravity Probe B (GP-B) mission spacecraftFor 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.

Maintaining satellite attitude or orientation in space is a challenge in space (near vacuum)

http://einstein.stanford.edu/TECH/technology2.html

How to get through the density of the atmosphere?

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 long-term effects of drag and plunged back to earth.http://www.videojug.com/film/the-skylab-space-stationVideo 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/nasa-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 GoddardBy 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...

http://www.ecnmag.com/Articles/2010/11/Main-Circuit/Passive-Heat-Transfer-Devices/

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/loop-heat-pipes-and-loop-devices.aspx

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 deep-freeze 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=solar-storms-effects-on-satellites