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Q: Edge of Space: resources (techtor, feilong,& + aerospace researchers) ( Answered 5 out of 5 stars,   7 Comments )
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Subject: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
Category: Science
Asked by: octopia-ga
List Price: $25.00
Posted: 16 Nov 2004 22:08 PST
Expires: 16 Dec 2004 22:08 PST
Question ID: 430019
Hi Techtor, Fielong, and all aerospace researchers....

Scientists know that the edge of space is around 100Km from sea level.
I am interested to learn more about this edge (and why is it
considered an edge at all?) For example, what is the air pressure (or
gas concentration) below and above the edge of space? And why is it
that passing this successfully is one of the most difficult stages for
a spaceship?

Request for Question Clarification by techtor-ga on 17 Nov 2004 08:03 PST
Hi Octopia, long time no hear. Thanks for mentioning us again... seems
you have a different topic in mind this time! Well, let's see what we
can find for you.

Clarification of Question by octopia-ga on 17 Nov 2004 09:22 PST
Hi Techtor, thanks for responding promptly. Basically, I am trying to
find some resources on the subject. Thanks to Latitude, I understand a
little bit more about now. I am especially interested in gas pressure
at various altitudes, and. I know that 99% of the gas concentration is
only below the first 35Km. So, what is so special about that edge. I
mean, once you get rid of most of air pressure around you, what
difference does it make if you fly to at 100,500, or 5000Km (taking in
consideration Latitude's point of getting back in one piece, of
course)?
Answer  
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
Answered By: techtor-ga on 17 Nov 2004 10:06 PST
Rated:5 out of 5 stars
 
Hello Octopia,
I've tried to answer this question based on the sources listed after
and I'll piece together an explanation based on them.

Perhaps I can start by saying that 100 kms above the Earth's surface
is not really considered the edge of the Earth yet. It may be called
the start of the edge of the Earth, as Latitude below implies, for the
Earth's atmosphere with air molecules and all still present can extend
up to 1000 kms. But you could say the 100 km layer is where
significant changes take place in the conditions that affect the
flight of an object into space.

Firstly let's look at the layers. According to the "Why is the Sky
Blue?" article, 100 kms is commonly the border separating the kinds of
layers. In layers of the atmosphere according to electrical
properties, it's between the Neutral atmosphere and Ionosphere.
According to layers by temperature, it separates the Mesosphere and
Thermosphere. According to layers by composition, it separates the
Homosphere and Heterospere.

I believe that 100 km can be considered the edge of normal flight,
since at this level, the air would be so thin that it would not be
able to provide lift for aircraft, no matter how big the wings.
According to the Powerpoint presentation titled "Basic Properties of
the Atmosphere," the pressure at 100 kms up is about 0.00056 millbars
- which calculated in the Google calculator is 8.12211331  10 raised
to -06 pounds per square inch. Not enough to hold a wing up. So the
craft would have to be totally dependent on its propulsion system. The
propulsion system of a craft should produce power many times the
weight of the craft to be able to overcome the Earth's gravity. For
example, the Saturn V rocket produced around 7.5 million pounds of
thrust to get into space. Without that much power, it would have to
achieve Escape Velocity, the speed an object should travel so that
Earth's gravity would not pull it back down, which would be at least
11.2 km a second, or 42,000 km and hour,

Perhaps once a craft has reached 100 kms up, the gravity will also be
considerably less, so that less thrust is needed to proceed further
into space and lesser power propulsion can be used.

One other thing that might make this stage difficult to bypass is the
existence of the ionosphere, a layer composed of electrically charged
particles or ions, created by the absorption of ultraviolet light. It
is also located somewhat above that 100 km level above the earth. Any
object that passes through this layer slowly can be fried to a crisp.
Spacecraft that have passed through this layer, like the Apollo 11
mission, pass it at such speed that the ions did very little damage to
the craft passing through it. Moon landing debunkers use the
explanation that nothing could pass through the ionosphere at all, but
given enough escape speed, a craft can pass through safely. Once past
this, there can be other problems to worry about, like meteors, space
debris and space radiation.

100 kms as the border between the two layers of the atmosphere based
on composition, the Homosphere and the Heterosphere shows a
significant change. Below 100 kms, heavier molecules like oxygen and
nitrogen (which composes 70+% of the Earth's atmosphere). Above,
lighter substances like hydrogen are more abundant.

Referring to Latitude's comment, getting back down in one piece is
hard, since when you hit the atmosphere, you will dragged at high
speed through searing air friction, and retro rockets will have to
provide very high amounts of thrust to break the fall, or like the
Space shuttle, the craft will have to hit the atmosphere at a very
specific attitude and manner to avoid burnup. The tragic loss of the
Columbia demonstrated this problem.

So I believe that makes 100 kms significant is the begining of the
"edge" of space. It's not the edge per se, but forms an important part
of it. Once a craft breaks this barrier, it should start making
adjustments to adapt it to travel in different conditions in
near-space and space.


Sources:
Karman line - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Edge_of_space

Earth's atmosphere - Wikipedia, the free encyclopedia:
http://en.wikipedia.org/wiki/Earth's_atmosphere

Thickness of Earth's Atmosphere:
http://hypertextbook.com/facts/1998/AndreaPark.shtml

Blue Sky - Why is the Sky Blue?
http://www.sciencemadesimple.com/sky_blue.html

Thinkquest: The Atmosphere
http://mediatheek.thinkquest.nl/~ll125/en/atmos.htm

Meteo 465/565 -- The Middle Atmosphere Chemical Composition
http://www.ems.psu.edu/~brune/m465/m465l03.htm
- "A transition occurs at about 100 km.  Below about 100 km, the
mixing of air parcels and thus air molecules is dominated by eddy
motions.  Above, 100 km, the mixing of air parcels is dominated by
molecular diffusion.  With molecular diffusion in control, molecules
of different mass are no longer uniformly mixed.  Thus, the region
below 100 km is called the homosphere, while the region above 100 km
is called the heterosphere." - indication of changes at 100 kms.

Basic Properties of the Atmosphere
http://www.uwgb.edu/dutchs/EnvSC102Notes/102BasicAtmo.ppt


Google search terms used:
100 km atmosphere
100 km atmosphere density
100 km atmosphere density psi

I hope this answer has been helped you a lot. Don't hesitate to ask if
you need something clarified, or have a problem with the answer. Thank
you.

Clarification of Answer by techtor-ga on 17 Nov 2004 10:15 PST
Octopia,
Let me address that last clarification you posted, as I hadn't seen
that before I posted my answer. I guess Latitude's point involves the
air's being too thin to slow your descent. So even if you have a big
parachute, it won't take effect until you hit much thicker air after
100 kms. However, that air isn't to thin to burn up your craft with
air friction. So by the time you've hit 100 kms reentering at normal
speed, you'll be hot enough to be a literal meteor, and too hot for
any parachutes. So I believe strong retro rockets are needed for that.
As for flying at 100,500 km or 5000 km, you can't use wings and
rudders to steer. You need variable-pitch propulsion exhausts, or
retro rockets, or other propulsion-based system to allow you to change
direction.

Tell me if you need other information.

Request for Answer Clarification by octopia-ga on 07 Dec 2004 00:35 PST
Thanks Techtor, and sorry for the late reply. Well, I am spending some
time a little here and a little there, and we?ll see. Techtor, how can
I get in touch with you directly?

Clarification of Answer by techtor-ga on 10 Dec 2004 21:03 PST
Hi, Octopia, nice to hear from you again! Unfortunately, it's against Google
Answers policy to get in touch with Researchers directly, outside of
Google Answers. What do you have in mind, anyway? By the way, please
respond in the Comments section.
octopia-ga rated this answer:5 out of 5 stars and gave an additional tip of: $3.00
Same Day Answer. Wow, this keeps on getting better...
Thanks Techtor.

Comments  
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: latitude-ga on 17 Nov 2004 03:47 PST
 
1: The edge is just a convention taken as being where 'space' begins
2: There is no sudden 'drop-off' in gas pressure above and below the 100km line
3: Actually, getting up to 100km was a challenge set as a sort of goal
to reach (i.e: you've reached the commonly considered "edge of
space"). The real difficulty is to get back down in one piece!

Please note: Getting up to 100km and down again is a piece of cake
when compared to getting into orbit. This is a much more difficult
task...

Hope this was useful...
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: techtor-ga on 19 Nov 2004 19:18 PST
 
Thanks a lot for the five-star rating and tip!
I wonder how you've been doing with your recent ventures, Octopia. I
hope you've had some measure of success.
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: mark3141-ga on 27 Nov 2004 22:18 PST
 
One of the responses stated that gravity would be lower at 100 km. At
the Earth's surface the acceleration due to gravity is about 9.8
m/s^2. At 100 km, gravity is reduced to about 9.5 m/s^2. There isn't
that much of a difference.
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: octopia-ga on 30 Nov 2004 04:54 PST
 
Thank Techtor, and sorry for the late reply. Well, I am spending some
time a little here and a little there, and we?ll see. Techtor, how can
I get in touch with you directly?
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: octopia-ga on 30 Nov 2004 04:54 PST
 
Thanks Techtor, and sorry for the late reply. Well, I am spending some
time a little here and a little there, and we?ll see. Techtor, how can
I get in touch with you directly?
Subject: Re: Edge of Space: resources (techtor, feilong,& + aerospace researchers)
From: techtor-ga on 07 Dec 2004 20:59 PST
 
Hi, Octopia, nice to see you again! Unfortunately, it's against Google
Answers policy to get in touch with Researchers directly, outside of
Google Answers. What do you have in mind, anyway?
Subject: Re: Edge of Space: resources: Techtor
From: octopia-ga on 25 Jan 2005 05:47 PST
 
Hi Techtor, thanks for your reply and sorry it took a while for me to get back. 

In most of my questions, I am happy to share info with everyone. But
shouldn't here be an option for some questions to be exclusively
communicated? Please let me know if GA has this option somehow....

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