Updating ISS Position
Posted: 02.07.2008, 12:29
Hey, All! Absolutely lovin' the new 1.5.1 build!
The question was once asked about having the current position of ISS displayed, and the answer from selden was that you'd have to do that manually... but didn't give any tips on how to go about it.
Okay, so, I opened up the spacecraft.ssc file...
...and then I went to Heavens Above...
Several items are self-explanatory (Eccentricity, Inclination, Ascending Node, Mean Anomaly), and I'm assuming that "Argument of Pericenter" is the same as "Argument of Perigee".
I'm also assuming that Epoch needs to be converted to Julian Date. (I've got 2454648.83463)
Now, I think I just need to know how to get the Period and the Semi-major Axis, and find out what to set as "Beginning".
Is the Period just 1/(Revs per Day)? That would be 0.0634964217, then.
Why is Semi-major Axis not listed anywhere? Isn't it one of the most important bits of orbital info?
I know that it's half the distance between Perigee (339 km) and Apogee (351 km), but the radius of the Earth varies a bit between the Equator (6,378.1 km) and the Poles (6,356.8 km).
When I average the two Earth radii, I get 6367.45, but the Mean Radius (according to Wikipedia) is listed as 6,371.0 km, which would make the diameter 12742 km.
Other sites give the diameter of the Earth as 12756.3 km. Obviously they just went with the Equatorial value.
So, (12756.3 + (339 + 351))/2 = 6723.15 km is what I get for Semi-major Axis.
Now then, what to do with this line...
Beginning 2451138 # Zarya module launched 20 Nov 1998
Hmmmm, any thoughts?
I so hope I'm doin' this all right!
The question was once asked about having the current position of ISS displayed, and the answer from selden was that you'd have to do that manually... but didn't give any tips on how to go about it.
Okay, so, I opened up the spacecraft.ssc file...
Code: Select all
"ISS" "Sol/Earth"
{
Class "spacecraft"
Mesh "iss.3ds"
Radius 0.040
Beginning 2451138 # Zarya module launched 20 Nov 1998
# Ending ????
EllipticalOrbit {
Period 0.064176392
SemiMajorAxis 6767
Eccentricity 0.0016886
Inclination 51.5684
AscendingNode 343.1518
ArgOfPericenter 346.2476
MeanAnomaly 13.8216
Epoch 2452028.18381755
}
UniformRotation
{
Inclination 51.5684 #
MeridianAngle 90 # orientation corrections by Matt McIrvin
AscendingNode 343.1518 #
}
Albedo 0.10
}...and then I went to Heavens Above...
1 25544U 98067A 08183.83463292 .00011154 00000-0 77774-4 0 7757
2 25544 051.6412 301.0484 0008682 320.4813 178.9640 15.74891896550830
Epoch (UTC): 8:01:52 PM, Tuesday, July 01, 2008
Eccentricity: 0.0008682
Inclination: 051.6412°
Perigee Height: 339 km
Apogee Height: 351 km
Right Ascension of Ascending Node: 301.0484°
Argument of Perigee: 320.4813°
Revolutions per Day: 15.74891896
Mean Anomaly at Epoch: 178.9640°
Orbit Number at Epoch: 55083
Several items are self-explanatory (Eccentricity, Inclination, Ascending Node, Mean Anomaly), and I'm assuming that "Argument of Pericenter" is the same as "Argument of Perigee".
I'm also assuming that Epoch needs to be converted to Julian Date. (I've got 2454648.83463)
Now, I think I just need to know how to get the Period and the Semi-major Axis, and find out what to set as "Beginning".
Is the Period just 1/(Revs per Day)? That would be 0.0634964217, then.
Why is Semi-major Axis not listed anywhere? Isn't it one of the most important bits of orbital info?
I know that it's half the distance between Perigee (339 km) and Apogee (351 km), but the radius of the Earth varies a bit between the Equator (6,378.1 km) and the Poles (6,356.8 km).
When I average the two Earth radii, I get 6367.45, but the Mean Radius (according to Wikipedia) is listed as 6,371.0 km, which would make the diameter 12742 km.
Other sites give the diameter of the Earth as 12756.3 km. Obviously they just went with the Equatorial value.
So, (12756.3 + (339 + 351))/2 = 6723.15 km is what I get for Semi-major Axis.
Now then, what to do with this line...
Beginning 2451138 # Zarya module launched 20 Nov 1998
Hmmmm, any thoughts?
I so hope I'm doin' this all right!
