Is the International Space Station really in outer space?

[elanachan]

After making my own station in KSP and looking over the info on the ISS, I'm starting to wonder if it really is in space and not just very high up in the atmosphere. In KSP, once you're above 70KM you are completely free of the atmosphere's influence, which means any orbit above that altitude will stay in orbit indefinitely as long as something doesn't alter it's trajectory bellow that. The ISS on the other hand must periodically raise it's altitude to maintain orbit. This suggests that the station is in fact very high up in the atmosphere and not actually in outer space.

According to "official" accounts made by the governments, the karman line which is at 100km represents the boundary of outer space, however this is still within the thermosphere, which extends up to roughly 690km, and then beyond that is the exosphere which is estimated to reach up to about 10,000km, or half the distance between the earth and the moon. If atmospheric drag doesn't completely go away until after you exit the exosphere, wouldn't that mean that with an apogee of 423km and a perigee of 420km that the ISS is in fact a high altitude construct within the upper atmosphere as apposed to something that is truly in space?

Edited April 9, 2014 by elanachan

[vger]

You can get pretty far from Earth and still find atmospheric particles, but their influence on a craft is negligible. IMO, Space is where you are high enough that atmospheric drag won't ruin your orbit.

[elanachan]

Well, given that the orbit of the ISS is in a constant (but gradual) state of decay, would that suggest it isn't high enough to truly count?

[Dunbaratu]

The atmosphere never disappears. It approaches zero density asymptotically on an exponential decay function. The idea of a hard dividing line where "space" begins always seemed to me to be utterly arbitrary and made up. It's basically asking "what's the fraction closest to zero, meaning there's no way to make a fraction that's even closer to zero than it is?" And of course, for any non-infinite N, you can always get closer than 1/N by taking 1/(N+1), so there is no such number.

[NERVAfan]

The ISS is in the upper atmosphere (thermosphere) AND in space.

The main definition of space is above 100km, but for some purposes (US astronaut wings) 50 miles (80km). These are fairly arbitrary and rounded numbers. The 100km is supposed to be an approximation/rounded version of the Karman line where an aircraft would have to travel at orbital speed to support itself by aerodynamic lift. I don't know the source of the 50 miles, beyond being a round number.

But both are also decent approximations of the top of the mesosphere/beginning of the thermosphere and also of the "turbopause" where the atmosphere stops having a pretty constant composition and stratifies out.

http://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line

http://en.wikipedia.org/wiki/Turbopause

http://en.wikipedia.org/wiki/Thermosphere

The thermosphere is incredibly thin, but at about 500km (or higher) it thins out to the exosphere, which isn't really a "gas" at all but a bunch of molecules that hardly ever collide with each other (don't behave as a gas). The exosphere then thins out to the interplanetary medium...

[Seret]

You can draw the line wherever you like, it's an entirely arbitrary point. You're always going to be under the influence of one astronomical body or another, whether it's due to atmospheric particles, gravity, charged particles, etc.

[WestAir]

The atmosphere never disappears. It approaches zero density asymptotically on an exponential decay function. The idea of a hard dividing line where "space" begins always seemed to me to be utterly arbitrary and made up. It's basically asking "what's the fraction closest to zero, meaning there's no way to make a fraction that's even closer to zero than it is?" And of course, for any non-infinite N, you can always get closer than 1/N by taking 1/(N+1), so there is no such number.

But there is a point where it does become zero. Unless you're saying we'll detect traces of our atmosphere over Pluto, or Andromeda.

Eventually it ends because everything does. That is the one constant of our Universe. The Karman Line is a very unrealistic measure of that point, however.

[Dodgey]

But there is a point where it does become zero. Unless you're saying we'll detect traces of our atmosphere over Pluto, or Andromeda.

Eventually it ends because everything does. That is the one constant of our Universe. The Karman Line is a very unrealistic measure of that point, however.

So are you saying that there are no gass particals just floating in space?

[Streetwind]

Eventually it ends because everything does. That is the one constant of our Universe. The Karman Line is a very unrealistic measure of that point, however.

The Karman line is an unrealistic measure only because it doesn't actually measure that. Its definition is not "the atmosphere ends here", and it never was. As NERVAfan says, it's the point where you need to travel at orbital velocity in order to get enough lift from wings, which renders the wings themselves pointless (because you are already at orbital speeds). That is the reason the Karman line is defined as the beginning of outer space: because from that point on, you no longer conduct atmospheric flight. Even if you tried, it is physically impossible to do so. Whether or not you are still within the atmosphere is irrelevant if you are forced to maneuver as if you were not, anyway.

Therefore the ISS is indeed a space station that is situated in outer space, because it does not perform atmospheric flight.

If you wanted to define outer space as "the place where no particles exact a force on the spacecraft anymore", you would need to place it beyond the heliopause (the point where the solar wind ceases). Because as long as you are within that area, the solar wind is pushing against your craft. It's a tiny bit of pushing only, but it's enough to be considered as a form of propulsion, and is already used to control satellites - for example, the crippled Kepler space telescope is able to continue working despite losing two of its three reaction wheels because they found a way of using the solar wind to stabilize it instead.

[WestAir]

So are you saying that there are no gass particals just floating in space?

I'm saying those gases are not part of the Earths exosphere or atmosphere. Earths gravitational influence for loose particles extends to about halfway between the Earth and the Moon. Above that, solar radiation pressure on atomic hydrogen exceeds that of the Earth’s gravitational pull.

The Karman line is an unrealistic measure only because it doesn't actually measure that.

I never argued the point that it did. The OP did.

Edited April 9, 2014 by WestAir

[Seret]

So are you saying that there are no gass particals just floating in space?

No, he's saying that there will come a point at which you'd no longer be able to detect them. There's always something in space, even in interstellar space. At some point you'd no longer be able to detect any particular concentration of gas that you could say belonged to an atmosphere.

[Dodgey]

Ok, I get what you mean.

[Zuni]

As well as those few atmo particles, theres the solar wind and conflicting SOIs... Remember, real life has infinite body physics. I don't know what kind of computer it takes to run that!

[SargeRho]

It's technically in space, but it's also still in the Atmosphere, the Thermosphere to be exact. It produces enough drag to need frequent orbit raising maneuvers.

[elanachan]

It's technically in space, but it's also still in the Atmosphere, the Thermosphere to be exact. It produces enough drag to need frequent orbit raising maneuvers.

If we were to use the definition KSP uses, space would begin where atmospheric drag ceases.

[Seret]

If we were to use the definition KSP uses, space would begin where atmospheric drag ceases.

Yes, but KSP is just a game, and has to make certain approximations that don't exist in the real world.

[Nibb31]

"Outer space" is only really used by the media. It has no scientific meaning.

The ISS is officially located in Low Earth Orbit.

[elanachan]

But the limits do exist, they just aren't well defined, saying there is no end to the atmosphere is like saying there is no end to the SOI of a planet.

edit:

Spacecraft with a perigee below about 2,000 km (1,200 mi) are subject to drag from the Earth's atmosphere, which will cause the orbital altitude to decrease. The rate of orbital decay depends on the satellite's cross-sectional area and mass, as well as variations in the air density of the upper atmosphere. Below about 300 km (190 mi), decay becomes more rapid with lifetimes measured in days.

This would seem to suggest that the boundary I'm talking about would be at the 2,000km mark.

Edited April 9, 2014 by elanachan

[NASAFanboy]

But the limits do exist, they just aren't well defined, saying there is no end to the atmosphere is like saying there is no end to the SOI of a planet.

edit:

This would seem to suggest that the boundary I'm talking about would be at the 2,000km mark.

That would mean Apollo 8 was the first crew to enter space, and my life is a lie.

That would also mean the Moon has a atmosphere because it has a Exosphere.

The boundary to space is 100km, to define it otherwise is absurd.

KSP has to cut off the atmosphere because gameplay and it simply is too complicated to completely simulate air particles outside of atmosphere and solar wind and all that. You don't want to time warp out of a Duna mission to find your 10-module station and half your satellites missing in Map View because you forgot to leave time warp every minute to go boost it up a little. No one wants that.

KSP is a game, real life is real life.

Learn to distinguish between the two.

Also, there are particles in interstellar space. Want to really get to someplace without the pesky particles?

Leave the galaxy and get halfway to Andromenda. Well, almost no particles, but that very empty. So much for spacefaring

Edited April 9, 2014 by NASAFanboy

[Seret]

But the limits do exist, they just aren't well defined, saying there is no end to the atmosphere is like saying there is no end to the SOI of a planet.

In practical terms there is an end to the atmosphere, it just overlaps with what's also defined as space. You can be in both simultaneously.

[Streetwind]

But the limits do exist, they just aren't well defined, saying there is no end to the atmosphere is like saying there is no end to the SOI of a planet.

In addition to what Seret said, there IS in fact no end to the SoI of a planet. This is because SoI's do not exist IRL as they do in KSP, so your simile here is actually countering your own point.

The game uses a simplification of orbital mechanics called the "patched conics" model. In this model, only one source of gravity affects the spaceship at any given time, and the spaceship is said to be in that gravity source's "sphere of influence". When gravity from that source becomes so weak over distance that another source becomes stronger, then that source takes over and the spaceship "switches spheres of influence". But in real life, the gravity from the previous source doesn't just magically disappear. In true n-body systems, gravity from an object behaves much like the atmosphere we're talking about here: it becomes progressively weaker up to the point where you cannot detect it anymore, but there's no real end to it.

For example, objects in Earth orbit are affected by the gravity of the Moon... and also the gravity of, for example, Jupiter. Our resident gas giant is so extremely massive that its orbital motions subtly disturb the entire solar system, and even affects the Sun: the barycenter of the Sun/Jupiter system is actually above the surface of the Sun, meaning Jupiter forces that massive star to wobble about like a drunkard. But the key word is "subtle"; for most of humanity's intents and purposes, the influence is negligible. But you can calculate it, and you can certainly measure it too.

All that despite the fact that there's two major orbits (Mars and the asteroid belt) separating Earth from Jupiter. In KSP terms, we would not even be anywhere near the SoI of our closest neighbors, much less those further out, but reality doesn't work that way.

[elanachan]

I'm talking about the SOI of the body being orbited, for the purposes of my analogy, anything that has gone to Venus or Mars has left Earth's SOI.

edit: The key to this whole thing is gradients, not solid lines, but at the same time, there comes a point where things even out such as the zone represented by the karman line, eventually you get high enough that you consistently cannot achieve significant lift with fixed wing aircraft. By that same token, there will be a point where you are far enough from earth that you consistently cannot maintain orbit and in effect escape the planet's influence. The SOI of any body can be drawn up in the same manor as the karman line.

Edited April 9, 2014 by elanachan

[vetrox]

In addition to what Seret said, there IS in fact no end to the SoI of a planet. This is because SoI's do not exist IRL as they do in KSP, so your simile here is actually countering your own point.

The game uses a simplification of orbital mechanics called the "patched conics" model. In this model, only one source of gravity affects the spaceship at any given time, and the spaceship is said to be in that gravity source's "sphere of influence". When gravity from that source becomes so weak over distance that another source becomes stronger, then that source takes over and the spaceship "switches spheres of influence". But in real life, the gravity from the previous source doesn't just magically disappear. In true n-body systems, gravity from an object behaves much like the atmosphere we're talking about here: it becomes progressively weaker up to the point where you cannot detect it anymore, but there's no real end to it.

For example, objects in Earth orbit are affected by the gravity of the Moon... and also the gravity of, for example, Jupiter. Our resident gas giant is so extremely massive that its orbital motions subtly disturb the entire solar system, and even affects the Sun: the barycenter of the Sun/Jupiter system is actually above the surface of the Sun, meaning Jupiter forces that massive star to wobble about like a drunkard. But the key word is "subtle"; for most of humanity's intents and purposes, the influence is negligible. But you can calculate it, and you can certainly measure it too.

All that despite the fact that there's two major orbits (Mars and the asteroid belt) separating Earth from Jupiter. In KSP terms, we would not even be anywhere near the SoI of our closest neighbors, much less those further out, but reality doesn't work that way.

I jsut want to butt in here and ask a quick question. If i were to orbit the moon (our lunar moon not that crazy mun in the game) at x vlocity that on paper with no other bodies would give me a perfect circular orbit of y kilometers. If we then plop earth nearby would that change our perfect circle to a slightly eliptic orbit? and be destined to have a permanent eliptic orbit as long as the earths gravity is taken into account.

Or is it closer to ksp physics in that, lunar gravity is so much stronger at that altitude, that the earths gravity has no hope of doing anything?

A side question as well (as I'm here) If my first statement turns out to be true would that mean if i left an object orbiting the moon that various factors would eventually cause it to get pushed closer and closer to earths gravity? or does it all cancel itself out. IE if the object is in a clockwise equitorial orbit solar winds would cause it to gain velocity at one point in the orbit but at the exact opposite point it also slows it down therefor keeping the orbit stable?

I'm just asking questions here so if I'm spouting a load of crap please be nice. Thats why I'm asking these questions

[Dunbaratu]

In practical terms there is an end to the atmosphere, it just overlaps with what's also defined as space. You can be in both simultaneously.

Exactly. There's loose hydrogen atoms in space (about 1 atom per cubic meter, if I recall). So how many hydrogen atoms per cubic meter are needed before you assume those atoms are part of the atmosphere? 2? 3? 100? 1000000? There is no hard and fast line that can be called the *start* of outer space.

[Dunbaratu]

But there is a point where it does become zero. Unless you're saying we'll detect traces of our atmosphere over Pluto, or Andromeda.

I am in fact saying that. The 1 atom per cubic meter near-vacuum of space contains atoms that have gotten there from other planets. They get mixed together.