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Author Topic:   Where Earth ends and outer space begins
Hawkman
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Posts: 400
From: Union, New Jersey
Registered: Jan 2001

posted 05-21-2004 07:42 PM     Click Here to See the Profile for Hawkman   Click Here to Email Hawkman     Edit/Delete Message   Reply w/Quote
I've always thought that "space" started at 50 miles up. I've been reading on a few of these civilian space websites that they have been sending their rockets to an altitude of 100 kilometers, which is a little over 62 miles up. I also read yesterday that "space" starts around 120 kilometers, which would put it around 74 miles up.

Are these guys coming up short or does space start at 50 miles up?

nasamad
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Posts: 2088
From: Essex, UK
Registered: Jul 2001

posted 05-21-2004 08:03 PM     Click Here to See the Profile for nasamad   Click Here to Email nasamad     Edit/Delete Message   Reply w/Quote
I think the definition of space depends on who which body is defining it.

If I remember correctly the U.S. Air Force awards astronaut wings to people who fly over 50 miles high.

Other bodies may have different definitions, but as it is a gradual transition, which I believe can change according to temperature and pressure, who is to say who is right or wrong?

Robert Pearlman
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Posts: 39788
From: Houston, TX
Registered: Nov 1999

posted 05-21-2004 08:41 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Physically, there is no constant border between where the atmosphere ends and space begins.

Strategically, the U.S. has never defined an altitude for space so as not to set a limit where its (restricted) airspace ends. (To that end Eisenhower was briefed by Asst. Secretary of Defense Donald Quarles that the Russians had done the United States a "good turn" by launching Sputnik, thus "establishing the concept of freedom of space." [Source: "Sputnik: The Shock Of The Century" by Dickson]).

The U.S. Air Force did award astronaut wings for flights above 50 miles, however this was arguably in response to NASA having already declared one of its sub-orbital pilots (Shepard) as having reached space.

The world air sports federation, the Federation Aeronautique Internationale (FAI) set 100 km (62 miles) as the beginning of space to set a ruler by which all flights could be measured. It is the FAI definition that the X Prize has based its rules for defining a successful space flight by its sub-orbital contestants.

Hawkman
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Posts: 400
From: Union, New Jersey
Registered: Jan 2001

posted 05-21-2004 11:41 PM     Click Here to See the Profile for Hawkman   Click Here to Email Hawkman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Robert Pearlman:
The world air sports federation, the Federation Aeronautique Internationale (FAI) set 100 km (62 miles)...
Ah! No wonder 100 km keeps showing up on these sub-orbital rocket sites.

Robert Pearlman
Editor

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From: Houston, TX
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posted 07-29-2004 04:10 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Received today from the National Air and Space Museum:
Where does 'space' begin?

By Louise Thorn, Astronomy Education Assistant, National Air and Space Museum

When humankind first began going into space, there was no worldwide consensus as to what "space" was, and surprisingly, there still isn't. The need for an official definition became apparent with the launch of Earth's first artificial satellite, Sputnik, on October 4, 1957, which traveled around Earth at altitudes between 227 kilometers (142 miles) at the closest point and 945 kilometers (591 miles) at the farthest.

In the 1960s, the X-15 space plane missions gave us the first glimpses of human space travel. The pioneering X-15 pilots were awarded "astronaut wings" whenever they exceeded the threshold of 80 kilometers (50 miles) altitude, the definition of "space" as deemed by the U.S. Air Force.

However, the Federation Aeronautique Internationale (FAI), the recognized world authority for aeronautical records, declared that aircraft would have to exceed 100 kilometers (62.5 miles) in order for the pilot to qualify for astronaut status. To win the X Prize, competitors must reach the 100 kilometer altitude.

Why 100 kilometers? Because for an aircraft, flying above this altitude is impossible, since lift is no longer effective in the thinning atmosphere. And a spacecraft moving below this altitude would encounter increasing drag, thus reducing its circular orbital speed and causing it to spiral toward Earth. Tests with a Soviet low-altitude satellite in the 1960s confirmed this theory by completing a few orbits above 100 kilometers before rapidly tumbling to earth as it dipped below the 100 kilometer threshold.

This 100 kilometer boundary is known as the Karman Line, having been proposed by Hungarian scientist Theodore Von Karman. Simply put, it denotes where aeronautics becomes astronautics, aeronautics being flight that requires atmosphere, and astronautics being flight that does not require atmosphere. Although 100 kilometers sounds suspiciously convenient, the Karman line can actually be scientifically measured as a definite change.

As the Space Race between the United States and the Soviet Union intensified, the United Nations decided to create an Office for Outer Space Affairs to add legal definition to space activities. Intriguingly, the 1967 Outer Space Treaty itself does not include a definition of where outer space begins, so we can find no clues here.

The only legal document containing a definition of space is the Australian Space Activities Act of 1998 which requires all objects launched from the continent to an altitude greater than 100 kilometers be licensed. Although major space agencies such as the National Aeronautics and Space Administration and the European Space Agency use the general consensus of 100 kilometers, there is still no legally binding stipulation to accept this value. Other definitions of space include: in medicine, the point at which humans must have life-support systems to survive is 24 kilometers/15 miles; in propulsion, the distance where a propulsion system needs to provide its own oxygen as well as fuel is 45 kilometers/28 miles; and the 'atmospheric interface' encountered by the Space Shuttle orbiter on re-entry is at a distance of 122 kilometers/76 miles.

So, to answer our question, "Where does space begin?" we can only reply, "Depends on who you ask!"

Hawkman
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Posts: 400
From: Union, New Jersey
Registered: Jan 2001

posted 07-29-2004 07:39 PM     Click Here to See the Profile for Hawkman   Click Here to Email Hawkman     Edit/Delete Message   Reply w/Quote
So, to answer our question, "Where does space begin?" we can only reply, "Depends on who you ask!"
Well... I guess that settles it!!!

Voskhod
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Posts: 72
From: Oxfordshire, UK
Registered: Jul 2001

posted 07-30-2004 03:23 AM     Click Here to See the Profile for Voskhod     Edit/Delete Message   Reply w/Quote
I believe that the space shuttle detects the atmosphere at 400,000 feet as it starts its re-entry. I know the X-15 could not go above this height as it would have had problems coming back down.

Rob Joyner
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Posts: 1308
From: GA, USA
Registered: Jan 2004

posted 07-30-2004 03:31 AM     Click Here to See the Profile for Rob Joyner   Click Here to Email Rob Joyner     Edit/Delete Message   Reply w/Quote
Why don't we designate space starting where the effects of space definitely begin? Like the absolute moment and height at which things begin to float? No one could dispute that.

Madon_space
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Posts: 652
From: uk
Registered: Sep 2002

posted 07-30-2004 04:51 AM     Click Here to See the Profile for Madon_space   Click Here to Email Madon_space     Edit/Delete Message   Reply w/Quote
I was just reading through these posts and thinking the same thing, but is there an absolute moment when things start to float or does it happen gradually?

Robert Pearlman
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Posts: 39788
From: Houston, TX
Registered: Nov 1999

posted 07-30-2004 07:17 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Rob Joyner:
Like the absolute moment and height at which things begin to float?
Astronauts or items float in space not because they have crossed some barrier defined by the atmosphere or gravity, but rather because they are in free fall as a result of their velocity. So unfortunately, there is no demarcation line by which to define where items begin to float.

Robert Pearlman
Editor

Posts: 39788
From: Houston, TX
Registered: Nov 1999

posted 04-09-2009 10:18 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
SPACE.com: Edge of Space Found
Hold on to your hats, or in this case, your helmets: Scientists have finally pinpointed the so-called edge of space -- the boundary between Earth's atmosphere and outer space.

With data from a new instrument developed by scientists at the University of Calgary, scientists confirmed that space begins 73 miles (118 kilometers) above Earth's surface.

A lot remains very fuzzy, however, as the boundary is surrounded by a host of misconceptions and confusing, conflicting definitions.

music_space
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Posts: 1170
From: Canada
Registered: Jul 2001

posted 04-09-2009 11:19 PM     Click Here to See the Profile for music_space   Click Here to Email music_space     Edit/Delete Message   Reply w/Quote
I was just listening to the Mercury Seven introduction press conference. Schirra states:
Space to anyone of us really begins at about twenty-two to twenty-five thousand feet.

At twenty-two to twenty-five thousand feet, we can't live without survival equipment, so we really are in space.

We've been flying in space as far as our environment goes for many years. But as far as getting higher that's just one more step.

Philip
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Posts: 5752
From: Brussels, Belgium
Registered: Jan 2001

posted 04-10-2009 07:38 AM     Click Here to See the Profile for Philip   Click Here to Email Philip     Edit/Delete Message   Reply w/Quote
For the FIA (French "International Aeronautics Federation") space starts at 100 kilometers. But the Exosphere (top layer of the atmosphere) extends to 700 kilometers...

From the ground up:

  • Strato-sphere (12 km)
  • Tropo-sphere (50 km)
  • Meso-sphere (90 km)
  • Thermo-sphere (500 km)
  • Exo-sphere (above 600 km)

Robert Pearlman
Editor

Posts: 39788
From: Houston, TX
Registered: Nov 1999

posted 07-25-2018 08:58 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
A new study argues that the boundary between Earth's atmosphere and outer space — known as the Kármán line — is 20 kilometers, or about 20%, closer than scientists thought, reports Science.
A close look shows that the traditional definition flies in the face of evidence, says Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. As a hobby, McDowell compiles an influential, detailed record of rocket launches online. "I've been making lists of rockets since I was 13," he says. He often has to decide which launches qualify as reaching outer space, and which do not. Given how low many orbiting satellites fly, the 100-kilometer limit never seemed right to McDowell. He preferred the mesopause, the coldest point in Earth's atmosphere, located roughly 85 kilometers up. (Recent estimates have bumped it somewhat higher.)

...He started with data: namely, public records of satellite telemetry he had downloaded from the North American Aerospace Defense Command about the orbits of 43,000 satellites. Most didn't matter for his project—they orbited far too high above the edge of outer space. But at least 50 had orbits that occasionally operated below 100 kilometers, such as the Soviet Elektron-4 satellite, which made 10 spins at 85 kilometers or below before disintegrating into the atmosphere in 1997. "Are you going to say [these satellites are] in space and then not in space every 2 hours?" he asked. "That doesn't seem very helpful."

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