Celestia Forums

On Thursday night, me and few friends saw the ISS go over Portsmouth, England - great sight.

The next day I was going to do a screen dump from Celestia to show them the view 'from space'. BUT, entering correct time and date, Celestia shows the ISS hundreds of miles away over Africa.

Is the orbit of the ISS supposed to be accurate here - or is it just an 'artist's impression' of the way it orbits?

BTW, you can check the passes of ISS from your current location here:

http://spaceflight1.nasa.gov/realdata/s ... aSSOP.html

Nick

OK, ignore this. I found the info that low orbit stuff does go awry over time.

I also found this excellent page, and using the Two Line Element Translation: tle.xls I have correctly the ISS orbit information.

# ssc file by Ulrich Dickmann (Adirondack)

Modify "ISS" "Sol/Earth"
{
Mesh "ISSjun08.3ds"

# UniformRotation
# {
# Inclination 51.5684
# MeridianAngle -90
# AscendingNode 343.1518
# }

# Radius 0.005

EllipticalOrbit {
Epoch 2454736.03954084
Period 0.06360410
SemiMajorAxis 6730.667
Eccentricity 0.0006106
Inclination 51.6387
AscendingNode 216.6333
ArgOfPericenter 153.2490
MeanAnomaly 206.8988
}
Obliquity 51.6387
EquatorAscendingNode 216.6333
RotationOffset 243.9341


Orientation [90 0 0 1]
}


http://www.lepp.cornell.edu/~seb/celest ... heets.html

Nick

Another issue is that Celestia v1.5.1 and older use a fixed rotation speed for the Earth. Since the Earth's rotation speed varies slightly, the Earth's surface in Celestia is displaced from where it should be. This adds errors to the line-of-sight direction from your position to low orbiting satellites like the ISS.

By default, Celestia v1.6 uses a predefined variable rotation speed for the Earth, which makes a difference of about 70km in southern California in 2008. This should be an improvement, but I suspect it is still not enough to place the ISS in the right part of Celestia's sky when seen from a viewpoint on the Earth's surface.

The orbit of the ISS is always changing from the docking and manoeuvring of supply ships.