Celestia Forums

Hi there,

don't know if this has been discussed and not a bug as such but the position of the ISS given here

http://science.nasa.gov/temp/StationLoc.html

is different to the position celestia has placed it, (time is set to current utc/gmt real time)

cheers

lib

Yes, it has been discussed.

The orbit of the ISS changes continuously and unpredictably due to the many forces acting on it. (atmospheric drag, docking of Progress delivery vehicles, etc.). Celestia cannot model these effects.

If you want Celestia to show more accurate ISS positions, you have to update its orbital definition daily.

selden wrote:Yes, it has been discussed.
The orbit of the ISS changes continuously and unpredictably due to the many forces acting on it. (atmospheric drag, docking of Progress delivery vehicles, etc.). Celestia cannot model these effects.
If you want Celestia to show more accurate ISS positions, you have to update its orbital definition daily.

Just out of interest, how much impact does a single shuttle docking have on the ISS orbit. I would imagine that the force imparted by the shuttle docking at a fraction of a m/s would have a relatively insignificant impact on the inertia of the ISS at orbital speed.
Anyone???

Chuft-Captain wrote:

selden wrote:Yes, it has been discussed.
The orbit of the ISS changes continuously and unpredictably due to the many forces acting on it. (atmospheric drag, docking of Progress delivery vehicles, etc.). Celestia cannot model these effects.
If you want Celestia to show more accurate ISS positions, you have to update its orbital definition daily.

Just out of interest, how much impact does a single shuttle docking have on the ISS orbit. I would imagine that the force imparted by the shuttle docking at a fraction of a m/s would have a relatively insignificant impact on the inertia of the ISS at orbital speed.
Anyone???

Thats a very good question, If the force was strong enough the ISS could either fall to earth or float off into space.
I wonder what it would look like if it exploded in space?8)

The ISS is falling to Earth.
It has to be periodically boosted to keep it orbiting at an appropriate altitude.

Each of the effects is small but measurable. Orbital mechanics are not "all or nothing". Over long periods of time, small effects accumulate into distances noticable even to the untrained observer.

,Your to smart for us Seldon

selden wrote:The ISS is falling to Earth.
It has to be periodically boosted to keep it orbiting at an appropriate altitude.

Each of the effects is small but measurable. Orbital mechanics are not "all or nothing". Over long periods of time, small effects accumulate into distances noticable even to the untrained observer.

Any idea how often is 'periodically'? I know it took quite a few years for the MIR orbit to degrade.
Do you know if the Space Shuttle orbiter engines are used to boost the ISS orbit when docked?
Does the ISS have it's own supply of propellant and means to significantly alter it's orbit independently of the shuttle.

If not, how long can it go without the shuttle before things become 'interesting'?

I'm interested in the comparative impact of each of these effects. From a laymans point of view I have always thought that the major thing effecting orbits was atmospheric drag, perhaps then followed by perturbation from the moon. I thought that relatively speeaking, dockings were insignificant compared to drag, but perhaps not!

Anyone know the relative magnitudes of each of these effects (typically)?

Is there such a thing as Atmospheric Drag?

Stew2000 wrote:Is there such a thing as Atmospheric Drag?

It's also known as "wind".

Oh
Are you gonna celebrate your 5000 post

Probably not

There are several types of orbit perturbations, drag being the most dominate in Low Earth Orbit (LEO) such as the ISS. There are other perturbations from the Sun, Moon and other planets, as well as the Earth not being perfectly spherical but in fact being an ellipsoid meaning that the gravity over different points of the Earth will be different. These perturbations are often referred to as zonal harmonics. There is also solar radiation pressure (SRP), sometimes referred to as the ?€?solar wind?€

Janice,

You wrote

Drag is not wind.

I was not trying to use a formal definition.
It was clear that Stew didn't know anything about atmospheric effects (as they affect satellites or aircraft) so I wanted to use a term that he'd be familiar with. The popular use of the word "wind" includes the effects caused by something passing rapidly through the air.

selden wrote:The popular use of the word "wind" includes the effects caused by something passing rapidly through the air.

Yes, but:

will this wind......be so mighty......as to lay low......the moun-taynes......of the....
........earth.

(a prize to the first person to post the source of this rather obscure reference)

Chuft-Captain wrote:(a prize to the first person to post the source of this rather obscure reference)

Rowan Atkinson, from the first Amnesty International charity concert The Secret Policeman's Ball. (Boxed set of all the concerts now available on DVD ... )

Well done Hamiltonian!

The skit was "The end of the world".

Your prize is some stunning pictures of Mars, here: http://celestiaproject.net/forum/viewtopic.php?t=8756